Unlocks a read-write lock object.
Threads Library (libthreads.a)
#include <pthread.h>
int pthread_rwlock_unlock (pthread_rwlock_t *rwlock);
The pthread_rwlock_unlock function 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 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 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 function 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 function 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 function 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 functions are called with an uninitialised read-write lock.
If successful, the pthread_rwlock_unlock function returns zero. Otherwise, an error number is returned to indicate the error.
The pthread_rwlock_unlock function will fail if:
| EINVAL | The value specified by rwlock does not refer to an initialised read-write lock object. |
| EPERM | The current thread does not own the read-write lock. |
Similar functions are being developed by IEEE PASC. In keeping with its objective of ensuring that CAE Specifications are fully aligned with formal standards, The Open Group intends to add any new interfaces adopted by an official IEEE standard in this area.
The pthread.h file.
The pthread_rwlock_init (pthread_rwlock_init, pthread_rwlock_destroy Subroutine), pthread_rwlock_wrlock (pthread_rwlock_wrlock or pthread_rwlock_trywrlock Subroutines), pthread_rwlockattr_init (pthread_rwlockattr_init or pthread_rwlockattr_destroy Subroutines), pthread_rwlock_rdlock (pthread_rwlock_rdlock or pthread_rwlock_tryrdlock Subroutines) subroutines.