c - pthread_join() 在压力测试中挂起

Question

我正在运行一个 phread 测试程序，直到它失败。这是代码的主要框架:

int authSessionListMutexUnlock()
{
    int rc = 0;
    int rc2 = 0;

    rc2 = pthread_mutex_trylock(&mutex);
    ERR_IF( rc2 != EBUSY && rc2 != 0 );

    rc2 = pthread_mutex_unlock(&mutex);
    ERR_IF( rc2 != 0 );

    cleanup:

    return rc;  
}

static void cleanup_handler(void *arg)
{
    int rc = 0;

    (void)arg;

    rc = authSessionListMutexUnlock();
    if (rc != 0)
        AUTH_DEBUG5("authSessionListMutexUnlock() failed\n");
}


static void *destroy_expired_sessions(void *t)
{
    int rc2 = 0;

    (void)t;

    pthread_cleanup_push(cleanup_handler, NULL);

    rc2 = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
    if (rc2 != 0)
        AUTH_DEBUG5("pthread_setcancelstate(): rc2 == %d\n", rc2);

    rc2 = pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
    if (rc2 != 0)
        AUTH_DEBUG5("pthread_setcanceltype(): rc2 == %d\n", rc2);

    while (1)
    {
        ... // destroy expired session
        sleep(min_timeout);
    }
    pthread_cleanup_pop(0);
}

int authDeinit( char *path )
{
    ...
    rc2 = authSessionListDeInit();
    ERR_IF( rc2 != 0 );

    rc2 = pthread_cancel(destroy_thread);
    ERR_IF( rc2 != 0 );

    rc2 = pthread_join(destroy_thread, &status);
    ERR_IF( rc2 != 0 || (int *)status != PTHREAD_CANCELED );

    ...
    return 0
}

它在测试程序中运行良好，但测试程序在第 53743 轮与 pthread_join() 挂起:

(gdb) bt
#0  0x40000410 in __kernel_vsyscall ()
#1  0x0094aa77 in pthread_join () from /lib/libpthread.so.0
#2  0x08085745 in authDeinit ()
    at /users/qixu/src/moja/auth/src//app/libauth/authAPI.c:1562
#3  0x0807e747 in main ()
    at /users/qixu/src/moja/auth/src//app/tests/test_session.c:45

看起来 pthread_join() 导致了死锁。但是看代码，感觉死锁没有理由是pthread_join()造成的。当 pthread_join() 有机会运行时，唯一的互斥操作是线程本身。应该没有冲突吧？真的很困惑...

Answer 1

你的代码中至少有一个“奇怪”的地方；您的清理处理程序将始终解锁互斥量 ，即使您不是持有它的线程也是如此。

来自手册；

Calling pthread_mutex_unlock() with a mutex that the calling thread does not hold will result in undefined behavior.