条件变量的陷阱，惊群效应（转载）

转自：http://originlee.com/2015/01/21/trick-in-conditon-variable/

class ConditionBase
{
public:
    ConditionBase()
    {
        pthread_mutex_init(&mutex_, NULL);
        pthread_cond_init(&cond_, NULL);
    }

    ~ConditionBase()
    {
        pthread_mutex_destroy(&mutex_);
        pthread_cond_destroy(&cond_);
    }

private:
    pthread_mutex_t  mutex_;
    pthread_cond_t   cond_;
};
class Condition4 : public ConditionBase
{
public:
    Condition4()
        : signal_(false)
    {
    }

    void wait()
    {
        pthread_mutex_lock(&mutex_);
        while (!signal_)
        {
            pthread_cond_wait(&cond_, &mutex_);
        }
        signal_ = false;
        pthread_mutex_unlock(&mutex_);
    }

    void wakeup()
    {
        pthread_mutex_lock(&mutex_);
        signal_ = true;
        pthread_cond_signal(&cond_);
        pthread_mutex_unlock(&mutex_);
    }

private:
    bool signal_;
};

附录：惊群效应

https://blog.csdn.net/lyztyycode/article/details/78648798