PTHREAD_RWLOCK_UNLOCK(P) POSIX Programmer's Manual PTHREAD_RWLOCK_UNLOCK(P)
pthread_rwlock_unlock - unlock a read-write lock object
int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
The pthread_rwlock_unlock() function shall 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 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 Sched-
uling 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 prior-
ity order when the lock becomes available. For equal priority threads, write locks shall
take precedence over read locks. If the Thread Execution Scheduling option is not sup-
ported, it is implementation-defined whether write locks take precedence over read locks.
Results are undefined if any of these functions are called with an uninitialized read-
If successful, the pthread_rwlock_unlock() function shall return zero; otherwise, an error
number shall be returned to indicate the error.
The pthread_rwlock_unlock() function may fail if:
EINVAL The value specified by rwlock does not refer to an initialized read-write lock
EPERM The current thread does not hold a lock on the read-write lock.
The pthread_rwlock_unlock() function shall not return an error code of [EINTR].
The following sections are informative.
pthread_rwlock_destroy() , pthread_rwlock_rdlock() , pthread_rwlock_timedrdlock() ,
pthread_rwlock_timedwrlock() , pthread_rwlock_tryrdlock() , pthread_rwlock_trywrlock() ,
pthread_rwlock_wrlock() , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 PTHREAD_RWLOCK_UNLOCK(P)