互斥锁是linux下多线程资源保护的常用手段,但是在时序复杂的情况下,很容易会出现死锁的情况。
可以通过设置锁的属性,避免同一条线程重复上锁导致死锁的问题。
通过int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type)接口设置
一般是以下四种属性:
pthread_mutex_normal this type of mutex does not detect deadlock. a thread attempting to relock this mutex without first unlocking it will deadlock. attempting to unlock a mutex locked by a different thread results in undefined behaviour. attempting to unlock an unlocked mutex results in undefined behaviour. pthread_mutex_errorcheck this type of mutex provides error checking. a thread attempting to relock this mutex without first unlocking it will return with an error. a thread attempting to unlock a mutex which another thread has locked will return with an error. a thread attempting to unlock an unlocked mutex will return with an error. pthread_mutex_recursive a thread attempting to relock this mutex without first unlocking it will succeed in locking the mutex. the relocking deadlock which can occur with mutexes of type pthread_mutex_normal cannot occur with this type of mutex. multiple locks of this mutex require the same number of unlocks to release the mutex before another thread can acquire the mutex. a thread attempting to unlock a mutex which another thread has locked will return with an error. a thread attempting to unlock an unlocked mutex will return with an error. pthread_mutex_default attempting to recursively lock a mutex of this type results in undefined behaviour. attempting to unlock a mutex of this type which was not locked by the calling thread results in undefined behaviour. attempting to unlock a mutex of this type which is not locked results in undefined behaviour. an implementation is allowed to map this mutex to one of the other mutex types.
这里主要指同一条线程重复上锁,不同线程上锁,无论设置什么属性,当锁已经被锁定后都会互斥阻塞。
使用pthread_mutex_recursive属性,当同一条线程在没有解锁的情况下尝试再次锁定会返回成功。
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