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PROLOG
       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.


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 this function is 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 shall not return an error code of [EINTR].

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       None.


RATIONALE
       If an  implementation  detects  that  the  value  specified  by  the  rwlock  argument  to
       pthread_rwlock_unlock()  does  not  refer  to an initialized read-write lock object, it is
       recommended that the function should fail and report an [EINVAL] error.

       If an  implementation  detects  that  the  value  specified  by  the  rwlock  argument  to
       pthread_rwlock_unlock()  refers  to  a read-write lock object for which the current thread
       does not hold a lock, it is recommended that  the  function  should  fail  and  report  an
       [EPERM] error.


FUTURE DIRECTIONS
       None.


SEE ALSO
       pthread_rwlock_destroy(), pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(),
       pthread_rwlock_timedwrlock(), pthread_rwlock_trywrlock()

       The Base  Definitions  volume  of  POSIX.1‐2008,  Section  4.11,  Memory  Synchronization,
       <pthread.h>


COPYRIGHT
       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .