pthread_rwlock_unlock.c

/* Copyright (C) 2003-2016 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <sysdep.h>
#include <lowlevellock.h>
#include <futex-internal.h>
#include <pthread.h>
#include <pthreadP.h>
#include <stap-probe.h>
#include <elide.h>


/* Unlock RWLOCK.  */
int
__pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
  int futex_shared =
      rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;

  LIBC_PROBE (rwlock_unlock, 1, rwlock);

  if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
		    && rwlock->__data.__nr_readers == 0))
    return 0;

  lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  if (rwlock->__data.__writer)
    rwlock->__data.__writer = 0;
  else
    --rwlock->__data.__nr_readers;
  /* If there are still readers present, we do not yet need to wake writers
     nor are responsible to wake any readers.  */
  if (rwlock->__data.__nr_readers == 0)
    {
      /* Note that if there is a blocked writer, we effectively make it
	 responsible for waking any readers because we don't wake readers in
	 this case.  */
      if (rwlock->__data.__nr_writers_queued)
	{
	  ++rwlock->__data.__writer_wakeup;
	  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
	  futex_wake (&rwlock->__data.__writer_wakeup, 1, futex_shared);
	  return 0;
	}
      else if (rwlock->__data.__nr_readers_queued)
	{
	  ++rwlock->__data.__readers_wakeup;
	  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
	  futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
		      futex_shared);
	  return 0;
	}
    }
  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  return 0;
}

weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock)
hidden_def (__pthread_rwlock_unlock)