pthread_rwlock_unlock( ) function shall release a lock held on the read-write lock objectreferenced by rwlock If this function is called to release a read lock from the read-write lock object and there are other read locks currently held on this read-write lock object, the read-write lock object remains in the read locked state. If this function releases the last read lock for this read-write lock object, the read-write lock object shall be put in the unlocked state with no owners. If this function is called to release a write lock for this read-write lock object, the read-write lock object shall be put in the unlocked state. If there are threads blocked on the lock when it becomes available, the scheduling policy shall determine which thread(s) shall acquire the lock. If the Thread Execution Scheduling option is supported, when threads executing with the scheduling policies SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC are waiting on the lock, they shall acquire the lock in priority order when the lock becomes available. For equal priority threads, write locks shall take precedence over read locks. If successful, the pthread_rwlock_unlock( ) function shall return zero; otherwise, an error number shall be returned to indicate the error. [EINVAL] rwlock doesn't refer to an initialized read-write lock [EPERM] the current thread doesn't hold the lock on the rwlock The pthread_rwlock_unlock( ) function shall not return an error code of [EINTR].