x265多線程-event

x265中的event類模擬生產者消費者模型
生產者生產臨界資源，並通過條件變量通知消費者
消費者消耗臨界資源，若無臨界資源則被阻塞等待生產者生產臨界資源

/*
	模擬生產者消費者模型
*/
class Event
{
public:

	// 構造函數，初始化信號量m_counter = 0，初始化互斥量m_mutex和條件變量m_cond
    Event()
    {
        m_counter = 0;
        if (pthread_mutex_init(&m_mutex, NULL) ||
            pthread_cond_init(&m_cond, NULL))
        {
            x265_log(NULL, X265_LOG_ERROR, "fatal: unable to initialize conditional variable\n");
        }
    }

	// 析構銷燬互斥量m_mutex和條件變量m_cond
    ~Event()
    {
        pthread_cond_destroy(&m_cond);
        pthread_mutex_destroy(&m_mutex);
    }

	// 消費者：消耗一個資源，若資源數 = 0，則被阻塞，等待生產者生產資源
    void wait()
    {
        pthread_mutex_lock(&m_mutex);

        /* blocking wait on conditional variable, mutex is atomically released
         * while blocked. When condition is signaled, mutex is re-acquired */
        while (!m_counter)
            pthread_cond_wait(&m_cond, &m_mutex);

        m_counter--;
        pthread_mutex_unlock(&m_mutex);
    }

	// 生產者：生產一個資源，並通過條件變量m_cond通知因資源不夠而被阻塞的消費者
    void trigger()
    {
        pthread_mutex_lock(&m_mutex);
        if (m_counter < UINT_MAX)
            m_counter++;
        /* Signal a single blocking thread */
        pthread_cond_signal(&m_cond);
        pthread_mutex_unlock(&m_mutex);
    }

	// 消費者：最多等待waitms毫秒，若在waitms毫秒內等到了資源則消耗它，
	// 若沒有等到則返回超時
	bool timedWait(uint32_t waitms)
	{
		bool bTimedOut = false;

		pthread_mutex_lock(&m_mutex);
		if (!m_counter)
		{
			// 基於waitms構造時間ts
			struct timeval tv;
			struct timespec ts;
			gettimeofday(&tv, NULL);
			/* convert current time from (sec, usec) to (sec, nsec) */
			ts.tv_sec = tv.tv_sec;
			ts.tv_nsec = tv.tv_usec * 1000;

			ts.tv_nsec += 1000 * 1000 * (waitms % 1000);    /* add ms to tv_nsec */
			ts.tv_sec += ts.tv_nsec / (1000 * 1000 * 1000); /* overflow tv_nsec */
			ts.tv_nsec %= (1000 * 1000 * 1000);             /* clamp tv_nsec */
			ts.tv_sec += waitms / 1000;                     /* add seconds */

															/* blocking wait on conditional variable, mutex is atomically released
															* while blocked. When condition is signaled, mutex is re-acquired.
															* ts is absolute time to stop waiting */
			// 最多等待ts時間，直到生產者signal或超時，返回是否超時
			bTimedOut = pthread_cond_timedwait(&m_cond, &m_mutex, &ts) == ETIMEDOUT;
		}
		// 若有資源則進行消耗
		if (m_counter > 0)
		{
			m_counter--;
			bTimedOut = false;
		}
		pthread_mutex_unlock(&m_mutex);
		return bTimedOut;
	}

protected:

    pthread_mutex_t m_mutex;	// 互斥鎖
    pthread_cond_t  m_cond;		// 條件變量
    uint32_t        m_counter;	// 信號量
};