pthread_mutex_unlock() returns 1

[anhpnt]

When I use pthread_mutex_u nlock(), it returns value 1, which means EPERM or 'Operation not permitted'. The strange thing is it happens when my program have been executed for a while.
I have searched the solution, and some results say that something is wrong with memory.
Any suggestion?

[RRick]

Actually, EPERM means that the thread does not own the mutex. In particular:

The pthread_mutex_u nlock() function unlocks the mutex specified. If the calling thread does not currently hold the mutex (via a previous call to pthread_mutex_l ock(), pthread_mutex_t rylock(), or pthread_mutex_t imedlock_np()) the unlock request fails with the EPERM error.