The pthread_rwlock_wrlock() function applies 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 blocks (that is, does not return from the pthread_rwlock_wrlock() call) until it can acquire the lock. Results are undefined if the calling thread holds the read-write lock (whether a read or write lock) at the time the call is made.

Implementations are allowed to favor writers over readers to avoid writer starvation. The current implementation favors writers over readers.

The function pthread_rwlock_trywrlock() applies a write lock like the pthread_rwlock_wrlock() function, with the exception that the function fails if any thread currently holds rwlock (for reading or writing).

Results are undefined if any of these functions are called with an uninitialized read-write 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 returns 0. Otherwise, an error number is returned to indicate the error.

The function pthread_rwlock_trywrlock() returns 0 if the lock for writing on the read-write lock object referenced by rwlock is acquired. Otherwise an error number is returned to indicate the error.

The pthread_rwlock_trywrlock() function will fail if:

EBUSY

The read-write lock could not be acquired for writing because it was already locked for reading or writing.

See attributes(5) for descriptions of the following attributes:

pthread_rwlock_init(3THR), pthread_rwlock_unlock(3THR), pthread_rwlockattr_init(3THR), pthread_rwlock_rdlock(3THR), attributes(5)