pthread_rwlock_wrlock( ) function shall apply a write lock to the read-write lock referenced by rwlock. The calling thread acquires the write lock if no other thread (reader or writer) holds the read-write lock rwlock. Otherwise, the thread shall block until it can acquire the lock If a signal is delivered to a thread waiting for a read-write lock for writing, upon return from the signal handler the thread resumes waiting for the read-write lock for writing as if it was not interrupted. If successful, the pthread_rwlock_wrlock( ) function shall return zero; otherwise, an error number shall be returned to indicate the error. It may fail if: [EDEADLK] The current thread already owns the rwlock for writing or reading. Shall not return an error code of [EINTR].