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glibc  2.9
sem_trywait.c
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00001 /* sem_trywait -- wait on a semaphore.  Generic futex-using version.
00002    Copyright (C) 2003 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004    Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
00005 
00006    The GNU C Library is free software; you can redistribute it and/or
00007    modify it under the terms of the GNU Lesser General Public
00008    License as published by the Free Software Foundation; either
00009    version 2.1 of the License, or (at your option) any later version.
00010 
00011    The GNU C Library is distributed in the hope that it will be useful,
00012    but WITHOUT ANY WARRANTY; without even the implied warranty of
00013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014    Lesser General Public License for more details.
00015 
00016    You should have received a copy of the GNU Lesser General Public
00017    License along with the GNU C Library; if not, write to the Free
00018    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00019    02111-1307 USA.  */
00020 
00021 #include <errno.h>
00022 #include <sysdep.h>
00023 #include <lowlevellock.h>
00024 #include <internaltypes.h>
00025 #include <semaphore.h>
00026 
00027 #include <shlib-compat.h>
00028 
00029 
00030 int
00031 __new_sem_trywait (sem_t *sem)
00032 {
00033   int *futex = (int *) sem;
00034   int val;
00035 
00036   if (*futex > 0)
00037     {
00038       val = atomic_decrement_if_positive (futex);
00039       if (val > 0)
00040        return 0;
00041     }
00042 
00043   __set_errno (EAGAIN);
00044   return -1;
00045 }
00046 versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
00047 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
00048 strong_alias (__new_sem_trywait, __old_sem_trywait)
00049 compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
00050 #endif