pthread_rwlock_unlock Subroutine

Purpose

Unlocks a read-write lock object.

Library

Threads Library (libthreads.a)

Syntax

#include <pthread.h>

int pthread_rwlock_unlock (rwlock)
pthread_rwlock_t *rwlock;

Description

The pthread_rwlock_unlock subroutine is called to release a lock held on the read-write lock object referenced by rwlock. Results are undefined if the read-write lock rwlock is not held by the calling thread.

If this subroutine 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 subroutine releases the calling thread's last read lock on this read-write lock object, then the calling thread is no longer one of the owners of the object. If this subroutine releases the last read lock for this read-write lock object, the read-write lock object will be put in the unlocked state with no owners.

If this subroutine is called to release a write lock for this read-write lock object, the read-write lock object will be put in the unlocked state with no owners.

If the call to the pthread_rwlock_unlock subroutine results in the read-write lock object becoming unlocked and there are multiple threads waiting to acquire the read-write lock object for writing, the scheduling policy is used to determine which thread acquires the read-write lock object for writing. If there are multiple threads waiting to acquire the read-write lock object for reading, the scheduling policy is used to determine the order in which the waiting threads acquire the read-write lock object for reading. If there are multiple threads blocked on rwlock for both read locks and write locks, it is unspecified whether the readers acquire the lock first or whether a writer acquires the lock first.

Results are undefined if any of these subroutines are called with an uninitialized read-write lock.

Parameters

Return Values

If successful, the pthread_rwlock_unlock subroutine returns zero. Otherwise, an error number is returned to indicate the error.

Error Codes

The pthread_rwlock_unlock subroutine may fail if: