NAME

       pthread_rwlock_unlock - unlock a read-write lock object

SYNOPSIS

       #include <pthread.h>

       int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);

DESCRIPTION

       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
       Scheduling 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 priority 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 supported, 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-
       write lock.

RETURN VALUE

       If successful, the pthread_rwlock_unlock() function shall return zero; otherwise, an error
       number shall be returned to indicate the error.

ERRORS

       The pthread_rwlock_unlock() function may fail if:

       EINVAL The  value  specified  by  rwlock  does not refer to an initialized read-write lock
              object.

       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.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       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>

COPYRIGHT

       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
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .