nptl/pthread_rwlock_tryrdlock.c

   1 /* Copyright (C) 2002-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include "pthreadP.h"
  21 #include <lowlevellock.h>
  22 #include <elide.h>
  23
  24
  25 int
  26 __pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
  27 {
  28   int result = EBUSY;
  29
  30   if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
  31                      rwlock->__data.__lock == 0
  32                      && rwlock->__data.__nr_readers == 0
  33                      && rwlock->__data.__writer, 0))
  34     return 0;
  35
  36   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  37
  38   if (rwlock->__data.__writer == 0
  39       && (rwlock->__data.__nr_writers_queued == 0
  40           || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
  41     {
  42       if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
  43         {
  44           --rwlock->__data.__nr_readers;
  45           result = EAGAIN;
  46         }
  47       else
  48         result = 0;
  49     }
  50
  51   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  52
  53   return result;
  54 }
  55 strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)