The function int pthread_mutex_trylock(pthread_mutex_t *mutex); is equivalent to pthread_mutex_lock() except that if the mutex object referenced by 'mutex' is currently locked (by any thread, including the current thread), the call returns immediately. If the mutex type is PTHREAD_MUTEX_RECURSIVE and the mutex is currently owned by the calling thread, the mutex lock count shall be incremented by one and the pthread_mutex_trylock() function immediately returns success. It returns 0 if a lock on the mutex object referenced by 'mutex' is acquired. Upon failure, it shall return: -[EINVAL] The mutex was created with the protocol attribute PTHREAD_PRIO_PROTECT and the calling thread's priority is higher than the mutex's current priority calling. -[EBUSY] The mutex could not be acquired because it was already locked. It may fail if: -[EINVAL] 'mutex' does not refer to an initialized mutex object It shall not return [EINTR].