Home

JamaicaVM 6.0 — User Manual

1. 79 TETTO 80 8 2 1 Usage of the Memory Analyzertool 80 Cu 80 baia 81 10 82 8 2 5 Constant Garbage Collection Work 84 8 2 6 Comparing dynamic mode and constant GC work mode 85 8 2 7 Determination of the worst case execution time of an al SM 86 ane a te ee 86 9 Debugging Support 89 9 1 Enabling the Debugger Agent 89 oor ee ee 90 ere ae ee d ee a 90 93 10 1 Realtime programming with the 5 93 rrr 96 TT re ee ee 96 Sain aw 96 10 3 2 Thread Priorities 97 10 3 3 Runtime checks for NoHeapReal meThread 97 10 3 4 Static In itializers 97 deed ne dg dee 98 10 4 Strict RISJ 98 10 4 44 Use of Memory Areas 98 6 CONTENTS 10 4 2 Thread priorities 98 10 4 3 Runtime checks for NoHeapRealtimeThread 99 10 4 4 Static Initializers 2 ee ee 99 99 s xt 99 11 Realtime Programming Guidelines 101 11 1 General 101 11 2 Computational Transparency 101 11 2 1 Efficient Java Statements 102 NM 104 ponen 105 ere 107 11 2 5 Operations Causing Class Loading 108 s ee oe CE Box wea Rc E ees ended 109 11 3 1 Real Tim
2. The runtime performance for the built application is slightly better compared to an interpreted version using jamaicavm slim buta stronger performance in crease will be achieved by compilation as shown in the next section below gt caffeine interpret Sieve score 416 98 Loop score 395 2017 Logic score 419 0 String score 2127 708 Float score 331 185 Method score 200 166650 Overall score 461 gt jamaicavm slim CaffeineMarkEmbeddedApp Sieve score 346 98 Loop score 277 2017 Logic score 411 0 String score 1699 708 Float score 276 185 Method score 212 166650 Overall score 397 7 1 2 Using Compilation Compilation can be used to increase the runtime performance of Java applications significantly Compiled code is typically about 20 to 30 times faster than inter preted code However due to the fact that Java bytecode is very compact com pared to machine code on CISC or RISC machines fully compiled applications 7 1 CODE SIZE VS RUNTIME PERFORMANCE 61 require significantly more memory This is why we recommend using a profile as decribed in instead of fully compiling the application Using Default Compilation If none of the options interpret compile or useProfile is specified the default compilation will be used The default means that a pre generated profile will be used for the system classes and all application classes will be compiled fully This
3. The JVMTI is a replacement for the Java Virtual Machine Debug Interface JVMDI which has been deprecated Chapter 10 The Real Time Specification for Java JamaicaVM supports the Real Time Specification for Java V 1 0 2 RTSJ see 1 The specification is available at The API documen tation of the JamaicaVM implementation is available online at http www aicas com jamaica doc rtsj_api and is included in the API docu mentation of the Jamaica class library jamaica home doc jamaica api index html The RTSJ resides in package javax realtime Itis generally recommended that you refer to the RTSJ documentation provided by aicas since it contains a detailed description of the behavior of the RTSJ functions and includes specific comments on the behavior of JamaicaVM at places left open by the specification 10 1 Realtime programming with the RTSJ The aim of the Real Time Specification for Java RTSJ is to extend the Java language definition and the Java standard libraries to support realtime threads i e threads whose execution conforms to certain timing constraints Nevertheless the specification is compatible with different Java environments and backwards compatible with existing non realtime Java applications The most important improvements of the RTSJ affect the following seven ar eas e thread scheduling e memory management 93 94 CHAPTER 10 THE REAL TIME SPECIFICATION FOR JAVA e synchronization
4. will im prove the builder performance JAMAICA BUILDER HEAPSIZE Maximum heap size of the jamaica program itself in bytes If the initial heap size of the builder is not sufficient it will increase its heap dynamically up to this value To build large applications you may have to set this maximum heap size to a larger value e g 640M JAMAICA BUILDER JAVA STACKSIZE Java stack size of the jamaica pro gram itself in bytes JAMAICA BUILDER NATIVE STACKSIZE Native stack size of the jamaica program itself in bytes 14 5 EXITCODES Normal termination Error NIe Invalid argument 64 Insufficient memory 100 Internal error Table 14 1 Jamaica Builder jamaicah and numblocks exitcodes 14 5 Exitcodes 179 Tab lists the exit codes of the JamaicaVM Builder The jamaicah and num blocks tools use the same exitcodes If you get an exit code of an internal error please contact aicas support with a full description of the tool usage command line options and input 180 CHAPTER 14 THE JAMAICA BUILDER Chapter 15 The Jamaica ThreadMonitor The JamaicaVM ThreadMonitor enables to monitor the realtime behaviour of ap plications and helps developers to fine tune the threaded Java applications run ning on Jamaica run time systems These run time systems can be either the Ja maicaVM or any application that was created using the Jamaica Builder The ThreadMonitor tool collects and
5. Window gt Preferences Section Jamaica Add the installation directo ries of all distributions you wish to use The plug in creates Java Runtime Environments JREs for all added Jamaica distributions A JRE comprises the Java class libraries Javadoc documentation and the virtual machine A Jamaica distribution additionally contains classes and documentation for the RTSJ After setting up a Jamaica distribution as a JRE it can be used like any other JRE in Eclipse For example it is possible to choose Jamaica as a project specific environment for a Java project either in Create Java Project wizard or by changing JRE System Library in the properties of an existing project It is also possible to choose a Jamaica as default JRE for the workspace If you added a new Jamaica distribution and its associated JRE installation is not visible afterwards please restart Eclipse 5 3 Setting Virtual Machine Parameters The JamaicaVM Virtual Machine is configured through runtime parameters which for example control the heap size or the size of memory areas such as scoped memory These settings are controlled via environment variables refer to section 8 13 5 for a list of available variables To do so create or open a run configuration of type Java Application in your project The environment variables can be defined on the tab named Environment 5 4 Building applications with Jamaica Builder The plug in extends Eclipse with sup
6. 1 maximum number of threads attached via JNI LE VERS Keyword PROF Values ON Groups all 1 version of Jamaica the profile was created with 56 CHAPTER 6 PERFORMANCE OPTIMIZATION 6 3 2 Example We can sort the profiling output to find the application methods where most of the execution time is spent Under Unix the 25 methods which use the most execu tion time in number of bytecode instructions can be found with the following command gt grep PROFILE HelloWorld prof sort rn k2 head n25 PROFILE 7186606 21 sun nio cs UTF_8SEncoder encode PROFILE 7186606 21 sun nio cs UTF_8SEncoder encode PROFILE 7186606 21 sun nio cs UTF_8SEncoder encode PROFILE 5705490 17 java lang String getChars II CI PROFILE 5705490 17 java lang String getChars II CI PROFILE 5705490 17 java lang String getChars II CI PROFILE 1323056 3 java lang StringBuilder append PROFILE 1323056 3 java lang StringBuilder append PROFILE 1323056 3 java lang StringBuilder append PROFILE 1200060 3 java io BufferedWriter write Lj PROFILE 1200060 3 java io BufferedWriter write Lj PROFILE 1200060 3 java io BufferedWriter write Lj PROFILE 960096 2 java nio Buffer position I Lja PROFILE 960096 2 java nio Buffer position I Lja PROFILE 960096 2 java nio Buffer position I Lja PROFILE 880044 2 sun nio cs StreamEncoder write PROFILE 880
7. 145 lt class gt lt package gt lt method gt lt method gt Sh destination o lt gt lt name gt gt timezone setProto cde se smart showExcl compile lt ti s cols ldc closed udedFeatu in protocol lt protocol gt crementalCompilation showIncludedFeatures inline lt n gt res interpret Xint optimise optimiz lt type gt heapSize n K M target lt platform gt maxHeapSize lt n gt K M maxHeaps heapSizeIncrement lt n gt K M javaStackSize cn K nativeStackSize n maxNumThreads c n numJniAttachableThreads c n threadPreemption cn finalizerPri pri 1 K M numThreads lt n gt timeSlice lt n gt heapSizeFromEnv lt var gt izeFromEnv lt var gt numThrea dsFromE heapSizeIncrementFromEnv lt var gt javaStackSizeFromEnv var nativeStackSizeFromEnv lt var gt nv lt var gt maxNumThreadsFromEnv lt var gt numJniAttac finalizerPr hableT lt priMapFromE nv lt var gt hreadsFrom iFromEnv lt var gt jp gt lt sp gt lt jp gt lt sp gt analyse analyze lt t analyzeFrom constGCwork atomicGC reservedMem olerance Env lt var gt FromE
8. At the end of execution the total number of bytecode instructions executed by each method is written to a file with the name of the main class of the Java application and the suffix prof such that it can be used for further processing Hot spots the most likely sources for further performance enhancements by optimization in the application can easily be determined using this file 6 1 1 Creating a profiling application The compilation technology of Jamaica s builder is able to use the data generated during profile runs using the profile option to guide the compilation process 47 48 CHAPTER 6 PERFORMANCE OPTIMIZATION producing optimal performance with a minimum increase in code size Here is a demonstration of the profiler using the HelloWorld example pre sented in B 4 First it is built using the profile option gt jamaicabuilder cp classes profil interpret HelloWorld Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed HelloWorld c HelloWorld h Class file compaction gain 58 739178 21654255 gt 8934724 C compiling HelloWorld__ c HelloWorld nc o linking stripping Application memory demand will be as follows initial max
9. Error codes 64 JamaicaVM failure 65 VM not initialized 66 Insufficient memory 67 Stack overflow 68 Initialization error 69 Setup failure 70 Clean up failure 71 Invalid command line arguments 72 No main class 73 Exec failure Internal errors 100 Serious error HALT called 101 Internal error 102 Internal test error 103 Function or feature not implemented 104 Exit by signal 105 Unreachable code executed 255 Unexpected termination Table 13 1 Exitcodes of the Jamaica VMs 13 6 EXITCODES 141 13 6 Exitcodes Tab 13 1 lists the exit codes of the Jamaica VMs Standard exit codes are exit codes of the application program Error exit codes indicate an error such as insuf ficient memory If you get an exit code of an internal error please contact aicas support with a full description of the runtime condition or if available an example program for which the error occurred 142 CHAPTER 13 THE JAMAICA VIRTUAL MACHINE COMMANDS Chapter 14 The Jamaica Builder Traditionally Java applications are stored in a set of Java class files To run an application these files are loaded by a virtual machine prior to their execution This method of execution emphasizes the dynamic nature of Java applications and allows easy replacement or addition of classes to an existing system However in the context of embedded systems this approach ha
10. IDEs such as Eclipse and Netbeans These are popular IDEs for the Java plat form Debugging is possible on instances of the JamaicaVM running on the host platform as well as for applications built with Jamaica which run on an embed ded device The latter requires that the device provides network access In this chapter it is shown how to set up the IDE debugging facilities with Jamaica A reference section towards the end briefly explains the underlying tech nology JPDA and the supported options 9 1 Enabling the Debugger Agent While debugging the IDE s debugger needs to connect to the virtual machine or the running application in order to inspect the VM s state set breakpoints start and stop execution and so forth Jamaicacontains a communication agent which must be either enabled for the VM or built into the application This is done through the agent Lib option gt jamaicavm agentlib BuiltInAgent transport dt socket gt address localhost 4000 server y suspend y HelloWorld launches JamaicaVM with debug support enabled and HelloWorld as the main class The VM listens on port 4000 at localhost The VM is suspended before the main class is loaded The user may send a command through the debugger to resume the VM and start the user application after setting required breakpoints etc In order to build debugging support into an application the builder option agentlib BuiltInAgent should be used If the application is t
11. The jamaicavmdi command is a variant of jamaicavm slim that includes support for the JVMTI debugging interface It includes a debugging agent that can communicate with remote source level debuggers such as Eclipse 13 4 1 Additional options of jamaicavmdi Option agentlib libname options The agent 1ib option loads and runs the dynamic JVMTI agent library libname with the given options Be aware that JVMTI is not yet fully implemented so not every agent will work Jamaica comes with a statically built in debugging agent that can be selected by setting BuiltInAgent as name The transport layer must be sockets A typical example of using this option is agentlib BuiltInAgent transport dt socket server y suspend y address 8000 To be typed in a single line This starts the application and waits for an incoming connection of a debugger on port 8000 See D 1 for further information on the options that can be provided to the built in agent for remote debugging 13 5 Environment Variables The following environment variables control jamaicavm and its variants CLASSPATH Path list to search for class files 13 6 EXITCODES 139 JAMAICA SCHEDULING Select native thread scheduling mode for Linux and Solaris only Available values are OTHER default scheduling RR round robin and FIFO first in first out JAMAICAVM HEAPSIZE Heap size in bytes default 2M JAMAICAVM MAXHEAPSIZE Max heap size in bytes default 256M
12. method The XloadJNIDynamic option will cause the Builder to know which native de clared methods calls at runtime a dynamic library Arguments have to be separated by spaces and enclosed in double quotes Here are examples of class arguments com user MyClass com user2 x and com An example of a method argrument is com user MyClass toString Ljava lang String Option Xinclude dirs The Xinclude option adds the specified directories to the include path This path should contain the include files generated by jamaicah for the native code referenced from Java code The include files are used to determine whether the Java Native Interface JNI or Jamaica Binary Interface JBI is used to access the native code This option expects a list of paths that are separated using the platform depen dent path separator character e g Option XobjectFormat default none C ELF PECOFF The XobjectFormat option sets the object format to one of default C PECOFF and ELF Option XobjectProcessorFamily type The XobjectProcessorFamily option sets the processor type for code gen eration Available types are none 1386 1486 1586 1686 ppc sparc arm mips sh4 and cris The processor type is only required if the ELF or PECOFF object formats are used Otherwise the type may be set to none Option XobjectSymbolPrefix prefix ec 29 The XobjectSymbolPrefix sets the object symbol prefix e g 14 3
13. 8 2 7 Determination of the worst case execution time of an al location As we have just seen the worst case execution time of an allocation depends on the amount of garbage collection work that has to be performed for the allocation The configuration of the heap as shown above gives a worst case number of garbage collection work units that need to be performed for the allocation of one block of memory In order to determine the actual time an allocation might take in the worst case it is also necessary to know the number of blocks that will be allocated and the platform dependent worst case execution time of one unit of garbage collection work For an allocation statement S we get the following equation to calculate the Worst case execution time weet S numblocks S max gc units wcet of gc unit Where e wcet S is the worst case execution time of the allocation e numblocks S gives the number of blocks that need to be allocated e max gc units is the maximum number of garbage collection units that need to be performed for the allocation of one block e wcet of gc unit is the platform dependent worst case execution time of a single unit of garbage collection work 8 2 8 Examples Imagine that we want to determine the worst case execution time wcet of an allocation of a StringBuffer object as was done in the HelloWorld java exam ple shown above If this example was built with the dynamic garbage collection option and a heap size
14. JNI The Java Native Interface JNI is a standard mechanism for interoperability be tween Java and native code 1 code written with other programming languages like C Jamaica implements version 1 4 of the Java Native Interface Creating and destroying the vm via the Invocation API is currently not supported 16 1 Using JNI Native code that is interfaced through the JNI interface is typically stored in shared libraries that are dynamically loaded by the virtual machine when the application uses native code Jamaica supports this on many plattforms but since dynamically loaded libraries are usually not available on small embedded systems that do not provide a file system Jamaica also offers a different approach Instead of loading a library at runtime you can statically include the native code into the application itself 1 link the native object code directly with the application The Builder allows direct linking of native object code with the created appli cation through the option object fileor XstaticLibraries file Multi ple files can be linked Separate the file names with spaces and enclose the whole option argument within double quotes object files containing native code should be presented to the Builder using this option Building an application using native code on a target requiring manual linking may require providing these object files to the linker Here is a short example on the use of the Java Nat
15. Once the unpredictability of the garbage collector has been solved realtime pro gramming is possible even without the need for special thread classes or the use of specific memory areas for realtime code Realtime Tasks In Jamaica garbage collection activity is performed within application threads and only when memory is allocated by a thread A direct consequence of this is that any realtime task that performs no dynamic memory allocation will be entirely unaffected by garbage collection activity These realtime tasks can access objects on the normal heap just like all other tasks As long as realtime tasks use a priority that is higher than other threads they will be guaranteed to run when they are ready Furthermore even realtime tasks may allocate memory dynamically Just like any other task garbage collection work needs to be performed to pay for this allocation Since a worst case execution time can be determined for the allocation the worst case execution time of the task that performs the allocation can be determined as well Communication The communication mechanisms that can be used between threads with differ ent priority levels and timing requirements are basically the same mechanisms as those used for normal Java threads shared memory and Java monitors Shared Memory Since all threads can access the normal garbage collected heap without suffering from unpredictable pauses due to garbage collector ac tivity this normal
16. The JamaicaVM allows class files to be linked with the virtual machine code into a standalone executable The resulting executable can be stored in ROM or flash memory since all files required by a Java application are packed into the stan dalone executable There is no need for file system support on the target platform as all data required for execution is contained in the executable application 2 5 Native code support The JamaicaVM implements the Java Native Interface V1 2 JNI This allows for direct embedding of existing native code into Java applications or to encode hardware accesses and performance critical code sections in C or machine code routines The usage of the Java Native Interface provides execution security even with the presence of native code while binary compatibility with other Java im plementations is ensured Unlike other Java implementations JamaicaVM pro vides exact garbage collection even with the presence of native code Realtime guarantees for the Java code are not affected by the presence of native code 2 6 Dynamic Linking One of the most important features of Java is the ability to dynamically load code in the form of class files during execution e g from a local file system or from a remote server The JamaicaVM supports this dynamic class loading enabling the full power of dynamically loaded software components This allows for exam ple on the fly reconfiguration hot swapping of code dynamic add
17. This is done with jamaicac Jamaica s version of javac The source code resides in the src folder and we wish to generate byte code in a classes folder which must be created if not already present mkdir classes gt jamaicac d classes src HelloWorld java Before generating an executable we test the byte code with the Jamaica virtual machine 3 4 BUILDING AND RUNNING AN EXAMPLE JAVA PROGRAM 29 gt jamaicavm cp classes HelloWorld Hello World Hello World Hello World Hello World Hello World Hello World en Having convinced ourselves that the program exhibits the desired behaviour we now generate an executable with the Jamaica Builder In the context of the Ja maicaVM Tools one speaks of building an application gt jamaicabuilder cp classes interpret HelloWorld Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed HelloWorld__ c HelloWorld__ h Class file compaction gain 58 893684 21654255 gt 8901266 C compiling HelloWorld__ c HelloWorld nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB
18. a Ja maica distribution provides support for the target platform that hosts the tool chain as well as for an embedded or real time operating system 3 4 Building and Running an Example Java Program A number of sample applications is provided These are located in the directory jJamaica home target platform examples In the following instructions it is assumed that a Unix host system is used For Windows please note that the Unix path separator character should be replaced by V Before using the examples it is recommended to copy them from the instal lation directory to a working location that is copy each of the directories jamaica home platform examples to user home examples platform The HelloWorld example is an excellent starting point for getting acquainted with the Jamaica VM tools In this section the main tools are used to build an application executable for a simple HelloWorld both for the host and target plat forms Below it is assumed that the example directories have been copied to user home examples host and user home examples target for host and target platforms respectively 3 41 Host Platform In order to build and run the HelloWorld example on the host platform go to the corresponding examples directory gt cd user home examples host Depending on your host platform host will be 1inux x86 windows x86 or solaris sparc First the Java source code needs to be compiled to byte code
19. purpose The priMap option allows one to replace the default mapping used for a target system with a specific priority mapping The Java thread priorities are integer values in the range 1 through 127 where 1 corresponds to the lowest priority and 127 to the highest priority Since not all Java priorities need or can be mapped to system level priorities the maximal avialable Java priority may be less than 127 The Java priorities 1 through 10 cor respond to the ten priority levels of jJava lang Thread threads while prior ities starting at 11 represent the priority levels of Realt imeThreads package javax realtime The maximal priority is not available for Java threads as it is used for the synchronization thread that permits round robin scheduling of threads of equal priorities Each single Java priority up to the maximal priority can and must be mapped to a system priority To simplify the description of a mapping a range of priorities can be described using from to Example 1 1 11 50 12 39 51 78 40 85 will cause all java lang Thread threads to use system priority 50 while the realtime threads will be mapped to priorities 51 through 78 and the synchronization thread will use priority 85 There will be 28 priority levels available for threads from javax realtime RealtimeThread Example 2 priMap 1 52 22 104 will cause the use of system pri orities 2 4 6 through 102 for the Java priorities 1 through 51 The sy
20. 224 dle eis 225 B 7 1 Installation 225 Boe PUR EA EEUU RR HORIS EUR ee 225 B 8 225 27 C m 227 PP 230 233 Limitations 235 E VMLlumiatios RR RR 235 E2 Builder Limitations ns 236 Internal Environment Variables 239 10 CONTENTS Part I Introduction Chapter 1 Preface The Java programming language with its clear syntax and semantics is used widely for the creation of complex and reliable systems Development and main tenance of these systems benefit greatly from object oriented programming con structs such as dynamic binding and automatic memory management Anyone who has experienced the benefits of these mechanisms on software development productivity and improved quality of resulting applications will find them essen tial when developing software for embedded and time critical applications This manual describes JamaicaVM a Java implementation that brings tech nologies that are required for embedded and time critical applications and that are not available in classic Java implementations This enables this new application domain to profit from the advantages that have provided an enormous boost to most other software development areas 1 1 Intended Audience of This Book Most developers familiar with Java environments will quickly be able to use the tools provided with Jamaic
21. 6 Miscellaneous Miscellaneous options 178 CHAPTER 14 THE JAMAICA BUILDER Option XignoreLineNumbers Specifying the XignoreLineNumbers option instructs the Builder to remove the line number information from the classes that are built into the target applica tion The resulting information will have a smaller memory footprint and RAM demand However exception traces in the resulting application will not show line number information Option agent1ib lib option val option val The agent lib option loads and runs the dynamic JVMTI agent library libname with the given options Be aware that JVMTI is not yet fully implemented so not every agent will work Jamaica comes with a statically built in debugging agent that can be selected by setting BuiltInAgent as name The transport layer must be sockets A typical example would be agentlib BuiltInAgent transport dt _ socket server y suspend y address 8000 This starts the applica tion and waits for a incoming connection of a debugger on port 8000 14 4 Environment Variables The following environment variables control the Builder JAMAICA The Jamaica Home directory jamaica home This variable sets the path of Jamaica to be used Under Unix systems this must be a Unix style pathname while under Windows this has to be a DOS style pathname JAMAICA BUILDER MIN HEAPSIZE Initial heap size of the jamaica pro gram itself in bytes Setting this to a larger value e g 512M
22. B will prevent A and C from running because A is blocked and C has lower priority In fact this is a programming error If a thread might enter a monitor which a higher priority thread might require then no other thread should have a priority in between the two Since errors of this nature are very hard to locate the programming environ ment should provide a means for avoiding priority inversion The RTSJ defines two possible mechanisms for avoiding priority inversion Priority Inheritance and Priority Ceiling Emulation The Jamaica VM implements both mechanisms Priority Inheritance Priority Inheritance is a protocol which is easy to understand and to use but that poses the risk of causing deadlocks If priority inheritance is used whenever a higher priority thread waits for a monitor that is held by a lower priority thread 11 5 SCHEDULING AND SYNCHRONIZATION 121 Task A Task B Task C Figure 11 4 Priority Inversion Task A Task B Task C Figure 11 5 Priority Inheritance the lower priority thread s priority is boosted to the priority of the blocking thread Fig illustrates this Priority Ceiling Emulation Priority Ceiling Emulation is widely used in safety critical system The priority of any thread entering a monitor is raised to the highest priority of any thread which could ever enter the monitor Fig I1 6 illustrates the Priority Ceiling Emulation protocol As long as no thread that holds a priority
23. Eclipse A Yes There is a plugin available that will help you to configure the Builder download and execute your application on your target For more infor mation see http www aicas com eclipse html For a quick start you can use the Eclipse Update Site Manager with the following Update Site URL http www aicas com download eclipse This conveniently downloads and installs the plugin Does Jamaica VM support the Real Time Specification for Java RTSJ A Yes The RTSJ V1 0 2 is supported by JamaicaVM 6 0 The API documenta tion of the implementation can be found at jamaica doc rtsj api index html Q Is Linux a real time operating system A No However kernel patches exist which add the functionality for real time behavior to a regular Linux system A 2 Jamaica VM Q When I try to execute an application with the JamaicaVM I get the error mes sage OUT OF MEMORY What can I do 205 206 APPENDIX FAQ FREQUENTLY ASKED QUESTIONS A The JamaicaVM has a predefined setting for the internal heap size If it is exhausted the error message OUT OF MEMORY is printed JamaicaVM exits with an error code The predefined heap size of 256MB is usually large enough but for some applications it may not be sufficient You can set the heap size via the jamaicavm options Xmxsize via the environment variable JAMAICAVM MAXHEAPSIZE e g under bash with export JAMAICAVM MAXHEAPSIZE 268435456 o
24. Emulation PCE can never cause deadlocks but care has to be taken that a monitor is never used in a thread of higher priority than the monitor Both protocols are efficiently implemented in the Jamaica VM 126 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES Part III Tools Reference 127 Chapter 12 The Jamaica Java Compiler The command jamaicac is a compiler for the Java programming language and is based on OpenJDK s Java Compiler It uses the system classes of the Jamaica distribution as default bootclasspath 12 1 Usage of jamaicac The command line syntax for the jamaicac is as follows jamaicac options source files and directories If directories are specified their source contents are compiled The command line options of jamaicac are those of javac As notable difference the additional useTarget option enables specifying a particular target platform 12 1 1 Classpath options Option useTarget platform The useTarget option specifies the target platform to compile for It is used to compute the bootclasspath in case boot classpath is omitted By default the host platform is used Option cp classpath path The classpath option specifies the location for application classes and sources The path is a list of directories zip files or jar files separated by the platform specific separator usually colon Each directory or file can specify access rules for types between and P e g X java t
25. GC Option reservedMemory percentage Jamaica VM s realtime garbage collector performs GC work at allocation time This may reduce the responsiveness of applications that have long pause times with little or no activity and are preempted by sudden activities that require a burst of memory allocation The responsiveness of such burst allocations can be improved significantly via reserved memory If the reservedMemory option is set to a value larger 0 then a low priority thread will be created that continuously tries to reserve memory up to the percent age of the total heap size that is selected via this option Any thread that performs memory allocation will then use this reserved memory to satisfy its allocations whenever there is reserved memory available For these allocations of reserved memory no GC work needs to be performed since the low priority reservation thread has done this work already Only when the reserved memory is exhausted will GC work to allow further allocations be performed The overall effect is that a burst of allocations up to the amount of reserved memory followed by a pause in activity that was long enough during this alloca tion will require no GC work to perform the allocation However any thread that performs more allocation than the amount of memory that is currently reserved will fall back to the performing GC work at allocation time The disadvantage of using reserved memory is that the worst case GC work that
26. INCLUDE RTP SHELL CMD e INCLUDE POSIX PTHREAD SCHEDULER If WindML graphics is used it must be included as well e INCLUDE WINDML In addition the following parameters should be set Parameter Value NUM FILES 1024 DKM only RTP FD NUM MAX 1024 RTP only TASK USER EXC STACK SIZE 16384 If some of this functionally is not included in the VxWorks kernel image linker errors may occur when loading an application built with Jamaica and the application may not run correctly B 1 2 Installation The VxWorks version of Jamaica is installed as described in the section Installa tion 3 1 In addition the following steps are necessary Configuration for Tornado VxWorks 5 x e Set the environment variable WIND_BASE to the base directory of the Tor nado installation e We recommend you set the environment variable WIND_BASE in your boot or login script to the directory where Tornado is installed top level direc tory e Add the Tornado tools directory to the PATH environment variable so that tools like ccppc exe resp ccpent ium exe can be found Do not use the DOS Windows Style path separator backslash in WIND BASE because some programs interpret the backslash as an escape sequence for special characters Use slash in path names Configuration of platform specific tools see 8 3 1 1 is only required in
27. Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB gt ls s caffeine_nolibs 3569868 caffeine nolibs About 75 of the class file data can be removed so that the resulting application occupies only 783kB 7 2 4 Memory Required for Threads To reduce the Non Java heap memory one must reduce the stack sizes and the number of threads that will be created for the application This can be done in the following ways 1 Reducing Java stack size The Java stack size can be reduced via setting option javaStackSize to a lower value than the default typically 20K To reduce the size to 4 kilobytes javaStackSize 4K can be used 2 Reducing C stack size The C stack size can be set accordingly via option nat iveStackSize 3 Disabling finalizer thread A Java application typically uses one thread that is dedicated to running the finalize methods of objects that were found to be unreachable by the garbage collector An application that does not allocate any of such objects 7 2 OPTIMIZING RAM MEMORY DEMAND 71 may not need this finalizer thread The priority of the finalizer thread can be adjusted through the option finalizerPri Setting the priority to zero finalizerPri 0 deactivates the finalizer thread completely Note that deactivating the finalizer thread may cause a memory leak since any objects that have a finalize method can no longer be reclaimed Sim
28. Plug In see 8 5 provides the required setup for debug ging with the JamaicaVM on the host system automatically It is sufficient to select Jamaica as the Java Runtime Environment of the project 9 3 Reference Information Jamaica supports the Java Platform Debugger Architecture JPDA Debugging is possible with IDEs that support the JPDA Tab 9 1 shows the debugging options accepted by Jamaica s communication agent The Jamaica Debugging Interface has the following limitations e Local variables of compiled methods cannot be examined e Stepping through a compiled method is not supported e Setting a breakpoint in a compiled method will silently be ignored e Notification on field access modification is not available 9 3 REFERENCE INFORMATION 91 Create manage and run configurations Attach to a Java virtual machine accepting debug connections Bi Name type filter text E Common Eclipse Application Java Applet v 27 Application Main O SpinningLogo Ju JUnit Jt JUnit Plug in Test OSGi Framework Connection Properties v m Remote Java Application 1 Ell New configuration Host device local Port 4000 C Allow termination of remote VM New configuration Connection Type LET Filter matched 10 of 10 items Figure 9 1 Setting up a remote debugging connection in Eclipse 3 5 92 CHAPTER 9 DEBUGGING SUPPORT Syntax Description tr
29. Pri orities of normal threads may be in the range permitted forRealtimeThreads see option priMap Furthermore any thread may access objects allocated on the heap without having to fear being delayed by the garbage collector Any thread is safe from being interrupted or delayed by garbage collector activity Only higher priority threads can interrupt lower priority threads When using Jamaica VM it is thus not necessary to use non heap memory areas for realtime tasks It is possible for any thread to access objects on the heap Furthermore scoped memory provided by the classes defined in the RTSJ are available to normal threads as well The strict semantics of the RTSJ require a significant runtime overhead to check that an access to an object is legal Since these checks are not needed by Jamaica VM they are disabled by default However setting strict RTSJ forces Jamaica VM to perform these checks If the option st rict RTSJ is set the following checks are performed and the corresponding exceptions are thrown MemoryAccessError aNoHeapRealtimeThread attempts to access an object stored in normal Java heap a MemoryAccessError is thrown IllegalStateException anon RealtimeThread attempts to enter javax realtime MemoryArea or tries to access the scope stack by call ing the methods get CurrentMemoryArea getMemoryAreaStackDepth getOuterMemoryArea or getInitialMemoryAreaIndex which are de fined in class javax realtime RealtimeThread La
30. _ cplusplus fendif fendif The native code is implemented in JNITest c finclude jni h Env xenv jclass c 16 1 USING JNI 193 include JNITest h include lt stdio h gt JNIEXPORT jint JNICALL Java JNITest write 1HW lRegister JNIEnv xenv jclass c jint vO jint v1 printf Now we could write the value i into memory address x n vl v0 return vl return the written value Note that the mangling of the Java name into a name for the C routine is defined in the JNI specification In order to avoid typing errors just copy the function declarations from the generated header file A C compiler is used to generate an object file Here gcc the GNU C compiler is used but other C compilers should also work Note that the include search directories provided with the option I may be different on your system For Unix users using gcc the command line is gt gcc I usr 1local jamaica target linux gnu i686 include gt c m32 JNITest c For Windows user using the Visual Studio C compiler the command line is gt c Programs cl Ic programs jamaica target windows x86 include c m32 JNITest c Finally the Builder can be called to generate a binary file which contains all nec essary classes as well as the object file with the native code from JNITest c The Builder is called by gt jamaicabuilder object JNITest o JNITest Reading co
31. a class calls of static methods accesses to static fields and the creation of an instance of a class Setting this option causes Jamaica VM to load and link classes lazily This behaviour may be required to execute applications that reference classes that are not available and that are never used during runtime Also it helps to reduce startup time of an application that refers to large library code that is not actually needed at runtime Option lazyFromEnv var This option causes the creation of an application that reads its Lazy setting from the specified environment variable If this variable is not set the value of boolean option lazy will be used The value of the environment variable must be 0 for lazy false or 1 for lazy true Option destination The dest ination option specifies the name of the destination executable to be generated by the Builder If this option is not present the name of the main class is used as the name of the destination executable The destination name can be a path into a different directory E g destination myproject bin application may be used to save the created executable applicationinmyproject bin Option tmpdir name The tmpdir option may be used to specify the name of the directory used for temporary files generated by the Builder such as C source and object files for compiled methods Option resource This option causes the inclusio
32. a target that executes the binary that resulted from the specific Builder configuration Click Invoke Ant on this target to start the application If the ap plication needs runtime parameters those can be specified by clicking configure at the end of the arguments line property task s env attribute is not supported 44 CHAPTER 5 SUPPORT FOR THE ECLIPSE IDE Part II Tools Usage and Guidelines Chapter 6 Performance Optimization The most fundamental measure employed by the Jamaica Builder to improve the performance of an application is to statically compile those parts that contribute most to the overall runtime These parts are identified in a profile run of the application Identifying these parts is called profiling The profiling information is used by the Builder to decide which parts of an application need to be compiled and whether further optimizations such as inlining the code are necessary 6 1 Creating a profile The builder s profile option and the jamaicavmp command provide sim ple means to profile an application Setting the profile option enables pro filing The builder will then link the application with the profiling version of the JamaicaVM libraries During profiling the Jamaica Virtual Machine counts among other things the number of bytecode instructions executed within every method of the application The number of instructions can be used as a measure for the time spent in each method
33. an intermediary target code allowing easy porting to different target platforms The Jamaica compiler is tightly inte grated into the memory management system allowing highest performance and reliable realtime behavior No conservative reference detection code is required enabling fully exact and predictable garbage collection 22 CHAPTER 2 KEY FEATURES OF JAMAICAVM 2 9 Tools for Realtime and Embedded System De velopment JamaicaVM comes with a set of tools that support the development of applications for realtime and embedded systems e Jamaica Builder a tool for creating a single executable image out of the Jamaica Virtual Machine and a set of Java classes This image can be loaded into flash memory or ROM avoiding the need for a file system in the target platform For most effective memory usage the Jamaica Builder finds the amount of memory that is actually used by an application This allows both system memory and heap size to be precisely chosen for optimal run time perfor mance In additon the Builder enables the detection of performance critical code to control the static compiler for optimal results e Thread Monitor enables to analyse and fine tune the behaviour of threaded Java applications e VeriFlux a static analysis tool for the object oriented domain that enables to prove the absence of potential faults such as null pointer exceptions or deadlocks in Java programs Thread Monitor and VeriFlux are not
34. available for scoped memory areas javax realtime LTMemory and javax realtime VTMemory This memory lies outside of the normal Java heap but it is nevertheless scanned by the garbage collector for references to the heap Objects allocated in scoped memory will never be reclaimed by the garbage collector Instead their memory will be freed when the last thread exits a the scope Option scopedMemorySizeFromEnv var The scopedMemorySizeFromEnv option enables the application to read its scoped memory size from the environment variable specified within If this vari 168 CHAPTER 14 THE JAMAICA BUILDER able is not set the scoped memory size specified using scopedMemorySize n will be used Option physicalMemoryRanges range range The RawMemory and PhysicalMemory classes in the javax realtime package provide access to physical memory for Java applications The memory ranges that may be accessed by the Java application can be specified using the option physicalMemoryRanges The default behavior is that no access to physical memory is permitted by the application The physicalMemoryRanges option expects a list of address ranges Each address range is separated by and gives the lower and upper address of the range lower upper The lower address is inclusive and the upper address is exclusive Le the difference upper lower gives the size of the accessible area There can be an arbitrary number of memory ranges Example 1
35. cause a potentially high overhead for exiting this scope The finalizers of objects that are allocated in ImmortalMemory will never be executed As an alternative to finalizers the consequent use of finally clauses in Java code to free unused resources at a predefined time is highly recommended Using finalizers may be helpful during debugging to find programming bugs like leakage of resources or to visualize when an object s memory is recycled In a production release any finalizers even empty ones should be removed due to the impact they have on the runtime and the potential for memory leaks caused by their presence 11 4 3 Configuring a Realtime Garbage Collector To be able to determine worst case execution times for memory allocation opera tions in a realtime garbage collector one needs to know the memory required by the realtime application With this information a worst case number of garbage collector increments that are required on an allocation can be determined see 818 Automatic tools can help to determine this value The heap size can then be lected to give sufficient headroom for the garbage collector while a larger heap size ensures a shorter execution time for allocation Tools like the analyzer in the 116 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES JamaicaVM help to configure a system and find suitable heap size and allocation times 11 4 4 Programming with the RTSJ and Realtime Garbage Col lection
36. ceiling emulation monitor blocks any thread that tries to enter such a monitor can be sure not to quently the use of priority ceiling emulation automatically ensures that system is deadlock free If any other thread owns the monitor its priority will have been boosted to the ceiling priority Consequently the current thread cannot run and try to enter this monitor 122 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES Task A Task B Priority Ceiling Task C Figure 11 6 Priority Ceiling Emulation Protocol Lock y Task A Task B Lock x Lock y Figure 11 7 Deadlocks are possible with Priority Inheritance Priority Inheritance vs Priority Ceiling Emulation Priority Inheritance should be used with care because it can cause deadlocks when two threads try to enter the same two monitors in different order This is shown in Fig Thus it is safer to use Priority Ceiling Emulation since when used correctly deadlocks cannot occur there Priority Inheritance deadlocks can be avoided if all programmers make sure to always enter monitors in the same order Unlike classic priority ceiling emulation the RTSJ permits blocking while holding a priority ceiling emulation monitor Other threads that may want to enter the same monitor will be stopped exactly as they would be for a normal monitor This fall back to standard monitor behavior permits the use of priority ceiling emulation even for monitors that are
37. classes will be added dynamically Setting option closed to true enables such optimizations a significant enhance ment of the performance of compiled code is usually the result The additional optimization performed when closed is set include static binding of virtual method calls for methods that are not redefined by any of the classes built into the application The overhead of dynamic binding is removed and even inlining of a virtual method call becomes possible which often results in even further possibilities for optimizations Note that care is needed for an open application that uses dynamic loading even when closed is not set For an open application it has to be ensured that all classes that should be available for dynamically loaded code need to be included fully using option includeClasses or includeJAR Otherwise the Builder may omit these classes if they are not referenced by the built in application or it may omit parts of these classes certain methods or fields that happen not to be used by the built in application 14 2 BUILDER USAGE 155 Option showIncludedFeatures The showIncludedFeatures option will cause the Builder to display a list of all classes methods and fields that will be part of the created application Any classes methods or fields removed from the target application through mecha nisms such as smart linking will not be displayed Used in conjunction with includeClasses excludeClasses includeJAR an
38. cumulatively require most of the execution time gt grep PROFILE CYCLES HelloWorld prof sort rn k2 head n25 javax realtime AffinitySet lt cl java util BitSet clinit V i java lang Class desiredAsserti PROFILE CYCLES PROFILE CYCLES PROFILE CYCLES 1803030931 1774328122 1759095288 PROFILE CYCLES 1232845675 java lang System lt clinit gt V i PROFILE_CYCLES 411827088 java io PrintStream init Lja PROFILE CYCLES 411762656 java io PrintStream init Lja PROFILE CYCLES 407908263 java lang System 4 init Ljav PROFILE CYCLES 397958325 java io OutputStreamWriter in PROFILE CYCLES 382076564 sun nio cs StreamEncoder forOu PROFILE CYCLES 366630363 java lang String intern Ljava PROFILE CYCLES 322935075 sun misc URLClassPath pathTOoUR PROFILE CYCLES 277977307 java nio charset Charset clin PROFILE CYCLES 268836921 java lang ClassLoader loadClas PROFILE CYCLES 268802918 java lang ClassLoader loadClas PROFILE CYCLES 268769712 java lang ClassLoader loadClas PROFILE CYCLES 268300354 java lang ClassLoader SystemCl PROFILE CYCLES 268236844 java net URLClassLoader findCl PROFILE CYCLES 264332693 java io BufferedInputStream c PROFILE CYCLES 259179348 java util concurrent atomic At PROFILE CYCLES 256416238 java security AccessController PROFILE CYCLES 256392827 java net URLClassLoader 1 run PROFILE CYCLES 256361948 java net URLClassL
39. default heap size is 64K bytes as specified by the following default 1d directive heap align 16 pad 0x10000 NOCLEAR This can be increased in myapplication ld to 8MB as follows heap align 16 pad 0x800000 NOCLEAR If you need to control where in RAM the kernel is placed you may specify the rambase and ramlimit to identify the starting base of the kernel image and set the limit of where free memory ends This is only valid for the KernelSpace program s linker directives file e g default 1d ramlimit 0x800000 ramlimit defines the size of available RAM 8MB by default for sim800 BSP The devguide manual provides detailed instructions on how to build applica tions for INTEGRITY B 3 3 Additional Target configuration If any additional configuration of your target is required e g of the network it may be defined in the file jamaica home target integrity x include target configuration h This file will be included when the application is built B 4 Windows B 4 1 Limitations The current release of Jamaica for the desktop versions of Windows contains the following limitations e Norealtime signals are available e On multicore systems Jamaica will always run on the first CPU in the sys tem 224 B 5 APPENDIX B INFORMATION FOR SPECIFIC TARGETS WindowsCE B 5 1 Limitations The current release of Jamaica for WindowsCE contains the following limitations WindowsCE Version 5 limits pro
40. default usually results in good performance for small applications but it causes extreme code size increase for larger applications and it results in slow execution of applications that use the system classes in a way different than recorded in the system profile gt jamaicabuilder cp classes CaffeineMarkEmbeddedApp gt destination caffeine Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed Vf8981d50b7d603bf c D osa caffeine c caffeine h Class file compaction gain 58 973328 21665933 gt 8888811 C compiling caffeine__ c Des caffeine nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB gt ls s caffeine 12726072 caffeine The runtime performance is better than the interpreted version But compared to the executable in the next section the application size is bigger and the per 62 CHAPTER 7 REDUCING FOOTPRINT AND MEMORY USAGE formance is slightly worse It is strongly recommended to create a profile as desc
41. displays Builder usage and a short description of all possible standard command line options Option Xhelp Xhelp The Xhelp option displays Builder usage and a short description of all possible extended command line options Extended command line options are not needed for normal control of the Builder command They are used to configure tools and options and to provide tools required internally for Jamaica VM development Option version Print the version of the Builder and exit Option verbose n The verbose option sets the verbosity level for the Builder If the verbosity level is larger than 0 additional output on the state of the build process is printed to standard out The information provided in verbose mode includes external tools called warnings or the list of all class files that are loaded and the methods that are compiled in case compilation is switched on Option showSettings Print the builder settings in property file format To make these setting the de fault replace the file jamaica home target platform etc jamaica conf by the output Option saveSettings ile Ifthe saveSettings option is used Jamaica Builder options currently in effect are written to the provided file in property file format To make these setting the default replace the file jamaica home target platform etc jamaica conf by the output 148 CHAPTER 14 THE JAMAICA BUILDER Option configuration file The configuration op
42. dynamic determination of garbage collection work The disadvantage is that any allocation requires this worst case amount of garbage collection work The output generated using the option analyze also shows possible values for the constant garbage collection option In the example above the amount of garbage collection work required varies from 3 to 24 units for heap sizes between 7366K and 2246K bytes A unit of garbage collection work is the same as in the dynamic case about 160 machine instructions on the PowerPC processor Similarly if we want to give the same guarantee of 14 units of work for the worst case execution time of the allocation of a block of memory with con stant garbage collection work a heap size of 2427K bytes is sufficient To in form the builder that constant garbage collection work should be used the op tion constGCwork and the number of units of work should be specified when building the application gt jamaicabuilder cp classes heapSize 2427K maxHeapSize 2427K gt constGCwork 14 HelloWorld Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed PKG__V66c2f3114d534efc__ o reusing existing file for package HelloWorld__ c
43. for each element of the list For example the following are equivalent classpath system classes user classes classpath system classes classpath user classes The separator for list elements depends on the agrument type and is documented for the individual options As a general rule paths and file names are separated by the system specific separator character colon on Unix systems semicolon on Windows for identifiers such as class names and package names the separator is space and for maps the separator is comma Note that arguments in particular file names and argument lists that contain spaces must be enclosed in double quotes The following are well formed declarations includeClasses java lang java util classpath t system classes installation directory Options that permit a list of mappings as their arguments require one equals sign to start the arguments list and another equals for each mapping in the list priMap 1 5 2 7 3 9 Default values for many options are target specific The actual settings may be obtained by invoking the Builder with he1p In order to find out the the settings for a target other than the host platform include target platform 14 2 BUILDER USAGE 147 14 2 1 General The following are general options which provide information about the Builder itself or enable the use of script files that specifying further options Option help help h The help option
44. for multiprogramming in hard real time environment Journal of the ACM 20 1973 241 Index 134 147 194 197 extdirs 130 agentlib finalizerPri 160 all finalizerPriFromEnv 161 analyse 163 jeu E analyze i63 A 147 194 197 analyzeFromEnv 163 heapSize 157 atomicGC heapSizeFromEnv bootelasspath cdc 153 help L34 147 194 197 196 help immortalMemorySize 167 immortalMemorySizeFromEnv Raid includeClasses 148 Ponpe includeFilename 195 configuration includeJAR 150 constGCwork lation I constGCworkFromEnv 164 incrementalCompilation 153 inline 156 cp 129 interpret 155 D 134 H J d 148 deprecation javaStackSize 157 destination 151 javaStackSizeFromEnv dwarf2 jni 195 ea 148 js 135 enableassertions 148 lazy 150 encoding Jaz FroinBoy 151 excludeClasses 149 i M excludeFromCompile 150 main 148 excludeJAR maxHeapSize 157 242 INDEX maxHeapSizeFromEnv maxNumThreads 158 maxNumThreadsFromEnv mi ms 135 mx nativeStackSize 158 nativeStackSizeFromEnv nowarn ns 136 numJniAttachableThreads numJniAttachableThreadsFromEnv numThreads numThreadsFromEnv 0 object 169 optimise 156 optimize 156 percentageCompiled physicalMemoryRanges 168 priMap priMapFromEn
45. gt XstaticLibraries library lt library gt XlinkDynamicPrefix prefix XlinkStaticPrefix prefix XlinkDynamicFlags switch XlinkStaticFlags switch XlibraryPaths path path Xstrip tool XnoRuntimeChecks XavailableTargets XprofileFilename lt name gt XenableDynamicJNILibraries XloadJNIDynamic lt class gt lt method gt lt class gt lt method gt Xinclude lt dirs gt XobjectFormat default none C ELF PECOFF XobjectProcessorFamily lt type gt XobjectSymbolPrefix prefix XignoreLineNumbers agentlib lib option val option val classl classn 14 3 1 General The following are general options which provide information about the Builder itself or enable the use of script files that specifying further options 14 3 BUILDER EXTENDED USAGE 171 Option XdefineProperty name value The XdefineProperty option sets a system property for the resulting binary For security reasons system properties used by the VM cannot by changed The Unicode character U EEEE is reserved and may not be used within the argument of the option Option XdefinePropertyFromEnv name At program start the resulting binary will set a system property to the value of an environment variable This feature can only be used if the target OS supports environment variables Fo
46. java lang Runtime runFinalization It can be useful on very small systems not to use a finalizer thread This reduces the use of system resources The priority must be one of the Java priorities 1 through 10 corre sponding to the ten priority levels of java lang Thread Option heapSizeFromEnv var The heapSizeFromEnv option enables the application to read its heap size from the specified environment variable If this variable is not set the heap size specified using heapSize n will be used Option maxHeapSizeFromEnv var The maxHeapSizeFromEnv option enables the application to read its maxi mum heap size from the specified environment variable If this variable is not set the maximum heap size specified using maxHeapSize n will be used Option heapSizelIncrementFromEnv var The heapSizeIncrementFromEnv option enables the application to read its heap size increment from the specified environment variable within If this vari able is not set the heap size increment specified using heapSizelncrement n will be used 14 2 BUILDER USAGE 161 Option javaStackSizeFromEnv var The javaStackSizeFromEnv option enables the application to read its Java stack size from the specified environment variable If this variable is not set the stack size specified using javaStackSize n will be used Option nativeStackSizeFromEnv var The nativeStackSizeFromEnv option enables the application to read its native stack size from
47. libraries or extensions such as the Real Time Specification for Java Please refer to the JavaDoc documentation of these li braries provided with JamaicaVM see 3 3 1 2 Contacting aicas Please contact aicas or one of aicas s sales partners to obtain a copy of JamaicaVM for your specific hardware and RTOS requirements or to discuss licensing ques tions for the Jamaica binaries or source code The full contact information for the aicas main offices is reproduced in the front matter of this manual page 2 The current list of sales partners is available online at http www aicas com An evaluation version of JamaicaVM may be downloaded from the aicas web site athttp www aicas com download html Please help us improve this manual and future versions of Jamaica VM E mail your bug reports and comments to bugs aicas Please include the exact version of JamaicaVM you use the host and target systems you are developing for and all the information required to reproduce the problem you have encountered 1 3 Whatis New in JamaicaVM 6 0 Version 6 0 of Jamaica VM provides numerous enhancements The most important additions are e Support for Java 6 0 features including Java 6 0 source and class file com patibility e The standard classes library is based on the OpenJDK code This leads to a more conformant implementation of the standard classes in particular AWT and Swing features 1 3 WHAT IS NEW IN JAMAICAVM 6 0 15 e
48. memory classes ImmortalMemory and ScopedMemory provide these memory areas One important consequence of using special memory areas is of course that the advantages of dynamic memory management is not fully available to realtime threads Synchronization In realtime systems with threads of different priority levels priority inversion situ ations must be avoided Priority inversion occurs when a thread of high priority is blocked by waiting for a monitor that is owned by a thread of a lower priority that 11 3 SUPPORTED STANDARDS 111 is preempted by some thread with intermediate priority The RTSJ provides two alternatives priority inheritance and the priority ceiling protocol to avoid priority inversion Limitations of the RTSJ and their solution The RTSJ provides a solution for realtime programming but it also brings new difficulties to the developer The most important consequence is that applications have to be split strictly into two parts a realtime and a non realtime part Commu nication between these parts is heavily restricted realtime threads cannot perform memory operations such as the allocation of objects on the normal heap which is under the control of the garbage collector Synchronization between realtime and non realtime threads is also severely restricted to prevent realtime threads from being blocked by the garbage collector due to priority inversion The JamaicaVM removes these restrictions by using its realti
49. needed for one object of this class 3 block size in bytes 4 number of bytes needed for all objects of this class 5 relative heap usage of objects of this class 6 3 INTERPRETING THE PROFILING OUTPUT 53 6 total number of objects of this class organized in a tree structure 7 relative number of objects of this class organized in a tree structure 8 name of the class Keyword INSTANTIATION_COUNT Groups memory Values 1 total number of instantiated objects of this class 2 number of blocks needed for one object of this class 3 number of blocks needed for all objects of this class 4 number of bytes needed for all objects of this class 5 total number of objects of this class organized in a tree structure 6 relative number of objects of this class organized in a tree structure 7 class loader that loaded the class 8 name of the class Keyword PROFILE Groups builder Values 1 total number of bytecodes spent in this method 2 relative number of bytecodes spent in this method 3 signature of the method 4 class loader that loaded the class of the method Keyword PROFILE_CLASS_USED_VIA_REFLECTION Groups builder Values 1 name of the class used via reflection 54 CHAPTER 6 PERFORMANCE OPTIMIZATION Keyword PROFILE_CYCLES Groups speed Values 1 total number of processor cycles spent in this method if available on the target 2 signature of the method Ke
50. null tmp class C classSC tmp 11 3 SUPPORTED STANDARDS 109 else tmp classSC Class class_C tmp This code sequence causes loading of new classes from the current class loading context Le it may involve memory allocation and loading of new class files If the new classes are provided by a user class loader this might even involve network activity etc Starting with JDK 1 5 the classname class notation will be supported by the JVM directly The complex code above will be replaced by a simple bytecode instruction that references the desired class directly Consequently the referenced class can be loaded by the JamaicaVM at the same time the referencing class is loaded and the statement will be replaced by a constant number of memory accesses 11 3 Supported Standards Thus far only standard Java constructs have been discussed However libraries and other APIs are also an issue Timely Java development needs support for timely execution and device access There are also issues of certifiability to con sider The JamaicaVM has at least some support for all of the following APIs 11 3 1 Real Time Specification for Java The Real Time Specification for Java RTSJ provides functionality needed for time critical Java applications RTSJ introduces an additional API of Java classes mainly with the goal of providing a standardized mechanism for realtime ex tensions of Java Virtual Machines RTSJ extensi
51. object will ever be recycled by the system and that a finalizer will ever be called Furthermore if several unreachable objects have a finalizer the execution order of these finalizers is undefined For these reasons it is generally unwise to use finalizers in Java at all The developer cannot rely on the finalizer ever being executed Moreover during the execution of a finalizer the developer cannot rely on the availability of any other resources since their finalizers may have been executed already In addition to these unpredictabilities the use of finalizers has an important impact on the memory demand of an application The garbage collector cannot reclaim the memory of any object that has been found to be unreachable before its finalizer has been executed Consequently the memory occupied by such objects remains allocated The finalizer methods are executed by the finalizer thread which by default runs at the lowest priority available to Java threads If this finalizer thread does not obtain sufficient execution time or it is stopped by a finalizer that is blocked the system may run out of memory In this case explicit calls to Runt ime run Finalization may be required by some higher priority task to empty the queue of finalizable objects The use of finalizers is more predictable for objects allocated in Scoped Memory or ImmortalMemory For ScopedMemory all finalizers will be executed when the last thread exits a scope This may
52. of 443K bytes we get max gc units 14 as has been shown above If our target platform gives a worst case execution time for one unit of garbage collection work of 1 6us we have wcet of gc unit 1 8 2 CONFIGURATION FOR HARD REALTIME APPLICATIONS 87 We use the numblocks tool see 8 I7 to find the number of blocks required for the allocation of a java lang StringBuffer object numblocks java lang StringBuffer 1 A StringBuffer object requires just a single block of memory so that numblocks new StringBuffer 1 and the total worst case execution time of the allocation becomes weet new StringBuffer 1 14 1 6us 22 4us Had we used the constant garbage collection option with the same heap size the amount of garbage collection work on an allocation of one block could have been fixed at 6 units In that case the worst case execution time of the allocation be comes WceteonstGCwork new StringBuffer 1 6 1 9 After creation of the java lang StringBuffer object a character array of 16 ele ments is allocated during the execution of StringBuffer s initialization routine For this allocation we can determine the worst case execution time by first deter mining the number of blocks required gt numblocks char 16 2 and we get weet new char 16 2 14 1 6ys 44 8us and WcCetconstGCworkl new Char 16 2 6 1 19 2 5 Typical values for the number of blocks required for the alloca
53. of allocation activity with sufficient idle time between these bursts will see an improved performance The maximum amount of memory that will be reserved by the memory reser vation thread is given as a percentage of the total memory The default value for this percentage is 10 It can be set via the builder options reservedMemory and reservedMemoryFromEnv or for the virtual machine via the environ ment variable JAMAICAVM RESERVEDMEMORY An allocation burst that exceeds the amount of reserved memory will have to fall back to perform garbage collection work as soon as the amount of reserved memory is exceeded This may occur if the maximum amount of reserved memory is less than the memory allocated during the burst or if there is too little idle time in between consecutive bursts such as when the reservation thread cannot catch up and reserve the maximum amount of memory For an application that cannot guarantee sufficient idle time for the memory reservation thread the amount of reserved memory should not be set to a high per centage Higher values will increase the worst case garbage collection work that will have to be performed on an allocation since after the reserved memory was allocated there is less memory remaining to perform sufficient garbage collection work to reclaim memory before the free memory is exhausted 78 CHAPTER 8 MEMORY MANAGEMENT CONFIGURATION A realtime application without allocation bursts and suff
54. option as follows gt jamaicabuilder cp classes interpret gt setLocales none setProtocols none setGraphics none gt setFonts none javaStackSize 4K finalizerPri 0 gt numThreads 1 timeSlice 0ns reservedMemory 0 gt XdefineProperty jamaica no_sig_int_handler true gt gt gt gt jamaica no sig quit handler true jamaica no sig term handler true CaffeineMarkEmbeddedApp XignoreLineNumbers true destination caffeine nolibs js fP tS nL Reading configuration from usr local jamaica 6 0 1 etc jamaica conf 74 CHAPTER 7 REDUCING FOOTPRINT AND MEMORY USAGE Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed caffeine nolibs js fP tS c caffeine nolibs js tS nL h Class file compaction gain 83 21974 8835298 gt 1482586 C compiling caffeine_nolibs_js_fP_tS_nL__ c mcpu is deprecated Use mtune or march instead caffeine nolibs js fP tS nL nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 128KB 1 128KB 63MB 511 128KB Thread Java stacks 4096B 1 4096B 2044KB 511 4096B Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 2308KB 337MB gt ls
55. package class package The includeClasses option forces the inclusion of the listed classes and packages into the created application The listed classes with all their methods 14 2 BUILDER USAGE 149 and fields will be included This is useful or even neccessary if you use reflection with these classes Arguments for this option can be a class name to include the class with all methods and fields a package name followed by an asterisk to include all classes in the package or a package name followed by to include all classes in the package and in all sub packages of this package Example includeClasses java beans XMLEncoder java util java lang includes the class java beans XMLEncoder all classes in java util and all classes in the package java lang and in all sub packages of java lang such as java lang ref f The includeClasses option affects only the listed classes themselves Subclasses of these classes remain subject to smart linking Option excludeClasses class package class package The excludeClasses option forces exclusion of the listed classes and pack ages from the created application The listed classes with all their methods and fields will be excluded even if they were previously included using includeJAR or includeClasses This is useful if you want to load classes at runtime Arguments for this option can be a class name to exclude the class with all methods and fields a pack
56. part of the standard Jamaica license Chapter 3 Getting Started 3 1 relea Installation of JamaicaVM se of the JamaicaVM tools consists of an info file with detailed information about the host and target platform and optional features such as graphics support and a package for the Jamaica binaries library and documentation files The Jamaica version build number host and target platform and other properties of a release is encoded as release identification string in the names of info and package file according to the following scheme U U Jamaica version build features host target in o Jamaica version build features host target suffix Package files with the following package suffixes are released Host Platform Suffix Package Kind Linux rpm Package for the rpm package manager tar gz Compressed tape archive file Windows exe Interactive installer zip Windows zip file Solaris tar gz Compressed tape archive file In order to install the JamaicaVM tools the following steps are required e Unpack and install the Jamaica binaries library and documentation files e Configure the tools for host and target platform C compiler and native li braries e Set environment variables e Install license keys 23 24 CHAPTER 3 GETTING STARTED The actual installation procedure varies from host platform to host platform see the sections below For additi
57. physicalMemoryRanges 0x0c00 0x1000 will allow access to the memory range from address 0x0c00 to 0x1000 i e to a range of 1024 bytes 14 2 8 Profiling Profiling can be used to guide the compilation process and to find a good trade off between fast compiled code and smaller interpreted byte code This is particularly important for systems with tight memory and CPU resources Option profile The profile option builds an application that collects information on the amount of run time spent for the execution of different methods This information is printed to the standard output after a test run of the application has been per formed The information collected in a profiling run can then be used as an input for the option useProfile to guide the compilation process Profiling information can only be collected when using the Jamaica VM in terpreter as compiled code cannot be profiled Consequently profile does not work in combination with compile Option XprofileFilenameFromEnv var The XprofileFilenameFromEnv creates an application that reads the name of a file for profiling data from the environment variable var If this variable is not 14 2 BUILDER USAGE 169 set the name specified using XprofileFilename will be used default not used Option percentageCompiled n Use profiling information collected using profile to restrict compilation to those methods that were most frequently executed during the profiling run The pe
58. running resch ready blocked detached 210 15 raise priority set to base priority ThreadName lt none gt start enter contended finish gc work a 8000000000 reschedule a J O user event allocated memory w thread state change W thread priority change thread names monitor enter exit L GC activity v start execution reschedule C ready yield w user event lv allocated memory 127 0 0 1 2712 IP Address Port advanced Buffer size Sample Period v show thread headers v show fixed time scale Start recording Figure 15 1 Control view of the ThreadMonitor 15 3 DATA WINDOW 185 File Quit Select this menu item will close all windows of the ThreadMonitor tool and quit the application 15 3 Data Window The data window will display scheduler data that was recorded through Start Stop recording in the control window or that was loaded from a file To better understand the ThreadMonitor output it is helpful to have some un derstanding of the JamaicaVM scheduler The JamaicaVM scheduler provides real time priority enforcement within Java programs on operating systems that do not offer strict priority based scheduling e g Linux for user programs The scheduler reduces the overhead for JNI calls and helps the operating system to better schedule CPU resources for thre
59. special situations Normally setting the environment variable WIND BASE and extend ing PATH is sufficient 216 APPENDIX B INFORMATION FOR SPECIFIC TARGETS Configuration for Workbench VxWorks 6 x e Set the environment variable WIND_HOME to the base directory of the Wind River installation e g opt WindRiver e Set the environment variable WIND_BASE to the VxWorks directory in the WindRiver installation The previously declared environment variable WIND HOME may be used e g SWIND HOME vxworks 6 6 e Set the environment variable WIND USR to the RTP header files directory of the WindRiver installation e g SWIND_BASE target usr We recommend using wrenv sh located in the WindRiver base directory to set all necessary environment variables The VxWorks subdirectory has to be specified as the following example shows for VxWorks 6 6 gt opt WindRiver wrenv sh p vxworks 6 6 1 Donotadd wrenv sh to your boot or login script It starts a new shell which tries to process its login script and thus you create a recursion Configuration of platform specific tools see 83 1 1 is only required in special situations Normally executing wrenv sh is sufficient B 1 3 Starting an application DKM The procedure for starting an application on VxWorks depends on whether down loadable kernel modules DKM or real time processes RTP are used For DKM if the target system is configur
60. that an application that on startup requires significantly more memory than the initial heap size will see its startup time increased by repeated incremental heap size expansion The obvious solution here is to set the initial heap size to a value large enough for the application to start The Jamaica builder option heapSize see 8 14 and 75 76 CHAPTER 8 MEMORY MANAGEMENT CONFIGURATION the virtual machine option Xmssize can be employed to set a higher size Starting off with a larger initial heap not only prevents the overhead of in cremental heap expansion but it also reduces the garbage collection work during startup This is because the garbage collector determines the amount of garbage collection work from the amount of free memory and with a larger initial heap the initial amount of free memory is larger 8 1 2 Maximum heap size The maximum heap size specified via builder option maxHeapSize see 8 14 and the virtual machine option Xmx should be set to the maximum amount of memory on the target system that should be available to the Java application Set ting this option has no direct impact on the performance of the application as long as the application s memory demand does not come close to this limit If the maximum heap size is not sufficient the application will receive an Out Of MemoryError at runtime However it may make sense to set the initial heap size to the same value as the maximum heap size whenever the initia
61. the user are displayed in angular brackets For example cat file instead of cat file 3 5 2 Argument Syntax In the specification of command line arguments and options the following nota tions are used TNI Alternative the pipe symbol denotes alternatives For example XobjectFormat default C ELF means that the Xob jectFormat option must be set to exactly one of the specified values default C or ELF Option optional arguments that may appear at most once are enclosed in brack ets For example heapSize n K M means that the heapSize option must be set to a numeric value which may be followed by either K or M Repetition optional arguments that may be repeated are enclosed in braces For example priMap jp sp jp sp means that the priMap accepts one or several comma separated arguments of the form jp sp These are assignments of Java priorities to system prior ities Alternative option names are indicated in parentheses For example 1 1 h means that the option help may be invoked by any one of he 1p help h and 3 5 NOTATIONS AND CONVENTIONS 33 3 5 3 Jamaica Home and User Home The file system location where the JamaicaVM Tools are installed is referred to as jamaica home In order for the tools to work correctly the environment variable JAMAICA must be set to jamaica home see 8B 1 The JamaicaVM Tools store user related information such as lice
62. to be included The libraries that should be included can be set through the option set Libraries For our example application it is sufficient to have the default encoding iso 8859_1 and no support for network protocols or text locales Furthermore security management and logging is not needed and a minimal charset is sufficient Con sequently we can set iso_encodings to 8859_1 while all of protocols and locales can be set to the empty set security and logger can be set to off and charsetprovider to minimal The resulting call to build the application looks as follows gt jamaicabuilder cp classes interpret gt setProtocols none setLocales none gt setGraphics none setFonts none gt CaffeineMarkEmbeddedApp destination caffeine nolibs Reading configuration from usr local jamaica 6 0 1 etc jamaica conf 70 CHAPTER 7 REDUCING FOOTPRINT AND MEMORY USAGE Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed caffeine nolibs c caffeine nolibs h Class file compaction gain 80 13192 8834956 gt 1755336 C compiling caffeine nolibs c caffeine nolibs nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread
63. useful on the host platform clean Remove all generated files 3 4 4 Overview of Further Examples For an overview of the available examples see Tab Examples that require graphics or network support are only provided for platforms that support graphics or network respectively Each example comes with a README file that provides further information and lists the available build targets 3 5 Notations and Conventions Notations and typographic conventions used in this manual and by the JamaicaVM Tools in general are explained in the following sections 3 5 1 Typographic Convertions Throughout this manual names of commands options classes files etc are set in this monospaced font Output in terminal sessions is reproduced in slanted monospaced in order to distinguish it from user input Entities in command lines and other user inputs that have to be replaced by suitable user input are shown in italics As little example here is the description of the the Unix command line tool cat which outptuts the content of a file on the terminal 32 CHAPTER 3 GETTING STARTED Use cat file to print the content of file on the terminal For example the content of the file song txt may be inspected thus cat song txt Mary had a little lamb Little lamb little lamb Mary had a little lamb Its fleece was white as snow In situations where suitable fonts are not available say in terminal output entities to be replaced by
64. worst case execution times win dow are based on the measured scheduling data Consequently they can only dis play the worst case times that were encountered during the actual run which may 190 CHAPTER 15 THE JAMAICA THREADMONITOR be fully unrelated to the theoretical worst case execution time of a given thread In addition to this fundamental limitation please be aware of the following detailed limitations Releases are the points in time when a waiting thread becomes ready If a re lease is caused by another thread e g via Java function Object notify this state change is immediate However if a release is caused by a timeout of a call to Object wait Thread sleep RealtimeThread wait ForNextPeriod or similar functions the state change to ready may be de layed if higher priority threads are running and the OS does not assign CPU time to the waiting thread A means to avoid this inaccuracy is to use a high priority timer e g class javax realtime Timer to wait for a release Blocking waits within a release will result in the worst case execution time anal ysis to treat one release as two independent releases Therefore the analysis is wrong for tasks that perform blocking waits during a release Any blocking within native code e g blocking I O operations is not affected by this so the analysis can be used to determine the execution times of I O operations Chapter 16 Jamaica and the Java Native Interface
65. 044 2 sun nio cs StreamEncoder write PROFILE 880044 2 sun nio cs StreamEncoder write PROFILE 720036 2 sun nio cs StreamEncoder write PROFILE 720036 2 sun nio cs StreamEncoder write PROFILE 720036 2 sun nio cs StreamEncoder write PROFILE 720036 2 java nio ByteBuffer arrayOffse PROFILE 720036 2 java nio ByteBuffer arrayOffse PROFILE 720036 2 java nio ByteBuffer arrayOffse PROFILE 652295 1 java lang String length I bo In this small example program it is not surprise that nearly all execution time is spent in methods that are required for writing the output to the screen The dom inant function is java nio ByteBufferImpl put which is used while converting Java s unicode characters to the platform s ISO 8859 1 encoding Also important is the time spent in StringBuffer append Calls to the StringBuffer meth ods have been generated automatically by j amaicac compiler for string con catenation expressions using the operator On systems that support a CPU cycle counter the profiling data also contains a cumulative count of the number of cycles spent in each method This information is useful to obtain a more high level view on where the runtime performance was spent 6 3 INTERPRETING THE PROFILING OUTPUT 57 The CPU cycle profiling information is contained in lines starting with the tag PROFILE_CYCLES A similar command line can be used to find the methods that
66. 1 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB 68 CHAPTER 7 REDUCING FOOTPRINT AND MEMORY USAGE Running the resulting application will print the amount of RAM memory that was required during the execution gt caffeine_analyse Sieve score 556 98 Loop score 604 2017 Logic score 733 0 String score 207 708 Float score 482 185 Method score 334 166650 Overall score 449 Application used at most 2120672 bytes for reachable objects on the Java heap accuracy 1 Worst case allocation overhead using 10 reserved memory TEE heapSize dynamic GC const GC work TEE 7423K 6 3 TEE 6164K 7 4 TEE 5366K 8 4 ttt 4828K 9 4 TEE 4435K 10 4 TEE 3908K 12 5 TEE 3577K 14 5 TEE 3341K 16 6 TEE 3172K 18 6 TEE 3042K 20 7 TEE 2857K 24 8 TEE 2733K 28 9 TEE 2645K 32 10 TEE 2576K 36 11 TEE 2523K 40 12 TEE 2446K 48 14 TEE 2392K 56 15 TEE 2354K 64 17 TEE 2264K 96 24 TEE 2220K 128 30 TEE 2176K 192 42 TEE 2155K 256 52 TEE 2135K 384 67 Here the application requires 2120672 bytes for the Java heap that is under the control of the garbage collector The minimum suggested heap size is 2135K while a larger heap size provides better worst case allocation overhead Nor mally it is a good choice to set the heap to the size associated with a dynamic 7 2 OPTIMIZING RAM MEMORY DEMAND 69 GC overhead of 20 in this example 3042K For further information on heap size analysi
67. 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB The builder has now generated the executable HelloWorld gt HelloWorld Hello World Hello World Hello World Hello World Hello World Hello World its uu 30 CHAPTER 3 GETTING STARTED 3 4 2 Target Platform With the JamaicaVM Tools building an application for the target platform is as simple as for the host platform First go to the corresponding examples directory gt cd user home examples platform Then compile and build the application specifiying the target platform gt mkdir classes gt jamaicac useTarget platform d classes src HelloWorld java gt jamaicabuilder target platforn cp classes interpret HelloWorld The target specific binary HelloWorld is generated For instructions how to launch this on the target operating system please consult the documentation of the operating system Additional target specific hints are provided in 8 B 3 4 53 Improving Size and Performance The application binaries in the previous two sections provide decent size opti misation but no performance optimisation at all The JamaicaVM Tools offer a wide range of controls to fine tune the size and performance of a built application These optimisations are mostly controlled through command line options of the Jamaica Builder While performance is not an issue for such a simple example in order to show the possibilities sets of o
68. AM requirements are available in Jamaica RAM memory is required for three main purposes 1 Memory for the application s data structures such as objects or arrays allo cated during runtime 2 Memory required to store internal data of the VM such as representation of classes methods method tables etc 3 Memory required for each thread such as Java and C stacks 7 2 1 Measuring RAM requirements The amount of RAM memory required by an application can be determined by setting the option analyse Apart from setting this option it is important that exactly the same arguments are used than in the final version Here analyse is set to 1 gt jamaicabuilder cp classes interpret analyse 1 gt CaffeineMarkEmbeddedApp destination caffeine_analyse Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed caffeine analyse c caffeine analyse h Class file compaction gain 58 882584 21665933 gt 8908472 C compiling caffeine analyse c caffeine analyse nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 51
69. CA BUILDER 14 2 3 Smart linking Smart linking and compaction are techniques to reduce the code size and heap memory required by the generated application These techniques are controlled by the following options Option smart If the smart option is set smart linking is enabled for the created application Smart linking enables the builder to remove unused code for example unused methods of a class and to perform better optimisation This results in smaller binary files smaller memory usage and faster execution Smart linking is enabled by default Smart linking may not be used for applications that use Java s reflection API including reflection via the Java Native Interface JNI to load classes that are un known at buildtime and therefore cannot be included into the application This is for example the case for classes which are loaded from a web server at runtime In such situations use smart false to disable smart linking Classes loaded via reflection that are known at buildtime should be included via builder options includeClasses or includeJAR These options selec tively disable smart linking for the included classes Option closed For an application that is closed i e that does not load any classes dynamically that are not built into the application by the Builder additional optimization may be performed by the Builder and the static compiler These optimizations cause incorrect execution semantics when additional
70. DE the task definition used by the configuration or add options to the body part Each option in the configuration is displayed by an input mask allowing you to perform various actions e Modify options The input masks reflect the characteristics of their asso ciated option e g an option that expects a list will be displayed as a list control Input masks that consists only of a text field show an asterisk after the option name when modified Please press Enter to accept the new value e Remove options Each input mask has a x control that will remove the option from the configuration e Disable options Options can also be disabled instead of removed e g in order to test the configuration without a specific option Uncheck the check box in front of an input mask to disable that option e Show help texts and load default values The arrow control in the upper right corner brings up a context menu You can show the option s description or load its default value not available for all options The values of all options are immediately validated If a value is not valid for a specific option the input mask will be annotated with the text invalid and an error message is shown Invalid options will be ignored when you try to build your application Multiple configurations It is possible to store more than one configuration in a buildfile Click Add a Jamaica Builder target to create a new minimal configuration The new co
71. DIST char 16 2 Nu0000 uffff int 32 4 231 poe long 64 8 993 265 float 32 4 1 4E 45F 3 4028235E38F double 64 8 4 9E 324 1 7976931348623157E308 Java reference 32 4 Table D 1 Memory Demand of Primitive Types Data Structure Memory Demand Object header containing garbage collection state object z ei 12 Bytes type inlined monitor and memory area Array header containing object header array layout in 16 Bytes formation and array length Java object size on heap minimum 32 Bytes Java array size on heap minimum 32 Bytes Minimum size of single heap memory chunk 64 KBytes Garbage Collector data overhead for heap memory For a usable heap of a given size the garbage collector will 6 25 allocate this proportion of additional memory for its data Stack slot 8 Bytes Java stack frame of normal method 4 slots Java stack frame of synchronized method 5 slots Java stack frame of static initializer 7 slots Java stack frame of asynchronously interruptible method 8 slots Additional Java stack frame data in profile mode 2 slots Table D 2 Memory Demand of Objects Arrays and Frames Appendix E Limitations This appendix lists limitations of the Jamaica virtual machine and tools E 1 VM Limitations Aspect Limit Number of Java Threads 511 Maximum Monitor Nest Count repeated monitor en ter of the same monitor in neste
72. Extended range of supported graphics systems New are DirectFB Linux Windows GF QNX This adds to existing support for X11 Linux WindML VxWorks GDI WindowsCE and Maui OS9 e The Java 2D API a set of classes for advanced 2D graphics and imaging is supported on all graphics systems e Bindings for OpenGL OpenGL ES and OpenGL SC are available e Improved handling of system resources such as files and sockets Even though a Java application may fail to correctly close or release these re sources the VM now tracks these and releases them on shutdown e Full crypo support By default cryptographic strength is limited to 48 Bits this is due to export restrictions Please contact aicas for details e Dynamic loading of native libraries on selected platforms only For user relevant changes between minor releases of JamaicaVM see the release notes which are provided in the Jamaica installation folder doc file RELEASE _ NOTES 16 CHAPTER 1 PREFACE Chapter 2 Key Features of JamaicaVM The Jamaica Virtual Machine JamaicaVM is an implementation of the Java Vir tual Machine Specification It is a runtime system for the execution of applications written for the Java 6 Standard Edition It has been designed for realtime and em bedded systems and offers unparalleled support for this target domain Among the extraordinary features of JamaicaVM are e Hard realtime execution guarantees e Support f
73. HelloWorld__ h Class file compaction gain 58 96339 21654255 gt 8886172 C compiling HelloWorld__ c HelloWorld__nc o linking x stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB 8 2 CONFIGURATION FOR HARD REALTIME APPLICATIONS 85 Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 1429KB 1429KB GC data 89KB 89KB TOTAL 2670KB 73MB 8 2 6 Comparing dynamic mode and constant GC work mode Which option you should choose dynamic mode or constant garbage collection depends strongly on the kind of application If worst case execution time and low jitter are the most important criteria constant garbage collection work will usu ally provide the better performance with smaller heap sizes But if average case execution time is also an issue dynamic mode will typically give better overall throughput even though for equal heap sizes the guaranteed worst case execution time is longer with dynamic mode than with constant garbage collection work Gradual degradation may also be important Dynamic mode and constant garbage collection work differ significantly when the application does not stay within the memory bounds that were fixed when the application was built There are a number of reasons an application might be using more memory e The application input data might be bigger than originally anticipated e The application
74. Is provided by the RTSJ with the predictable execution obtained through realtime garbage collection and a realtime implementation of the virtual machine 2 3 Minimal footprint JamaicaVM itself occupies less than 1 MB of memory depending on the target platform such that small applications that make limited use of the standard li braries typically fit into a few MB of memory The biggest part of the memory re quired to store a Java application is typically the space needed for the application s class files and related resources such as character encodings Several measures are taken by JamaicaVM to minimize the memory needed for Java classes e Compaction Classes are represented in an efficient and compact format to reduce the overall size of the application e Smart Linking JamaicaVM analyzes the Java applications to detect and remove any code and data that cannot be accessed at run time e Fine grained control over resources such as character encodings time zones locales supported protocols etc Compaction typically reduces the size of class file data by over 50 while smart linking allows for much higher gains even for non trivial applications This footprint reduction mechanism allows the usage of complex Java library code without worrying about the additional memory overhead Only code that is really needed by the application is included and is represented in a very compact format 2 4 ROMABLE CODE 19 2 4 ROMable code
75. JAMAICAVM HEAPSIZEINCREMENT Heap size increment in bytes default 4M JAMAICAVM JAVA STACKSIZE Java stack size in bytes default 64K JAMAICAVM NATIVE STACKSIZE Native stack size in bytes default 64K JAMAICAVM NUMTHREADS Maximum number of Java threads default 10 JAMAICAVM FINALIZERPRI The Java priority of the finalizer thread This thread executes the finalize method of objects before their memory is reclaimed by the GC default 10 JAMAICAVM PRIMAP Priority mapping of Java threads to native threads JAMAICAVM ANALYSE Enable memory analysis mode with a tolerance given in percent see Builder option analyse default 0 disabled JAMAICAVM RESERVEDMEMORY Set the percentage of memory that shold be reserved by a low priority thread for fast burst allocation see Builder option reservedMemory default 10 JAMAICAVM SCOPEDSIZE Size of scoped memory default 0 JAMAICAVM IMMORTALSIZE Size of immortal memory default 32768 JAMAICAVM_LAZY Use lazy class loading linkage 1 or load link all classes at startup 0 default 1 JAMAICAVM STRICTRTSJ Use strictRTSJ rules 1 or relaxed Jamaica rules 0 default 0 JAMAICAVM PROFILEFILENAME File name for profile default class prof where class is the name of the main class 140 CHAPTER 13 THE JAMAICA VIRTUAL MACHINE COMMANDS Standard exit codes 0 Normal termination 1 Exception or error in Java program 2 63 Application specific exit code from System exit
76. JamaicaVM 6 0 User Manual Java Technology for Critical Embedded Systems aicas GmbH JamaicaVM 6 0 User Manual Java Technology for Critical Embedded Systems Published July 8 2010 1999 2010 aicas GmbH Karlsruhe All rights reserved No licenses expressed or implied are granted with respect to any of the technology described in this publication aicas GmbH retains all intellectual property rights associated with the technology described in this publication This publication is intended to assist application developers to develop applications only for the Jamaica Virtual Machine Every effort has been made to ensure that the information in this publication is accurate aicas GmbH is not responsible for printing or clerical errors Although the information herein is provided with good faith the supplier gives neither warranty nor guarantee that the information is correct or that the results described are obtainable under end user conditions aicas GmbH phone 49 721 663 968 0 Haid und Neu Strake 18 fax 49 721 663 968 99 76131 Karlsruhe email info aicas com Germany web http www aicas com aicas incorporated phone 1 203 359 5705 6 Landmark Square Suite 400 Stamford CT 06901 email info aicas com USA web http www aicas com aicas SARL phone 33 1 4997 1762 9 Allee de l Arche fax 133 1 4997 1700 92671 Paris La Defense email infoGaicas com France web http www aicas com Java and all Java based trademarks a
77. List for Iterator i list iterator i hasNext Object value i next can be written as ArrayList list new ArrayList for Object value list The allocation of a temporary Iterator that is performed by the call to list iterator is hidden in this new syntax Variable Argument Lists JDK 1 5 There is still another feature of JDK 1 5 that requires implicit memory allocation The new variable argument lists for methods is implemented by an implicit ar ray allocation and initialization Variable argument lists should consequently be avoided 11 2 4 Operations Causing Class Initialization Another area of concern for computational transparency is class initialization Java uses static initializers for the initialization of classes on their first use The first use is defined as the first access to a static method or static field of the class in question its first instantiation or the initialization of any of its subclasses The code executed during initialization can perform arbitrarily complex oper ations Consequently any operation that can cause the initialization of a class may take arbitrarily long for its first execution This is not acceptable for time critical code Consequently the execution of static initializers has to be avoided in time critical code There are two ways to achieve this either time critical code must not perform any statements or expressions that may cause the initiali
78. M and for compiled code Option object file file The object option specifies object files that contain native code that has to be linked to the destination executable Unlike other Java implementations Jamaica does not access native code through shared libraries Instead the object files that contain native code referenced from within Java code are linked into the destina tion application file 170 CHAPTER 14 THE JAMAICA BUILDER Multiple object files should be separated by the system specific path separator colon on Unix systems and semicolon on Windows 14 3 Builder Extended Usage A number of extended options provide additional means for finer control of the Builder s operation for the more experienced user The following sections list these extended options and describe their effect Default values may be obtained by jamaicabuilder target platform xhelp jamaicabuilder XdefineProperty lt name gt lt value gt XdefinePropertyFromEnv lt name gt XjamaicaHome path XjavaHome path Xbootclasspath classpath XextendedGlobalCPool XlazyConstantStrings XlazyConstantStringsFromEnv var XnoMain XnoClasses XenableZIP XfullStackTrace XexcludeLongerThan n XlinkStatic libraries lt gt XCFLAGS cflags Xld linker XLDFLAGS lt ldflags gt dwarf2 XstripOptions options Xlibraries lt library gt lt library
79. PowerPC e SuperH4 e x86 B 1 1 Configuration of VxWorks For general information on the configuration of VxWorks please refer to the user documentation provided by WindRiver For Jamaica VxWorks should be config ured to include the following functionality e INCLUDE POSIX SEM e INCLUDE LOADER e INCLUDE SHELL e INCLUDE SHOW ROUTINES e INCLUDE STANDALONE SYM TBL Package names refer to VxWorks 6 6 names for other version vary 213 214 If VxWorks real time processes aka RTP are used the following components are also required DE_START APPENDIX B INFORMATION FOR SPECIFIC TARGETS DE_UNLOADER U DE UP SCRI ET PI NG U DE_NFS_CLIENT_ALL DE_TELNET_CL ENT U DE_TASK_UTI DE_ROUTECMD L S DE NFS MOUNT ALL GNALS U DE_POS DE STORY F U DE_NETWORK DE_ATA DE_RTL8169_VXB_END U U DE_D DE_TC3C905_VXB_END LE SHELL DE SHELL EMACS MODE SK UTIL U DE DE SHELL CMD E DE TASK SHELL CMD DR SHELL CMD H STORY U DE U DEBUG SHELL CMD LE SHELL CMI U DE_ DE KERNEL HARDENI NG U DE_ IPTELNETS PWRAP_GETI FAD DRS B 1 VXWORKS 215 e INCLUDE_RTP e
80. RTSJ implementation in the Jamaica VM does not limit access to heap objects within any threads there is no need to execute static initializers within ImmortalMemory However objects allocated in static initializers typ ically must be accessible by all threads Therefore they cannot be allocated in a scoped memory area when this happens to be the current thread s allocation environment when the static initializer is executed The JamaicaVM executes all static initializers within heap memory Objects allocated by static initializers may be accessed by all threads and they may be reclaimed by the garbage collector There is no memory leak if classes are loaded dynamically by a user class loader Class PhysicalMemoryManager Names and instances of class javax realtime PhysicalMemoryType Filter that are passed to method registerFilter ofthe class javax realtime PhysicalMemoryManager are by the RTSJ required to be al located in immortal memory Realtime garbage collection obviates this require ment The JamaicaVM does not enforce it either 11 4 2 Finalizers Care needs to be taken when using Java s finalizers A finalizer is a method that can be redefined by any Java class to perform actions after the garbage collector 11 4 MEMORY MANAGEMENT 115 has determined that an object has become unreachable Improper use of finalizers can cause unpredictable results The Java specification does not give any guarantees that an
81. Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB The generated executable HelloWorld now prints the profiling information after execution The output may look like this HelloWorld 10000 Hello World Hello World Hello World Hello World Hello World Hello World Ls d 6 1 2 Using the profiling VM Alternatively in simple cases the profile can also be created using the jamaicavmp command on the host without first building a stand alone executable lFor better results we run the application with the command line argument 10000 such that startup code does not dominate 6 1 CREATING A PROFILE 49 gt jamaicavmp HelloWorld 10000 Hello World Hello World Hello World Hello World Hello World Hello World fox ead The use of jamaicavmp is subject to the following restrictions e It can generate a profile for the host only e Setting builder options for the application to be profiled is not possible 6 1 5 Dumping a profile via network If the application does not exit or writing a profile is very slow on the target you can request a profile dump with the jamaica remoteprofile com mand You need to set the jamaica profile request port property when building the application or using the profiling VM to an open TCP IP port and then request a dump remotely gt jamai
82. VM offers a myriad of sometimes overlapping features for real time Java development The realtime Java developer needs to understand these features and when to apply them Particularly with realtime specific features per taining to memory management and task interaction the programmer needs to understand the tradeoffs involved This chapter does not offer cut and dried so lutions to specific application problems but instead offers guidelines for helping the developer make the correct choice 11 2 Computational Transparency In contrast to normal software development the development of realtime code re quires not only the correctness of the code but also the timely execution of the code For the developer this means that not only the result of each statement is im portant but also the approximate time required to perform the statement must be obvious One need not know the exact execution time of each statement when this statement is written as the exact determination of the worst case execution time can be performed by a later step however one should have a good understanding of the order of magnitude in time a given code section needs for execution early on in the coding process For this the computational complexity can be described in 101 102 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES categories such as a few machine cycles a few hundred machine cycles thousands of machine cycles or millions of machine cycles Side effects su
83. VM tools valid licenses are required P License keys are provided in key ring files which have the suffix aicas_key Prior to use keys need to be installed This is done with the Jamaica Key Installer Utility which is available for the supported host platforms It is necessary to place the Key Installer Utility and the key ring whose keys are to be installed into the same directory Then execute the Utility as follows gt JamaicaKeyInstaller platform jamaica aicas_key This will extract the keys contained in jamaica aicas_key and add the in dividual key files to user home jamaica Keys that are already installed are not overwritten The Utility reports which keys get installed and which tools they enable Installed keys are for individual tools Of the tools documented in this manual the Builder see 8 14 and the Thread Monitor see 8 15 require keys 3 3 JamaicaVM Directory Structure The Jamaica installation directory is called jamaica home The environment vari able JAMAICA should be set to this path see the installation instructions above After successful installation the following directory structure as shown in Tab 1 is created in this example for a Linux x86 system The Jamaica API specification may be browsed with an ordinary web browser Its format is compatible with common IDEs such as Eclipse and Netbeans If the Jamaica Eclipse Plug In is used see 8 5 Eclipse will automatically use the Some Windows
84. XECUTION 21 Processor Architectures JamaicaVM is highly processor architecture independent New architectures can be supported easily Currently Jamaica runs on the following processor architec tures e ARM StrongARM XScale e ERC22 on request e MIPS on request e Nios e PowerPC e SH 4 on request e Sparc e x86 Ports to any required combination of target OS and target processor can be sup ported with little effort Clear separation of platform dependent from platform independent code reduces the required porting effort for new target OS and target processors If you are interested in using Jamaica on a specific target OS and target processor combination or on any operating system or processor that is not listed here please contact aicas 2 8 Fast Execution The JamaicaVM interpreter performs several selected optimizations to ensure op timal performance of the executed Java code Nevertheless realtime and embed ded systems are often very performance critical as well so a purely interpreted solution may be unacceptable Current implementations of Java runtime systems use just in time compilation technologies that are not applicable in realtime sys tems The initial compilation delay breaks all realtime constraints The Jamaica compilation technology attacks the performance issue in a new way methods and classes can selectively be compiled as a part of the build pro cess static compilation C code is used as
85. aVM to produce immediate results It is therefore tempting to go ahead and develop your code without studying this manual fur ther Even though immediate success can be achieved easily we recommend that you have a closer look at this manual since it provides a deeper understanding of how the different tools work and how to achieve the best results when optimizing for runtime performance memory demand or development time The JamaicaVM tools provide a myriad of options and settings that have been collected in this manual Developing a basic knowledge of what possibilities are available may help you to find the right option or setting when you need it Our experience is that significant amounts of development time can be avoided by a 13 14 CHAPTER 1 PREFACE good understanding of the tools Learning about the correct use of the JamaicaVM tools is an investment that will quickly pay off during daily use of these tools This manual has been written for the developer of software for embedded and time critical applications using the Java programming language A good under standing of the Java language is expected from the reader while a certain fa miliarity with the specific problems that arise in embedded and realtime system development is also helpful This manual explains the use of the JamaicaVM tools and the specific fea tures of the Jamaica realtime virtual machine It is not a programming guidebook that explains the use of the standard
86. able code 2 3 26 DynamucLmkmg 4 4 9 2448224448 iw xw RW eet eats Ste eead 2 1 Development platforms gre TU D DOR s M A oS ee ee ee ee 2 9 Tools for Realtime and Embedded System Development Getting Started 3 1 Installation of JamaicaVM BLT LandX 222 c x n om oo b ooo ee ho no hom oko 3 1 2 Sun Solans 3 1 3 Windows pig eh Ra cqdesmeqeg how a de al ee ed 341__ amp 3 4 2 3 4 3 Improving Size and Performance 3 4 4 Overview of Further Examples 3 11 13 13 14 14 17 17 18 18 19 19 19 19 19 20 21 22 3 5 Notations and Conventions 3 5 1 Typographic Convertions 3 5 2 Argument Syntax 3 5 3 Jamaica Home and User Home 4 Tools Overview 4 1 Jamaica JavaCompiler 4 2 Jamaica Virtual Machine 4 3 Jamaica Builder Creating Target Executables 4 4 Jamaica ThreadMonitor Monitoring Realtime Behaviour Support for the Eclipse IDE 5 1 Plug in installation 5 2 Setting up JamaicaVM Distributions 5 3 Setting Virtual Machine Parameters 5 4 Building ap
87. ack overflow will occur and a corresponding error reported The stack size may be followed by the letter K or M to specify a size in KBytes 1024 bytes or MBytes 1048576 bytes The minimum stack size is 1k 158 CHAPTER 14 THE JAMAICA BUILDER Option nativeStackSize n The nativeStackSize option sets the stack size to be used for the native runtime stacks of all Java threads in the built application Each Java thread has its own native stack Depending on the target system the stack is either allocated and managed by the underlying operation system as in many Unix systems or allocated from the global heap as in some small embedded systems When native stacks are allocated from the global heap stack size consequently has an important impact on the heap memory required by an application A small stack size is recommended for systems with tight memory constraints If the selected stack size is too small an error may not be reported because the stack usage of native code may cause a critical failure For some target systems like many Unix systems a stack size of 0 can be selected meaning unlimited In that case the stack size is increased dynamically as needed The stack size may be followed by the letter or M to specify a size in KBytes 1024 bytes or MBytes 1048576 bytes The minimum stack size is 1k if not set to unlimited value of 0 Option numThreads n The numThreads option spec
88. ad Headers If this option is selected the top part of the window will be used for a fixed time scale that does not participate in vertical scrolling This is useful in case many threads are displayed and the time scale should remain visible when scrolling through these threads Navigate Fit Width This menu item will change the time contraction such that the whole data fits into the current width of the window Navigate Fit Height This menu item will change the zoom factor such that the whole data fits into the current height of the window 188 CHAPTER 15 THE JAMAICA THREADMONITOR Navigate Fit Window This menu item will change the time contraction and the zoom factor such that the whole data fits into the current size of the data window Tools Worst Case Execution Times This menu item will start the execution time analysis and show the Worst Case Execution Time window see 15 3 5 Tools Reset Monitors The display of monitor enter and exit events can be suppressed for selected mon itors via a context menu on an event of the monitor in questions This menu item re enables the display of all monitors 15 3 3 Data Window Context Window The data window has a context menu that appears when pressing the right mouse button over a monitor event This context window permits to suppress the display of events related to a monitor This display can be re enabled via the Tools Reset Monitors menu item 15 3 4 Data Window Tool Tip
89. ads associated with the VM These im provements let the JamaicaVM integrate better with the target OS and increase the throughput of threaded Java applications The VM scheduler controls which thread runs within the VM at any given time This means it effectively protects the VM internal data structures like the heap from concurrent modifications The VM scheduler does not replace but rather supports the operating system scheduler This allows for example for a light implementation of Java monitors instead of using heavy system semaphores All threads created in the VM are per default attached to the VM i e they are controlled by the VM scheduler Threads that execute system calls must detach themselves from the VM This allows the VM scheduler to select a different thread to be the running thread within the VM while the first thread for example blocks on an IO request Since it is critical that no thread ever blocks in a system call while it is attached all JNI code in the JamaicaVM is executed in detached mode For the interpretation of the ThreadMonitor data the distinction between at tached and detached mode is important A thread that is detached could still be using the CPU meaning that the thread that is shown as running within the VM might not actually be executing any code Threads attached to the VM may be in the states running rescheduling ready or blocked Running means the thread that currently executes within the context of t
90. ads do not access objects allocated on the heap are not performed by JamaicaVM 10 3 4 Static Initializers To permit the initialization of classes even if their first reference is performed within ScopedMemory or ImmortalMemory within a RealtimeThread or NoHeapRealtimeThread and to permit the access of static fields such as System out from within these threads static initializers are typically executed within ImmortalMemory that is accessible by all threads However this pre vents these objects from being reclaimed when they are no longer used Also it can cause a serious memory leak if dynamic class loading is used since mem ory allocated by the static intializers of dynamically loaded classes will never be reclaimed Since JamaicaVM does not limit access to heap objects within any threads there is no need to execute static initializers within ImmortalMemory However objects allocated in static initializers typically must be accessible by all threads so they cannot be allocated in a scoped memory area if this happens to be the current thread s allocation environment when the static initializer is executed JamaicaVM therefore executes all static initializers within heap memory Ob jects allocated by static initializers may be accessed by all threads and they may 98 CHAPTER 10 THE REAL TIME SPECIFICATION FOR JAVA be reclaimed by the garbage collector There is no memory leak if classes are loaded dynamically by a user cl
91. age name followed by an asterisk to exclude all classes in the package or a package name followed by to exclude all classes in the package and in all sub packages of this package Example excludeClasses java beans XMLEncoder java util x java lang excludes the class java beans XMLEncoder allclassesin java util and all classes in the package java lang and in all sub packages of java lang such as java lang ref The excludeClasses option affects only the listed classes themselves e 150 CHAPTER 14 THE JAMAICA BUILDER Option excludeFromCompile method method The excludeFromCompile option forces exclusion of the listed methods from compilation Separate method names by spaces and enclose them in double quotes 7 Example excludeFromCompile java lang Math cos D D java lang Math sin D D excludes the methods double cos double anddouble sin double The excludeFromCompile option affects only the listed methods them selves Option includeJAR file file The includeJAR option forces the inclusion of all classes and all resources con tained in the specified files Any archive listed here must be in the classpath or in the bootclasspath If a class needs to be included the implementation in the includeJAR file will not necessarily be used Instead the first implementation of this class which is found in the classpath will be used This is to ensure the appli cation behaves in t
92. aica VM or any application that was created using the Jamaica Builder 38 CHAPTER 4 TOOLS OVERVIEW Chapter 5 Support for the Eclipse IDE Integrated development environments IDEs make a software engineer s life eas ier by aggregating all important tools under one user interface aicas provides a plug in to integrate the JamaicaVM Virtual Machine and the JamaicaVM Builder into the Eclipse IDE which is a popular IDE for Java 5 1 Plug in installation The JamaicaVM plug in can be installed and updated through the Eclipse plug in manager The plug in requires Eclipse 3 2 or later and a Java 1 5 compatible virtual machine However using the latest available Eclipse version and an up to date virtual machine is recommended The following instructions refer to Eclipse 3 5 Earlier versions of Eclipse differ slightly in the menu item labels To install the plug in select the menu item Help gt Install New Software add the aicas Update Site whose location is http aicas com download eclipse plugin and install JamaicaVM Tools The plug in is available after a restart of Eclipse To perform an update select Help gt Check for updates You will be notified of updates 5 2 Setting up JamaicaVM Distributions Jamaica distributions must be made known to the Jamaica plug in before they can be used within Eclipse This is done in the global preferences dialog usually 39 40 CHAPTER 5 SUPPORT FOR THE ECLIPSE IDE
93. ansport dt socket The only supported transport protocol is dt socket address host port Transport address for the connection server y n If y listen for a debugger application to attach otherwise attach to the debugger application at the specified address suspend y n If y suspend this VM before main class loads Table 9 1 Arguments of Jamaica s communication agent e Information about java monitors cannot be retrieved The Java Platform Debugger Architecture JPDA consists of three interfaces designed for use by debuggers in development environments for desktop systems The Java Virtual Machine Tools Interface JVMTT defines the services a VM must provide for debugging The Java Debug Wire Protocol JDWP defines the format of information and requests transferred between the process being debugged and the debugger front end which implements the Java Debug Interface JDI The Java Debug Interface defines information and requests at the user code level A JPDA Transport is a method of communication between a debugger and the virtual machine that is being debugged The communication is connection oriented one side acts as a server listening for a connection The other side acts as a client and connects to the server JPDA allows either the debugger application or the target VM to act as the server The transport implementations of Jamaica allows communications between processes running on different machines
94. archive Please follow the installation instructions in 3 1 5 Windows On Windows the recommended means of installation is using the interactive in staller which may be launched by double clicking the file Jamaica release identification string exe in the Explorer or by executing it in the CMD shell You will be asked to pro vide a destination directory for the installation and the locations of tools and SDK for host and target platforms The destination directory is referred to as jamaica home lt defaults to the subdirectory jamaica in Window s default program 26 CHAPTER 3 GETTING STARTED directory for example C Programs jamaica if an english language lo cale is used Defaults for tools and SDKs are obtained from the registry The installer will set the environment variable JAMAICA to jamaica home An alternative installation method is to unpack the Windows zip file into a suitable installation destination directory For configuration of platform specific tools follow the instructions provided in 8 B 1 1 In order to set the JAMAICA environment variable to jamaica home open the Control Panel choose System select Advanced System Settings choose the tab Advanced and press Envrion ment Variables It is also recommended to add jamaica home bin to the PATH environment variable in order to be able to run the Jamaica executables conve niently 3 2 Installation of License Keys In order to use the Jamaica
95. as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB 8 2 3 Measuring an application s memory requirements The build process is performed exactly as it would be without the analyze op tion except that the garbage collector is told to measure the application s memory usage with the given accuracy The result of this measurement is printed to the console after execution of the application HelloWorld Hello World Hello World Hello World Hello World Hello World Hello World erosut e Application used at most 2104384 bytes for reachable objects on the Java heap accuracy 5 ttt ttt Worst case allocation overhead using 10 reserved memory TET heapSize dynamic GC const GC work TUE 7366K 6 3 dE 6117K 7 4 TUE 5324K 8 4 TUE 4791K 9 4 TUE 4401K 10 4 ttt 3878K 12 5 82 CHAPTER 8 MEMORY MANAGEMENT CONFIGURATION THE 3550K 14 5 THE 3315K 16 6 THE 3148K 18 6 THE 3018K 20 7 THE 2835K 24 8 THE 2712K 28 9 THE 2625K 32 10 THE 2557K 36 11 THE 2504K 40 12 THE 2427K 48 14 THE 2374K 56 15 THE 2336K 64 17 THE 2246K 96 24 TEE 2203K 128 30 THE 2159K 192 42 THE 2139K 256 52 THE 2119K 384 67 The output consists of the maximum heap memory demand plus a table of possible heap sizes and their allocation overheads for both dynamic and constant garbage
96. ass loader 10 3 5 Class PhysicalMemoryManager According to the RTSJ names and instances of class PhysicalMemoryType Filterinpackage javax realtime thatare passed to method register Filter of class PhysicalMemoryManager in the same package must be allocated in immortal memory This requirement does not exist in JamaicaVM 10 4 Strict RTSJ Semantics When the builder option st rict RTSJ is chosen the relaxations just described are deactivated and strict RTSJ semantics are enforced Applications that should be portable to different RTSJ implementations should consequently be developed with this options switched on when an application is built 10 4 1 Use of Memory Areas All NoHeapRealtimeThreads of applications built in st rictRTSJ mode must run in scoped or immortal memory In addition the thread object itself the thread logic scheduling release memory and group parameters must not be allocated in heap memory Otherwise a Memory AccessError is thrown on the creation of such a thread RealtimeThreads are free to use heap memory even in strictRTSJ mode and they still profit from the lack of garbage collection pauses in Jamaica VM Application code that needs to be portable to other Java implementations that are not based on realtime garbage collection should not use heap memory for time critical threads Normal threads are not allowed to enter non heap memory areas in strict RTSJ mode 10 4 2 Thread priorities Thread p
97. at inherits these variables from the shell the task must be spawned with the VX PRIVATE ENV bit set To do so use the taskSpawn command taskSpawn jamaica 0 0x01000080 0x020000 jvm HelloWorld args Running two Jamaica applications at the same time In order to run two Jamaica applications at the same time matching of common symbols by the kernel must be switched off This is achieved by setting the global VxWorks variable 1dCommonMatchAL1 to false prior to loading the applica tions gt ldCommonMatchAl1 20 ld RTHelloWorld ld HelloWorld sp jvm RTHelloWorld sp jvm HelloWorld In the example if 1dCommonMatchA11 were not set to 0 HelloWorld would reuse symbols defined by RTHelloWorld Note that this functionality is not available on all versions of VxWorks Please check the VxWorks kernel API reference 218 APPENDIX B INFORMATION FOR SPECIFIC TARGETS Restarting a Jamaica application To restart a Jamaica application after it has terminated it should be unloaded with the un1d command and then reloaded This is illustrated in the following example ld HelloWorld value 783931720 0x2eb9d948 H sp jvm HelloWorld Ex unld 783931720 value 0 0x0 ld HelloWorld value 784003288 0x2ebaf0d8 K sp jvm HelloWorld es Note that the application should not be unloaded while still running The unld command is optional and the VxWorks image n
98. aware that if exten sions of the RTSJ without sticking to restrictions imposed by the RTSJ the code will not run unmodified on other JVMs To make sure code is portable one should use the st rictRTSJ switch StrictRTSJ mode can safely be used by any Java program without modifications 11 7 5 EventHandlers AsyncEventHandlers should be used for tasks that are triggered by some external event Many event handlers can be used simultaneously however they should not block or run for a long time Otherwise the execution of other event handlers may be blocked For longer code sequences or code that might block event handlers of class BoundAsyncEventHandler provide an alternative that does not prevent the execution of other handlers at the cost of an additional thread 11 7 SUMMARY 125 The scheduling and release parameters of event handlers should be set accord ing to the scheduling needs for the handler Particularly when rate monotonic analysis is used an event handler with a certain minimal interarrival time should be assigned a priority relative to any other events or periodic threads using this minimal interarrival time as the period of this schedulable entity 11 7 4 Monitors Priority Inheritance is the default protocol in the RTSJ It is safe and easy to use but one should take care to nest monitor requests properly and in the same order in all threads Otherwise it can cause deadlocks When used properly Priority Ceiling
99. ay be cleared In JamaicaVM the finalizer thread is responsible for clearing soft references The default value for this property is 1096 jamaica xprof n If set to an integer value larger than 0 and less or equal to 1000 this property enables the jamaicavm s option Xprof If set the property s value specifies the number of profiling samples to be taken per second e g Djamaica xprof 100 causes the profiling to make 100 samples per second See 13 1 2 for more details C 2 Predefined Properties The JamaicaVM defines a set of additional properties that contain information specific to Jamaica jamaica boot class path The boot class path used by JamaicaVM This is not set when a stand alone application has been built using the Builder see 14 jamaica buildnumber The build number of the Jamaica VM jamaica byte order One of BIG ENDIAN or LITTLE ENDIAN depending on the endianness of the target system jamaica heapSizeFromEnv If the initial heap size may be set via an environment variable this is set to the name of this environment variable jamaica home The JamaicaVM installation directory This property is not set on systems where the JamaicaVM installation is not needed i e when a stand alone application has been built using the Builder see 8 14 jamaica immortalMemorySize The size of the memory available for immortal memory C 2 PREDEFINED PROPERTIES 231 jamaica maxNumTh
100. be statically linked to the destination binary The libraries must include the option that is passed to the linker Static linking creates larger executables but may be nec essary if the target system doesn t provide the library Multiple libraries should be separated using spaces and enclosed in quotation marks Example setting XstaticLibraries m pthread causes static link ing against 1ibm and libpthread Option XlinkDynamicPrefix prefix The XLinkDynamicPrefix option specifies a prefix to link a library dynamic to the created executable e g W1 Bdynamic 14 3 BUILDER EXTENDED USAGE 175 Option XlinkStaticPrefix prefix The XlinkStaticPrefix option specifies a prefix to link a library statically to the created executable e g W1 Bstatic Option XlinkDynamicFlagsc switch The XlinkDynamicFlags option specifies flags for dynamic linkage of an executable e g dynamic Option XlinkStaticFlags switch The XlinkStaticFlags option specify flags for dynamic linkage of an exe cutable e g static Option XlibraryPaths path path The XlibraryPaths option adds the directories in the specified paths to the library search path Multiple directories should be separated by the system specific path separator colon on Unix systems and semicolon on Windows E g to use the directories usr local lib and usr 1lib as library path the option X1ibraryPaths usr local lib usr lib mustbe speci
101. be used Option stopTheWorldGC The stopTheWorlsGC option enables blocking GC i e no GC activity is per formed until the heap is fully filled Only then a complete GC cycle is performed at once causing a potentially long pause for the application During this GC cy cle any thread that performs heap memory allocation will be blocked but threads that do not perform heap allocation may continue to run If stop the world GC is enabled via this option even RealtimeThreads and NoHeapRealtimeThreads may be blocked by GC activity if they al locate heap memory RealtimeThreads and NoHeapRealtimeThreads that run in ScopedMemory or ImmortalMemory will not be stopped by the GC A stop the world GC enables a higher average throughput compared to incre mental GC but at the cost of losing realtime behaviour for all threads that perform heap allocation Option atomicGC The atomicGC option enables atomic GC i e no GC activity is performed until the heap is fully filled Only then a complete GC cycle is performed at once causing a potentially long pause for the application During this GC cycle all Java threads will be blocked 14 2 BUILDER USAGE 165 When this option is set even NoHeapRealtimeThreads will be stopped by GC work so all realtime guranatees will be lost This mode permits more efficient code compared to stopTheWor1dGC since it disables certain tracking code write barriers that is required for the incremental
102. ble Any event handler that may block should therefore have one Realtime Thread that is assigned to it alone for the execution of its event handler Handlers for class BoundAsyncEventHandler provide this feature They do not share their thread with any other event handler and they may consequently block without disturbing the execution of other event handlers Due to the additional resources required for a BoundAsyncEventHandler their use should be restricted to blocking or long running events only The sharing of threads used for normal AsyncEventHandlers permits the use of a large number of event handlers with minimal resource usage 11 5 2 Synchronization Synchronization is essential to data sharing especially between cooperating real time tasks Passing data between threads at different priorities without impairing the realtime behavior of the system is the most important concern It is essential to ensure that a lower priority task cannot preempt a higher priority task The situation in Fig depicts a case of priority inversion when using monitors the most common priority problem The software problems during the Pathfinder mission on Mars is the most popular example of a classic priority in version error see Michael Jones web page 4 In this situation a higher priority thread A has to wait for a lower priority thread B because another thread C with even lower priority is holding a monitor for which A is waiting In this situation
103. ca remoteprofile target port DUMPING DONE In the above command target denotes the IP address or host name of the target system By default the profile is written on the target to a file with the name of the main class and the suffix prof You can change the file name with the file option or you can send the profile over the network and write it to the file system with an absolute path or relative to the current directory of the host with the net option gt jamaica_remoteprofile net filename target port 6 1 4 Creating a micro profile To speed up the performance of critical sections in the application you can use mi cro profiles that only contain profiling information of such a section see 8 5 22 You need to reset the profile just before the critical part is executed and dump a profile directly after To reset a profile you can use the command jamaica_ remoteprofile with reset option gt jamaica_remoteprofil reset net filename target port 50 CHAPTER 6 PERFORMANCE OPTIMIZATION 6 2 Using a profile with the Builder Having collected the profiling data the Jamaica Compiler can create a compiled version of the application using the profile information This compiled version benefits from profiling information in several ways e Compilation is limited to the most time critical methods keeping non critical methods in smaller interpreted byte code format e Method inlining prefers inlining of calls that hav
104. cah program in bytes Chapter 17 The Numblocks Command An important value required to calculate the worst case execution time of an allo cation is the number of blocks required to represent the allocated object Jamaica VM provides the NumBlocks tool to determine this number of blocks In this chapter the usage of this tool is described in detail 17 1 Command Line Options A variety of arguments can be provided to control the NumBlocks tool The argu ments can be provided either directly to numblocks or by using the property file numblocks conf The syntax is as follows numblocks help help h 7 Xhelp version verbose showSettings saveSettings lt file gt lt file gt all classpath lt classpath gt bootclasspath oe ee lt classpath gt numThreads lt n gt class1 lt len gt classn lt len gt 17 1 General These are general options providing information about numblocks itself or en abling the use of script files that specify further options Option help help h Display the usage of the NumBlocks tool and a short description of all possible standard command line options 197 198 CHAPTER 17 THE NUMBLOCKS COMMAND Option Xhelp Display the usage of the NumBlocks tool and a short description of all possible standard and extended command line options Extended command line options are not needed for normal control of the n
105. cation Maximum number of name and type entries references to different methods or fields in the global constant pool ex 216 ceeding this value will result in a larger application Maximum Java array Iength Independent of the heap size Java arrays may not have more than this number of elements However the array length is not restricted by the heap size increment i e even a heap consisting of several increments 227 1 each of which is smaller than the memory required for a Java array permits the allocation of arrays up to this length pro vided that the total available memory is sufficient Maximum number of virtual methods per Java class includ 916 ing inherited virtual methods Jae Maximum number of interface methods per Java interface 4095 including interface methods inherited from super interface On posix systems where time_spec tv_sec is a 32 Bit Tue Jan 19 value it is not possible to wait until a time and date that is 04 14 07 2038 later than Table E 1 JamaicaVM limitations E 2 Builder Limitations The static compiler does not compile certain Java methods but leaves them in interpreted bytecode format independent of the compiler options or their signifi cance in a profile e Static initializer methods methods with name lt clinit gt are not com piled E 2 BUILDER LIMITATIONS 237 A simple way to enable compilation is to change a static intializer into a static method wh
106. cess classes in ZIP or JAR files 14 3 BUILDER EXTENDED USAGE 173 14 3 3 Compilation Compilation and different optimisation techniques are used for optimal runtime performance of Jamaica applications These techniques are controlled using the following options Option XfullStackTrace Compiled code usually does not contain full Java stack trace information if the stack trace is not required as in a method with a try catch clause or a synchro nized method For better debugging of the application the XfullStackTrace option can be used to create a full stack trace for all compiled methods Option XexcludeLongerThan n Compilation of large Java methods can cause large C routines in the intermediate code especially when combined with aggressive inlining Some C compilers have difficulties with the compilation of large routines To enable the use of Jamaica with such C compilers the compilation of large methods can be disabled using the option XexcludeLongerThan The argument specified to XexcludeLongerThan gives the minimum num ber of bytecode instructions a method must have to be excluded from compilation Option XlinkStatic libraries Libraries are system jamaica implicit all or none The resulting binary is linked statically against those libraries even if they were specified by Xlibraries rather than XstaticLibraries jamaica refers to the Ja maica VM library system to all other libraries default jamaica Optio
107. cess memory to 32MB of RAM Therefore the application executable plus the amount of native stack for all threads in the thread pool plus the amount of memory required to display graphics must be less than 32MB It is not possible to redirect the standard IO for processes created with Runtime exec WindowsCE does not support the notion of a current working directory In Jamaica all relative paths are interpreted as relative to root WindowsCE does not support envrionment variables If you have a registry editor on your target you can create string entries with the name of the environment variable in HKEY CURRENT USERNSoftwareNaicas V jamaica environment to use the variable in Jamaica File locking through FileChannel lock is not supported for all file systems on WindowsCE If WindowsCE does not support file locking for a given file system calls to FileChannel lock will fail silently In particular the UNC networkfile systems does not support this mechanism B 6 OS 9 B 6 1 Limitations The current release of Jamaica for OS 9 contains the following known limitations java net Socket connect does not support a timeout The value is ignored java net Socket bind does not throw an exception if called several times with the same address java nio FileChannel map is not supported B 7 QNX 225 B 7 QNX B 7 1 Installation To use the QNX toolchain ensure that the following environme
108. ch as blocking for I O operations or memory allocation should be understood as well The term computational transparency refers to the degree to which the compu tational effort of a code sequence written in a programming language is obvious to the developer The closer a sequence of commands is to the underlying machine the more transparent that sequence is Modern software development tries to raise the abstraction level at which programmers ply their craft This tends to reduce the cost of software development and increase its robustness Often however it masks the real work the underlying machine has to do thus reducing the computational transparency of code Languages like Assembler are typically completely computationally transpar ent The computational effort for each instruction can be derived in a straightfor ward way e g by consulting a table of instruction latency rules The range of possible execution times of different instructions is usually limited as well Only very few instructions in advanced processor architectures have an execution time of more than O 1 Compiled languages vary widely in their computational complexity Program ming languages such as C come very close to full computational transparency AII basic statements are translated into short sequences of machine code instructions More abstract languages can be very different in this respect Some simple con structs may operate on large data structures e g s
109. code running on the Jamaica Virtual Machine The Memory Analyzer is integrated into the Builder tool It can be activated by setting the command line option analyze accuracy Using the Memory Analyzer Tool is a three step process First an application is built using the Memory Analyzer The resulting executable file can then be ex ecuted to determine its memory requirements Finally the result of the execution can be used to fine tune the final version of the application 8 2 2 Building using the Memory Analyzer As an example we will build the HelloWorld example application that was pre sented in 8 3 4 This can be done by providing the option analyze to the builder and giving the required accuracy of the analysis in percent In this exam ple we use an accuracy of 5 gt jamaicabuilder cp classes analyze 5 HelloWorld Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed 8 2 CONFIGURATION FOR HARD REALTIME APPLICATIONS 81 PKG__V66c2 3114d534efc__ c tan HelloWorld c HelloWorld__ h Class file compaction gain 58 96339 21654255 gt 8886172 C compiling HelloWorld__ c sl HelloWorld nc o linking x stripping Application memory demand will be
110. collection work We first consider dynamic garbage collection work since this is the default In this example the application uses a maximum of 2104384 bytes of memory for the Java heap The specified accuracy of 596 means that the actual memory usage of the application will be up to 5 less than the measured value but not higher JamaicaVM uses the Java heap to store all dynamic data structures internal to the virtual machine as Java stacks classes etc which explains the relatively high memory demand for this small application 8 2 4 Fine tuning the final executable application In addition to printing the measured memory requirements of the application in analyze mode Jamaica also prints a table of possible heap sizes and corresponding worst case allocation overheads The worst case allocation overhead is given in units of garbage collection work that are needed to allocate one block of memory typically 32 bytes The amount of time in which these units of garbage collection work can be done is platform dependent For example on the PowerPC processor a unit corresponds to the execution of about 160 machine instructions From this table we can choose the minimum heap size that corresponds to the desired worst case execution time for the allocation of one block of memory A heap size of 3018K corresponds to a worst case of 20 units of garbage col lection work 3200 machine instructions on the PowerPC per block allocation while a small
111. d by the path separator char on Unix systems can be specified This list will be traversed from left to right when the builder tries to load a class Option bootclasspath Xbootclasspath classpath Specifies the default path used for loading system classes 17 1 3 Memory and threads settings Option numThreads n This Builder option has an influence on the number of blocks required for some objects Consequently it must be provided to numblocks for all applications that are built with a specified number of threads 17 2 Environment Variables The following environment variables control numblocks command JAMAICA NUMBLOCKS HEAPSIZE Heap size of the numblocks program in bytes 200 CHAPTER 17 THE NUMBLOCKS COMMAND Chapter 18 Building with Apache Ant Apache Ant is a popular build tool in the Java world Ant tasks for the Jamaica Builder and other tools are available In this chapter their use is explained Ant build files normally named build xml are created and maintained by the Jamaica Eclipse Plug In see 8D They may also be created manually To obtain Apache Ant and for an introduction see the web page http ant Apache Ant is not provided with Jamaica In the following sec tions basic knowledge of Ant is presumed 18 1 Task Declaration Ant tasks for the Jamaica Builder and jamaicah are provided In order to use these tasks taskdef directives are required The following code should be placed af
112. d excludeJAR this can help you to identify which methods are included in the application The output of this option consists of lines starting with the string INCLUDED CLASS INCLUDED METHOD or INCLUDED FIELD followed by the name of a class or the name and signature of a method or field respectively Option showExcludedFeatures The showExcludedFeatures option will cause the Builder to display a list of all classes methods and fields that where removed from the built applica tion Any classes methods or fields removed from the target application through mechanisms such as smart linking will be displayed Used in conjunction with includeClasses excludeClasses includeJAR and excludeJAR this can help you to identify which methods are excluded from the application The output of this option consists of lines starting with the string EXCLUDED CLASS EXCLUDED METHOD or EXCLUDED FIELD followed by the name of a class or the name and signature of a method or field respectively 14 2 4 Compilation Compilation and different optimisation techniques are used for optimal runtime performance of Jamaica applications These techniques are controlled using the following options Option interpret Xint The interpret option disables compilation of the application This results in a smaller application and in faster build times but it causes a significant slow down of the runt
113. d synchronized statements or nested calls to synchronized meth ods Exceeding this value will result in throwing an java lang InternalError with detail message Max monitor nest count reached 255 255 Minimum Java heap size 64KB Maximum Java heap size 2GB Minimum Java heap size increment 64KB Maximum number of heap increments The Java heap may not consist of more than this number of chunks i e when dynamic heap expansion is used max heap size is larger than initial heap size no more than this number of increments will be performed including the initial chunk To avoid this limit the heap size increment will automatically be set to a larger value when more than this number of increments would be needed to reach the maximum heap size 256 235 236 APPENDIX E LIMITATIONS Aspect Limit Maximum number of memory areas instances of javax realtime MemoryArea Note that two in 256 stances are used for HeapMemory and ImmortalMemory Maximum size of Java stack 64MB Maximum size of native stack 2GB Maximum number of constant UTFS strings names and sig natures of methods fields classes interfaces and contents of constant Java strings in the global constant pool exceeding this value will result in a larger application Maximum number of constant Java strings in the global con stant pool exceeding this value will result in a larger appli 216
114. dic sampling This profile is used to provide an estimate of the methods which use the most CPU time during the execution of an application During each sample the currently executing method is determined and its sample count is incremented independent of whether the method is currently executing or is blocked waiting for some other event The total number of samples found for each method are printed when the application terminates Note that compiled methods may be sampled incorrectly since they do not necessarily have a stack frame We therefore recommend to use Xprof only for interpreted applications 13 1 3 Environment variables used by JamaicaVM Next to the command line options JamaicaVM also permits the specification of options via environment variables 8 lists the environment variables and their meanings 13 2 jamaicavm slim jamaicavm slimis a variant of jamaicavm command that does not have the standard library built in Instead it has to load all standard library classes that are required by the application from the target specific rt jar provided in the JamaicaVM installation Compared to jamaicavm jamaicavm slim is significantly smaller in size jamaicavm slim may start up more quickly for small applications but it will require more time for larger applications Also since jamaicavm con tains standard library classes that were pre compiled and optimized by the Ja maica builder tool see 8 14 jamaicavm slim will perfo
115. e SpecificatonforJava 109 11 32 Java Native 111 ee ee ee ee 112 11 4 Memory 112 11 4 1 Memory Management 5 113 11 4 2 F nalzers zx Sais ee eet So RRC uU Ek ae ee eH o 114 Mee 115 eee ee E OST TT eee F 116 pain ea acter 117 eh tenes Went We trees 118 11 5 1 Schedulable Entities 118 eo ee ee ee we eS 120 11 6 Libraries RRR x 30x 3X 6 EEE HO 123 123 use 124 ee ac Seve a oe Be e N wu Me we A 124 11 7 3 EventHandlers 124 11 7 4 Monitors 125 Tools Reference 127 129 p Rok Be eiui lead ER ro bee See d 129 12 1 1 Clasppathopions leen 129 CONTENTS 12 4 2 Compliance options 12 1 3 Warning options 12 1 4 Debug options 12 1 5 Otheroptions ese ee Gee eee eae ERI 12 2 Environment Variables 13 The Jamaica Virtual Machine Commands do Chae eae Aen eon en whee T TOM DIVI aa be ee fas DG 13 3 13 3 1 Additional extended options of jamaicavmp 13 4 13 4 1 Additional options of ja
116. e asynchronous events e asynchronous flow of control thread termination and e physical memory access With this the RTSJ also covers areas that are not directly related to realtime ap plications However these areas are of great importance to many embedded real time applications such as direct access to physical memory e g memory mapped I O or asynchronous mechanisms Thread Scheduling To enable the develop ment of realtime software in an environment with a garbage collector that stops the execution of application threads in an unpredictable way new thread classes RealtimeThread and NoHeapRealtimeThread are defined These thread types are unaffected or at least less heavily affected by garbage collection activ ity Also at least 28 new priority levels logically higher than the priority of the garbage collector are available for these threads Memory Management In order for realtime threads not to be affected by garbage collector activity they need to use memory areas that are not under the con trol of the garbage collector New memory classes ImmortalMemory and ScopedMemory provide these memory areas One important consequence of the use of special memory areas is of course that the advantages of dynamic memory management are not fully available to realtime threads Synchronization In realtime systems with threads of different priority levels priority inversion situations must be avoided Priority inversion occurs when a t
117. e but at time of first use of any constant string This saves Java heap memory and startup time since constant strings that are never touched will not be created However this has the effect that accessing a constant Java string may cause an OutOfMemoryError Option XlazyConstantStringsFromEnv var Causes the creation of an application that reads its X1azyConstantStrings setting from the specified environment variable If this variable is not set the value of boolean option XlazyConstantStrings will be used The value of the environment variable must be 0 for XlazyConstantStrings false 1 for XlazyConstantStrings true Option The XnoMain option builds a standalone VM Do not select a main class for the built application Instead the first argument of the argument list passed to the application will be interpreted as the main class Option XnoClasses The XnoClasses option does not include any classes in the built application Setting this option is only needed when building the jamaicavmcommand itself Option XenableZIP The XenableZIP option enables ZIP and JAR support in the generated binary This makes binaries significantly larger Set this this option only if you are build ing a virtual machine see the XnoMain option and the application application executed on the target system might access ZIP and JAR files in the class path at runtime Independently of this option the Jamaica Builder can always pro
118. e command line options optimize size or optimize speed respectively Note that speed is normally the default For comparision we build the caffeine example optimising for size gt jamaicabuilder cp classes gt useProfile CaffeineMarkEmbeddedApp prof gt optimize size CaffeineMarkEmbeddedApp gt destination caffeine useProfilel0 size Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation size PKG__V744a379db03fd860__ c bee J caffeine_useProfilel0_size__ c caffeine useProfilelO0 size h Class file compaction gain 58 83032 21684433 gt 8927412 C compiling caffeine_useProfilel0_size__ c zie caffeine useProfilelO0 size linking stripping To check the default invoke jamaicabuilder help or inspect the builder status mes sages 7 1 CODE SIZE VS RUNTIME PERFORMANCE 65 Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB gt ls s caffeine_useProfilel0_size 12675936 caffeine_useProfilel0_size The resulting pe
119. e priority and the length of the period of this peri odic thread need to be provided A call to waitForNextPeriod causes the thread to wait after the completion of one activation for the start of the next period An introduction to the RTSJ with numerous further examples is given in the book by Peter Dibble 2 The RTSJ provides a solution for realtime programming but it also brings new difficulties to the developer The most important consequence is that applications have to be split strictly into two parts a realtime and a non realtime part The communication between these parts is heavily restricted realtime threads cannot perform memory operations such as the allocation of objects on the normal heap which is under the control of the garbage collector Synchronization between realtime and non realtime threads is heavily restricted since it can cause realtime threads to be blocked by the garbage collector 96 CHAPTER 10 THE REAL TIME SPECIFICATION FOR JAVA 10 2 Realtime Garbage Collection In JamaicaVM a system that supports realtime garbage collection this strict sep aration into realtime and non realtime threads is not necessary The strict splitting of an application is consequently not required Threads are activated depending only on their priorities The realtime garbage collector performs its work predictably within the appli cation threads It is activated when memory is allocated The work done on an allocation must be preemp
120. e relies on some internal features in the boot classes Thus it is in general not possible to replace the boot classes by those of a different virtual machine or even by those of another version of the Jamaica virtual machine or even by those of a different Java virtual machine Option Xms ms size The Xms option sets initial Java heap size the default setting is 2M This option takes precedence over a heap size set via an environment variable Option Xmx mx size The Xmx option sets maximum Java heap size the default setting is 256M This option takes precedence over a maximum heap size set via an environment vari able Option Xmi mi size The Xmi option sets heap size increment the default setting is 4M This option takes precedence over a heap size increment set via an environment variable Option Xss ss size The Xss option sets stack size native and interpreter This option takes prece dence over a stack size set via an environment variable Option Xjs js size The X js option sets interpreter stack size the default setting is 64K This option takes precedence over a java stack size set via an environment variable 136 CHAPTER 13 THE JAMAICA VIRTUAL MACHINE COMMANDS Option Xns ns size The Xns option sets native stack size set default setting is 64K This option takes precedence over a native stack size set via an environment variable Option Xprof Collect simple profiling information using perio
121. e shown to be executed most frequently during the profiling run e Profiling information also collects information on the use of reflection so an application that cannot use smart linking due to reflection can profit from smart linking even without manually listing all classes referenced via reflec tion 6 2 1 Building with a profile The builder option useProfile is used to select the generated profiling data gt jamaicabuilder cp classes useProfile HelloWorld prof HelloWorld Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed V591866ffa60dffcb c Ixus HelloWorld c HelloWorld h Class file compaction gain 58 833664 21672755 gt 8921879 C compiling HelloWorld__ c HelloWorld__nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB 6 3 INTERPRETING THE PROFILING OUTPUT 51 Due to the profile guided optimizations performed by the compiler the runtime performance of the application built using a profile a
122. ead objects all share the same priority range The lowest possible thread priority for all of these threads is defined in package java lang class Thread by field MIN PRIORITY The highest possible priority is can be ob tained by querying instance getMaxPriority class Priority Scheduler package javax realtime 114 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES Runtime checks for NoHeapRealtimeThread Since even NoHeapRealtimeThreads are immune to interruption by garbage collector activities JamaicaVM does not restrict these threads from accessing ob jects allocated on the normal heap Runtime checks that typically ensure that these threads do not access objects allocated on the heap can be disabled in the JamaicaVM The result is better overall system performance Static Initializers In order to permit the initialization of classes even when their first reference is per formed within ScopedMemory or ImmortalMemory within a Realtime ThreadorNoHeapRealtimeThread and to permit the access of static fields such as System out from within these threads static initializers are typically executed within ImmortalMemory that is accessible by all threads However this prevents these objects from being reclaimed when they are no longer in use This can result in a serious memory leak when dynamic class loading is used since memory allocated by the static initializers of dynamically loaded classes will never be reclaimed Since the
123. ed for disk FTP or NFS access simply enter the following command on the target shell ld filename Here filename is the complete filename of the created application The main entry point for an application built with the Jamaica Builder is the name specified by the Builder option destination with the prefix jvm The name jvm may also be used If the option dest ination is not specified the name of the class file containing the main method is used For example in the VxWorks target shell the HelloWorld application may be started with sp jvm HelloWorld args B 1 VXWORKS 217 The example shows how to pass arguments to the process even though the Hel loWorld application does not use the arguments Note even if the Builder generates a file with the specified name it may be renamed later because the name of the main entry point is read from the symbol table included in the object file Optional parameters like classpathorXbootclasspath may be passed to the application as a single C argument string with text enclosed in double quotes Multiple arguments in the string are separated by spaces The start code of the created application parses this string and passes it as a standard Java string array to the main method Setting environment variables Environment variables may be set in the VxWorks shell via the putenv com mand gt putenv VARIABLE value In order to start a user task th
124. eeds to be configured to include it by adding INCLUDE UNLOADER to the configuration as suggested in B 1 4 Starting an application RTP If real time processes aka RTP are used the dynamic library 1ibc so must be renamed to 1ibc so 1 and added to the folder of the executable This library is located in the WorkBench installation SWIND_USR 11ib architecture architecture variant common 1e libc so where architecture is for example pent ium and architecture variant is for ex ample PENTIUM in case of an x86 architecture To start the application please use the following shell command rtpSp Filename If you would like to specify command line parameters add them as space seper ated list in the following fashion rtpSp filename argl arg2 arg3 The rtpSp command will pass environment variables from the shell to the spawned process B 1 VXWORKS 219 B 1 5 Linking the application to the VxWorks kernel image The built application may also be linked directly to the VxWorks kernel image for example for saving the kernel and the application in FLASH memory In the Vx Works kernel a user application can be invoked enabling the VxWorks configura tion define INCLUDE_USER_APPL and defining the macro USER_APPL_INIT when compiling the kernel see VxWorks documentation and the file usrConfig c The prototype to invoke the application created with the Builder is int jvm main con
125. eineMarkEmbeddedApp pro gt CaffeineMarkEmbeddedApp destination caffeine_useProfilel0 Reading configuration from 7 1 CODE SIZE VS RUNTIME PERFORMANCE 63 usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed Vf71376adaaf8ea99 __ c scu caffeine useProfilelO0 c caffeine useProfilelO0 h Class file compaction gain 58 83032 21684433 gt 8927412 C compiling caffeine_useProfilel0__ c Lx caffeine useProfilelO0 nc o linking x stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB gt ls s caffeine_useProfilel0 12778336 caffeine useProfilelO The resulting application size is only slightly larger than the interpreted version but the runtime performance is nearly the same as that of the fully compiled ver sion as presented in 8 gt caffeine useProfilel10 Sieve score 10583 98 Loop score 33002 2017 Logic score 50558 0 String score 10105 708 Float score 12747 185 Method score 7357 166650 Overall score 15993 When a profi
126. en for each file or directory by suffixing with encoding e g X java utf8 Option Joption This option is ignored Option X The X option prints non standard options and exits 12 2 Environment Variables The following environment variables control jamaicac JAMAICAC MIN 2 Initial heap size of the jamaicac command it self in bytes Setting this to a larger value will improve the jamaicac performance JAMAICAC HEAPSIZE Maximum heap size of jamaicac command itself in bytes If the initial heap size is not sufficient it will increase its heap dynamically up to this value To compile large applications you may have to set this maximum heap size to a larger value JAMAICAC JAVA STACKSIZE Java stack size of the jamaicac command itself in bytes 132 CHAPTER 12 THE JAMAICA JAVA COMPILER JAMAICAC NATIVE STACKSIZE Native stack size of the jamaicac com mand itself in bytes Chapter 13 The Jamaica Virtual Machine Commands The Jamaica virtual machine provides a set of commands that permit the execution of Java applications by loading a set of class files and executing the code The command lauches the standard Jamaica virtual machine Its variants jamaicavm_slim jamaicavmp and jamaicavdi provide special features like debug support 13 1 jamaicavm The jamaicavm is the standard command to execute non optimized Java appli cations in interpreted mode jamaicavm option
127. er and a client A typical server program creates some remote objects makes references to these objects accessible and waits for clients to invoke methods on these objects A typical client program obtains a remote reference to one or more remote objects on a server and then invokes methods on them RMI provides the mechanism by which the server and the client communicate and pass information back and forth Like any other Java application a distributed application built by using Java RMI is made up of interfaces and classes The interfaces declare methods The classes implement the methods declared in the interfaces and perhaps declare additional methods as well In a distributed application some im plementations might reside in some Java virtual machines but not others Objects with methods that can be invoked across Java virtual machines are called remote objects An object becomes remote by implementing a remote interface which has the following characteristics e A remote interface extends the interface java rmi Remote e n addition to any application specific exceptions each method sig nature of the interface declares java rmi RemoteExceptionin its throws clause Using RMI to develop a distributed application involves these general steps 1 Designing and implementing the components of your distributed ap plication 2 Compiling sources 3 Making classes network accessible 4 Starting the application First de
128. er heap size of for example 2504K can only guarantee a worst case 8 2 CONFIGURATION FOR HARD REALTIME APPLICATIONS 83 execution time of 40 units of garbage collection work that is 6400 PowerPC instructions per block allocation If we find that for our application 14 units of garbage collection work per allocation is sufficient to satisfy all realtime requirements we can build the final application using a heap of 3550K gt jamaicabuilder cp classes heapSize 3550K maxHeapSize 3550K gt HelloWorld Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed PKG__V66c2f3114d534efc__ o reusing existing file for package Dou HelloWorld c HelloWorld h Class file compaction gain 58 96339 21654255 gt 8886172 C compiling HelloWorld__ c HelloWorld nc o linking x stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 3550KB 3550KB GC data 221KB 221KB TOTAL 4923KB 75MB Note that both options heapSize and maxHeapSize are set to the same value This creates an application that has the same initial
129. et a list of all possible values invoke the Builder with help Option setLocales locale locale The set Locales option can be used to choose the set of locales to be included in the target application This involves date currency and number formats Lo cales are specified by a lower case two letter code as defined by ISO 639 Example setLocales de en will include German and English lan guage resources All country information of those locales e g Swiss currency will also be included To get a list of all possible values invoke the Builder with help Option setTimeZones timezone timezone The setTimeZones option can be used to choose the set of time zones to be included in the target application By default all time zones are built in Examples set TimeZones Europe Berlin will include the time zone of Berlin only set TimeZones Europe will include all European time zones setTimeZones Europe Berlin America Detroit includes time zones for Berlin and Detroit 14 2 BUILDER USAGE 153 See the folder jamaica home target platform 1ib zi for the available time zones Option setProtocols protocol protocol The setProtocols option can be used to choose the set of protocols to be included in the target application Example setProtocols ftp http will include handlers for FTP and HTTP protocols To get a list of all possible values invoke the Builder with help Option cdc T
130. ets thus take an unbounded amount of time Originally Java was a language that was very close to C in its syntax with comparable computational complexity of its statements Only a few exceptions where made Java has evolved particularly in the area of class libraries to ease the job of programming complex systems at the cost of diminished computational transparency Therefore a short tour of the different Java statements and expres sions noting where a non obvious amount of computational effort is required to perform these statements with the Java implementation Jamaica VM is provided here 11 2 1 Efficient Java Statements First the good news Most Java statements and expressions can be implemented in a very short sequence of machine instructions Only statements or constructs for which this is not so obvious are considered further 11 2 COMPUTATIONAL TRANSPARENCY 103 Dynamic Binding for Virtual Method Calls Since Java is an object oriented language dynamic binding is quite common In the JamaicaVM dynamic binding of Java methods is performed by a simple lookup in the method table of the class of the target object This lookup can be performed with a small and constant number of memory accesses The total overhead of a dynamically bound method invocation is consequently only slightly higher than that of a procedure call in a language like C Dynamic Binding for Interface Method Calls Whereas single inheritance makes normal meth
131. fied Option Xstrip f ool The Xstrip option uses the specified tool to remove debug information from the generated binary This will reduce the size of the binary file by removing information not needed at runtime Option XnoRuntimeChecks The XnoRuntimeChecks option disables runtime checks for compiled Java code This option deactivates runtime checks to obtain better runtime perfor mance This may be used only for applications that do not cause any runtime checks to fail Failure to run these checks can result in crashes memory cor ruption and similar disasters When untrusted code is executed disabling these checks can cause vulnerability through attacks that exploit buffer overflows type inconsistencies etc The runtime checks disabled by this option are checks for use of null point ers out of bounds array indices out of bounds string indices array stores that are 176 CHAPTER 14 THE JAMAICA BUILDER not compatible with the array element type reference assignments between in compatible memory areas division by zero and array instantiation with negative array size These runtime checks usually result in throwing one of the following exceptions NullPointerException ArrayIndexOutOfBoundsException StringIndexOutOfBoundsException ArrayStoreException IllegalAssignmentError ArithmeticException NegativeArraySizeException When deactivated the system will be in an undefined state if any of these condi t
132. g 16 2 The Jamaicah Command 16 2 1 General lll 16 2 3 Environment Variables 17 Numblocks Command MD DER 17 1 1 General lll nuc T 17 2 Environment Variables 18 Building with Apache Ant 18 1 Task Declaration 18 2 Task IV Additional Information A FAQ Frequently Asked Questions Mac pep TM A Died Go hie eh Be Beye 2 a Lucus SUP Sere EU Sas Be NNUS A 6 VxWorksTargetl llle CONTENTS B E CONTENTS 9 Information for Specific Targets 213 VXxWOtFKS za oe OR eae eee 213 B 1 1 Configuration of VxWorks 213 Eurum 215 B 1 3 Starting an application DKM 216 B 1 4 Starting an application 218 2 1219 1 __1 219 B 1 7 Additnonalnotes 220 2 5 220 B 2 Installation 220 _ RENDER ENS 221 ee Gs td EE 221 ar eee 221 B 3 1 Installation 222 B 3 2 Linker Directives File 222 MD 223 B 4 Widows 223 B 4 1 Lamitations 223 B 5 WindowsCEH Re 224 5 1 Lamitations 0 224 224 B 61 Lamitations
133. have to set the property jamaica profile groups to select one or more profiling groups The default value is builder to collect data used by the builder You can set the property to the values builder memory speed all or a comma separated combination of those Example gt jamaicavmp cp classes gt Djamaica profile groups builder speed gt HelloWorld The format of the profile file is likely to change in future versions of Jamaica Builder 52 CHAPTER 6 PERFORMANCE OPTIMIZATION 6 3 1 Format of the profile file Every line in the profiling output starts with a keyword followed by space sepa rated values The meaning of these values depends on the keyword For a better overview the corresponding values in different lines are aligned as far as possible and words and signs that improve human reading are added Here for every keyword the additional words and signs are omitted and the values are listed in the same order as they appear in the text file Keyword BEGIN PROFILE DUMP Groups all Values 1 unique dump ID Keyword END PROFILE DUMP Groups all Values 1 unique dump ID Keyword HEAP REFS Groups memory Values 1 total number of references in object attributes 2 total number of words in object attributes 3 relative number of references in object attributes Keyword HEAP USE Groups memory Values 1 total number of currently allocated objects of this class 2 number of blocks
134. he Eclipse Plug In The following example shows an Ant target for executing the Jamaica Builder target name build app lt jamaicabuilder jamaica usr local jamaica gt lt target value linux x86 classpath value classes gt lt classpath value extLib jar gt lt interpret value true enabled false gt lt heapSize value 32M gt lt Xlibraries value extLibs append true gt lt XdefineProperty value window size 800x600 gt lt main value Application gt lt jamaicabuilder gt lt target gt This is equivalent to the following command line usr local jamaica bin jamaicabuilder target linux x86 classpath classes extLib jar heapSize 32M Xlibraries t extLibs XdefineProperty window size 800x600 Application Note that some options take arguments that contain the equals sign For example the argument to XdefineProperty is of the form property value As shown in the example the entire argument should be placed in the value attribute liter ally Ant pattern sets and related container structures are currently not supported by the Jamaica Ant tasks Part IV Additional Information 203 Appendix A FAQ Frequently Asked Questions Check here first when problems occur using JamaicaVM and its tools A 1 General Information Q I use Eclipse to develop my Java applications Is there a plug in available which will help me to use JamaicaVM and the Builder from within
135. he VM Rescheduling is a sub state of the running thread The running thread state is changed to rescheduling when another thread becomes more eligible to execute This happens when a thread of higher priority becomes ready either by unblocking or attaching to the VM The running thread will then run to the next synchronization point and yield the CPU to the more eligible thread Ready threads are attached threads which can execute as soon as no other thread is more eligible to run Attached threads may block 186 CHAPTER 15 THE JAMAICA THREADMONITOR for a number of reasons the most common of which are calls to Thread sleep Object wait and entering of a contended monitor 15 3 1 Data Window Navigation The data window permits easy navigation through the displayed scheduler data Two main properties can be changed The time resolution can be contracted or expanded and the total display can be enlarged or reduced zoom in and zoom out Four buttons on the top of the window serve to change these properties Selection of displayed area The displayed area can be selected using the scroll bars or via dragging the con tents of the window while holding the left mouse button Time resolution The displayed time resolution can be changed via the buttons expand time and contract time or via holding down the left mouse button for expansion or the middle mouse button for contraction Instead of the middle mouse button the control key
136. he cdc option forces the inclusion of all standard library code within the CDC configuration This Connected Device Configuration is intended for use in small connected devices Providing this option forces the Builder to include all classes fields methods and constructors that form part of the CDC configuration The resulting application will hence be able to access all code in the CDC configuration through dynamically loaded classes or the reflection API even if this code would otherwise not be included in the application Option cldc The cldc option forces the inclusion of all standard library code within the CLDC configuration This Connected Limited Device Configuration is intended for use in very small connected devices Providing this option forces the Builder to include all classes fields methods and constructors that form part of the CLDC configuration The resulting application will hence be able to access all code in the CLDC configuration through dynamically loaded classes or the reflection API even if this code would otherwise not be included in the application Option incrementalCompilation If the incrementalCompilation option is set to t rue C code is split into several files for incremental compilation The generated code is split into one file per package This is the default behavior If this option is set to false all C code is put into one single potentially large C source file 154 CHAPTER 14 THE JAMAI
137. he finalizer thread priority to a low value if your system has enough idle time e f your application uses allocation bursts with sufficient CPU idle time in between two allocation bursts set the amount of reserved memory to fit with the largest allocation burst e f your application does not have idle time with intermittent allocation bursts set the amount of reserved memory to 0 80 CHAPTER 8 MEMORY MANAGEMENT CONFIGURATION e Enable the GC thread if your system has idle time that can be used for garbage collection 8 2 Configuration for hard realtime applications For predictable execution of memory allocation more care is needed when select ing memory related options No dynamic heap size increments should be used if the break introduced by the heap size expansion can harm the realtime guarantees required by the application Also the heap size must be set such that the implied garbage collection work is tolerable The memory analyzer tool is used to determine the garbage collector settings during a runtime measurement Together with the numblocks command see 8 17 they permit an accurate prediction of the time required for each memory al location The following sections explain the required configuration of the system 8 2 1 Usage of the Memory Analyzer tool The Memory Analyzer is a tool for fine tuning an application s memory require ments and the realtime guarantees that can be given when allocating objects within Java
138. he same way as it would if it were called with the jamaicavm or java command Despite its name the option accepts directories as well Multiple archives or 66 0 99 directories should be separated by the system specific path separator colon ec 99 on Unix systems and semicolon on Windows Option excludeJAR file file The excludeJAR option forces the exclusion of all classes and resources con tained in the specified files Any class and resource found will be excluded from the created application Use this option to load an entire archive at runtime Despite its name the option accepts directories as well Multiple archives or oo 0 99 directories should be separated by the system specific path separator colon ee 99 on Unix systems and semicolon on Windows Option lazy Jamaica VM by default uses static linking of all Java classes This means that all classes that are referenced from the main class will be loaded before execution of the application starts This early loading and linking of classes ensures that 14 2 BUILDER USAGE 151 during the execution of the Java application no further class loading and linking will be required ensuring the predictable execution of statements that can cause class loading in a traditional Java environment The statements that may cause loading and linking of classes are the same statements that may cause the execution of static initalizers of
139. he use of final local variables any private fields that are accessed from within an inner class require the call to a hidden access method since these accesses would otherwise not be permitted by the virtual machine 11 2 COMPUTATIONAL TRANSPARENCY 105 11 2 3 Statements Causing Implicit Memory Allocation Thus far only execution time has been considered but memory allocation is also a concern for safety critical systems In most cases memory allocation in Java is performed explicitly by the keyword new However some statements per form memory allocations implicitly These memory allocations do not only re quire additional execution time but they also require memory This can be fa tal within execution contexts that have limited memory e g code running in a ScopedMemory or ImmortalMemory as itis required by the Real Time Spec ification for Java for NoHeapRealtimeThreads A realtime Java programmer should be familiar with all statements and expressions which cause implicit mem ory allocation String Concatenation Java permits the composition of strings using the plus operator Unlike adding scalars such as int or float values string concatenation requires the allocation of temporary objects and is potentially very expensive As an example the instruction rnt Object thing String msg x is x thing is thing will be translated into the following statement sequence THE 2 Object th
140. heap can be used for shared memory communication between all threads Any high priority task can access objects on the heap even while a lower priority thread accesses the same objects or even while a lower priority thread allocates memory and performs garbage collection work In the latter case the small worst case execution time of an increment of garbage collection work ensures a bounded and small thread preemption time typically in the order of a few microseconds 11 4 MEMORY MANAGEMENT 117 Synchronization The use of Java monitors in synchronized methods and explicit synchronized statements enables atomic accesses to data structures These mechanisms can be used equally well to protect accesses that are performed in high priority realtime tasks and normal non realtime tasks Unfortunately the standard Java semantics for monitors does not prevent priority inversion that may result from a high priority task trying to enter a monitor that is held by another task of lower priority The stricter monitor semantics of the RTSJ avoid this priority inversion All monitors are required to use priority inheritance or the priority ceiling protocol such that no priority inversion can occur when a thread tries to enter a monitor As in any realtime system the developer has to ensure that the time that a monitor is held by any thread must be bounded when this monitor needs to be entered by a realtime task that requires an upper bound for the time required t
141. heap size and maxi mum heap size i e the heap size is not increased dynamically This is required to ensure that the maximum of 14 units of garbage collection work per unit of allocation is respected during the whole execution of the application With a dy namically growing heap size an allocation that happens to require increasing the heap size will otherwise be blocked until the heap size is increased sufficiently The resulting application will now run with the minimum amount of memory that guarantees the selected worst case execution time for memory allocation The actual amount of garbage collection work that is performed is determined dynam ically depending on the current state of the application including for example its memory usage and will in most cases be significantly lower than the described worst case behavior so that on average an allocation is significantly cheaper than 84 CHAPTER 8 MEMORY MANAGEMENT CONFIGURATION the worst case allocation cost 8 25 Constant Garbage Collection Work For applications that require best worst case execution times where average case execution time is less important Jamaica also provides the option to statically select the amount of garbage collection work This forces the given amount of garbage collection work to be performed at any allocation without regard to the current state of the application The advantage of this static mode is that worst case execution times are lower than using
142. hread of high priority is blocked by waiting for a monitor that is owned by a thread of a lower priority The RTSJ provides the alternatives priority inheritance and the priority ceiling protocol to avoid priority inversion The RTSJ offers powerful features that enable the development of realtime applications The following program in shows an example how the RTSJ can be used in practice Small demonstration of a periodic thread Java import javax realtime x public class HelloRT public static void main String args priority for new thread min 10 10 1 REALTIME PROGRAMMING WITH THE RTSJ 95 int pri PriorityScheduler instance getMinPriority 10 PriorityParameters prip new PriorityParameters pri period 20ms RelativeTime period new RelativeTime 20 ms 0 ns x release parameters for periodic thread PeriodicParameters perp new PeriodicParameters null period null null null null create periodic thread RealtimeThread rt new RealtimeThread prip perp public void run int n 1 while waitForNextPeriod amp amp n lt 100 System out printin Hello ntt start periodic thread rt start In this example a periodic thread is created This thread becomes active every 20ms and writes output onto the standard console A RealtimeThreadis used to implement this task Th
143. ich will be compiled That is replace a static initializer class A static lt initialisation code gt by the following code class A static init private static void init lt initialisation code gt e Methods with bytecode that is longer than the value provided by builder option XexcludeLongerThan are not compiled e When option lazy is set which is the default methods that reference a class field or method that is not present at build time are not compiled The referenced class will be loaded lazily by the interpreter 238 APPENDIX E LIMITATIONS Appendix F Internal Environment Variables Additional debugging output can be activated through environment variables if an application was built with the internal option debug t rue This option and its environment variables are used for debugging Jamaica itself and are not normally relevant for users of JamaicaVM JAMAICA DEBUGLEVEL Defines the debug level of an application that was built with the option debug A level of 0 means that only a small amount of debug output is printed a level of 10 means that very detailed debug output is printed Note that at a debug level of 10 a simple HelloWorld application will pro duce thousands of lines of debug output A good choice is a level of about 5 JAMAICA DEBUGCALLNATIVE Defines a string that gives the name of a native method Any call to that method is printed in additio
144. icient idle time should therefor run with the maximum amount of reserved memory set to 0 The priority default of the memory reservation thread is the Java priority 1 with the scheduler instructed to give preference to other Java threads that run at priority 1 ie with a priority micro adjustment of 1 The priority can be changed by setting the Java property jamaica reservation thread priority toan integer value larger than or equal to 0 If set the memory reser vation thread will run at the given Java priority A value of 0 will result at a Java priority 1 with micro adjustment 1 i e the scheduler will give preference to other threads running at priority 1 8 1 5 Using a GC thread In JamaicaVM the garbage collection work is by default performed in the ap plication threads so there is no need for a dedicated garbage collection thread However in an application that provides idle CPU time one might wish to use this idle time to take load from the main threads and perform garbage collection work during idle time JamaicaVM permits this by enabling the use of a garbage collection thread GC thread The GC thread is by default not activated It can be activated by setting a Java system property jamaica gcthread pri The value of this property must be the desired thread priority the GC thread should run at Typically the lowest Java thread priority 1 is the best value to use an application s idle time Since the application may
145. ics of threads for realtime systems These threads can use a priority range that is higher than that of all normal Java Threads with at least 28 unique priority levels The default scheduler uses these priori ties for fixed priority preemptive scheduling In addition to this the new thread classes can use the new memory areas ScopedMemory and ImmortalMemory that are not under the control of the garbage collector As previously mentioned threads of class NoHeapRealt imeThreads are not permitted to access any object that was allocated on the garbage collected heap Consequently these threads do not suffer from garbage collector activity as long as they run at a priority that is higher than that of any other schedulable object that accesses the garbage collected heap In the Jamaica VM Java environment the memory access restrictions present in NoHeapRealtimeThreads are not required to achieve realtime guarantees Consequently the use of NoHeapReal timeThreads is neither required nor recommended Apart from the extended priority range RealtimeThreads provide fea tures that are required in many realtime applications Scheduling parameters for periodic tasks deadlines and resource constraints can be given for Realtime Threads and used to implement more complex scheduling algorithms For instance periodic threads in the JamaicaVM use these parameters In the Ja maicaVM Java environment normal Java threads also profit from strict fixed pri orit
146. ictRTSd is set names and instances of class PhysicalMemory TypeFilter in package javax realtime that are passed to method registerFilter of class PhysicalMemoryManager in the same pack age must be allocated in immortal memory as required by the RTSJ 10 5 Limitations of RTSJ Implementation The following methods or classes of the RTSJ are not fully supported in Ja maicaVM 6 0 e Class VTPhysicalMemory e Class LTPhysicalMemory e Class ImmortalPhysicalMemory e In class AsynchronouslyInterruptedException the deprecated method propagate is not supported 100 CHAPTER 10 THE REAL TIME SPECIFICATION FOR JAVA Cost monitoring is supported and cost overrun handlers will be fired on a cost overrun However cost enforcement is currently not supported The reason is that stopping a thread or handler that holds a lock is dangerous since it might cause a deadlock RTSJ cost enforcement is based on the CPU cycle counter This is available on x86 and PPC systems only so cost enforcement will not work on other systems Chapter 11 Guidelines for Realtime Programming in Java 11 1 General Since the timeliness of realtime systems is just as important as their functional correctness realtime Java programmers must take more care using Java than other Java users In fact realtime Java implementations in general and the JamaicaVM in particular offer a host of features not present in standard Java implementations The Jamaica
147. ifies the initial number of Java threads supported by the destination application These threads and their runtime stacks are gener ated at startup of the application A large number of threads consequently may require a significant amount of memory The minimum number of threads is two one thread for the main Java thread and one thread for the finalizer thread Option maxNumThreads n The maxNumThreads options specifies the maximum number of Java threads supported by the destination application If the maximum number of threads is larger than the values specified for numThreads threads will be added dynam ically Adding new threads requires unfragmented heap memory It is strongly rec ommended to use maxNumThreads only in conjunction with maxHeapSize set to a value larger than heapSize This will permit the VM to increase the heap when memory is fragmented The absolute maximum number of threads for the Jamaica VM is 511 14 2 BUILDER USAGE 159 Option numJniAttachableThreads n The numJniAttachableThreads specifies the initial number of Java thread structures that will be allocated and reserved for calls to the JNI Invocation API functions These are the functions JNI AttachCurrentThread and JNI AttachCurrentThreadAsDaemon These threads will be allocated on VM startup such that no additional allocation is required on a later call to JNI AttachCurrentThreadorJNI AttachCurrentThreadAsDaemon Even if this option is set to zero i
148. ilarly weak soft and phantom references rely on the presence of a final izer If the resources available on the target system do not permit the use of a finalizer thread the application may execute finalize method ex plicitly by frequent calls to Runtime runFinalization This will also permit the use of weak soft and phantom references even if no finalizer thread is present 4 Setting the number of threads The number of threads available for the application can be set using option numThreads The default setting for this option is two which is enough for the finalizer thread and the main thread of the application If the finalizer thread is deactivated and no new threads are started by the application the number of threads can be reduced to one by using the setting numThreads l Note that if profiling information was collected and is provided via the useProfile option the number of threads provided to the numTh reads option will be checked to ensure it is at least the the number of threads that were required during the profiling run If not a warning message with the minimum number of threads during the profiling run will be displayed This information can be used to adjust the number of threads to the minimum re quired by the application 5 Disabling time slicing On non realtime systems that do not strictly respect thread priorities Ja maica uses one additional thread to allow time slicing between threads On realti
149. ime performance If none of the options interpret compile or useProfile is spec ified then the default compilation will be used The default means that a pre generated profile will be used for the system classes and all application classes will be compiled fully This default usually results in good performance for small applications but it causes extreme code size increase for larger applications and it results in slow execution of applications that use the system classes in a way different than recorded in the system profile 156 CHAPTER 14 THE JAMAICA BUILDER Option compile The compile option enables static compilation for the created application All methods of the application are compiled into native code causing a significant speedup at runtime compared to the interpreted code that is executed by the virtual machine Use compilation whenever execution time is important However it is often sufficient to compile about 10 percent of the classes which results in much smaller executables of comparable speed You can achieve this by using the options profile and useProfile instead of compile Option inline n When methods are compiled via one of the options compile useProfile orinterpret false this option can be used to set the level of inlining to be used by the compiler Inlining typically causes a significant speedup at runtime since the overhead of performing method calls is avoided Nevertheless inlining causes duplicatio
150. imeThread to run in their own memory area not under the con trol of the garbage collector Instead any thread can use and access the normal garbage collected heap Nevertheless any thread can make use of the new memory areas such as LTMemory or ImmortalMemory if the application developer wishes to do so 10 3 RELAXATIONS IN JAMAICAVM 97 Since these memory classes are not controlled by the garbage collector alloca tions do not require garbage collector activity and may be faster or more pre dictable than allocations on the normal heap However great care is required in these memory areas to avoid memory leaks since temporary objects allocated in scoped or immortal memory will not be reclaimed automatically 10 3 2 Thread Priorities In JamaicaVM RealtimeThread NoHeapRealtimeThread and normal Thread objects all share the same priority range The lowest possible thread priority for all of these threads is MIN PRIORITY which is defined in pack age java lang class Thread The the highest possible priority may be ob tainded by querying instance getMaxPriority inpackage javax realtime class PriorityScheduler 10 3 3 Runtime checks for NoHeapRealtimeThread Even NoHeapRealtimeThread objects will be exempt from interruption by garbage collector activities JamaicaVM does not therefore prevent these threads from accessing objects allocated on the normal heap Runtime checks that typi cally ensure that these thre
151. in point e g after a timeout or on a certain user input The easiest means to terminate an application is via a call to System exit Otherwise all threads that are not daemon threads need to be terminated To request a remote profile the property jamaica profile request port has to be set to a port number Then a request to write the profile can be sent via the command jamaicavm com aicas jamaica lang Profile host port See C for more information on this mechanism Profiling information is always appended to the profiling file This means that profiling information from several profiling runs of the same application e g using different input data will automatically be written into a single profiling file To fully overwrite the profiling information e g after a major change in the application the profiling file must be deleted manually 138 CHAPTER 13 THE JAMAICA VIRTUAL MACHINE COMMANDS The collection of profiling information requires additional CPU time and mem ory to store this information It may therefore be necessary to increase the memory size Also expect poorer runtime performance during a profiling run 13 3 1 Additional extended options of jamaicavmp Option XprofileFilename filename This option selects the name of the file to which the profile data is to be written If this option is not provided the default file name is used consisting of the main class name and the suffix prof 13 4 jamaicavmdi
152. ing StringBuffer tmp sb new StringBuffer tmp sb append x is tmp sb append x tmp sb append thing is tmp sb append thing toString String msg tmp sb toString The code contains hidden allocations of a StringBuffer object of an internal character buffer that will be used within this StringBuffer atemporary string allocated for thing toString and the final string returned by sb toString gt Apart from these hidden allocations the hidden call to thing toString can have an even higher impact on the execution time since method toString can be redefined by the actual class of the instance referred to by thing and can cause arbitrarily complex computations 106 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES Array Initialization Java also provides a handy notation for array initialization For example an array with the first 8 Fibonacci numbers can be declared as Inti tibs 1 14 2 3 5 8 13 21 47 Unlike C where such a declaration is converted into preinitialized data the Java code performs a dynamic allocation and is equivalent to the following code se quence int fib new int 8 fib fib fib fib fib fib fib fib 1 1 2 3 5 8 13 21 Initializing arrays in this way should be avoided in time critical code When pos sible constant array data should be initialized within the static initiali
153. ing data among cooperat ing tasks This interaction requires synchronization to ensure data integrity There are implications on scheduling of threads and synchronization beyond memory access issues 11 5 1 Schedulable Entities The RTSJ introduces new scheduling entities to Java RealtimeThread and NoHeapRealtimeThread are thread types with clearer semantics than nor mal Java threads of class Thread and additional scheduling possibilities Events are the other new thread like construct used for transient computations To save resources mainly operating system threads and thus memory and performance AsyncEvents can be used for short code sequences instead They are easy to use because they can easily be triggered programmatically but they must not be used for blocking Also there are BoundAsyncEvents which each require their own thread and thus can be used for blocking They are as easy to use as normal AsyncEvents but do not use fewer resources than normal threads AsyncEventHandlers are triggered by an asynchronous event AII three exe cution environments RealtimeThreads NoHeapRealtimeThreads and AsyncEventHandlers are schedulable entities 1 they all have release pa rameters and scheduling parameters that are considered by the scheduler 11 5 SCHEDULING AND SYNCHRONIZATION 119 RealtimeThreads and NoHeapRealtimeThreads The RTSJ includes new thread classes Realt imeThreads and NoHeapReal timeThreads to improve the semant
154. ions occurs Option XavailableTargets The XavailableTargets option lists all available target platforms of this Ja maica distribution 14 3 4 Profiling Profiling can be used to guide the compilation process and to find a good trade off between fast compiled code and smaller interpreted byte code This is particularly important for systems with tight memory and CPU resources Option XprofileFilename name The XprofileFilename option sets name of file for profiling data If profiling is enabled output is written to this file If a profile filename is not specified then the profile data is written a the file with the name of the destination see option destination with the extension prof added 14 3 5 Native code Native code is code written in a different programming language than Java typ ically C or C This code can be called from within Java code using the Java Native Interface JNI Jamaica internally uses a more efficient interface the Ja maica Binary Interface JBI for native calls into the VM and for compiled code Option XenableDynamicJNILibraries The XenableDynamicJNILibraries option activates support for loading JNI libraries at runtime This feature is currently implemented for the architec 14 3 BUILDER EXTENDED USAGE 177 tures x86 and ARM ABI calling convention without FPU support On other sys tems JNI libraries must be linked at build time Option XloadJNIDynamic class method class
155. is performed on an allocation never exceeds the amount allowed to ensure timely execution of the application s realtime code Using analyze can cause a significant slowdown of the application The ap plication slows down as the tolerance is reduced 1 the lower the value specified as an argument to analyze the slower the application will run In order to configure the application heap a version of the application must be built using the option analyze and in addition the exact list of arguments used for the final version The heap size determined in a test run can then be used to build a final version using the preferred heap size with desired garbage collection overhead To reiterate the argument list provided to the Builder for this final version must be the same as the argument list for the version used to analyze the memory requirements Only the heapSize option of the final version must be set accordingly and the final version must be built without setting analyze Option analyseFromEnv analyzeFromEnv var The analyseFromEnv option enables the application to read the amount of analyze accuracy of the garbage collector from the environment variable specified within If this variable is not set the value specified using analyze n will be used Setting the environment variable to 0 will disable the analysis and cause the garbage collector to use dynamic garbage collection mode Option constGCwork n The constGCwork option
156. is required per unit of allocation increases as the size of reserved memory is increased For a detailed output of the effect of using reserved memory run the application with option analyse set together with the desired value of reserved memory Option reservedMemoryFromEnv var The reservedMemoryFromEnv option enables the application to read the per centage of reserved memory from the environment variable specified within If this variable is not set the value specified using reservedMemory n will be used See option reservedMemory for more information on the effect of this option 166 CHAPTER 14 THE JAMAICA BUILDER 14 2 7 RTSJ settings The following options set values that are relevant for the Real Time Specifica tion for Java extensions through classes javax realtime that are provided by Ja maicaVM Option strictRTSJ The Real Time Specification for Java RTSJ defines a number of classes in the package javax realtime These classes can be used to create realtime threads with stricter semantics than normal Java threads In particular these threads can run in their own memory areas scoped memory that are not part of the Java heap such that memory allocation is independent of garbage collector in tervention It is even possible to create threads of class javax realtime NoHeapRealtimeThread that may not access any objects stored on the Java heap In Jamaica VM normal Java Threads do not suffer from these restrictions
157. itions of new features or applet execution 2 7 Supported Platforms During development special care has been taken to reduce porting effort of the JamaicaVM to a minimum JamaicaVM is implemented in C using the GNU C compiler Threads are based on native threads of the operating system 2 7 Development platforms Jamaica is available for the following development platforms host systems POSIX threads under many Unix systems 20 CHAPTER 2 KEY FEATURES OF JAMAICAVM e Linux e SunOS Solaris e Windows 2 7 2 Target platforms With JamaicaVM application programs for a large number of platforms target systems can be built The operating systems listed in this section are supported as target systems only You may choose any other supported platform as a devel opment environment on which the Jamaica Builder runs to generate code for the target system Realtime Operating Systems e INTEGRITY e Linux RT e OS 9 on request e PikeOS e QNX RTEMS on request e ThreadX on request e WinCE e VxWorks Non Realtime Operating Systems Applications built with Jamaica on non realtime operating systems may be inter rupted non deterministically by other threads of the operating systems However Jamaica applications are still deterministic and there are still no unexpected in terrupts within Jamaica application themselves unlike with standard Java Virtual Machines e Linux e SunOS Solaris e Windows 2 8 FAST E
158. ive Interface with Jamaica This example simply writes a value to a hardware register using a native method We use the file JNITest java which contains the following code public class JNITest static native int write HW Register int address 191 192 CHAPTER 16 JAMAICA AND THE JAVA NATIVE INTERFACE JNI int value public static void main String args int value value write HW Register 0xfc000008 0x10060 System out println Result value Jamaica provides a tool jamaicah for generating C header files that con tain the function prototypes for all native methods in a given class Note that jamaicah operates on Java class files so the class files have to be created first using jamaicac as described in 12 The header file for JNITest java is created by the following sequence of commands gt jamaicac JNITest java gt jamaicah JNITest Reading configuration from usr local jamaica etc jamaicah conf JNITest h header This created the include file JNITest h DO NOT EDIT THIS FILE it is machine generated finclude lt jni h gt Header for class JNITest x ifndef Included JNITest define Included JNITest ifdef _ cplusplus extern C fendif Class JNITest Method write HW Register Signature II I x ifdef _ cplusplus extern C fendif JNIEXPORT jint JNICALL Java JNITest write lRegister JNI ifdef
159. ize may be succeeded by the letter K or M to specify a size in KBytes 1024 bytes or MBytes 1048576 bytes The minimum required heap size for a given application can be determined using option analyze Option maxHeapSize 7 The maxHeapSize option sets maximum heap size to the specified size given in bytes If themaximum heap size is larger than the heap size the heap size will be increased dynamically on demand The maximum heap size may be succeeded by the letter K or M to specify a size in KBytes 1024 bytes or MBytes 1048576 bytes The minimum value is 0 for no dynamic heap size increase Option heapSizeIncrement r The heapSizeIncrement option specifies the steps by which the heap size can be increased when the maximum heap size is larger than the heap size The maximum heap size may be succeeded by the letter K or M to specify a size in KBytes 1024 bytes or MBytes 1048576 bytes The minimum value is 64k Option javaStackSize n K M The javaStackSize option sets the stack size to be used for the Java runtime stacks of all Java threads in the built application Each Java thread has its own stack which is allocated from the global Java heap The stack size consequently has an important impact on the heap memory required by an application A small stack size is recommended for systems with tight memory constraints If the stack size is too small for the application to run a st
160. l heap demand of the application is of no importance for the remaining system Setting initial heap size and maximum heap size to the same value has two main consequences First as has been seen in 8 8 1 1 above setting the initial heap size to a higher value avoids the overhead of dynamically expanding the heap and reduces the amount of garbage collection work during startup Second JamaicaVM s memory management code contains some optimizations that are only applicable to a non increasing heap memory space so overall memory management overhead will be reduced if the same value is chosen for the initial and the maximum heap size 8 1 3 Finalizer thread priority Before the memory used by an object that has a finalize method can be re claimed this finalize method needs to be executed A dedicated thread the FinalizerThread executes these finalize methods and otherwise sleeps waiting for the garbage collector to find objects to be finalized In order to prevent the system from running out of memory the Finalizer Thread must receive sufficient CPU time Its default priority is therefore set to 10 the highest priority a Java thread may have Consequently any thread with a lower priority will be preempted whenever an object is found to require finaliza tion Selecting a lower finalizer thread priority may cause the finalizer thread to starve if a higher priority thread does not yield the CPU for a longer period of time However if it can be g
161. lder argument Xinclude How can I set properties using Dname value for an application that was built using the builder A For commands like jamaicavm parsing of arguments like Dname value stops at the name of the main class of the application After the application has been built the main class is an implicit argument so there is no direct 210 APPENDIX FAQ FREQUENTLY ASKED QUESTIONS way to provide additional options to the VM However there is a way out of this problem the Builder option XnoMain removes the implicit argu ment for the main class so jamaicavm s normal argument parsing is used to find the main class When launching this application the name of the main class must then be specified as an argument so it is possible to add additional VM options such as Dname value before this argument When I run the Builder an error exec fail is reported when the interme diate C code should be compiled The exit code is 69 What happened A An external C compiler is called to compile the intermediate C code The compiler command and arguments are defined in etc jamaica conf If the compiler command can not be executed the Builder terminates with an error message and the exitcode 69 see list of exit codes in the appendix Try to use the verbose output with the option verbose and check if the printed compiler command call can be executed in your command shell If not check the parameter
162. le is used to guide the compiler by default 10 of the methods executed during the profile run are compiled This results in a moderate code size increase compared with fully interpreted code and typically results in a run time performance very close to fully compiled code Using the builder option percentageCompiled this default setting can be adjusted to any value be tween 0 and 100 Note that setting the value to 100 is not the same as 64 CHAPTER 7 REDUCING FOOTPRINT AND MEMORY USAGE setting the option compile see 7 1 2 since the percentage value only refers to those methods executed during the profiling run Methods not executed during the profiling run will not be compiled when useProfile is used Entries in the profile can be edited manually for example to enforce compila tion of a method that is performance critical For example the profile generated for this example contains the following entry for the method size of class java util Vector PROFILE 64 0 oo java util Vector size I To enforce compilation of this method even when percentageCompiled is not set to 100 the profiling data can be changed to a higher value e g PROFILE 1000000 0 java util Vector size I Selecting C compiler optimization level Enabling C compiler optimizations for code size or execution speed can have an important effect on the the size and speed of the application These optimiza tions are enabled via setting th
163. leaving of the monitor at all since the code sequence is guaranteed to be executed atomically due to the fact that it does not contain a synchronization point 11 6 Libraries The use of a standard Java libraries within realtime code poses severe difficulties since standard libraries typically are not developed with the strict requirements on execution time predictability that come with the use in realtime code For use within realtime applications any libraries that are not specifically written and documented for realtime system use cannot be used without inspection of the library code The availability of source code for standard libraries is an important prerequi site for their use in realtime system development Within the JamaicaVM large parts of the standard Java APIs are taken from OpenJDK which is an open source project The source code is freely available so that the applicability of certain methods within realtime code can be checked easily 11 7 Summary As one might expect programming realtime systems in Java is more complicated than standard Java programming A realtime Java developer must take care with many Java constructs With timely Java development using JamaicaVM there are instances where a developer has more than one possible implementation construct to choose from Here the most important of these points are recapitulated 124 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES 11 7 1 Efficiency All method calls and i
164. lication domains are layered on top of these configurations e g Mobile Information Device Profile MIDP on CLDC and Personal Profile on CDC The Jamaica VM supports both base configurations Smaller Java configura tions are interesting not only on systems with hardware limitations but also for certification The vast number of classes in J2SE would make any JVM certifica tion daunting Again the choice between J2SE and J2ME is a trade off between flexibility on the one hand and leanness and robustness on the other A safety critical version of JamaicaVM may well support a safety critical profile for CDC in the future 11 4 Memory Management In a system that supports realtime garbage collection RTSJ s strict separation into realtime and non realtime threads is not necessary The strict splitting of an application is consequently not required Threads are activated only depending on their priorities as depicted in Fig The realtime garbage collector performs its work predictably within the appli cation threads It is activated when memory is allocated The work done on an allocation must be preemptible so that more urgent threads can become active The implementation of a realtime garbage collector must solve a number of technical challenges Garbage collector activity must be performed in very small single increments of work In the JamaicaVM one increment consists of process ing and possibly reclaiming only 32 bytes of memory On ever
165. lows 104 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES ArrayList lt String gt list new ArrayList lt String gt list add 0 some string String str list get 0 Generics still require type casts but these casts are hidden from the developer This means that access to list using list get 0 in this example in fact performs the type cast to String implicitly causing additional runtime over head However since type casts are performed efficiently and in constant time in JamaicaVM the use of generics can be recommended even in time critical code wherever this appears reasonable for a good system design 11 2 3 Non Obvious Slightly Inefficient Constructs A few constructs have some hidden inefficiencies but can still be executed within a short sequence of machine instructions final Local Variables The use of final local variables is very tempting in conjunction with anonymous inner classes since only variables that are declared final can be accessed from code in an anonymous inner class An example for such an access is shown in the following code snippet final int data getData new RealtimeThread new PriorityParameters pri public void run for x data All uses of the local variable within the inner class are replaced by accesses to a hidden field In contrast to normal local variables each access requires a memory access Accessing private Fields from Inner Classes As with t
166. ludeFilename file Specify the name of the include file to be included in stubs Option version Prints the version of the jamaicah tool and exits Option showSettings Options of jamaicah currently in use are written to standard output in property file format To make these the default settings write the output into jamaica home etc jamaicah conf 196 CHAPTER 16 JAMAICA AND THE JAVA NATIVE INTERFACE JNI Option saveSettings file Options of jamaicah currently in use are written to the specified file in property file format Option configuration file The set of options used to build the application are read from the provided file The format used to define options must be identical to the default configuration file jamaica home etc jamaicah conf With this option given the other default configuration files i e user home jamaica jamaicah conf and jamaica home et c jamaicah conf are ignored 16 2 2 Classes files and paths Option classpath cp classpath Specifies default path used for loading classes Option bootclasspath Xbootclasspath classpath Specifies default path used for loading system classes Option classname class class Generate header files for the listed classes Multiple items must be separated by spaces and enclosed in double quotes 16 2 3 Environment Variables The following environment variables control jamaicah JAMAICA JAMAICAH HEAPSIZE Heap size of the jamai
167. maicavmdi 13 5 Environment Variables 13 6 Exitcod s oho oec i we RC Re ee Re 0 14 The Jamaica Builder 14 1 How the Builder tool 14 2 Builder Usage 4 2x 2 2 ee ee de Rom RO ed ew UR ed os eS 14 2 1 Generi x03 BORG a SG ee HEY GOES ES RE HRSG EHH aS HRS 14 2 3 5 tb he Dike ees ee See Deus doth Me had Meee he Oe Oe a he Se LA X xA G SRE 142 7 RVSWseunes s 2 ee ede er dee ed wee 4 2 5 ProBhngl vos ace aes om eee Dew EORR Ems 14 2 9 TUM ME 14 3 1 General s 2 se See SERA EER Ewe pee So ee her a a es St me 14 3 3 Compilation 14 3 4 Profiling 14 3 5 14 3 6 Miscellaneous 14 4 Environment Variables 14 5 Bxitcodes o 2h Sn we ee eS eR eee ESR EER 130 130 131 131 131 133 133 134 134 136 136 137 138 138 138 138 141 15 The Jamaica ThreadMonitor 15 1 Run time system configuration 15 2 Control Window rp cx Ln TIME da oe ee oe 15 3 4 Data Window Tool Tips 15 3 5 Worst Case Execution Time Window 16 Jamaica and the Java Native Interface JNI 16 1 Usin
168. mand line options and environment variables are possible the command line settings have precedence To inspect the relevant command line options issue gt jamaicavm Xhelp Option xhelp X The xhelp option prints a short help summary on the extended options of Ja maicaVM 13 1 2 JamaicaVM Extended Options JamaicaVM supports a number of extended options Some of them are supported for compatibility with other virtual machines while some provide functionality that is only available in Jamaica Please note that the extended options may change without notice Use them with care 13 1 JAMAICAVM 135 Option Xbootclasspath path The Xbootclasspath option sets bootstrap search paths for class files The argument must be a list of directories or JAR ZIP files separated by the platform dependent path separator char on Unix Systems 5 on Windows Note that the jamaicavm command has all boot and standard API classes built in The boot classpath has the built in classes as an implicit first entry in the path list so it is not possible to replace the built in boot classes by other classes which are not built in However the boot class path may still be set to add additional boot classes For commands jamaicavm slim jamaicavmp etc that do not have any built in classes setting the boot classpath will force loading of the system classes from the directories provided in this path However extreme care is required The virtual machin
169. me garbage col lection technology Realtime garbage collection obviates the need to make a strict separation of realtime and non realtime code Combined with static memory deal location that automatically replaces some dynamic memory allocations dynamic allocations in realtime code may even be eliminated completely Using RTSJ with realtime garbage collection provides necessary realtime facilities without the cumbersomeness of having to segregate a realtime application 11 3 2 Java Native Interface Both the need to use legacy code and the desire to access exotic hardware may make it advantageous to call foreign code out of a JVM The Java Native Inter face JNI provides this access JNI can be used to embed code written in other languages than Java usually C into Java programs While calling foreign code through JNI is flexible the resulting code has sev eral disadvantages It is usually harder to port to other operating systems or hard ware architectures than Java code Another drawback is that JNI is not very high performing on any Java Virtual Machine The main reason for the inefficiency is that the JNI specification is independent of the Java Virtual Machine Significant additional bookkeeping is required to insure that Java references that are handed over to the native code will remain protected from being recycled by the garbage collector while they are in use by the native code The result is that calling JNI methods is usually ex
170. me systems this thread can be used to enforce round robin scheduling of threads of equal priorities On systems with tight memory demand the thread required for time slicing can be deactivated by setting the size of the time slice to zero using the option timeSlice O0ns In an application that uses threads of equal priorities explicit calls to the method Thread yield are required to permit thread switches to an other thread of the same priority if the time slicing thread is disabled 72 CHAPTER 7 REDUCING FOOTPRINT AND MEMORY USAGE Note that the number of threads set by option numThreads does not in clude the time slicing thread Unlike when disabling the finalizer thread which is a Java thread when the time slicing thread is disabled the argu ment to numThreads should not be changed Disabling memory reservation thread The memory reservation thread is a low priority thread that continously tries to reserve memory up to a specified threshold This reserved memory is used by all other threads As long as reserved memory is available no GC work needs to be done This is especially efficient for applications that have long pause times with little or no activity that are preempted by sudden activities that require a burst of memory allocation On systems with tight memory demand the thread required for memory reservation can be deactivated by setting reservedMemory 0 Disabling signal handlers The default handler
171. mmand line are read from configuration files in the following manner e The default target is read from jamaica home et c jamaica conf This file should not contain any other information e If the builder option configuration is used the remaining options are read from the file specified with this options e Otherwise if the file user home jamaica jamaica conf exists and is non empty the remaining options are read from there e Otherwise jamaica home target platform etc jamaica conf the target specific configuration file is used The full command line syntax for the Builder tool is as follows jamaicabuilder help help h Xhelp Xhelp version verbose lt n gt showSettings saveSettings file configuration lt file gt classpath cp lt classpath gt enableassertions ea main lt class gt jar file includeClasses lt class gt lt package gt lt class gt lt package gt 14 2 BUILDER USAGE xcludeClas lt class gt lt pack excludeFrom ses age Compile includeJAR 2 fil e xcludeJAR lazyFromEnv lt fil lt var gt e gt lazy tmpdir nam setFonts setGraphics setLocales 2 resourc lt name gt lt font gt lt font gt lt system gt lt locale gt lt ocale gt setTimeZon mezon
172. module using MULTI See the MULTI and INTEGRITY documen tation on how to connect to your target and load modules B 3 2 Linker Directives File The files INTEGRITY BSP default ld and INTEGRITY INTEGRITY 1d are the default linker directives files used when building an INTEGRITY ap plication Alternate linker directives files can be specified by the user by adding the option T file to the XLDFLAGS integrity in the Jamaica configura tion file For example some INTEGRITY installations include the file flash ld an alternate to default ld that is appropriate for a flash build The default linker directives files have comments which describe the various sections in the map Custom Linker Directives File It may be necessary for the user to create a new linker directives file For example the size of the run time heap for the AddressSpace may need to be increased B 4 WINDOWS 223 or decreased Create a new linker directives file by first copying the default ld for KernelSpace or INTEGRITY ld for virtual AddressSpaces to a new file e g myapplication ld Starting with the default file as a template ensures that necessary sections will not be left out in the new file by mistake For example a heap section is needed in order for the KernelSpace to support C C dynamic memory allocation e g malloc and new If the default heap is too small it can be made larger in myapplication ld The KernelSpace
173. monitoring accuracy num This integer property specifies the resolution of the cost monitoring that is used for RTSJ s cost overrun handlers The accuracy is given in nanosec onds the default value is 5000000 i e an accuracy of 5ms The accuracy specifies the maximum value the actual cost may exceed the given cost bud get before a cost overrun handler is fired A high accuracy a lower value causes a higher runtime overhead since more frequent cost budget checking is required See also 8 10 5 Limitations of the RTSJ implementation jamaica cpu mhz num This integer option specifies the CPU speed of the system JamaicaVM ex ecutes on This number is used on systems that have a CPU cycle counter to measure execution time for the RTSJ s cost monitoring functions If the 221 228 APPENDIX C PROPERTIES THAT CONTROL THE VM CPU speed is not set and it could not be determined from the system e g on Linux via reading file proc cpuinfo the CPU speed will be mea sured on VM startup and a warning will be printed An example setting for a system running at 1 8GHz would be Djamaica cpu mhz 1800 90 jamaica err to file If a file name is given all output sent to System err will be redirected to this file jamaica err to null If set to true all output sent to System err will be ignored This is useful for graphical applications if textual output is very slow The default value for this property is false jamaica fontsprope
174. n Xcc cc The Xcc option specifies the C compiler to be used to compile intermediate C code that is generated by the Jamaica Builder Option XCFLAGS cflags The XCFLAGS option specifies the cflags for the invocation of the C compiler Note that for optimisations the compiler independent option optimise should be used 174 CHAPTER 14 THE JAMAICA BUILDER Option X1d linker The X1d option specifies the linker to be used to create a binary file from the object file generated by the C compiler Option XLDFLAGS ldflags The XLDFLAGS option specifies the Idflags for the invocation of the C linker Option dwarf2 The dwarf2 option generates a DWARF2 version of the application DWARF2 symbols are needed for tracing Java methods in compiled code Use this option with WCETA tools and binary debuggers Option XstripOptions options The XstripOptions option specifies the strip options for the invocation of the stripper See also option Xst rip Option Xlibraries library library The X1ibraries option specifies the libraries that must be linked to the desti nation binary The libraries must include the option that is passed to the linker Multiple libraries should be separated using spaces and enclosed in quotation marks E g Xlibraries m pthread causes linking against 1ibm and libpthread Option XstaticLibraries library library The XstaticLibraries option specifies the libraries that must
175. n is built smart linking is used to reduce the set of standard classes that become part of the application However due to the large set of library classes that are available this still results in a fairly large application In this example compilation is turned off gt jamaicabuilder cp classes CaffeineMarkEmbeddedApp interpret gt destination caffeine interpret Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed caffeine_interpret__ c caffeine_interpret__ h Class file compaction gain 58 882584 21665933 gt 8908472 C compiling caffeine_interpret__ c 59 60 CHAPTER 7 REDUCING FOOTPRINT AND MEMORY USAGE caffeine_interpret__nc o linking x stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB The size of the created binary may be inspected for example with a shell com mand to list directories We use 1s which is available on Unix systems On Windows use dir instead gt ls s caffeine interpret 12558788 caffeine interpret
176. n no default handler for POSIX signal SIGQUIT Ct r1 will be created The default handler that is used when this property is not set prints the current thread states via a call to com aicas jamaica lang Debug dump ThreadStates C 1 PROPERTIES SET BY THE USER 229 jamaica no sig term handler If this boolean property is set then no default handler for POSIX signal SIGTERM default signal sent by 11 will be created The default han dler that is used when this property is not set prints terminate to System err and calls System exit 130 jamaica out to file If a file name is given all output sent to System out will be redirected to this file jamaica out to null If set to true all output sent to System out will be ignored This is useful for graphical applications if textual output is very slow The default value for this property is false jamaica profile groups groups To analyze the application additional information can be written to the pro file file This can be done by specifing one or more comma separated groups with that property The follwing groups are currently supported builder default memory speed all See 8 6 for more details jamaica profile request port When using the profiling version of JamaicaVM jamaicavmp or an ap plication built with profile true then this property may be set to an integer value larger than 0 to permit an external request to dump the p
177. n of additional resources in the created application A resource is additional data such as image files sound files etc that can be accessed by the Java application Within the Java application the resource data can be accessed using the resource name specified as an argument to resource 152 CHAPTER 14 THE JAMAICA BUILDER To load the resource a call to Class getResourceAsStream name can be used If a resource is supposed to be in a certain package the resource name must include the package name Any must be replaced by E g the resource ABC from package foo bar can be added using resource foo bar ABC The Builder uses the class path provided through the option classpath to search for resources Any path containing resources that are provided using resource must therefore be added to the path provided to classpath This option expects a list of resource files that are separated using the platform dependent path separator character e g Option setFonts font font The setFonts option can be used to choose the set of TrueType fonts to be included in the target application The font families sans serif mono are supported If no fonts are required it can be set to none To use TrueType fonts a graphics system must be set Option setGraphics system The setGraphics option can be used to set the graphics system used by the target application If no graphics is required it can be set to none To g
178. n of code and hence might increase the binary size of the appli cation In systems with tight memory resources inlining may therefore not be acceptable Eleven levels of inlining are supported by the Jamaica compiler ranging from 0 no inlining to 10 aggressive inlining Option optimise optimize type The optimise option enables to specify optimisations for the compilation of intermediate C code to native code in a platform independent manner where type is one of none size speed and all The optimisation flags are only given to the C compiler if the application is compiled without the debug option Option target platform The target option specifies a target platform For a list of all available platforms of your Jamaica VM Distribution use XavailableTargets 14 2 5 Memory and threads Configuring heap memory and threads has an important impact not only on the amount of memory required by the application but on the runtime performance and the realtime characteristics of the code as well The Jamaica Builder therefore provides a number of options to configure memory and application threads 14 2 BUILDER USAGE 157 Option heapSize n The heapSize option sets the heap size to the specified size given in bytes The heap is allocated at startup of the application It is used for static global information such as the internal state of the Jamaica Virtual Machine and for the garbage collected Java heap The heap s
179. n to other debug output Printing of these calls requires a minimum debug level of 5 If the variable is not set or set to any native call will be printed JAMAICA DEBUGCALLJAVA Defines a string that gives the name of a Java class or method Any call to the specified method or to a method defined in the specified class will be printed in addition to the other debug output Printing of these calls requires a minimum debug level of 5 If the vari able is not set or set to any call is printed E g setting JAMAICA DEBUGCALLJAVA to java lang String length will print any call to the method java lang String length 239 240 APPENDIX F INTERNAL ENVIRONMENT VARIABLES Bibliography 1 Greg Bollella James Gosling Benjamin Brosgol Peter Dibble Steve Furr and Mark Turnbull The Real Time Specification for Java Addison Wesley 2000 2 Peter C Dibble Real Time Java Platform Programming Prentice Hall 2002 3 James Gosling Bill Joy Guy Steele and Gilad Bracha The Java Language Specification Addison Wesley Boston Mass third edition 2005 4 Mike Jones What really happened on Mars URL microsoft com mbj Mars Pathfinder 1997 5 Sheng Liang Java Native Interface Programmer s Guide and Specification Addison Wesley 1999 6 Tim Lindholm and Frank Yellin The Java Virtual Machine Specification Addison Wesley second edition 1999 7 C L Liu and J W Wayland Scheduling algorithms
180. name XprofileFilenameFromEnv Xss 135 XstaticLibraries 174 Xstrip XstripOptions 174 INDEX
181. nchroniza tion thread will use priority 104 There will be 40 priority levels available for RealtimeThread threads Note If no round robin scheduling is needed for threads of equal priority and the timeslice is set to zero t imeSlice 0 the synchronization thread is not required and an additional priority is available for the real time threds Option priMapFromEnv var The priMapFromEnv option creates an application that reads the priority map ping of Java threads to native threads from the environment variable var If this variable is not set the mapping specified using priMap jp sp jp sp will be used 14 2 6 GC configuration The following options provide ways to analyze the application s memory demand and to use this information to configure the garbage collector for the desired real time behavior 14 2 BUILDER USAGE 163 Option analyse analyze tolerance The analyse option enables memory analyze mode with tolerance given in per cent In memory analyze mode the memory required by the application during execution is determined The result is an upper bound for the actual memory re quired during a test run of the application This bound is at most the specified tolerance larger than the actual amount of memory used during runtime The result of a test run of an application built using analyze can then be used to estimate and configure the heap size of an application such that the garbage col lection work that
182. nfiguration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed Vfed7ce88el8ealli4 c eed JNITest__ c JNITest__ h Class file compaction gain 58 963017 21653991 gt 8886145 C compiling JNITest__ c 194 CHAPTER 16 JAMAICA AND THE JAVA NATIVE INTERFACE JNI mcpu is deprecated Use mtune or march instead JNITest nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB The created application can be executed just like any other executable gt JNITest Result 65632 Now we could write the value 65632 into memory address fc000008 16 2 The Jamaicah Command To control the jamaicah tool a variety of arguments can be provided The argu ments can be provided directly to jamaicah or using the property file jamaicah conf The syntax is as follows jamaicah help help h Xhelp jni de directory o lt file gt includeFilename lt file gt version showSettings saveSettings lt file gt configura
183. nfiguration will be displayed in a new page in the editor A configuration can be removed on the Overview page by clicking remove after the configuration s name Multiple distributions The plug in uses task definitions taskdefs in Ant s terminology to link the con figurations in a buildfile to a Jamaica distribution Each Jamaica buildfile needs at least one of these taskdefs however you can setup more to be used within the buildfile The section Configured Jamaica tasks shows the known task defini tions and lets you add new or remove existing ones 5 4 BUILDING APPLICATIONS WITH JAMAICA BUILDER 43 Task definitions can be unbound meaning that the definition references a Ja maica distribution that is currently not available or not yet known to the plug in In such a case you can create a new taskdef with the same name as the unbound one Ant properties Ant properties provide a text replacement mechanism within Ant buildfiles The editor supports Ant propertied in option values This is especially useful in con junction with multiple configurations in one buildfile when you create Ant prop erties for option values that are common to all configurations Launch built application The editor provides a simple way to launch the built application when it has been built for the host target platform If the wizard did not already generate a tar get named with a run prefix click Create new launch application target to add
184. nse keys in the folder jamaica inside the user s home directory The user s home directory is referred to as user home On Unix systems this is usually home user on Windows systems the user s home directory usually resides inside the Documents and Settings folder for example C NDocuments and Settings user 34 CHAPTER 3 GETTING STARTED Chapter 4 Tools Overview The JamaicaVM tool chain provides all the tools required to process Java source code into an executable format on the target system Fig 4 1 provides an overview over this tool chain 4 1 Jamaica Java Compiler JamaicaVM uses Java source code files see the Java Language Specification 3 as input to first create platform independent Java class files see the Java Vir tual Machine Specification 6 in the same way classical Java implementations do JamaicaVM provides its own Java bytecode compiler jamaicac to do this translation For a more detailed description of jamaicac see 8 12 We recommend using jamaicac However it is also possible to use your favorite Java source to bytecode compiler including JDK s javac command as long as you ensure that the bootclasspath is set properly to the Jamaica boot classes These are located in the following JAR file jamaica home target platform 1ib rt jar In addition please note that JamaicaVM 6 0 uses Java 6 compatible class files and requires a Java compiler capable of interpreting Java 6 compatible class file
185. nt variables are set correctly should be done during QNX installation e ONX HOST e g C Programs QNX632 host win32 x86 e ONX TARGET e g C Programs QNX632 target qnx6 For QNX 6 4 and higher the linker must be in the system path On Linux you can set this with the PATH environment variable export PATH SPATH opt QNX640 host linux x86 usr bin B 8 RedHawk Linux B 8 Running an application To use the realtime capabilities of Jamaica under RedHawk Linux the CPU and the thread scheduling must be configured before running an application built with Jamaica Example configuration system with 4 CPUs shield p 2 i 2 1 2 d 3 Enable FIFO scheduling in Jamaica export JAMAICA SCHEDULING FIFO The application is then started with run b 2 Application 226 APPENDIX B INFORMATION FOR SPECIFIC TARGETS Appendix C Properties that Control the VM This appendix lists the predefined properties in Jamaica These properties con trol the Jamaica VM commands as well as applications created with the Jamaica Builder C 1 Properties Set by the User The standard libraries that are delivered with JamaicaVM can be configured by setting specific Java properties A property is a string value that has an assigned value The property is passed to the Java code via the JamaicaVM option Dname value or when using the Builder via option XdefinePropert y name value jamaica cost
186. nterface calls are performed in constant time They are almost as efficient as C function calls so do not avoid them except in places where one would avoid a C function call as well When accessing final local variables or private fields from within inner classes in a loop one should generally cache the result in a local variable for performance reasons The access is in constant time but slower than normal local variables Using the String operator causes memory allocation with an execution time that is linear with regard to the size of the resulting String Using array initializa tion causes dynamic allocations as well For realtime critical applications avoid static initializers or explicitly call the static initializer at startup When using a java compiler earlier than version 1 5 the use of classname class causes dynamic class loading In realtime applications this should be avoided or called only during application startup Subsequent usage of the same class will then be cached by the JVM 11 7 2 Memory Allocation The RTSJ introduces new memory areas such as ImmortalMemoryArea and ScopedMemory which are inconvenient for the programmer and at the same time make it possible to write realtime applications that can be executed even on virtual machines without realtime garbage collection In JamaicaVM it is safe reliable and convenient to just ignore those restric tions and rely on the realtime garbage collection instead Be
187. nv lt var gt constGCwor analyseFrom Env lt var gt Env k lt n gt stopTheWorldGC reservedMemory lt percentage gt strictRTSJ oryFromEnv var StrictRTSJEF immortalMem immortalMem scopedMemor scopedMemor physicalMem profile percentageC useProfile m m rom orySize lt n gt Env lt var gt K M orySizeFrom ySize lt n gt ySizeFromE oryRanges XprofileF ompiled lt n gt lt file gt lt lenameFrom Env lt var gt M file lt range gt lt range gt Env lt var gt 146 CHAPTER 14 THE JAMAICA BUILDER object lt file gt lt file gt classi classn The following special syntax is accepted e To add values to an existing option in the configuration e g include use the following syntax include myIncludePath The value from the configuration is prepended with the value provided on the com mand line e To read values for an option that accepts a list of values e g include from a file instead from the command line or configuration file use this syn tax include file or include file This reads the values from file line by line Empty lines and lines starting with the character comment are ignored Options that permit lists of arguments can be set by either providing a single list or by providing an instance of the option
188. o be de bugged on an embedded device localhost must be replaced by the network address of the device 89 90 CHAPTER 9 DEBUGGING SUPPORT 9 2 Configuring the IDE to Connect to Jamaica Before being able to debug a project the code needs to compile and basically run Before starting a debugging session the debugger must be configured to connect to the VM by specifying the VM s host address and port Normally this is done by setting up a debug configuration In Eclipse 3 5 for example select the menu item Run gt Debug Configurations In the list of available items presented on the left side of the dialog window see Fig 9 1 choose a new configuration for a remote Java application then e configure the debugger to connect to the VM by choosing connection type socket attach and e enter the VM s network address and port as the connection properties host and port Clicking on Debug attaches the debugger to the VM and starts the debugging ses sion If the VM s communication agent is set to suspending the VM before loading the main class the application will only run after instructed to do so through the debugger via commands from the Run menu In Eclipse breakpoints may be set conveniently by double clicking in the left margin of the source code For instructions on debugging the documentation of the used debugger should be consulted in Eclipse for example though the Help menu The Jamaica Eclipse
189. o deny access to type X 129 130 CHAPTER 12 THE JAMAICA JAVA COMPILER Option bootclasspath path This option is similar to the option classpath but specifies locations for sys tem classes Option sourcepath path The sourcepath option specifies locations for application sources The path is a list of directories For further details see option classpath above Option extdirs dirs The ext dirs option specifies location for extension zip jar files where path is a list of directories Option d directory The d option sets the destination directory to write the generated class files to If omitted no directory is created 12 1 2 Compliance options Option source version Provide source compatibility for specified version e g 1 6 or 6 or 6 0 Option target version Generated class files for a specific VM version e g 1 6 or 6 or 6 0 12 1 3 Warning options Option deprecation The deprecation option checks for deprecation outside deprecated code Option nowarn The nowarn option disables all warnings 12 2 ENVIRONMENT VARIABLES 131 12 1 4 Debug options Option g The g option without parameter activates all debug info Option g none The g option with none disables debug info Option g lines vars source The g option is used to customize debug info 12 1 5 Other options Option encoding encoding The encoding option specifies custom encoding for all sources May be overrid d
190. o obtain this monitor Standard Data Structures The strict separation of an application into a realtime and non realtime part that is required when the Real Time Specification for Java is used in conjunction with a non realtime garbage collector makes it very difficult to have global data struc tures that are shared between several tasks The Real Time Specification for Java even provides special data structures such as WaitFreeWriteQueue that en able communication between tasks These queues do not need to synchronize and hence avoid running the risk of introducing priority inversion In a system that uses realtime garbage collection such specific structures are not required High priority tasks can share standard data structures such as java util Vector with low priority threads 11 4 5 Memory Management Guidelines The JamaicaVM provides four options for memory management Immortal Memory ScopedMemory static memory deallocation and realtime dynamic garbage collection on the normal heap They may all be used freely The choice of which to use is determined by what the best trade off between external require ments compatibility and efficiency for a given application ImmortalMemory is in fact quite dangerous Memory leaks can result from improper use Its use should be avoided unless compatibility with other RTSJ JVMs is paramount or heap memory is not allowed by the certification regime required for the project ScopedMemory is
191. oaderS 1 run PROFILE CYCLES 255459907 com aicas jamaica lang SigIntH PROFILE CYCLES 235701127 sun net www ParseUtil fileToEn PROFILE CYCLES 233656888 java lang Class getDeclaredFie The cumulative cycle count shows more clearly that the main method is running most of the time during the profiling run the next dominating methods are print and println of class java io PrintStreamP The cumulative cycle counts can now be used as a basis for a top down opti mization of the application execution time Since main calls only println one would expect the cumulative time spent in print 1n to exceed the time spent in print While this is actually the case for the calls from main there are however calls to print performed during startup of the virtual machine while executing the static initializer of class java lang System so that the total cumulative time in print is higher than the time spent in printin 58 CHAPTER 6 PERFORMANCE OPTIMIZATION Chapter 7 Reducing Footprint and Memory Usage In this section we give an example of how to achieve optimal runtime perfor mance for your Java application while reducing the code size and RAM memory demand to a minimum As example application we use Pendragon Software s em bedded CaffeineMark tm 3 0 The class files for this benchmark are part of the JamaicaVM Tools installation See 3 4 7 1 Code Size vs Runtime Performance 7 1 4 Using Smart Linking When an applicatio
192. od calls easy to implement effi ciently calling methods via an interface is more challenging The multiple inher itance implicit in Java interfaces means that a simple dispatch table as used by normal methods can not be used In the JamaicaVM the time needed to find the called method is linear with the number of interfaces implemented by the class Type Casts and Checks The use of type casts and type checks is very frequent in Java One example is the following code sequence that uses an instanceof check and a type cast Object o vector elementAt index if o instanceof Integer sum sum Integer o intValue These type checks also occur implicitly whenever a reference is stored in an array of references to make sure that the stored reference is compatible with the actual type of the array Type casts and type checks within the JamaicaVM are per formed in constant time with a small and constant number of memory accesses In particular instanceof is more efficient than method invocation Generics JDK 1 5 The generic types generics introduced in JDK 1 5 avoid explicit type cases that are required using abstract data types with older versions of Java Using generics the type cast in this code sequence ArrayList list new ArrayList list add 0 some string String str String list get 0 is no longer needed The code can be written using a generic instance of Array List that can only hold strings as fol
193. onal target specific installation hints please check B 3 1 Linux Unpack and Install Files The default is a system wide installation of Jamaica Super user privileges are re quired If the rpm package manager is available this is the recommended method gt rpm i Jamaica release identification string rpm Otherwise unpack the compressed tape archive file and run the installation script as follows gt tar xfz Jamaica release identification string tar gz gt Jamaica install This will install the Jamaica tools in the following directory which is referred to as jamaica home usr local jamaica version build In addition the symbolic link usr 10cal jamaica is created which points to jamaica home and symbolic links to the Jamaica executables are created in usr bin so it is not necessary to extend the PATH environment variable In order to deinstall the Jamaica tools depending on the used installation method either use the erase option of rpm or the provided deinstallation script Jamaica remove If super user privileges are not available the tools may alternatively be in stalled locally in a user s home directory gt tar xfz Jamaica release identification string tar gz tar xf Jamaica ss This will install the Jamaica tools in usr 10cal Jamaica version build rel ative to the current working directory Symbolic links to the executables are cre ated in usr bin so they will not be on the default
194. ons also cover other areas of great importance to many embedded realtime applications such as direct access to physical memory e g memory mapped I O or asynchronous mechanisms Currently RTSJ is available for the Jamaica VM and for TimeSys JTime JVMs from other vendors are likely to follow in the future Thread Scheduling in the RTSJ Ensuring that Java programs can execute in a timely fashion was a main goal of the RTSJ To enable the development of realtime software in an environment with a garbage collector that stops the execution of application threads in an un predictable way see Fig L 1 1 the new thread classes RealtimeThread and 110 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES Thread time GC User 1 User 2 EH m Figure 11 1 Java Threads in a classic JVM are interrupted by the garbage collec tor thread Thread time rtl rt2 GC User 1 User 2 Figure 11 2 RealtimeThreads can interrupt garbage collector activity NoHeapRealtimeThread were defined These thread types are unaffected or at least less severely affected by garbage collection activity Also at least 28 new priority levels logically higher than the priority of the garbage collector are available for these threads as illustrated in Fig Memory Management For realtime threads not to be affected by garbage collector activity these threads need to use memory areas that are not under the control of the garbage collector New
195. or the Real Time Specification for Java Version 1 0 2 e Minimal footprint e ROMable code e Native code support e Dynamic linking e Supported platforms e Fast execution e Powerful tools for timing and performance analysis 2 4 Hard Realtime Execution Guarantees JamaicaVM is the only implementation that provides hard realtime guarantees for all features of the languages together with high performance runtime effi ciency This includes dynamic memory management which is performed by the JamaicaVM garbage collector 17 18 CHAPTER 2 KEY FEATURES OF JAMAICAVM All threads executed by the JamaicaVM are realtime threads so there is no need to distinguish realtime from non realtime threads Any higher priority thread is guaranteed to be able to preempt lower priority threads within a fixed worst case delay There are no restrictions on the use of the Java language to program real time code Since the JamaicaVM executes all Java code with hard realtime guar antees even realtime tasks can use the full Java language 1 e allocate objects call library functions etc No special care is needed Short worst case execution delays can be given for any code 2 2 Real Time Specification for Java support JamaicaVM provides an industrial strength implementation of the Real Time Spec ification for Java Specification RTSJ V1 0 2 see 1 for a wide range of real time operating systems available on the market It combines the additional AP
196. path for executables Configure Platform Specific Tools In order for the Jamaica Builder to work platform specific tools such as the C compiler and linker and the locations of the libraries SDK need to be speci fied This is done by editing the appropriate configuration file named jamaica conf for the target and possibly also the host The precise location of the configuration file depends on the platform 3 1 INSTALLATION OF JAMAICAVM 25 jamaica home target platform etc jamaica conf For the full Jamaica directory structure please refer to 85 3 Note that the config uration for the host platform is also located in a target directory The following properties need to be set appropriately in the configuration files Property Value Xcc platform C compiler executable Xld platform Linker executable Xstrip platform Strip utility executable Xinclude platform Include path XlibraryPaths platform Library path Environment variables may be accessed in the configuration files through the no tation VARIABLE For executables that are on the standard search path envi ronment variable PATH it is sufficient to give the name of the executable Set Environment Variables The environment variable JAMATCA must be set to jamaica home On bash gt export JAMAICA jamaica home On csh gt setenv JAMAICA jamaica home 3 1 2 Sun Solaris The release for Solaris is provided as compressed tape
197. pensive An additional disadvantage of the use of native code is that the application of any sort of formal program verification of this code becomes virtually intractable Nevertheless because of its availability for many JVMs JNI is the most popu lar Java interface for accessing hardware It can be used whenever Java programs 112 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES need to embed C routines that are not called too often or are not overly time critical If portability to other JVMs is a major issue there is no current alternative to JNI When portability to other operating systems or hardware architectures is more important RTDA or RTSJ is a better choice for device access 11 3 3 Java 2 Micro Edition Usually when one refers to Java one thinks of the Java 2 Standard Edition J2SE but this is not the only Java configuration available For enterprise applications Sun Microsystems has defined a more powerful version of Java Java 2 Enterprise Edition J2EE which supports Web servers and large applications There is also a stripped down version of Java for embedded applications Java 2 Micro Edition J2ME This is interesting for timely Java development on systems with limited resources J2ME is in fact not a single Java implementation but a family of implementa tions At its base JAME has two configurations Connected Device Configuration CDC and Connected Limited Device Configuration CLDC Profiles for partic ular app
198. plications with Jamaica Builder 5 5 4 1 5 4 2 Getting started Jamaica Buildfiles II Tools Usage and Guidelines 6 Performance Optimization 6 1 Creating aprofile 7 S LI Creating a profiling application 6 1 2 Using the profiling VM 6 4 3 Dumping a profile via network 6 1 4 Creating a micro profile 6 2 Using a profile with the Builder 6 2 1 Building with a profile 6 2 2 Building with multiple profiles 6 3 Interpreting the profiling output 6 3 1 Format of the profile file 63 2 Example Reducing Footprint and Memory Usage 7 1 Code Size vs Runtime Performance 7 1 1 Using Smart Linking 7 1 2 Using Compilation 7 2 Optimizing RAM Memory Demand 1 2 1 Measuring RAM requirements CONTENTS 35 35 35 36 37 39 39 39 40 40 40 41 45 47 47 47 48 49 49 50 50 51 51 52 56 CONTENTS 5 7 2 Memory for an Application s Data Structures 69 Herc ir HD re ee 69 7 2 4 Memory Required for 70 7 2 5 Memory Required for Line Numbers 73 75 IT 75 8 1 1 Initial heap size cs ce cee Re wo Rn Rn 75 bee he Si ame oo te A ite acts A hte ge 76 8 1 3 Finalizer thread priority 76 8 1 4 Reserved memory 77 8 1 5 UsimgaGCthread 78 n 78 8 1 7 Recommendations
199. plus the left mouse button can also be used Zoom factor The size of the display can be changed via the buttons zoom in and zoom out or via holding down shift in conjunction with the left mouse button for enlarge ment or in conjunction with the right mouse button for shrinking Instead of shift and the middle mouse button the shift and the control key plus the left mouse button can also be used 15 3 2 Data Window Menu The data window s menu offers the following actions File Open This menu item will open a file requester to load previously recorded sched uler data that was saved through the data window s File Save as menu item see 15 3 2 15 3 DATA WINDOW 187 File Save as This menu item permits saving the displayed scheduler data such that it can later be loaded through the control window s File Open menu item see 15 2 1 File Close Select this menu item will close the data window but it will leave all other win dows open File Quit Select this menu item will close all windows of the ThreadMonitor tool and quit the application Options Grid Selecting this option will display light grey vertical grid lines that facilitate relat ing a displayed event to the point on the time scale Options Thread Headers If this option is selected the left part of the window will be used for a fixed list of thread names that does not participate in horizontal scrolling Options Thre
200. port for the Jamaica Builder tool In the context of this tool the term build is used to describe the process of translating compiled Java class files into an executable file Please note that in Eclipse s terminology build means compiling Java source files into class files 5 4 1 Getting started In order to build your application with Jamaica Builder you must create a Jamaica Buildfile A wizard is available and can be found in Eclipse s New dialog File New Other Select a Jamaica distribution and target platform and specify your application s main class name After finishing the wizard the newly created buildfile is opened in a graphical editor containing an overview page a configuration page and a source page You can review and modify the Jamaica Builder configuration on the second page or 5 4 BUILDING APPLICATIONS WITH JAMAICA BUILDER 41 in order to start the build process click Invoke Ant on this target on the Overview page 5 4 2 Jamaica Buildfiles This section gives a more detailed introduction to Jamaica Buildfiles and the graphical editor to edit them easily Concepts Jamaica Buildfiles are build files understood by Apache Ant See ant apache org These build files mainly consist of targets containing a sequence of tasks which accomplish a functionality like compiling a set of Java classes Many tasks come included with Ant but tasks may also be provided by a third party Third party task
201. presents data sent by the scheduler in the Jamaica run time system and is invoked with the jamaica_threadmonitor command When ThreadMonitor is started it presents the user a control window see Fig 15 1 15 1 Run time system configuration The event collection for ThreadMonitor in the Jamaica run time system is con trolled by two system properties e jamaica scheduler events port e jamaica scheduler events port blocking To enable the event collection in the JamaicaV M a user sets the value of one of these properties to the port number to which the ThreadMonitor GUI will connect later If the user chooses the blocking property the VM will stop after the bootstrapping and before the main method is invoked This enables a developer to investigate the startup behavior of an application gt jamaicavm cp classes Djamaica scheduler events port 2712 HelloWorld accepting Scheduler Events Recording requests on port 2712 Hello World Hello World Hello World 181 182 CHAPTER 15 THE JAMAICA THREADMONITOR Hello World Hello World Hello World s When event collection is enabled the requested events are written into a buffer and sent to the ThreadMonitor tool by a high priority periodic thread The amount of buffering and the time periods can be controlled from the GUI 15 2 Control Window The ThreadMonitor control window is the main interface to control recording scheduler data from applications running
202. ptimisations for both speed and application size are pro vided with the HelloWorld example These are provided in an ant buildfile In order to use the buildfile type ant build target where build target is one of the build targets of the example For example gt ant HelloWorld will build the unoptimised HelloWorld example In order to optimise for speed use the build target He 1 LoWorld_profiled in order to optimise for applica tion size use He11oWorld micro The following is the list of all build targets available for the HelloWorld example HelloWorld Build an application in interpreted mode The generated binary is HelloWorld HelloWorld profiled Build a statically compiled application based on a profile run The generated binary is He11oWorld profiled HelloWorld micro Build an application with optimized memory demand The generated binary is He11oWorld micro 3 5 NOTATIONS AND CONVENTIONS 31 Example Demonstrates Platforms HelloWorld Basic Java all RTHelloWorld Real time threads RTSJ all SwingHelloWorld Swing graphics with graphics caffeine CaffeineMark tm benchmark all test_JNI Java Native Interface all net Network and internet with network rmi Remote method invocation with network Table 3 2 Example applications provided in the target directories classes Convert Java source code to byte code all Build all three applications run Run all three applications only
203. r when using the builder via the builder option maxHeapSize Q When the built application terminates I see some output like WARNING termination of thread 7 failed Whatis wrong A Attermination of the application the JamaicaVM tries to shutdown all running threads by sending some signal If a thread is stuck in a native function e g waiting in some OS kernel call the signal is not received by the thread and there is no response In that case the Jamaica VM does a hard kill of the thread and outputs the warning Generally the warning can simply be ignored but be aware that a hard kill may leave the OS in an unstable state or that some resources e g memory allocated in a native function can be lost Such hard kills can be avoided by making sure no thread gets stuck in a native function call for a long time e g more than 100ms Q Does JamaicaVM include tools like rmic and rmiregistry to develop RMI applications A The rmiregistry tool is included in Jamaica VM and can be executed like this jamaicavm sun rmi registry RegistryImpl JamaicaVM 3 0 added support for the dynamic generation of stub classes at runtime obviating the need to use the Java Remote Method Invocation Java RMD stub compiler rmic to pregenerate stub classes for remote objects Remote Method Invocation RMI Q How can I use RMI A 3 REMOTE METHOD INVOCATION RMI 207 A RMI applications often comprise two separate programs a serv
204. r security reasons system properties used by the VM cannot be changed 14 3 2 Classes files and paths These options allow to specify classes and paths to be used by the builder Option XjamaicaHome path The XjamaicaHome option specifies the path to the Jamaica directory The Jamaica home path can also be set with the environment variable JAMATCA_ HOME Option XjavaHome path The XjamaicaHome option specifies the path to the Jamaica directory The Jamaica home path can also be set with the environment variable JAMAICA HOME Option Xbootclasspath classpath The Xbootclasspath specifies path used for loading system classes Option XextendedGlobalCPool Jamaica VM If set to true the global constant pool can take up to Ox7FFFFFF 31bit UTF8 strings The default is false OXFFFF 16bit Please note that this extension breaks runtime annotation and jvmti debugging 172 CHAPTER 14 THE JAMAICA BUILDER Option XlazyConstantStrings Jamaica VM by default allocates all String constants at class loading time such that later accesses to these strings is very fast and efficient However this approach requires code to be executed for this initialization at system startup and it requires Java heap memory to store all constant Java strings even those that are never touched by the application at run time Setting option XIazyConstantStrings causes the VM to allocate strings constants lazily i e not at class loading tim
205. rcentage of methods that are to be compiled is given as an argument to the op tion percentageCompiled It must be between 0 and 100 Selecting 100 causes compilation of all methods executed during the profiling run i e methods that were not called during profiling will not be compiled Option useProfile file file The useProfile option instructs the builder to use profiling information col lected using profile to restrict compilation to those methods that were most frequently executed during the profiling run The percentage of methods to be compiled is 10 by default unless percent ageCompiled is set to a different value It is possible to use this option in combination with the option profile This may be useful when the fully interpreted application is too slow to obtain a meaningful profile In such a case one may achieve sufficient speed up through an initial profile and use the profiled application to obtain a more precise profile for the final build Multiple profiles should be separated by the system specific path separator 0 99 oe 0 99 colon on Unix systems and semicolon on Windows 14 2 9 Native code Native code is code written in a different programming language than Java typ ically C or C This code can be called from within Java code using the Java Native Interface JNI Jamaica internally uses a more efficient interface the Ja maica Binary Interface JBI for native calls into the V
206. re registered trademarks of Oracle America Inc All other brands or product names are trademarks or registered trademarks of their respective holders ALL IMPLIED WARRANTIES ON THIS PUBLICATION INCLUDING IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE LIMITED IN DURATION TO NINETY 90 DAYS FROM THE DATE OF THE ORIGINAL RETAIL PURCHASE OF THIS PRODUCT Although aicas GmbH has reviewed this publication aicas GmbH MAKES NO WARRANTY OR REPRESENTATION EITHER EXPRESSED OR IMPLIED WITH RESPECT TO THIS PUBLICATION ITS QUALITY ACCURACY MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE AS A RESULT THIS PUBLICATION IS PROVIDED AS IS AND YOU THE PURCHASER ARE ASSUMING THE ENTIRE RISK AS TO ITS QUALITY AND ACCURACY IN NO EVENT WILL aicas GmbH BE LIABLE FOR DIRECT INDIRECT SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES RESULTING FROM ANY DEFECT OR INACCURACY IN THIS PUBLICATION even if advised of the possibility of such damages THE WARRANTIES SET FORTH ABOVE ARE EXCLUSIVE AND IN LIEU OF ALL OTHERS ORAL OR WRITTEN EXPRESSED OR IMPLIED Contents I Introduction 1 Preface 1 1 Intended Audience of This Book 002 L2 Contacting aas ix o x RUE R3 SLE GED 13 What is New in JamaicaVM 6 01 2 Key Features of JamaicaVM 3 2 Hard Realtime Execution Guarantees TM T 2 3 Minimal footprint ue x on ow Romx EROR OSS XOU ROS 25 ROM
207. readsFromEnv If the maximum number of threads may be set via an environment variable this is set to the name of this environment variable jamaica numThreadsFromEnv If the initial number of threads may be set via an environment variable this is set to the name of this environment variable jamaica release The release number of the JamaicaVM jamaica scopedMemorySize The size of the memory available for scoped memory jamaica strictRTSJ Boolean property Value depends on the setting of the st rict RTSJ op tion that was used when building the application See for more de tails jamaica version The version number of the Jamaica VM 232 APPENDIX C PROPERTIES THAT CONTROL THE VM Appendix D Heap Usage for Java Datatypes This chapter contains a list of in memory sizes of datatypes used by JamaicaVM For datatypes that are smaller than one machine word only the smallest mul tiple of eight Bits that fits the dataype will be occupied for the value I e several values of types boolean byte short and char may be packed into a single machine word when stored in an instance field or an array Tab D 1 shows the usage of heap memory for primitive types Tab D 2 shows the usage of heap memory for objects arrays and frames 233 234 APPENDIX D HEAP USAGE FOR JAVA DATATYPES Datatype Memory Demand Min Value Max Value Bits Bytes boolean 8 1 byte 8 1 2 short 16 2 21
208. red the maximum execution time started A mouse click on this cell will cause this position to be displayed in the center of the data window the worst case execution time window was created from This column will display N A in case no Worst case execution time was displayed for this thread Releases is the number of releases that of the given thread that where found during the recording See below for a definition of a release Average time is the average execution time for one release of this thread See below for a definition of execution time Comment will display important additional information that was found during the analysis E g in case the data the analysis is based on contains over flows i e periods without recorded information these times cannot be cov ered by this analysis and this will be displayed here Definitions Release of a thread T is a point in time at which a waiting thread T becomes ready to run that is followed by a point in time at which it will block again waiting for the next release Le a release contains the time a thread remains ready until it becomes running to execute its job and it includes all the time the thread is preempted by other threads or by activities outside of the VM Execution Time of a release is the time that has passed between a release and the point at which the thread blocked again to wait for the next release Limitations The worst case execution times displayed in the
209. rformance depends strongly on the C compiler that is employed and may even show anomalies such as better runtime performance for the version optimized for smaller code size gt caffeine_useProfilel0 Sieve score 10583 98 Loop score 33002 2017 Logic score 50558 0 String score 10105 708 Float score 12747 185 Method score 7357 166650 Overall score 15993 gt caffeine_useProfilel0_size Sieve score 10138 98 Loop score 33136 2017 Logic score 58124 0 String score 10140 708 Float score 13134 185 Method score 6984 166650 Overall score 16212 Using Full Compilation Full compilation can be used when no profiling information is available and code size or built time is not an important issue 1 Fully compiling an application leads to very poor turn around times and may require significant amounts of memory during the C compilation phase We recommend compilation be used only through profiling as described above To compile the complete application the option compile must be set gt jamaicabuilder cp classes compile CaffeineMarkEmbeddedApp gt destination caffeine compiled 66 CHAPTER 7 REDUCING FOOTPRINT AND MEMORY USAGE Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Genera
210. ribed in gt caffeine Sieve score 10576 98 Loop score 41677 2017 Logic score 50617 0 String score 9861 708 Float score 12807 185 Method score 7357 166650 Overall score 16574 Compilation via Profiling Generation of a profile for compilation is a powerful tool for creating small ap plications with fast turn around times The profile collects information on the runtime behavior of an application guiding the compiler in its optimization pro cess and in the selection of which methods to compile and which methods to leave in compact bytecode format To generate the profile we first have to create a profiling version of the ap plications using the builder option profile see 8 l6 or using the command jamaicavmp jamaicavmp CaffeineMarkEmbeddedApp Sieve score 250 98 Loop score 214 2017 Logic score 241 0 String score 1367 708 Float score 217 185 Method score 181 166650 Overall score 297 Start writing profile data into file CaffeineMarkEmbeddedApp prof Write threads data Write invocation data Done writing profile data This profiling run also illustrates the runtime overhead of the profiling data col lection the profiling run is significantly slower than the interpreted version Now an application can be compiled using the profiling data that was stored in file Ca feineMarkEmbeddedApp prof gt jamaicabuilder cp classes gt useProfile Caff
211. riorities for normal Java threads must be in a range specified in pack age java lang class Thread The minimal priority is MIN PRIORITY maximal priority MAX PRIORITY RealtimeThreads and NoHeapRealtimeThreads share the priority range defined in javax realtime class PriorityScheduler and which 10 5 LIMITATIONS OF RTSJ IMPLEMENTATION 99 may be obtained by querying method instance getMinPriority and instance getMaxPriority 10 4 3 Runtime checks for NoHeapRealtimeThread If st rictRTSd is set runtime checks on all memory read operations 1 ac cesses to static and instance fields and accesses to reference array elements are checked to ensure that no object on the garbage collected heap is touched by a NoHeapRealtimeThread These runtime checks are required by classical Java implementations with a non realtime garbage collector They may impose an important runtime overhead on the application 10 4 4 Static Initializers When st rictRTS J is set static initializers are executed within immortal mem ory This means that all objects allocated by static initializers are accessible by all threads Care is required since any allocations performed within static initial izers of classes that are loaded dynamically into a system will never be recycled Dynamic class loading consequently poses a severe risk of introducing a memory leak into the system 10 4 5 Class PhysicalMemoryManager When str
212. rm memory allocation may however continue execution even while the stop the world garbage collector is running The builder option st op TheWor1dGC enables the stop the world garbage collector Alternatively the builder option constGCwork 1 may be used or constGCworkFromEnv var with the environment variable var set to 1 JamaicaVM additionally provides an atomic garbage collector that requires stopping of all threads of the Java application during a stop the world garbage collection cycle This has the disadvantage that even threads that do not allocate heap memory will have to be stopped during the GC cycle However it avoids the need to track heap modifications performed by threads running parallel to the garbage collector so called write barrier code The result is a slightly increased performance of compiled code Specifying the builder option atomicGC enables the atomic garbage col lector Alternatively the builder option constGCwork 2 may be used or specify constGCworkFromEnv var with the environment variable var set to 24 Please note the use of the memory reservation thread or the GC thread should be disabled when stop the world or atomic GC is used 8 1 7 Recommendations In summary to obtain the best performance in your soft realtime application fol low the following recommendations e Set initial heap size as large as possible e Set initial heap size and maximum heap size to the same value if possible e Set t
213. rm standard library code more slowly The options arguments and environment variables accepted by jamaicavm_ slim the same as the options of the jamaicavm command See 13 1 for the detailed list 13 3 JAMAICAVMP 137 13 3 jamaicavmp jamaicavmp is a variant of jamaicavm slim that collects profiling informa tion This profiling information can be used when creating an optimized version of the application using option useProfile file of the Jamaica builder com mand see 14 The profiling information is written to a file whose name is the name of the main class of the executed Java application with the suffix prof The following run of the HelloWorld application available in the examples see 8B 4 shows how the profiling information is written after the execution of the application gt jamaicavmp cp classes HelloWorld Hello World Hello World Hello World Hello World Hello World Hello World leas Start writing profile data into file HelloWorld prof Write threads data Write invocation data Done writing profile data Profiling information is written after the termination of the application This re quires an additional mechanism for applications which are not self terminating There are two possible approaches adding an explicit termination mechanism to the application or requesting a profile dump remotely For an explicit termination the application needs to be rewritten to terminate at a certa
214. rofile information at any point in time See 8 6 for more details jamaica reservation thread priority n If set to an integer value larger than or equal to 0 this property instructs the virtual machine to run the memory reservation thread at the given Java priority A value of 0 will result at a Java priority 1 with micro adjustment 1 i e the scheduler will give preference to other threads running at prior ity 1 By default the priority of the reservation thread is set to 0 1 Java priority 1 with micro adjustment 1 The priority may be followed by a or character to select priority micro adjustment 1 or 1 respectively Setting this property e g to 10 will run the memory reservation thread at a priority higher than all normal Java threads but lower than all RTSJ threads See 8 8 1 4 for more details jamaica scheduler events port This property defines the port where the ThreadMonitor can connect to re ceive scheduler event notifications 230 APPENDIX C PROPERTIES THAT CONTROL THE VM jamaica scheduler events port blocking This property defines the port where the ThreadMonitor can connect to re ceive scheduler event notifications The Jamaica runtime system stops be fore entering the main method and waits for the ThreadMonitor to connect jamaica softref minfree Minimum percentage of free memory for soft references to survive a GC cycle If the amount of free memory drops below this threshold soft refer ences m
215. rties resource This property specifies the name of a resource that instructs Jamaica VM which fonts to load The default value is the resource com aicas jamaica awt fonts properties The property may be set to a user defined re source file to change the set of supported fonts The specified file itself is a property file that maps font names to resource file names jamaica gcthread pri mn If set to an integer value larger than or equal to 0 this property instructs the virtual machine to launch a garbage collection thread at the given Java pri ority A value of 0 will result in a Java priority 1 with micro adjustment 1 i e the scheduler will give preference to other threads running at priority 1 By default a GC thread is not used See 8 8 1 5 for more details jamaica loadLibrary ignore error This property specifies whether every unsuccessful attempt to load a native library dynamically via System loadLibrary should be ignored by the VM at runtime If set to true and System loadLibrary fails no UnsatifiedLink Error will be thrown at runtime The default value for this property is false jamaica no sig int handler If this boolean property is set then no default handler for POSIX signal SIGINT Ctr1 C will be created The default handler that is used when this property is not set prints break to System err and calls System exit 130 jamaica no sig quit handler If this Boolean property is set the
216. run other Java threads at priority 1 the property may be set to 0 which results in a GC thread Java priority 1 and the scheduler set to give preference to other Java threads running at priority 1 The GC thread uses this idle time to perform garbage collection work so that the amount of free memory is larger and the application threads can on average perform allocations faster However additional CPU time is taken from any other applications on the system that may run at lower priorities Even when a GC thread is used not all of the available CPU time is necessarily used by the Java application The GC thread will periodically stop its activity when only a little memory was reclaimed during a GC cycle Lower priority threads may therefore still obtain some CPU time even if a GC thread is used 8 1 6 Stop the world Garbage Collection For applications that do not have any realtime constraints but that require the best average time performance Jamaica VM s builder provides options to disable realtime garbage collection and to use a stop the world garbage collector instead 8 1 CONFIGURATION FOR SOFT REALTIME APPLICATIONS 79 In stop the world mode no garbage collection work will be performed un til the system runs out of free memory Then all threads that perform memory allocation will be stopped to perform garbage collection work until a complete garbage collection cycle is finished and memory was reclaimed Any thread that does not perfo
217. runs the garbage collector in static mode In static mode for every unit of allocation a constant number of units of garbage collection work is performed This results in a lower worst case execution time for the garbage collection work and allocation and more predictable behavior compared with dynamic mode because the amount of garbage collection work is the same for any allocation However static mode causes higher average garbage collection overhead compared to dynamic mode The value specified is the number for units of garbage collection work to be 164 CHAPTER 14 THE JAMAICA BUILDER performed for a unit of memory that is allocated This value can be determined using a test run built with analyze set A value of 0 for this option chooses the dynamic GC work determination that is the default for Jamaica VM A value of 1 enables stop the world GC see option stopTheWorldGC for more information A value of 2 enables a atomic GC see option at omicGC for more infor mation The default setting chooses dynamic GC the amount of garbage collection work on an allocation is then determined dynamically depending on the amount of free memory Option constGCworkFromEnv var The constGCworkFromEnv option enables the application to read the amount of static garbage collection work on an allocation from the environment variable specified within If this variable is not set the value specified with the option constGCwork will
218. s class args jamaicavm jar options jarfile args The jamaicavm permits a number of options followed by a class name or a Java archive file if option jar is present The class uses dots 7 as package separators and does not include the class extension i e to execute the Java application whose main class in in file com mycompany MyClass class or com mycompany MyClass class on Windows systems the class ar gument must be com mycompany MyClass An optional can be used to explicitly separate the options from the class or jar file argument 133 134 CHAPTER 13 THE JAMAICA VIRTUAL MACHINE COMMANDS 13 1 4 JamaicaVM Options Option classpath cp path The classpath option sets search paths for class files The argument must be a list of directories or JAR ZIP files separated by the platform dependent path separator char on Unix Systems on Windows Option Dname value The D option sets a system property with a given name to a given value The value of this property will be available to the Java application via functions such as System getProperty Option version The version option prints version of JamaicaVM Option help The help option prints a short help summary on the usage of JamaicaVM and lists the default values is uses These default values are target specific The default values may be overridden by command line options or environment variable set tings Where com
219. s 4 0 Jamaica Virtual Machine The command jamaicavm provides a version of the Jamaica virtual machine It can be used directly to quickly execute a Java application It is the equivalent to the java command that is used to run Java applications with SUN s JDK A more detailed description of the jamaicavm and similar commands that are part of Jamaica will be given in 8 13 35 36 CHAPTER 4 TOOLS OVERVIEW java jamaicac gt class jamaicavm jamaicabuilder gt executable Figure 4 1 The Jamaica Toolchain The jamaicavm first loads all class files that are required to start the ap plication It contains the Jamaica Java interpreter which then executes the byte code commands found in these class files Any new class that is referenced by a byte code instruction that is executed will be loaded on demand to execute the full application Applications running using the jamaicavm command are not very well op timized There is no compiler that speeds up execution and no specific measures to reduce footprint are taken We therefore recommend using the Jamaica builder presented in the next section and discussed in detail in 14 to run Java applications with Jamaica VM on an embedded system 4 3 Jamaica Builder Creating Target Executables In contrast to jamaicavm command jamaicabuilder does not execute the Java application directly Instead the builder loads all the classes that are part of a Java application and package
220. s When pointing onto a thread in the data window a tool tip appears that display in formation on the current state of this thread including its name the state running ready etc and the thread s current priority 15 3 5 Worst Case Execution Time Window Through this window the ThreadMonitor tool enables the determination of the maximum execution time that was encountered for each thread within recorded scheduler data If the corresponding menu item was selected in the data window see 8 15 3 2 execution time analysis will be performed on the recorded data and this window will be displayed The window shows a table with one row per thread and the following data given in each column Thread gives the Jamaica internal number of this thread Threads are numbered starting at 1 One Thread number can correspond to several Java threads in case the lifetime of these threads does not overlap 15 3 DATA WINDOW 189 Thread Name will present the Java thread name of this thread In case several threads used the same thread id this will display all names of these threads separated by vertical lines Worst case execution time presents the maximum execution time that was en countered in the scheduler data for this thread This column will display N A in case no releases where found for this thread See below for a definition of execution time Occurred at gives the point in time within the recording at which the release that requi
221. s and the Builder option analyze see 8 2 7 2 2 Memory for an Application s Data Structures To optimize the memory required for point 1 the application s data structures care is required by the application developer to allocate little memory and to make efficient use of it One important prerequisite to keeping application RAM demand low is that the Java implementation introduces only a small amount of memory overhead into every object This is particularly important since Java applications typically allocate many small objects The per object memory overhead in Jamaica is relatively small Typically three machine words are required for internal data such as the garbage collection state the object s type information a monitor for synchronisation and memory area information see 10 for details on memory areas 7 2 3 Memory for API libraries The amount of memory required for internal data structures using an application built using Jamaica is very low since only essential data that needs to be modified at runtime is stored in RAM Most data that is constant will be read directly from the application data that can be stored in ROM Nevertheless the amount of memory required for internal data depends on the size of the application including all library class files that may be required at run time Library classes such as character encodings or network protocols are not needed by all applications so they do not necessarily need
222. s caffeine_nolibs_js_fP_tS_nL 3291812 caffeine nolibs js fP tS nL JamaicaVM copies the line number information to RAM on startup such that also the RAM demand without line number information is significantly lower In this case the demand dropped from 471K with line number information to only 347K without this information Chapter 8 Memory Management Configuration JamaicaVM provides the only efficient hard realtime garbage collector available for Java implementations on the marked today This chapter will first explain how this garbage collection technology can be used to obtain the best results for applications that have soft realtime requirements before explaining the more fine grained tuning required for realtime applications 8 1 Configuration for soft realtime applications For most non realtime applications the default memory management settings of JamaicaVM perform well The heap size is set to a small starting size and is extended up to a maximum size automatically whenever the heap is not sufficient or the garbage collection work becomes too high However in some situations some specific settings may help to improve the performance of a soft realtime application 8 1 1 Initial heap size The default initial heap size is a small value The heap size is increased on demand when the application exceeds the available memory or the garbage collection work required to collect memory in this small heap becomes too high This means
223. s file compaction gain 80 13536 8835298 gt 1755100 C compiling caffeine_nolibs_js_fP_tS__ c caffeine nolibs js fP tS nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 128KB 1 128KB 63MB 511 128KB Thread Java stacks 4096B 1 4096B 2044KB 511 4096B Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 2308KB 337MB gt ls s caffeine nolibs js fP tS 3569804 caffeine nolibs js fP tS These additional options have little effect on the application size itself compared to the earlier version However the RAM demand of the application can be reduced to 2308K instead of 3328K for the version with larger Java stack finalizer thread and time slicing thread 7 23 5 Memory Required for Line Numbers An important advantage of programming in the Java language compared to other languages are the accurate error messages one obtains Run time exceptions con tain a complete stack trace with line number information on where the problem occured This information however needs to be stored in the application and be available at runtime After the debugging of an application is finished you may want to reduce the applications memory demand by removing this information The builder option XignoreLineNumbers can be set to disable this information Continuing the example from the previous section one can further reduce the application size and RAM demand by setting this
224. s for the POSIX signals can be turned off by setting properties with the option XdefineProperty The POSIX signals are SIGINT SIGQUIT and SIGTERM The properties are described in 8 d To turn off the signal handlers the properties jamaica no sig int _ handler jamaica no sig quit handler and jamaica no sig term handler have to be set to t rue Applying this to our example application we can reduce the Java stack to 4K deactivate the finalizer thread set the number of threads to 1 disable the time slicing thread and the memory reservation thread and turn of the signal handlers gt gt gt gt gt gt gt gt jamaicabuilder cp classes interpret setLocales none setProtocols none setGraphics none setFonts none javaStackSize 4K finalizerPri 0 numThreads 1 timeSlice 0ns reservedMemory 0 XdefineProperty jamaica no sig int handler true jamaica no sig quit handler true jamaica no sig term handler true CaffeineMarkEmbeddedApp destination caffeine nolibs js fP tS Reading configuration from usr local jamaica 6 0 1 etc jamaica conf Reading configuration from usr local jamaica 6 0 1 target linux x86 etc jamaica conf Jamaica Builder Tool 6 0 Release 1 User EVALUATION USER Expires 2010 06 10 Generating code for target linux x86 optimisation speed caffeine_nolibs_js_fP_tS__ c caffeine_nolibs_js_fP_tS__ h 7 2 OPTIMIZING RAM MEMORY DEMAND 73 Clas
225. s for the compiler in etc jamaica conf and the PATH environment variable Q Can I build my own VM as an application which expects the name of the main class on the command line like JamaicaVM does A With the Builder a standalone VM can be built with the option XnoMain If this option is specified the Builder does not expect a main class while compiling Instead the built application expects the main class later after startup on the command line Some classes or resources can be included in the created VM e g a VM can be built including all classes of the selected API except the main program with main class A 5 Fonts Q How can I change the mapping from Java fonts to native fonts A The mapping between Java font names and native fonts is defined in the font properties file Each target system provides this file with useful default values An application developer can provide a specialized version for this file To do this the new mapping file must exist in the classpath at build time The file must be added as a resource to the final application by adding resource t path where path is a path relative to a classpath root Setting the system property jamaica fontproperties with the option XdefineProperty jamaica fontproperties path will pro vide the graphics environment with the location of the mapping file A 6 VXWORKS TARGET 211 Why do fonts appear different on host and target A Jamaica relies on the targe
226. s must be defined within the buildfile by a task definition taskdef Ant tasks that invoke the Jamaica Builder and other tools are part of the JamaicaVM tools See 18 for the available Ant tasks and further details on the structure of the Jamaica Buildfiles The Jamaica specific tasks can be parameterized similarly to the tools they represent We define the usage of such a task along with a set of options as a configuration We use the term Jamaica Buildfile to describe an Ant buildfile that defines at least one of the Jamaica specific Ant tasks and contains one or many configura tions The benefit of this approach is that configurations can easily be used outside of Eclipse integrated in a build process and exchanged or stored in a version control system Using the editor The editor for Jamaica Buildfiles constists of three or more pages The first page is the Overview page On this page you can manage your configurations task definitions and Ant properties More information on this can be found in the following paragraphs The pages after the Overview page represent a configu ration The last page displays the XML sourecode of the buildfile Normally you should not need to edit the source directly Configure Builder options A configuration page consists of a header section and a body part Using the con trols in the header you can request the build of the current configuration change 42 CHAPTER 5 SUPPORT FOR THE ECLIPSE I
227. s several dis advantages An embedded system might not provide the necessary file system device and file system services Instead it is preferable to have all files relevant for an application in a single executable file which may be stored in read only memory ROM within an embedded system The Builder provides a way to create a single application out of a set of class files and the Jamaica virtual machine 14 1 How the Builder tool works Fig 14 illustrates the process of building a Java application and the JamaicaVM into a single executable file The Builder takes a set of Java class files as input and by default produces a portable C source file which is compiled with a native C compiler to create an object file for the target architecture The build object file is then linked with the files of the JamaicaVM to create a single executable file that contains all the methods and data necessary to execute the Java program 14 2 Builder Usage The builder is a command line tool It is named jamaicabuilder A variety of arguments control the work of the Builder tool The arguments can be given directly to the Builder via command line or by using configuration files Options 143 144 CHAPTER 14 THE JAMAICA BUILDER class gt C source file Y jamaicabuilder profiling data p object file executable lt Figure 14 1 The Builder tool given at the command line take priority Options not specified at the co
228. s shown usually exceeds the performance of a fully compiled application Furthermore the memory footprint is significantly smaller and the modify compile run cycle time is usually signif icantly shorter as well since only a small fraction of the application needs to be compiled It is not necessary to re generate profile data after every modification 6 2 2 Building with multiple profiles You can use several profiles to improve the performance of your application There are two possibilities to specify profiles that behave in a different way First you can just concatenate two profile files or dump a profile several times into the same file which will just behave as if the profiles were recorded sequen tially You can add a profile for a new feature this way If you want to favor a profile instead e g a micro profile for startup or a performance critical section as described in 8 6 1 4 you can specify the profile with another useProfile option In this case all profiles are normalized before they are concatenated so highly rated methods in a short run micro profile are more likely to be compiled 6 3 Interpreting the profiling output When running in profiling mode the VM collects data to create an optimized ap plication but can also be interpreted manually to find find memory leaks or time consuming methods You can make Jamaica collect information about perfor mance memory requirements etc To collect additional information you
229. s them together with the Jamaica runtime sys tem Java interpreter class loader realtime garbage collector JNI native interface etc into a stand alone executable This stand alone executable can then be exe cuted on the target system without needing to load the classes from a file system as is done by jamaicavm command but can instead directly proceed execut ing the byte codes of the application s classes that were built into the stand alone executable The builder has the opportunity to perform optimizations on the Java applica tion before it is built into a stand alone executable These optimizations reduce the memory demand smart linking bytecode compaction etc and increase its 4 4 JAMAICA THREADMONITOR MONITORING REALTIME BEHAVIOUR37 runtime performance bytecode optimizations profile guided compilation etc Also the builder permits fine grained control over the resources available to the application such as number of threads heap size stack sizes and enables the user to deactivate expensive functions such as dynamic heap enlargement or thread creation at runtime A more detailed description of the builder is given in sig 4 4 Jamaica ThreadMonitor Monitoring Realtime Behaviour The JamaicaVM ThreadMonitor enables to monitor the realtime behaviour of ap plications and helps developers to fine tune the threaded Java applications running on Jamaica run time systems These run time systems can be either the Jam
230. safer but it is generally inefficient due to the runtime checks required by its use When a memory check fails the result is a runtime exception which is also undesirable in safety critical code In many cases static 118 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES memory de allocation can do the same job without the runtime checks Escape analysis ensures that the checks are not needed and that no memory related ex ception is ever thrown by the corresponding memory access Therefore static memory deallocation is generally a better solution than ScopedMemory When static memory deallocation is not applicable one can always fall back on the realtime garbage collector It is both safe and relatively efficient Still any heap allocation has an associated garbage collection time penalty Realtime garbage collection makes an allocating thread pay the penalty up front One important property of the JamaicaVM is that any realtime code that runs at high priority and that does not perform memory allocation is guaranteed not to be delayed by garbage collection work This important feature holds for standard RTSJ applications only under the heavy restrictions that apply to NoHeapReal timeThreads 11 5 Scheduling and Synchronization As the reader may have already noticed in the previous sections scheduling and synchronization are closely related Scheduling threads that do not interact is quite simple however interaction is necessary for shar
231. st char commandLine where main is the name of the main class or the name specified via the Builder option destination To link the application with the VxWorks kernel image the macro USER INIT should be set to something like this extern int jvm main const char x jvm main args where args is the command line as a C string which should be passed to the application B 1 6 Limitations The current release of Jamaica for the VxWorks OS has the following limitations e java lang Runtime exec is not implemented e The following realtime signals are not available SIGSTKFLT SIGURG SIGXCPU SIGXFSZ SIGVTALRM SIGPROF SIGWINCH SIGIO SIGPWR SIGSYS SIGIOT SIGUNUSED SIGPOLL SIGCLD e Jamaica does not allow an application to set the resolution of the clock in javax realtime RealtimeClock The resolution of the clock depends on the frequency of the system ticker see sysClkRateGet and sysClkRateSet If a higher resolution for the realtime clock is needed the frequency of the system ticker must be increased Care must be taken when doing this because other programs running on the system may change their behavior and even fail In addition under VxWorks 5 4 the realtime clock must be informed about changes of the system ticker rate with the function clock setres The easiest way to do this is to add the following into a s
232. stalled In the Jamaica configuration file jamaica home etc jamaica conf the path of the Board Support Package BSP installation must be adjusted The following examples show the changes needed for an rtems i386 release B 3 INTEGRITY 221 e Change the include path property include rtems in the config file jamaica home et c jamaica conf to the include path of the BSP E g BSP INSTALL DIR i386 rtems pc686 lib include e Change the B option of the property XCFLAGS rtems to the path of your BSP library directory E g BSP INSTALL DIR i386 rtems pc686 1ib e Change the B option of the property XLDF LAGS rtems x to the path of your BSP library directory E g BSP INSTALL DIR i386 rtems pc686 1lib 2 2 RTEMS Configuration A RTEMS application should be configured using macros like define CONFIGURE APPLICATION NEEDS CONSOLE DRIVER These definitions may be made in the file jamaica home target rtems include jamaica target configuration h B 2 3 Running an application The Builder generates a bootable image of the application How this image is loaded and run depends on the BSP An application built for the target 1386 rtems with the pc686 BSP can for example be loaded and run using the GRUB boot loader INTEGRITY INTEGRITY from GreenHills Software is a secure royalty free Real Time Op erating System intended for use in embedded sy
233. stems that require maximum re liability The JamaicaVM is available for INTEGRITY and the following target hardware e ARM e Blackfin e PowerPC 227 APPENDIX B INFORMATION FOR SPECIFIC TARGETS B 3 1 Installation The INTEGRITY version of Jamaica is installed as described in section Installa tion see 83 1 In addition the following steps are required Configuration with INTEGRITY and BSP installed The path of the Board Support Package BSP installation in the Jamaica config uration file jamaica home et c jamaica conf must be adjusted e Check the include path property include integrity in jamaica home etc jamaica conf It must be set to the INTEGRITY include path default is usr local integrity INTEGRITY include e Check the property XCFLAGS integrity for appropriate values By default the compiler generates code to run on the INTEGRITY PPC simula tor isimppc The value of option bspname may be changed accordingly to your BSP e Check the property XLDFLAGS integrity for appropriate values By default the linker generates an INTEGRITY kernel of your applica tion i e it can be run directly using isimppc This is defined through integrity option kernel Changing theoptionto integrity option dynamic creates a dynamic downloadable module of the ap plication To run such a module start isimppc with a provided kernel isimppc usr local integrity sim800 kernel Then down load the
234. t JAMAICA BUILDER HEAPSIZE 1536MB Q When I build an application which contains native code it seems that some A fields of the class files can be accessed with the function Get FieldID from the native code but some others not What happened to those fields If an application is built the Builder removes from classes all unreferenced methods and fields If a field in a class 1s only referenced from native code the Builder can not detect this reference and protect the field from the smart linking process To avoid this use the includeClasses option with the class containing the field This will instruct the Builder to fully include the specified class es Q When I build an application with the Builder I get some warning like the A following WARNING Unknown native interface type of class name name h assume JNI calling convention Is there something wrong In general this is not an error The Builder outputs this warning when it is not able to detect whether a native function is implemented using JNI the stan dard Java native interface see chapter 8116 JBI Jamaica specific more efficient native interface used by the Jamaica boot classes Usually this means the appropriate header file generated with some prototype tool like jamaicah is not found or not in the proper format To avoid this warning recreate the header file with jamaicah and place it into a directory that is passed via the bui
235. t graphics system to render true type fonts Since that renderer is generally a different one than on the host system it is possi ble that the same font is rendered differently A 6 VxWorks Target Q When I load a built application I get errors of the dynamic linker Undefined symbol A This linker error occurs when the VxWorks system is configured without one or more of the following function sets listed in Configuration of VxWorks Please check your VxWorks configuration INCLUDE statements intarget config all configAll hin your VxWorks installation directory Probably you have to recompile a new VxWorks kernel image Q How can I pass parameters to an application under VxWorks A Because of the C like syntax of the VxWorks command shell parameters to an application have to be passed as a string An application can simply be started by jvm or classname where classname is the value specified via the destination option of the Jamaica Builder isa space separated list of arguments which should be passed to the application just like a command line 212 APPENDIX A FAQ FREQUENTLY ASKED QUESTIONS Appendix B Information for Specific Targets This appendix contains target specific documentation and descriptions B 1 VxWorks VxWorks from Wind River Systems is a real time operating system for embedded computers The JamaicaVM is available for VxWorks 5 4 to 6 7 and the following target hardware e
236. t still will be possible to use these functions However then these threads will be allocated dynamically when needed Since non fragmented memory is required for the allocation of these threads a later allocation may require heap expansion or may fail due to fragmented mem ory It is therefore recommended to pre allocate these threads The number of JNI attachable threads that will be required is the number of threads that will be attached simultaneously Any thread structure that will be detached via JNI_DetachCurrentThread will become available again and can be used by a different thread that calls JNI AttachCurrentThread or JNI AttachCurrentThreadAsDaemon Option threadPreemption n Compiled code contains special instructions that permit thread preemption These instructions have to be executed often enough to allow a thread preemption time that is sufficient for the destination application As the instructions cause an over head in code size and runtime performance one would want to generate this code as rarely as possible The threadPreemption option enables setting of the maximum number of intermediate instructions that are permitted between the execution of thread preemption code This directly affects the maximum thread preemption time of the application One intermediate instruction typically corresponds to 1 2 machine instructions There are some intermediate instructions calls arra
237. tartup script for VxWorks 220 APPENDIX B INFORMATION FOR SPECIFIC TARGETS sysClkRateSet 1000 timeSpec malloc 8 timeSpect0 0 x timeSpect 4 1000000 clock_setres 0 timeSpec free timeSpec This example sets the system ticker frequency to 1000 ticks per second and the resolution of the realtime clock to Ims B 1 7 Additional notes e Object files because applications for VxWorks DKM only are usually only partially linked missing external functions and missing object files cannot be detected at build time If native code is included in the application with the option ob ject Jamaica cannot check at build time if all needed native code is linked to the application This is only possible in the final linker step when the application is loaded on the target system B 2 RTEMS RTEMS Real Time Executive for Multiprocessor Systems is a commercial grade real time operating system designed for deeply embedded systems It is a free open source solution that supports multiprocessor systems RTEMS is designed to support applications with the most stringent real time requirements while being compatible with open standards The JamaicaVM is available for RTEMS 4 6 and the following target hardware e Intel x86 e ERC32 LEON B 2 Installation The RTEMS Version of Jamaica is installed as described in section Installation see 813 1 In addition the following steps are required Configuration with RTEMS and BSP in
238. ter the opening project tag of the build file taskdef name jamaicabuilder classpath jamaica home l1ib JamaicaTools jar classname com aicas jamaica tools ant JamaicaTask taskdef name jamaicah classpath jamaica home 1ib JamaicaTools jar classname com aicas jamaica tools ant JamaicahTask gt The task names are used within the build file to reference these tasks They may be chosen arbitrarily for stand alone build files For compatibility with the Eclipse Plug In the names jamaicabuilder and jamaicah should be used 18 2 Task Usage All Jamaica Ant tasks require the attribute jamaica which must be set to jamaica home the root directory of the Jamaica installation 201 202 CHAPTER 18 BUILDING WITH APACHE ANT Tool options are specified as nested elements For each tool option option a corresponding option element is available in the Ant task of that tool These option elements accept the attributes shown in the following table All attributes are optional Attribute Description Required value Option argument For options that re quire an argument enabled Whether the option is passed to the tool No default t rue append Value is appended to the value stored in No default false the tool s configuration file syntax Although Ant buildfiles are case insensitive the precise spelling of the option name should be preserved for compatibility with t
239. termine your application architecture including which components are local objects and which components are remotely accessible This step includes e Defining the remote interfaces A remote interface specifies the meth ods that can be invoked remotely by a client Clients program to re mote interfaces not to the implementation classes of those interfaces The design of such interfaces includes the determination of the types of objects that will be used as the parameters and return values for these methods If any of these interfaces or classes do not yet exist you need to define them as well 208 APPENDIX FAQ FREQUENTLY ASKED QUESTIONS e Implementing the remote objects Remote objects must implement one or more remote interfaces The remote object class may include implementations of other interfaces and methods that are available only locally If any local classes are to be used for parameters or return values of any of these methods they must be implemented as well Implementing the clients Clients that use remote objects can be im plemented at any time after the remote interfaces are defined includ ing after the remote objects have been deployed Example source code demonstrating the use of Remote Method Invocation is provided with the JamaicaVM distribution See 3 4 Q Does Jamaica support RMI A is supported by Jamaica 6 0 JamaicaVM 6 0 uses dynamically generated stub and skeleton classes So no pre
240. the specified environment variable If this variable is not set the stack size specified using nativeStackSize n will be used Option numThreadsFromEnv var The numThreadsFromEnv option enables the application to read the number of threads from the specified environment variable If this variable is not set the number specified using numThreads n will be used Option maxNumThreadsFromEnv var The maxNumThreadsFromEnv option enables the application to read the max imum number of threads from the environment variable specified within If this variable is not set the number specified using maxNumThreads n will be used Option numJniAttachableThreadsFromEnv var The numJniAttachableThreadsFromEnv option enables the application to read its initial number of JNI attachable threads from the environment variable specified within If this variable is not set the value specified using the option numJniAttachableThreads n will be used Option finalizerPriFromEnv var The finalizerPriFromEnv option enables the application to read its final izer priority from the environment variable specified within If this variable is not set the finalizer priority specified using finalizerPri n will be used Option priMap j p sp jp sp Java threads are mapped directly to threads of the operating system used on the target system The Java priorities are mapped to system level priorities for this 162 CHAPTER 14 THE JAMAICA BUILDER
241. tible so that more urgent threads can become active The implementation of a realtime garbage collector must solve a number of technical challenges Garbage collector activity must be performed in very small single increments of work In JamaicaVM one increment consists of garbage collecting only 32 bytes of memory On every allocation the allocating thread pays for the memory by performing a small number of these increments The number of increments can be analyzed such that this is possible even in realtime code The RTSJ provides a powerful extension to the Java specification Its full power however is achieved only by the combination with a realtime garbage collector that helps to overcome its restrictions 10 3 Relaxations in JamaicaVM Because JamaicaVM uses a realtime garbage collector the limitations that the Real Time Specification for Java imposes on realtime programming are not im posed on realtime applications developed for JamaicaVM The limitations that are relaxed in JamaicaVM affect the use of memory areas thread priorities runtime checks and static initializers For the development of applications that do not make use of these relaxations the builder option st rictRTSJ see below can be set to disable these relax ations 10 3 1 Use of Memory Areas Because JamaicaVM s realtime garbage collector does not interrupt application threads it is unnecessary for objects of class RealtimeThread or even of NoHeapRealt
242. ting code for target linux x86 optimisation speed PKG V2562a85066f42947 c Lez caffeine compiled _ caffeine compiled h Class file compaction gain 74 97414 21665933 gt 5422087 C compiling caffeine compiled _ Lead caffeine compiled nc o linking stripping Application memory demand will be as follows initial max Thread C stacks 1024KB 8 128KB 63MB 511 128KB Thread Java stacks 128KB 8 16KB 8176KB 511 16KB Heap Size 2048KB 256MB GC data 128KB 16MB TOTAL 3328KB 343MB gt ls s caffeine_compiled 45182172 caffeine_compiled The performance of the compiled version is significantly better than the inter preted version However there is only a small difference compared to the version created using the profile as described in the gt caffeine_compiled Sieve score 15508 98 Loop score 64680 2017 Logic score 77315 0 String score 6420 708 Float score 20781 185 Method score 12887 166650 Overall score 22602 For a better performance of a fully compiled application compile can of course be combined with the appropriate C compiler optimization level as shown in 87 1 2 7 2 OPTIMIZING RAM MEMORY DEMAND 67 7 2 Optimizing RAM Memory Demand In many embedded applications the amount of RAM memory required is even more important than the application performance and its code size Therefore a number of means to control the applications R
243. tion file classpath cp lt classpath gt bootclasspath Xbootclasspath lt classpath gt classname class class classl classn 16 2 1 General These are general options providing information about jamaicah itself Option help help h Display the usage of the jamaicah tool and a short description of all possible stan dard command line options 16 2 THE JAMAICAH COMMAND 195 Option Xhelp Display the usage of the jamaicah tool and a short description of all possible stan dard and extended command line options Extended command line options are not needed for normal control of the jamaicah command They are used to con figure tools and options and to provide tools required internally for Jamaica VM development Option jni Create Java Native Interface header files for the native declarations in the provided Java class files This option is the default and hence does not need to be specified explicitly Option d directory Specify output directory for created header files The filenames are deduced from and the extension ee the full qualified Java class names where are replaced by h 1s appended Option ozfile Specify the name of the created header file If not set the filename is deduced from and the extension 5 the full qualified Java class name where are replaced by h 1s appended Option inc
244. tion of different objects or arrays are shown in Tab The output of numblocks when using the a11 option can be used to get a quick overview on the number of blocks for all classes used by an application numblocks all HelloWorld Class Blocks HelloWorld 1 com aicas jamaica AccessCheck 1 com aicas jamaica Archive 1 com aicas jamaica ArchiveSPathVisitor 1 88 CHAPTER 8 MEMORY MANAGEMENT CONFIGURATION Class numblocks new java util Vector 1 new boolean 1024 5 new byte 64 3 new char 256 19 new int 1024 147 new Object 1000000 142 860 Table 8 1 Typical numbers of blocks for objects com aicas jamaica ArchiveSVisitor com aicas jamaica ArchiveDirectory com aicas jamaica ArchiveEntry com aicas jamaica BuilderError com aicas jamaica DirectoryEntry com aicas jamaica NYIException com aicas jamaica lang CpuTime com aicas jamaica lang Debug com aicas jamaica lang LowLevelRTSJ com aicas jamaica lang Process com aicas jamaica lang Profile com aicas jamaica lang Profile 1 com aicas jamaica lang Profile 2 com aicas jamaica lang Profiles3 com aicas jamaica lang ProfileSCount com aicas jamaica lang Wait com aicas jamaica util False com aicas java net protocol rom Handler com aicas java net protocol rom RomURLCnctn Eos Ea Ra Ba ka aou Bao NON ON Chapter 9 Debugging Support Jamaica supports the debugging facilities of integrated development environments
245. tion specifies a file to read the set of options used to build the application The option format must be identical to the one in the default configuration file jamaica home target platform etc jamaica conf When set the files jamaica home jamaica jamaica conf and jamaica home target platform etc jamaica conf are ignored 14 2 2 Classes files and paths These options allow to specify classes and paths to be used by the builder Option classpath cp classpath The classpath option specifies the paths that are used to search for class files A list of paths separated by the path separator char on Unix systems on Windows can be specified This list will be traversed from left to right when the Builder tries to load a class Option enableassertions ea The enableassertions option enables assertions for all classes Assertions are disabled by default Option main class The main option specifies the main class of the application that is to be built This class must contain a static method void main String args This method is the main entry point of the Java application If the main option is not specified the first class of the classes list that is provided to the Builder is used as the main class Option jarzfile The jar option specifies a JAR file with an application that is to be built This JAR file must contain a MANIFEST with a Main Class entry Option includeClasses class
246. uaranteed that the finalizer thread will not starve 8 1 CONFIGURATION FOR SOFT REALTIME APPLICATIONS 77 system performance may be improved by running the finalizer thread at a lower priority Then a higher priority thread that performs memory allocation will not be preempted by finalizer thread execution This priority can be set to a lower value using the option finalizerPri of the builder or the environment variable JAMAICAVM FINALIZERPRI In an application that has sufficient idle CPU time in between urgent activities a finalizer priority lower than the priority of all other threads may be sufficient 8 1 4 Reserved memory JamaicaVM s default behavior is to perform garbage collection work at memory allocation time This ensures a fair accounting of the garbage collection work Those threads with the highest allocation rate will perform correspondingly more garbage collection work However this approach may slow down threads that run only occasionally and perform some allocation bursts e g changing the input mask or opening a new window in a graphical user interface To avoid penalizing these time critical tasks by allocation work JamaicaVM uses a low priority memory reservation thread that runs to pre allocate a given percentage of the heap memory This reserved memory can then be allocated by any allocation bursts without the need to perform garbage collection work Consequently an application with bursts
247. uld send IP Address The IP address of the run time system Port The Port where the runtime system should be contacted see 815 1 Buffer Size The amount of memory that is allocated within the run time system to store event data during a period Sample Period The period length between sending data Start Recording When pressed connects the ThreadMonitor to the run time systems and collects data until pressed again Table 15 1 Threadmonitor Controls e User events contain user defined messages and can be triggered from Java code e Allocated memory gives an indication of the amount of memory that is cur rently allocated by the application The display is relatively coarse changes are only displayed if the amount of allocated memory changes by 64kB A vertical line gives indicates what thread performed the memory allocation or GC work that caused a change in the amount of allocated memory When ThreadMonitor is started it presents the user a control window Fig 15 21 Control Window Menu The control window s menu permits only three actions File Open This menu item will open a file requester to load previously recorded sched data that was saved through the data window s File Save as menu item see 5 15 3 2 File Close Select this menu item will close the control window but it will leave all other windows open 184 CHAPTER 15 THE JAMAICA THREADMONITOR File Event classes
248. umblocks command They are used to configure tools and options to provide tools required internally for Jamaica VM development Option version Prints the version of the Jamaica Builder Tool and exits Option verbose Set verbose level If verbose level is greater than 0 additional output on the state of the build process is printed to standard out Option showSettings The currently used options of Jamaica Numblocks are written to stdout in property file format To make these the default settings copy these options into jamaica home et c numblocks conf Option saveSettings file The currently used options of Jamaica VM Numblocks are written to stdout in property file format To make these the default settings copy these options into jamaica home et c numblocks conf Option configuration file The set of options used to perform numblocks are read from the provided file The format used to define options must be identical to the default configuration file jamaica home et c numblocks conf 17 1 2 Classes files and paths These options allow to specify classes and paths to be used by numblocks Option a11 If this option is set the number of blocks required for the allocation of objects of all classes in this application will be displayed 17 2 ENVIRONMENT VARIABLES 199 Option classpath cp classpath Specifies the paths that are to be used to search for class files A list of paths 66 99 separate
249. used by legacy code The advantage of a limited and short execution time for entering a priority ceil ing monitor working on a shared resource then leaving this monitor are however lost when a thread that has entered this monitor may block Therefore the system designer should restrict the use of priority ceiling monitors to short code sequences that only access a shared resource and that do not block Entering and exiting the 11 6 LIBRARIES 123 monitor can then be performed in constant time and the system ensures that no thread may try to enter a priority ceiling monitor that is held by some other thread Since priority ceiling emulation requires adjusting a thread s priority every time a monitor is entered or exited there is an additional runtime overhead for this priority change when using this kind of monitors This overhead can be significant compared to the low runtime overhead that is incurred to enter or leave a normal priority inheritance monitor In this case there is a priority change penalty only when a monitor has already been taken by another thread Future versions of the Jamaica Java implementation may optimize priority ceiling and avoid unnecessary priority changes The JamaicaVM uses atomic code sequences and restricts thread switches to certain points in the code A synchro nized code sequence that is protected by a priority ceiling monitor and that does not contain a synchronization point may not require entering and
250. versions only Evaluation keys are provided with evaluation versions of JamaicaVM 3 3 JAMAICAVM DIRECTORY STRUCTURE 27 jamaica home bin t doc t build info t jamaicavm manual pdf t jamaica api README x txt RELEASE NOTES t UNSUPPORTED tH lib license target l linux x86 bin etc examples include lib prof Host tool chain executables Comprehensive Jamaica distribution information Jamaica tool chain user manual this manual Jamaica API specification Javadoc Host platform specific documentation starting points User relevant changes in the present release Unsupported features list Tool documentation in Unix man page format Host platform configuration files Libraries for the development tools aicas evaluation license third party licenses Target specific files for the target Linux x8 6 Virtual machine executables some platforms only Default target platform configuration files Example applications System JNI header files Development and runtime libraries resources Default profiles Table 3 1 JamaicaVM Directory Structure 28 CHAPTER 3 GETTING STARTED API specification of the selected Jamaica runtime environment The Real Time Specification for Java is part of the standard Jamaica API The number of target systems supported by a distribution varies The target directory contains an entry for each supported target platform Typically
251. vious call to xmic is needed to generate those If the Builder is used to create RMI server applications the exported inter faces and implementation classes need to be included An example build file demonstrating the use of RMI with Jamaica is pro vided with the JamaicaVM distribution See Tab A 4 Builder Q When I try to start a Jamaica compiled executable in a Linux 2 4 x environ ment I get an error message like the following alloc pages 0 allocation failed gfp 0x1d0 0 from c0123886 A This is a bug in the Linux 2 4 10 kernel Please use a newer kernel version The problem seems to occur if the amount of allocated memory is close to the amount of available memory which is usually no problem if you use Jamaica on a desktop PC but occurs quite often on embedded systems running Linux 2 4 10 and Jamaica e g the DILNet PC Q When I try to compile an application with the Builder I get the error message OUT OF MEMORY What can I do A 4 BUILDER 209 A The Builder has a predefined setting for the internal heap size If the memory space is exhausted the error message OUT OF MEMORY is printed and Builder exits with an error code The predefined heap size 1024MB is usually large enough but for some applications it may not be sufficient You can set the heap size via the environment variable JAMAICA BUILDER HEAPSIZE e g under bash with the following command expor
252. was built with an incorrect or outdated heapSize argu ment e A bug in the application may be causing a memory leak and gradual use of more memory than expected Whatever the reason it may be important in some environments to understand the behavior of memory management in the case the application exceeds the as sumed heap usage In dynamic mode the worst case execution time for an allocation can no longer be guaranteed as soon as the application uses more memory But as long as the excess heap used stays small the worst case execution time will increase only slightly This means that the original worst case execution time may not be exceeded at all or only by a small amount However the garbage collector will still work properly and recycle enough memory to keep the application running If the constant garbage collection work option is chosen the amount of garbage collection work will not increase even if the application uses more memory than originally anticipated Allocations will still be made within the same worst case execution time Instead the collector cannot give a guarantee that it will recycle memory fast enough This means that the application may fail abruptly with an 86 CHAPTER 8 MEMORY MANAGEMENT CONFIGURATION out of memory error Static mode does not provide graceful degradation of per formance in this case but may cause abrupt failure even if the application exceeds the expected memory requirements only slightly
253. with Jamaica On the right hand side of the window IP address and port of the VM to be monitored may be entered The following list gives a short overview on which events data is collected e Thread state changes record how the state of a thread changes over time including which threads cause state changes in other threads e Thread priority changes show how the priority changed due to explicit calls to Thread setPriority as well as adjustments due to priority in heritance on Java monitors e Thread names show the Java name of a thread e Monitor enter exit events show whenever a thread enters or exits a monitor successfully as well as when it blocks due to contention on a monitor e GC activity records when the incremental garbage collector does garbage collection work e Start execution shows when a thread actually starts executing code after it was set to be running e Reschedule shows the point when a thread changes from running to ready due to a reschedule request e All threads that have the state ready within the JamaicaVM are also ready to run from the OS point of view So it might happen that the OS chooses a thread to run that does not correspond with the running thread within the VM In such cases the thread chosen by the OS performs a yield to allow a different thread to run 15 2 CONTROL WINDOW 183 Name Value Event classes Selection of event classes that the run time system sho
254. y profile 168 reservedMemory 165 reservedMemoryFromEnv resource 151 saveSettings 147 scopedMemorySize 167 scopedMemorySizeFromEnv setFonts 152 setGraphics 152 setLocales 152 setProtocols setTimeZones 152 showExcludedFeatures 155 showIncludedFeatures 155 showSettings 243 smart source 130 sourcepath ss 135 stopTheWorldGC strictRTSJ strictRTSJFromEnv 167 target threadPreemption 159 timeSlice 159 tmpdir useProfile 169 useTarget verbose 147 version 195 198 x BIA XavailableTargets 176 Xbootclasspath Xcc 173 XCFLAGS XdefineProperty 171 XdefinePropertyFromEnv XenableDynamicJNILibraries 176 XenableZIP 172 XexcludeLongerThan 173 XextendedGlobalCPool XfullStackTrace Xhelp H7 195 193 Xhelp xhelp XignoreLineNumbers 178 Xinclude Xint XjamaicaHome 171 XjavaHome 171 Xjs XlazyConstantStrings 172 XlazyConstantStringsFromEnv 244 Xld XLDFLAGS Xlibraries 174 XlibraryPaths 175 XlinkDynamicFlags 175 XlinkDynamicPrefix 174 XlinkStatic XlinkStaticFlags 175 XlinkStaticPrefix 175 XloadJNIDynamic 177 Xmi 135 Xms 135 Xmx 135 XnoClasses 172 XnoMain 172 XnoRuntimeChecks 175 Xns 136 XobjectFormat 177 XobjectProcessorFamily 177 XobjectSymbolPrefix 177 Xprof XprofileFile
255. y preemptive scheduling but for realtime code the use of Rea1t imeThread is still recommended AsyncEventHandlers vs BoundAsyncEventHandlers An alternative execution environment is provided through classes As yncEvent Handler and BoundAsyncEventHandler Code in an event handler is ex ecuted to react to an event Events are bound to some external happening e g a processor interrupt which triggers the event AsyncEventHandler and BoundAsyncEventHandler are schedula ble entities that are equipped with release and scheduling parameters exactly as RealtimeThread and NoHeapRealtimeThread The priority scheduler schedules both threads and event handlers according to their priority Also ad mission checking may take the release parameters of threads and asynchronous event handlers in account The release parameters include values such as execu tion time period and minimum interarrival time One important difference from threads is that an AsyncEventHandler is not bound to one single thread This means that several invocations of the same 120 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES handler may be performed in different thread environments A pool of preallo cated RealtimeThreads is used for the execution of these handlers Event handlers that may execute for a long time or that may block during their execution may block a thread from this pool for a long time This may make the timely execution of other event handlers impossi
256. y accesses that can be more expensive 20 50 machine instructions The thread preemption must be at least 10 intermediate instructions Option timeSlice n For threads of equal priority round robin scheduling is used when several threads are running simultaneously Using the t imeSlice option the maximum size of such a time slice can be given in nanoseconds A special synchronization thread is used that waits for the length of a time slice and permits thread switching after every time slice 160 CHAPTER 14 THE JAMAICA BUILDER If no round robin scheduling is needed for threads of equal priority the size of the time slice can be set to zero In this case the synchronization thread is not required so fewer system resources are needed and the highest priority threads will not be interrupted by the synchronization thread Option finalizerPri pri The finalizerPri option sets the Java priority of the finalizer thread to pri The finalizer thread is a daemon thread that runs in the background and executes the method finalize of objects that are about to be freed by the garbage collector The memory of objects that have such a method cannot be freed before this method is executed If the finalizer thread priority is set to zero no finalizer thread will be cre ated In that case the memory of objects that are found to be unreachable by the garbage collector cannot be freed before their finalizers are executed explicitly by calling
257. y allocation the 11 4 MEMORY MANAGEMENT 113 Thread time rtl 4 ON E OA rt2 H M rt3 TH IHH ENIM rt4 JMiIB LH HEN A Figure 11 3 JamaicaVM provides realtime behavior for all threads allocating thread pays for the memory by performing a small number of these increments The number of increments can be analyzed to determine worst case behavior for realtime code 11 4 4 Memory Management of RTSJ The RTSJ provides a powerful extension to the Java specification Its full power however is achieved only by the combination with a realtime garbage collector that helps to overcome its restrictions Since JamaicaVM uses a realtime garbage collector it does not need to impose the limitation that the Real Time Specifica tion for Java puts onto realtime programming onto realtime applications developed with the JamaicaVM The limitations that are relaxed in Jamaica VM affect the use of memory areas thread priorities runtime checks and static initializers Use of Memory Areas Since Jamaica s realtime garbage collector does not interrupt application threads RealtimeThreads and even NoHeapRealtimeThreads are not required to run in their own memory area outside the control of the garbage collector In stead any thread can use and access the normal garbage collected heap Thread priorities In Jamaica RealtimeThreads NoHeapRealtimeThreads and normal Java Thr
258. yword PROFILE INVOKE Groups builder Values 1 number of calls from caller method to called method 2 bytecode position of the call within the method 3 signature of the caller method 4 signature of the called method Keyword PROFILE_INVOKE_CYCLES Groups speed Values 1 number of processor cycles spent in the called method 2 bytecode position of the call within the method 3 signature of the caller method 4 signature of the called method Keyword PROFILE_NATIVE Groups all Values 1 total number of calls to the native method 2 relative number of calls to the native method 3 signature of the called native method Keyword PROFILE NEWARRAY Groups memory Values 6 3 INTERPRETING THE PROFILING OUTPUT 55 1 number of calls to array creation within a method 2 bytecode position of the call within the method 3 signature of the method Keyword PROF Values LE THREAD Groups memory speed 1 current Java priority of the thread 2 total amount of CPU cycles in this thread 3 relative time in interpreted code 4 relative time in compiled code 5 relative time in JNI code 6 relative time in garbage collector code 7 required C stack size 8 required Java stack size Keyword PROF Values LE THREADS Groups builder 1 maximum number of concurrently used threads Keyword PROF Values LE THREADS JNI Groups builder
259. zation of a class or the initialization has to be made explicit The statements and expressions that cause the initialization of a class are 108 CHAPTER 11 REALTIME PROGRAMMING GUIDELINES e reading a static field of another class writing a static field of another class calling a static method of another class and e creating an instance of another class using new An explicit initialization of a class C is best performed in the static initializer of the class D that refers to C One way to do this is to add the following code to class D x initialize class C x static C class initialize The notation C class itself has its own disadvantages see 8 11 2 5 So if possible it may be better to access a static field of the class causing initialization as a side effect instead initialize class C static int ignore C statioc field 11 2 5 Operations Causing Class Loading Class loading can also occur unexpectedly A reference to the class object of a given class C can be obtained using classname class as in the following code Class class C C class This seemingly harmless operation is however transformed into a code sequence similar to the following code static Class class String name try return Class forName name catch ClassNotFoundException e throw new NoClassDefFoundError e getMessage static Class class C Class tmp if class C
260. zer of the class that uses the data and assigned to a static variable that is marked final Due to the significant code overhead large arrays should instead be loaded as a resource using the Java standard API via method get ResourceAsStream from class java lang Class Autoboxing JDK 1 5 Unlike some Scheme implementations primitive types in Java are not internally distinguishable from pointers This means that in order to use a primitive data type where an object is needed the primitive needs to be boxed in its corresponding object JDK 1 5 introduces autoboxing which automatically creates objects for values of primitive types suchas int long or float whenever these values are assigned to a compatible reference This feature is purely syntactic An expression such as new Integer can be written as i Due to the hidden runtime overhead for the memory allocation autoboxing should be avoided in performance critical code Within code sequences that have heavy restrictions on memory demand such as realtime tasks that run in Immortal Memory or ScopedMemory autoboxing should be avoided completely since it may result in hidden memory leaks 11 2 COMPUTATIONAL TRANSPARENCY 107 For Loop Over Collections JDK 1 5 JDK 1 5 also introduces an extended for loop The extension permits the itera tion of a Collection using a simple for loop This feature is purely syntactic A loop such as ArrayList list new Array
261. zy linking is automatically disabled when st rict RTSJ is set This avoids runtime assignment errors due to lazily linked classes that may be allocated in a 14 2 BUILDER USAGE 167 memory area that is incompatible with a current scoped memory allocation con text when lazy linking is performed Option strictRTSJFromEnv var The st rictRTSJFromEnv option enables the application to read its setting of StrictRTSJ from the specified environment variable If this variable is not set the value of the Boolean option strictRTSJ will be used The value of the environment variable must be 0 for strictRTSJ false or 1 for strictRTSJ true Option immortalMemorySize n K M The immortalMemorySize option sets the size of the immortal memory area in bytes The immortal memory can be accessed through the class javax realtime ImmortalMemory The immortal memory area is guaranteed never to be freed by the garbage collector Objects allocated in this area will survive the whole application run Option immortalMemorySizeFromEnv var The immortalMemorySizeFromEnv option enables the application to read its immortal memory size from the environment variable specified using this op tion If this variable is not set the immortal memory size specified using the option immortalMemorySize will be used Option scopedMemorySize n The scopedMemorySize option sets the size of the memory that should be made

JamaicaVM 6.0 — User Manual

Contents

Download Pdf Manuals

Related Search

Related Contents

JamaicaVM 6.0 &mdash; User Manual

Contents

Download Pdf Manuals

Related Search

Related Contents

JamaicaVM 6.0 — User Manual