关于 pthread_cond_signal 和 pthread_cond_wait

我有以下问题pthread_cond_信号 and pthread_cond_wait。例如，在下面的代码中，根据我的理解，当增量计数 calls pthread_cond_信号, 计数 += 125 in 观看次数只能在之后执行计数互斥体已解锁于增量计数.

The 计数互斥体被解锁于观看次数 when pthread_cond_wait执行并仅在之后被锁定pthread_mutex_unlock in 增量计数被执行。我对吗？

void *inc_count(void *t) 
{
    int i;
    long my_id = (long)t;

    for (i = 0; i < TCOUNT; i++) 
    {
        pthread_mutex_lock(&count_mutex);
        count++;

        if (count == COUNT_LIMIT) 
        {
            pthread_cond_signal(&count_threshold_cv);
        }

        pthread_mutex_unlock(&count_mutex);
    }

    pthread_exit(NULL);
}

void *watch_count(void *t) 
{
    long my_id = (long)t;

    pthread_mutex_lock(&count_mutex);
    while (count < COUNT_LIMIT)
    {
        pthread_cond_wait(&count_threshold_cv, &count_mutex);
        count += 125;
    }

    pthread_mutex_unlock(&count_mutex);
    pthread_exit(NULL);
}

pthread_cond_wait()在进入时解锁互斥体并在退出时再次锁定它。如果另一个线程在此期间获取了锁，pthread_cond_wait()在其他线程释放锁之前无法返回。

So, if watch_count()被封锁在pthread_cond_wait(), and inc_count()运行和调用pthread_cond_signal(), then watch_count()不会返回pthread_cond_wait() until inc_count()已致电pthread_mutex_unlock().

然而，pthread_cond_wait()即使没有发出信号也可以唤醒。这称为虚假唤醒。watch_count()因此可以执行count+=125很多时候，即使inc_count()从不运行，或从不调用pthread_cond_signal().