FULL PRODUCT VERSION :
java version "1.6.0_14"
Java(TM) SE Runtime Environment (build 1.6.0_14-b08)
Java HotSpot(TM) Server VM (build 14.0-b16, mixed mode)


FULL OS VERSION :
SunOS desb0028.nyc.deshaw.com 5.10 127128-11 i86pc i386 i86pc


A DESCRIPTION OF THE PROBLEM :
The JIT compile kicks in and compiles the method ensureProperCallingThread() below into a version that null pointers. This should never happen, and the JIT is producing incorrect code.

If you compile this bug on Solaris 10, and then run with:

java -d64 -XX:CompileThreshold=100 JITBug



THE PROBLEM WAS REPRODUCIBLE WITH -Xint FLAG: No

THE PROBLEM WAS REPRODUCIBLE WITH -server FLAG: Yes

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See description

EXPECTED VERSUS ACTUAL BEHAVIOR :
Should not compile this code in such a way that it null pointers.
ERROR MESSAGES/STACK TRACES THAT OCCUR :

Eventually (may take a few runs) you will get this error:
Starting thread: 0
Starting thread: 1
Starting thread: 2
Exception in thread "Runner: 2" java.lang.NullPointerException
        at JITBug.ensureProperCallingThread(JITBug.java:99)
        at JITBug.run(JITBug.java:87)
        at java.lang.Thread.run(Thread.java:619)
Starting thread: 3
Exception in thread "Runner: 3" java.lang.NullPointerException
        at JITBug.ensureProperCallingThread(JITBug.java:99)
        at JITBug.run(JITBug.java:87)
        at java.lang.Thread.run(Thread.java:619)
Starting thread: 4
Exception in thread "Runner: 4" java.lang.NullPointerException
        at JITBug.ensureProperCallingThread(JITBug.java:99)
        at JITBug.run(JITBug.java:87)
        at java.lang.Thread.run(Thread.java:619)



REPRODUCIBILITY :
This bug can be reproduced often.

---------- BEGIN SOURCE ----------

/**
 * Highlights a bug with the JIT compiler.
 * @author Matt Bruce m b r u c e __\at/__ g m a i l DOT c o m
 */
public class JITBug implements Runnable
{
    private final Thread myThread;
    private Thread myInitialThread;
    private boolean myShouldCheckThreads;

    /**
     * Sets up the running thread, and starts it.
     */
    public JITBug(int id)
    {
        myThread = new Thread(this);
        myThread.setName("Runner: " + id);
        myThread.start();
        myShouldCheckThreads = false;
    }

    /**
     * @param shouldCheckThreads the shouldCheckThreads to set
     */
    public void setShouldCheckThreads(boolean shouldCheckThreads)
    {
        myShouldCheckThreads = shouldCheckThreads;
    }

    /**
     * Starts up the two threads with enough delay between them for JIT to
     * kick in.
     * @param args
     * @throws InterruptedException
     */
    public static void main(String[] args) throws InterruptedException
    {
        // let this run for a bit, so the "run" below is JITTed.
        for (int id = 0; id < 20; id++) {
            System.out.println("Starting thread: " + id);
            JITBug bug = new JITBug(id);
            bug.setShouldCheckThreads(true);
            Thread.sleep(2500);
        }
    }

    /**
     * @see java.lang.Runnable#run()
     */
    @Override
    public void run()
    {
        long runNumber = 0;
        while (true) {
            // run hot for a little while, give JIT time to kick in to this loop.
            // then run less hot.
            if (runNumber > 15000) {
                try {
                    Thread.sleep(5);
                }
                catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            runNumber++;
            ensureProperCallingThread();
        }
    }

    private void ensureProperCallingThread()
    {
        // this should never be null. but with the JIT bug, it will be.
        // JIT BUG IS HERE ==>>>>>
        if (myShouldCheckThreads) {
            if (myInitialThread == null) {
                myInitialThread = Thread.currentThread();
            }
            else if (myInitialThread != Thread.currentThread()) {
                System.out.println("Not working: " + myInitialThread.getName());
            }
        }
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Change compile threshold and ensure that the code is JIT compiled only after at least two threads have used the code.