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
sem_trywait(sem_t * sem)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 }
43