hang in Lion

[Charles K Pepperdine]

Hi,

I've got a chunk of code that mysteriously hangs on my new i7 Air running Lion. This code was given to me by a friend that is also running Lion. We've given it to another person that is also running Lion. I'm using 1.6.0_26-b02-383. It doesn't hang all the time and it doesn't hang on my older i7 17" MBP running Snow Leopard. It's also been tested on other MBP's running Snow Leopard without hanging. Forcing a core dump after the hang gave us this.

> Thread 24:  Java: Thread-1
> 0   libSystem.B.dylib             	0x00007fff89f88d7a mach_msg_trap + 10
> 1   libSystem.B.dylib             	0x00007fff89f893ed mach_msg + 59
> 2   libclient64.dylib             	0x000000010100d903 jio_snprintf + 37641
> 3   libclient64.dylib             	0x000000010100d7c3 jio_snprintf + 37321
> 4   libclient64.dylib             	0x000000010100d722 jio_snprintf + 37160
> 5   libclient64.dylib             	0x000000010100c5ad jio_snprintf + 32691
> 6   libclient64.dylib             	0x000000010100c4ef jio_snprintf + 32501
> 7   libclient64.dylib             	0x00000001011afefd JVM_GetClassInterfaces + 12075
> 8   libclient64.dylib             	0x00000001010a7c8c JVM_Lseek + 204251
> 9   libclient64.dylib             	0x00000001010a7bea JVM_Lseek + 204089
> 10  libclient64.dylib             	0x00000001011b4931 JVM_Socket + 5319
> 11  ???                           	0x000000010380f0e7 0 + 4353749223
> 12  ???                           	0x000000010386fd90 0 + 4354145680
> 
> Thread 25:  Java: Thread-2
> 0   libSystem.B.dylib             	0x00007fff89f88d7a mach_msg_trap + 10
> 1   libSystem.B.dylib             	0x00007fff89f893ed mach_msg + 59
> 2   libclient64.dylib             	0x000000010100db03 jio_snprintf + 38153
> 3   libclient64.dylib             	0x00000001010cb569 JVM_Write + 9130
> 4   libclient64.dylib             	0x00000001011ddfcd JVM_NanoTime + 39179
> 5   ???                           	0x000000010386ea60 0 + 4354140768

All of the other thread could be attributed to VM processes (GC, compiler etc...).

On my machine, the hang seems to only happen when thread-2 finishes before thread-1. I've never seen it hang when thread-1 finishes before thread-2 Again it doesn't hang all the time when thread-2 finishes first. This is a hard hang in that I can only get rid of the process with a kill -9. ^C and kill simply don't to anything.

Code follows,

Regards,
Kirk Pepperdine

public class Foo {

    private int counter;

    public static void main(String[] args) throws Exception {
        new Foo().run();
    }

    public void run() throws Exception {

        Thread[] threads = new Thread[2];

        for (int i = 0; i < threads.length; i++) {
            threads[i] = new Thread() {
                public void run() {

                    System.out.println("Thread started " + Thread.currentThread().getName());
                    System.out.flush();

                    for (int i = 0; i < 100000; i++) {
                        increment();
                    }

                    System.out.println("Thread done " + Thread.currentThread().getName());
                    System.out.flush();
                }
            };
        }

        for (Thread t : threads) {
            t.start();
        }

        System.out.println("Started");
        System.out.flush();

        System.out.println("Awaiting complete...");
        System.out.flush();

        for (Thread t : threads) {
            t.join();
        }

        System.out.println("Completed...");
        System.out.flush();
    }

    private synchronized void increment() {

        counter++;

        if (counter % 10000 == 0) {
            System.out.printf("%s: %d\n", Thread.currentThread().getName(), counter);
            System.out.flush();
        }
    }
}