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Asked: 2026-05-28T15:28:41+00:00

I’ve been experimenting with difference between intrinsic locks and java.util.concurrent.ReentrantLock for some time now.

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I’ve been experimenting with difference between intrinsic locks and java.util.concurrent.ReentrantLock for some time now. I’ve found very strange thing. Consider following code:

public class WriteOnceRunAnywhere {

    private static long counter = 0;

    public static void main(String[] args) throws InterruptedException {

        final int numThreads = 2;
        final int numIterations = Integer.MAX_VALUE;

        Runnable inc = new Runnable() {
            public void run() {
                for (int i = 0; i < numIterations; i++) {

                    increment();

                    if (i % 10000000 == 0)
                        System.out.println(Thread.currentThread().getName());
                }
            }
        };

        for (int i = 0; i < numThreads; i++)
            new Thread(inc).start();
    }

    public static synchronized void increment() {
        counter++;
    }
}

Simple thing, no fancy stuff. Right? Happens to break!
Most likely when you run it, it won’t end. After some ping-pong between threads you’ll see
only one thread is actually running. The other hangs forever:

Thread-1 Thread-2 Thread-1 Thread-2 Thread-1 … Thread-2 Thread-2
Thread-2 Thread-2 Thread-2 Thread-2 Thread-2 Thread-2 Thread-2 …

After that, java process can’t accept jvisualvm connection. CPU load drops and continuously stays at about 1.0%.

Mac OS X Lion 10.7.2 (11C74), 2.53 GHz Intel Core i5

java version “1.6.0_29” Java(TM) SE Runtime Environment (build
1.6.0_29-b11-402-11M3527) Java HotSpot(TM) 64-Bit Server VM (build 20.4-b02-402, mixed mode)

Can someone tell me what the heck is happening here?

UPD Looks like the bug will be fixed in 1.6.30 see

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1 Answer

  1. Editorial Team

    Looks like you are observing an existing bug in Mac OS 7 JDK 1.6. You can see the same issue occurred here:

    http://cs.oswego.edu/pipermail/concurrency-interest/2012-January/008778.html

    You may want to read from the start at

    http://cs.oswego.edu/pipermail/concurrency-interest/2012-January/008759.html

    Finally there seems to be a resolution in for Open JDK 7.

    http://cs.oswego.edu/pipermail/concurrency-interest/2012-January/008789.html

    Long story short. It will only fail with JDK 1.6_14 (or greater < JDK 7) and Max OS 7. Their test and the results you are seeing are very similar.

    I am guessing you can’t even get a jstack or load jconsole?

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