libpthread/nptl/sysdeps/unix/sysv/linux/sem_trywait.c

   1 /* sem_trywait -- wait on a semaphore.  Generic futex-using version.
   2    Copyright (C) 2003 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <errno.h>
  21 #include <sysdep.h>
  22 #include <lowlevellock.h>
  23 #include <internaltypes.h>
  24 #include <semaphore.h>
  25
  26
  27 int
  28 sem_trywait (sem_t *sem)
  29 {
  30   int *futex = (int *) sem;
  31   int val;
  32
  33   if (*futex > 0)
  34     {
  35       val = atomic_decrement_if_positive (futex);
  36       if (val > 0)
  37         return 0;
  38     }
  39
  40   __set_errno (EAGAIN);
  41   return -1;
  42 }