pthread_cond_wait will relock the mutex

于 2011-05-05 18:04:57 发布 · 97 阅读

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本文详细介绍了如何使用条件变量来同步线程。通过传递互斥锁给pthread_cond_wait函数，可以确保原子地将调用线程放入等待条件变化的线程列表，并解锁互斥锁。这样避免了检查条件和进入睡眠状态之间的窗口期问题，确保线程不会错过条件的变化。当pthread_cond_wait返回时，互斥锁再次被锁定。

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Quoting APUE2:

The mutex passed to pthread_cond_wait protects the condition. The caller passes it locked to the function, which then atomically places the calling thread on the list of threads waiting for the condition and unlocks the mutex. This closes the window between the time that the condition is checked and the time that the thread goes to sleep waiting for the condition to change, so that the thread doesn't miss a change in the condition. When pthread_cond_wait returns, the mutex is again locked.