pthread_cond_wait: random segmentation fault

Question

Update 3

recently, I noticed that my code randomly causes Segmentation Fault errors. But I think that my code is pretty simple so far and I cant figure out wh

Answer 1

pthread_cond_wait() is allowed to wake up spuriously, so you have to re-test the condition itself after every wakeup. This could be causing your problem - if the main thread wakes up spuriously before thread::terminated_thread_id has been set, it'll pass an invalid thread id to pthread_join().

There's also another problem in your code - there's no guarantee that the signalled thread will be the next to wake up after the mutex is unlocked, so it's possible for two threads to call thread::Exit() in quick succession, with the main thread not running until after the second exiting thread has unlocked the mutex. In this case you won't ever call pthread_join() on the first thread.

Something like this should fix those problems:

namespace thread {
    int terminate_thread_set = 0;
    pthread_mutex_t terminate_thread = PTHREAD_MUTEX_INITIALIZER;
    pthread_cond_t terminate_thread_set_cond = PTHREAD_COND_INITIALIZER;
    pthread_cond_t terminate_thread_unset_cond = PTHREAD_COND_INITIALIZER;

    /* ... */

    inline void Exit(void* value)
    {
        pthread_mutex_lock(&thread::terminate_thread);
        while (thread::terminate_thread_set)
            pthread_cond_wait(&thread::terminate_thread_unset_cond);
        thread::terminated_thread_id = pthread_self();
        thread::terminate_thread_set = 1;
        pthread_cond_signal(&thread::terminate_thread_set_cond);
        pthread_mutex_unlock(&thread::terminate_thread);

        pthread_exit(value);
    }
}

and in main:

pthread_mutex_lock(&thread::terminate_thread);

/* ... */

while(thread::total_thread_count > 0) {
    while (!thread::terminate_thread_set)
        pthread_cond_wait(&thread::terminate_thread_set_cond, &thread::terminate_thread);
    thread::terminate_thread_set = 0;
    pthread_join(thread::terminated_thread_id, NULL);
    pthread_cond_signal(&thread::terminate_thread_unset_cond);
...
}
pthread_mutex_unlock(&thread::terminate_thread);

That's not to say that you don't have other issues, of course.