nptl/pthread_rwlock_tryrdlock.c

   1 /* Copyright (C) 2002, 2007 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include "pthreadP.h"
  22 #include <lowlevellock.h>
  23
  24
  25 int
  26 __pthread_rwlock_tryrdlock (rwlock)
  27      pthread_rwlock_t *rwlock;
  28 {
  29   int result = EBUSY;
  30
  31   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  32
  33   if (rwlock->__data.__writer == 0
  34       && (rwlock->__data.__nr_writers_queued == 0
  35           || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
  36     {
  37       if (__builtin_expect (++rwlock->__data.__nr_readers == 0, 0))
  38         {
  39           --rwlock->__data.__nr_readers;
  40           result = EAGAIN;
  41         }
  42       else
  43         result = 0;
  44     }
  45
  46   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  47
  48   return result;
  49 }
  50 strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)