POSIX Conditions

****POSIX**** 条件锁需要互斥锁和条件两项来实现，虽然看起来没什么关系，但在运行时中，互斥锁将会与条件结合起来。线程将被一个互斥和条件结合的信号来唤醒。

首先初始化条件和互斥锁，当 ****ready_to_go**** 为 ****flase**** 的时候，进入循环，然后线程将会被挂起，直到另一个线程将 ****ready_to_go**** 设置为 ****true**** 的时候，并且发送信号的时候，该线程会才被唤醒。

pthread_mutex_t mutex;
pthread_cond_t condition;
Boolean     ready_to_go = true;

void MyCondInitFunction()
{
    pthread_mutex_init(&mutex);
    pthread_cond_init(&condition, NULL);
}

void MyWaitOnConditionFunction()
{
    // Lock the mutex.
    pthread_mutex_lock(&mutex);

    // If the predicate is already set, then the while loop is bypassed;
    // otherwise, the thread sleeps until the predicate is set.
    while(ready_to_go == false)
    {
        pthread_cond_wait(&condition, &mutex);
    }

    // Do work. (The mutex should stay locked.)

    // Reset the predicate and release the mutex.
    ready_to_go = false;
    pthread_mutex_unlock(&mutex);
}

void SignalThreadUsingCondition()
{
    // At this point, there should be work for the other thread to do.
    pthread_mutex_lock(&mutex);
    ready_to_go = true;

    // Signal the other thread to begin work.
    pthread_cond_signal(&condition);

    pthread_mutex_unlock(&mutex);
}