C中互斥锁返回的顺序

Question

Lets say there are 3 threads A, B and C. And a mutex X

A calls pthread_mutex_lock on X.

B calls pthread_mutex_lock on X.

*

C calls pthread_mutex_lock on X.

A calls pthread_mutex_unlock on X.

**

Who will now be able to use the shared resource first? B or C? And what happens if I try to use pthread_destroy_mutex in *? in **?

Answer 1

Who will now be able to use the shared resource first?

That depends on the kernel scheduler implementation. Posix words it this way:

If there are threads blocked on the mutex object referenced by mutex when pthread_mutex_unlock() is called, resulting in the mutex becoming available, the scheduling policy shall determine which thread shall acquire the mutex.

And what happens if I try to use pthread_destroy_mutex in *? in **?

Again from the manual :

Attempting to destroy a locked mutex results in undefined behavior.

If you have any further doubts along these lines then suggest consulting the relevant man pages.