glibc/nptl/pthread_rwlock_tryrdlock.c

/* Copyright (C) 2002-2015 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.

   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 "pthreadP.h"
#include <lowlevellock.h>
#include <elide.h>


int
__pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
  int result = EBUSY;

  if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
		     rwlock->__data.__lock == 0
		     && rwlock->__data.__nr_readers == 0
		     && rwlock->__data.__writer, 0))
    return 0;

  lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);

  if (rwlock->__data.__writer == 0
      && (rwlock->__data.__nr_writers_queued == 0
	  || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
    {
      if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
	{
	  --rwlock->__data.__nr_readers;
	  result = EAGAIN;
	}
      else
	result = 0;
    }

  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);

  return result;
}
strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)