PTHREAD_RWLOCK_UNLOCK(3C) Standard C Library Functions

NAME

pthread_rwlock_unlock - unlock read-write lock object

SYNOPSIS

cc -mt [ flag... ] file... -lpthread [ library... ]
#include <pthread.h>

int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);

DESCRIPTION

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
uninitialized read-write lock.

RETURN VALUES

If successful, the pthread_rwlock_unlock() function returns 0.
Otherwise, an error number is returned to indicate the error.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

pthread_rwlock_init(3C), pthread_rwlock_rdlock(3C),
pthread_rwlock_wrlock(3C), pthread_rwlockattr_init(3C), attributes(7),
standards(7)


March 23, 2005 PTHREAD_RWLOCK_UNLOCK(3C)