对 pthread_cond_wait 的困惑

Question

关于下面的代码，我的理解是线程1抢锁，检查条件，解锁时钟，将自己置为休眠状态。之后，线程 2 申请相同的锁和增量计数，然后唤醒休眠线程。我的问题是现在的条件还是false，但是唤醒了休眠的线程，会发生什么？而且条件变量是一组线程，那么如果有很多线程同时执行代码怎么办，wait()如何处理这种情况呢？最后请说明这段代码的正确执行顺序，非常感谢!!!

thread 1:
    pthread_mutex_lock(&mutex);
    while (!condition)
        pthread_cond_wait(&cond, &mutex);
    /* do something that requires holding the mutex and condition is true */
    pthread_mutex_unlock(&mutex);

thread2:
  while(1){
     pthread_mutex_lock(&mutex);
     count++;
     pthread_cond_signal(&cond);
     pthread_mutex_unlock(&mutex);
  }

Answer 1

My question is that the condition right now is still false, but it awakes the sleeping thread, what will happen?

这就是 pthread_cond_wait 在 while 循环中的原因。它仅在 pthread_cond_wait 解锁并且条件为真时才退出 while 循环。

这正是 pthread_cond_wait man page 的内容需要做笔记。

When using condition variables there is always a Boolean predicate involving shared variables associated with each condition wait that is true if the thread should proceed. Spurious wakeups from the pthread_cond_timedwait() or pthread_cond_wait() functions may occur. Since the return from pthread_cond_timedwait() or pthread_cond_wait() does not imply anything about the value of this predicate, the predicate should be re-evaluated upon such return.

(强调我的)。