rw_unlock(SYNCH)

rw_unlock -- release a reader-writer lock

Synopsis

   cc [options] -Kthread file
   
   #include <synch.h>
   

   int rw_unlock(rwlock_t *lock);

Description

rw_unlock releases a reader-writer lock previously acquired by rw_rdlock, rw_wrlock, rw_tryrdlock, or rw_trywrlock. The behavior differs according to whether the caller is a reader or a writer:

When a writer calls rw_unlock, the lock is unlocked.
When a reader calls rw_unlock, the reader count is decremented. If the reader count is zero, rw_unlock unlocks the lock, otherwise, the lock is not unlocked.

When rw_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) and the count of readers holding the lock is changed to reflect this.
If the thread activated is a writer, no other threads are activated and the lock is marked as being held by a writer.

lock must previously have been initialized (see rwlock_init(SYNCH)).

Parameters

lock: pointer to the lock to be released

Return values

rw_unlock returns zero for success and an error number for failure.

Errors

If any the following conditions is detected, rw_unlock fails and returns the corresponding value:

EINVAL: invalid argument specified
ENOLCK: lock not locked

References

Intro(SYNCH), rwlock(SYNCH), rwlock_destroy(SYNCH), rwlock_init(SYNCH), rw_rdlock(SYNCH), rw_tryrdlock(SYNCH), rw_trywrlock(SYNCH), rw_wrlock(SYNCH)