Java Pathfinder

The following system under test contains a simple race condition between two threads accessing the same variable d in statements (1) and (2), which can lead to a division by zero exception if (1) is executed before (2)

public class Racer implements Runnable {
     int d = 42;

     public void run () {
          doSomething(1001);
          d = 0;                              // (1)
     }

     public static void main (String[] args){
          Racer racer = new Racer();
          Thread t = new Thread(racer);
          t.start();

          doSomething(1000);
          int c = 420 / racer.d;              // (2)
          System.out.println(c);
     }
     
     static void doSomething (int n) {
          try { Thread.sleep(n); } catch (InterruptedException ix) {}
     }
}

Without any additional configuration, JPF would find and report the division by zero. If JPF is configured to verify absence of race conditions (regardless of their potential downstream effects), it will produce the following output, explaining the error and showing a counter example leading to the error

JavaPathfinder v6.0 - (C) RIACS/NASA Ames Research Center
====================================================== system under test
application: Racer.java
...
====================================================== error #1
gov.nasa.jpf.listener.PreciseRaceDetector
race for field Racer@13d.d
  main at Racer.main(Racer.java:16)
		"int c = 420 / racer.d;               "  : getfield
  Thread-0 at Racer.run(Racer.java:7)
		"d = 0;                               "  : putfield

====================================================== trace #1
---- transition #0 thread: 0
...
---- transition #3 thread: 1
gov.nasa.jpf.jvm.choice.ThreadChoiceFromSet[id="sleep",isCascaded:false,{main,>Thread-0}]
      [3 insn w/o sources]
  Racer.java:22                  : try { Thread.sleep(n); } catch (InterruptedException ix) {}
  Racer.java:23                  : }
  Racer.java:7                   : d = 0;                      
...
---- transition #5 thread: 0
gov.nasa.jpf.jvm.choice.ThreadChoiceFromSet[id="sharedField",isCascaded:false,{>main,Thread-0}]
  Racer.java:16                  : int c = 420 / racer.d;

JPF is an open system that can be extended in a variety of ways. The main extension constructs are

• listeners - to implement complex properties (e.g. temporal properties)
• peer classes - to execute code at the host JVM level (instead of JPF), which is mostly used to implement native methods
• bytecode factories - to provide alternative execution semantics of bytecode instructions (e.g. to implement symbolic execution)
• choice generators - to implement state space branches such as scheduling choices or data value sets
• serializers - to implement program state abstractions
• publishers - to produce different output formats
• search policies - to use different program state space traversal algorithms

JPF includes a runtime module system to package such constructs into separate JPF extension projects. A number of such projects are available from the main JPF server, including a symbolic execution mode, numeric analysis, race condition detection for relaxed memory models, user interface model checking and many more.

• JPF cannot analyze Java native methods. If the system under test calls such methods, these have to be provided within peer classes, or intercepted by listeners
• as a model checker, JPF is susceptible to Combinatorial explosion, although it performs on-the-fly Partial order reduction
• the configuration system for JPF modules and runtime options can be complex

• MoonWalker - similar to Java PathFinder, but for .NET programs instead of Java programs

• New NASA Software Detects 'Bugs' in Java Computer Code
• NASA Develops New Software to Detect "Bugs" in Java Computer Code

• Willem Visser, Corina S. Păsăreanu, Sarfraz Khurshid. Test Input Generation with Java PathFinder. In: George S. Avrunin, Gregg Rothermel (Eds.): Proceedings of the ACM/SIGSOFT International Symposium on Software Testing and Analysis 2004. ACM Press, 2004. ISBN 1-58113-820-2.
• Willem Visser, Klaus Havelund, Guillaume Brat, Seungjoon Park, Flavio Lerda, Model Checking Programs, Automated Software Engineering 10(2), 2003.
• Klaus Havelund, Willem Visser, Program Model Checking as a New Trend, STTT 4(1), 2002.
• Klaus Havelund, Thomas Pressburger, Model Checking Java Programs using Java PathFinder, STTT 2(4), 2000.