pthread_cond_wait

The pthread_cond_wait() and pthread_cond_timedwait() functions are used to block on a condition variable. They are called with mutex locked by the calling thread or undefined behaviour will result.

These functions atomically release mutex and cause the calling thread to block on the condition variable cond ; atomically here means "atomically with respect to access by another thread to the mutex and then the condition variable". That is, if another thread is able to acquire the mutex after the about-to-block thread has released it, then a subsequent call topthread_cond_signal() or pthread_cond_broadcast() in that thread behaves as if it were issued after the about-to-block thread has blocked.

 

(进入wait状态就unclock，在wait结束前lock)

pthread_cond_wait()函数一进入wait状态就会自动release mutex，一旦wait成功获得cond 条件的时候会 lock mutex.

T1:

pthread_mutex_lock(&mutex);   
pthread_cond_wait(&cond,&mutex);   
pthread_mutex_unlock(&mutex);  

T2:

pthread_mutex_lock(&mutex);   
pthread_cond_signal(&cond);   
pthread_mutex_unlock(&mutex)