The function int pthread_mutex_lock(pthread_mutex_t *mutex); locks the mutex object referenced by 'mutex'. If the mutex is already locked, the calling thread shall block until the mutex becomes available. This operation returns with the mutex object referenced by 'mutex' in the locked state with the calling thread as its owner. Upon success, it returns 0. 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. It may fail if: -[EINVAL] 'mutex' does not refer to an initialized mutex object -[EDEADLK] The current thread already owns the mutex It shall not return [EINTR]. If the mutex type is PTHREAD_MUTEX_RECURSIVE, the mutex shall maintain the concept of a lock count If a signal is delivered to a thread waiting for a mutex, when return from the signal handler the thread shall resume waiting.