pthread_rwlock_unlock(3pthread)
pthread_rwlock_unlock --
release a read-write lock
Synopsis
cc [options] -Kthread file
#include <pthread.h>
int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
Description
pthread_rwlock_unlock releases a reader-writer lock
previously acquired by pthread_rwlock_rdlock,
pthread_rwlock_wrlock, pthread_rwlock_tryrdlock,
or pthread_rwlock_trywrlock.
The behavior differs according to whether the caller
is a reader or a writer:
-
When a writer calls pthread_rwlock_unlock,
the lock is unlocked.
-
When a reader calls pthread_rwlock_unlock,
the reader count is decremented.
If the reader count is zero,
pthread_rwlock_unlock unlocks the lock,
otherwise,
the lock is not unlocked.
When pthread_rwlock_unlock unlocks the lock,
the first waiter (reader or writer) is activated.
-
If the thread activated is a reader,
all subsequent readers are activated
(up to the next writer or end of queue).
-
If the thread activated is a writer,
no other threads are activated.
If pthread_rwlock_unlock 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 pthread_rwlock_unlock 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 pthread_rwlock_unlock
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,
threads are awakened in the order in which
they arrived (that is, FIFO order).
Results are undefined if pthread_rwlock_unlock
is called with an uninitialized or unlocked read-write lock.
The rwlock
parameter is a
pointer to the lock to be released.
Return values
pthread_rwlock_unlock returns zero on success.
Otherwise, an error number is returned.
Diagnostics
rw_unlock
returns the following values
if the corresponding conditions are detected:
EINVAL-
Invalid argument specified.
The value specified by rwlock
does not refer to an initialized read-write lock object.
ENOLCK-
rwlock not locked.
Standards compliance
The Single UNIX Specification, Version 2; The Open Group.
References
Intro(3pthread),
pthread(4),
pthread_rwlockattr_init(3pthread),
pthread_rwlock_init(3pthread),
pthread_rwlock_rdlock(3pthread),
pthread_rwlock_wrlock(3pthread)
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004