JBACI Concurrency Simulator User's Guide
Contents
1. 1 4 installed in order to run sBACI Open the distri bution jbaciN zip into the directory jbaci To run JBACI execute java jar jbaci jar You can also create a shortcut to the jar file and use the icon supplied There are also batch files run bat which runs the above command and runp bat and runc bat which allow a source file name without the extension pm or cm to be included This document describes the operation of the sBACI IDE and the graphics extensions only For documentation of the dialects of Pascal and C that are accepted as well as of the synchronization primitives refer to the original BACI documentation which for convenience is included in the directory doc Most aspects of the GUI are defined in the file Config java and can be easily changed Certain options can also be changed by editing the configuration file config cfg which is written out when JBACI is closed Note that the configuration includes in the location of the executable compiler files and the default source directory so they must be changed if you do not install to the default directory or need to use Unix file syntax 3 The Integrated Development Environment The sBACI IDE is similar to other IDEs When you run the program you are presented with a menu structure as well as with a toolbar of buttons for common operations Selection of menu entries and buttons using mouse clicks or keyboard mnemonics and shortcuts will be familiar to a user of GUIs In the f2. divided into three areas the Source area the PCode area and Variables area The Source area shows the source code of the entire program not just the code of the process A green arrow indicates the next source line to be executed Breakpoints are denoted by red dots and the green arrow is colored red when a breakpoint is reached The PCode area displays the PCode for the current source line The same indications are used as for the Source area The Variables area displays the values of the local variables of the process The variables are displayed in a tree format so that values of arrays can be expanded or folded 3 3 4 Displaying process windows The default in sBACI is to display a process window when the instruction being executed has been taken from that process that is the process window is displayed if it has not been displayed before and brought to the front of the frame if it has You can deselect Options Show Active Window in which case the window for the active process will not be displayed or brought to the front 3 4 History file The history of all source or PCode instructions executed can be written to a file as selected by Options Write History File The file has the extension his and is re opened whenever Run is selected Make sure to select Run again if you change the option The file is flushed and closed when the end of the program is reached If you to flush and close a file before termination or for a non terminatin
3. JBACI Concurrency Simulator User s Guide Moti Ben Ari July 18 2004 Copyright c 2003 4 by Mordechai Moti Ben Ari Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 2 or any later version published by the Free Software Foundation with Invariant Section History no Front Cover Texts and no Back Cover Texts A copy of the license is included in the file fd1 txt included in this archive 1 History Over twenty years ago I developed a concurrency simulator for teaching concurrent program ming The simulator was based upon Niklaus Wirth s Pascal P interpreter and was subsequently published in its entirety in my textbook Principles of Concurrent Programming Prentice Hall In ternational 1982 Later I made many modifications to the simulator in particular I developed an Integrated Development Environment IDE based upon the user interface features in Turbo Pas cal The software has now become too fragile to maintain and the character interface is unattractive to students In the intervening years other educators have developed concurrency simulators of their own The most comprehensive and widely used is BACI and I am flattered that it was named after me Ben Ari Concurrency Interpreter BACI http www mines edu fs_home tcamp baci was developed at William and Mary College by Bill Bynum and Tracy Camp While versions of BACI exist for se
4. based upon a global tuple space you can read input and output tuples to the tuple space If you try to read or input a formal tuple for which no matching actual tuple exists the process blocks The terminology and the operations which are implemented are not standard but are based upon a course developed at the Weizmann Institute of Science The implementation is sufficient to demonstrate interesting examples of Linda like load balancing The tuple space is defined as a board upon which you can post remove or read notes The board is displayed in a separate window as described above A note consists of a triple a character and two integer values The following operations are available e postnote to post a note on the board e removenote and readnote to remove and read a note from the board The first parameter must be a character value while the two optional parameters must be integer variables The operations search for an arbitrary note with the character value and return the integer values in the variables If there is no matching note the process blocks until a matching note is posted The operations can be called with one two or three parameters unused integer parameters are given the default value 32767 11 postnote a Equivalent to postnote a 32767 32767 postnote a 5 Equivalent to postnote a 5 32767 postnote a 5 10 For historical reasons there are two syntaxes f
5. cording to commands within its own process In sBACI the standard procedure read blocks the entire simulator while nbread is non blocking that is an input statement returns immediately after it is called If the user has entered a value it is returned otherwise a dummy value is returned 32767 for integer type and r for character type To wait for input in one process without blocking other processes you need to write a loop that calls the input statement until a non flag value is returned You can use the functions getNum and getChar in the example programs ioint pm cm and io pm cm respectively 4 3 Monitors The syntax and semantics of monitors is described in the BACI documentation As described there the conditions queues are not FIFO but priorities can be used to simulate a FIFO queue Accord ing to the immediate resumption requirement a signaling process is blocked after unblocking a 10 process waiting on a condition in JBACI the interpreter has been modified to assign an artificial priority of 1 to a signaling process so that it will be unblocked before new processes waiting to enter the monitor In Pascal a monitor must be declared global to a Pascal main program the globals window dis plays the monitor variables monitor pc var procedure Take procedure Append begin end program ProducerConsumer 4 4 Linda Linda is a concurrent programming paradigm developed by David Gelernter It is
6. e The Globals window displays the values of the global variables In a Pascal program the global variables are actually local to the main program so the Globals window will be empty e The History window displays the last 150 source or PCode instructions that have been exe cuted The History window is displayed at the bottom right of Figure 2 Options History on Source Step selects whether an entry will be added to the History window after each source step or each PCode step if this is selected the PCode will not appear in the display e The Linda window displays the tuple space You can turn the display of these windows on or off by selecting entries in the Window menu The system windows displayed by default is controlled by flags in the configuration 3 3 3 Process windows The heart of the display in the run state is the set of process windows one for each process A process window consists of three tabbed panes the Code pane the Console pane and the Details pane The Console pane show the output from the process but since the output is also shown on the global Console window you may not need to display this pane The Details pane shows the contents of the process stack as well as the concurrency status of the process However since the concurrency status of all processes is displayed in the process table the Details pane is mainly useful if you are tracing the effect of PCode operations on the stack The Code pane is itself
7. from the subdirectories of jbaci compilers into the equivalent BACI subdirectories I do not have a Unix system at my disposal so the current distribution includes compilers for Windows only They were created using the MinGW soft ware http www mingw org batch files for building them can be found in the compilers directory 13 6 Release notes 1 4 5 1 4 4 1 4 3 1 4 2 1 4 1 1 4 0 1 3 4 1 3 3 1 3 2 Alternate syntax for Linda formal parameters Fix bugs in display of monitor variables and in display of process table when using monitors Signaling processes are given priority at monitor exit Fix bug when writing uninitialized variable a message is printed instead of throwing an uncaught exception There are now separate commands read cin for blocking read and nbread nbcin for non blocking read User interface changes accelerators are defined for all keys in the first three menus the Display button has been removed Fix bug postnote in Linda was waking only one blocked process Editor changed it is no longer a separate frame line numbers appear to the left of the text area if you modify the file an asterisk is displayed in the title border Font changed to Java standard Lucida Font sizes for source PCode and tables can be changed from the configuration file The location of the non blocking input option pane can be set in the configuration file Linda primitives implemented within the compilers and
8. g program you must select Edit or File Exit and then save the file before running the program again 4 Language extensions 4 1 Graphics The portable Java API has been used in sBACI to enable graphics routines to be used in concurrent programs This is useful in order to demonstrate synchronization in a game like environment The graphics facilities have been based on the shapes example from BlueJ http www bluej org which uses a single hidden Canvas upon which graphics figures are drawn Figure 3 ziaz File olor Program Options Window Help open Save Copy cut Paste Fina Find again Edit Compile Run Go Pause Step Source Step Pcode Processes FA Proces _Process Active Suspend CTT O graph false shoot true 2 movealien faise is Taa Figure 3 JBACI graphics canvas Each graphics figure is given a handle when it is created so that subsequent graphics commands can refer to that figure There are five procedures for drawing the figures e create handle figure color x y sizel size2 creates a graphics figure with the specified color location and size e changecolor handle color changes the color of the figure e makevisible handle flag displays or hides the figure according to the flag 1 or 0 e moveto handle x y moves the figure to a new position e moveby handle deltax deltay moves the figure relative to its current position All parameters are of type i
9. he correct compiler automatically The output of the BACI compiler is displayed in a popup frame which can be erased by pressing Enter If there are compilation errors the cursor will then be positioned at the beginning of the line with the first error 3 2 Running the program When a program has been successfully compiled select Run to enter the run state and begin program execution Figure 2 The only buttons enabled are those relevant to running the program R pasdow 100 wait Rept yl s pi w By signal Pelli Figure 2 JBACI run mode and the Edit button to return to the edit state Selecting Go will execute the program normally the execution can be halted by selecting Pause and restarted from the beginning by reselecting Run If Options Pause on Process Swap is selected the execution is automatically halted when a context switch between processes is done Step Source and Step PCode enable you to execute a single step of the program either a single step of source code or a single step of the PCode A source code step is defined by a single line in the source code file regardless of how many language statements appear on the line Writing several statements on a single line enables you to step over them quickly when they have no algorithmic importance like initialization statements Breakpoints can be set by clicking on a source code or PCode line in a process window see below and then selecting the Add button ab
10. interpreter Read in main program is blocking for normal I O PCode is not shown by default in process window you have to click the divider Windows are tiled not cascaded locations and sizes of windows can be set in configuration file A history file can be written as selected by a configuration file option History display and file does not display PCode if history of source steps selected Bugs fixed exception in display of suspend on condition in monitor exception if file name contains the substring line mistaken cross monitor call in the Pascal compiler and the interpreter array assignment did not work in Pascal Modifications Pascal compiler allows implicit cast between integer and char C compiler allows explicit casts int c and char i Additions Linda tuple space implemented as BACI source modules Bugs fixed cannot select window of main process run without compile caused exception For Pascal programs Globals windows redundantly shows the variables of main program History window shows source code lines and an option has been added to select whether to update the window after each source or PCode step Default file extensions remain pm and cm but other extensions are allowed Non blocking read Compatibility with previ ous simulator parbegin parend in addition to cobegin coend process in addition to procedure init 1 syntax for semaphore initialization in Pascal 14 1 3 1 Pascal compiler modifications a
11. nteger The encodings for the figures circle line rectangle triangle and colors red black blue yellow green magenta white are given by constants declared in the include files gdefs pm and gdefs cm These files as well as sample programs graph pm alien pm graph cm can be found in the directory examples The positions and sizes are in pixels the top left corner is 0 0 and the bottom right corner is 600 450 which can be changed in Config java The meaning of the location and size parameters for each figure is as follows Circle The location is the top left corner of the circumscribed square size1 is the diameter and size2 is ignored Triangle The location is the top vertex of an isosceles triangle size1 is the height and size2 is the width of the triangle Line The location pair and size pair are the endpoints of the line Rectangle The location is the top left corner size1 is the width and size2 is the height of the rectangle 4 2 Non blocking read In BACI input statements are blocking that is the entire program blocks waiting for the user to input a value While this is acceptable for entering initial values in the main process it is not representative of concurrent programs where an input statement should not block execution at all or at most block only the process containing that statement In the example alien pm input is used to launch blue and green missiles against a red alien spaceship which moves ac
12. ollowing description button names like Save will be used even when a menu entry like File Save also exists The IDE can be in one of two states the edit state and the run state Edit and Run change from one state to the other Buttons and menu entries are enabled and disabled accordingly In both states you can select File Exit and Hel p About 3 1 Editing and compiling Figure 1 shows the sBACI window when you are editing a source file The edit buffer contains the File Editor Program Options Window Help Open Save Copy Cut Paste Find Findagain st Compite Run So pavse step Source Step Pode C conway pm rogram Conway ar Bi BZ B3 integer Emptyl binarysem 1 Empty2 binarysem ty3 binarysem binarysem 2 binarysem 0 Pull3 banarysem procedure Producer ar R I integer R random 100 wnat Empty Bl R signal Fullt end end Producer procedure CheckEven ar N integer Figure 1 JBACI edit mode file conway pm and the only buttons enabled are those relevant to editing and compiling and the Run button to change to the run state The file and editing operations in the edit state are familiar Open New Save Save as Copy Cut Paste Find Find again Files are displayed in a text area and the usual editing keys can be used Source files must have the extension cm or pm for C and Pascal respectively This enables the Conpile operation to select t
13. or matching the values of a tuple to the current values of the parameters e If the equal sign appears after a variable the value of the note in that position must match the current value of that variable For example the following statements will remove any tuple of the form a 5 i2 5 removenote a i1 i2 e removenoteeq readnoteeq is like removenote readnote but the two parameters values of the note must match the current values of both variables For example the follow ing statements will remove only the tuple a 1 2 il 1 i2 2 removenoteeq a i1 i2 Note that removenoteeq a i1 i2 is equivalent to removenote a il i2 12 5 Software structure JBACI is a single Java package baci the main class baci gui Debugger is specified in the manifest file so that the software can be executed directly from the jar file The subpackages are event exception graphics gui gui actionbuttons gui treetable interpreter program Most of my modifications to Strite s code were to the GUI code in gui including the addition of the class Editor based in part on code by Michael Gratton The addition of the graphics facility led to the new subpackage graphics as well as to the addition of classes in program for the new graphics instructions To rebuild the IDE and interpreter simply execute build bat from the jbaci baci directory To rebuild the compilers first copy the files
14. ove the display of the code A red dot will appear in front of the line To remove a breakpoint click on the line and select Renove 3 3 Displays When executing a program the window below the toolbar is divided into two areas The size of the areas can be adjust by dragging the dividing bar with the mouse The left area contains the process table and the right area is used to display the system windows and the process windows 3 3 1 Process table The process table contains a line for each process giving the process number and name and the concurrency status for example if the process is Active and if it is Finished The field Suspended is non empty if the process is suspended on a semaphore a monitor entry or a monitor condition The field Monitor will display the monitor name if the process has entered a monitor procedure See the BACI documentation for the meaning of Priority and Atonic The next instruction to be executed will be from the process whose entry is highlighted You can change the highlighted entry by selecting Next or Previous or by clicking on the process table entry or the process window This will also display that the process window of the highlighted process if it is not already displayed 3 3 2 System windows There are four system windows e The Console window displays the output from the program this is in addition to the output from each process which is displayed in a pane of the process window
15. pplied to version which enables Boolean initializers and nested procedures 1 3 Configuration file is now a Java properties file clicking on process table entry or process window selects current process 1 2 Initial public release 15
16. veral systems a graphical user interface GUD exists only for Unix systems Recently David Strite of Penn State Harrisburg developed a new interpreter for the BACI virtual code that includes a GUI The interpreter http cs hbg psu edu null baci is written in Java and thus portable over all platforms JBACI is an integration of the original BACI compilers and Strite s interpreter into an IDE that contains an editor together with extensions to the GUI to simplify its use by novices In addition I have modified the compilers and interpreter to include commands for drawing graphics on a canvas this enables the student to write concurrent programs that are more fun than character based programs JBACI also supports Linda like synchronization primitives Cheap concurrent programming Software Practice and Experience 11 1981 1261 1264 2 Installation and execution The student distribution is in two zip files called jbaciN zip and jbaciNdocs zip where N is a version number The distribution contains the executable jar file and several directories compilers contains the exe files of the Pascal and C compilers docs contains documentation files and examples contains sample programs in both Pascal and C The zip file jbaciNsrc zip contains the directory baci with the Java source code as well as the directory compilers which contains files for rebuilding the compiler to accept the graphics commands You must have Java SDK or JRE Version
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