1 /*
2 * -------------------------------------------------------------
3 *
4 * Module: sem_trywait.c
5 *
6 * Purpose:
7 * Semaphores aren't actually part of the PThreads standard.
8 * They are defined by the POSIX Standard:
9 *
10 * POSIX 1003.1b-1993 (POSIX.1b)
11 *
12 * -------------------------------------------------------------
13 *
14 * --------------------------------------------------------------------------
15 *
16 * Pthreads-win32 - POSIX Threads Library for Win32
17 * Copyright(C) 1998 John E. Bossom
18 * Copyright(C) 1999,2005 Pthreads-win32 contributors
19 *
20 * Contact Email: rpj@callisto.canberra.edu.au
21 *
22 * The current list of contributors is contained
23 * in the file CONTRIBUTORS included with the source
24 * code distribution. The list can also be seen at the
25 * following World Wide Web location:
26 * http://sources.redhat.com/pthreads-win32/contributors.html
27 *
28 * This library is free software; you can redistribute it and/or
29 * modify it under the terms of the GNU Lesser General Public
30 * License as published by the Free Software Foundation; either
31 * version 2 of the License, or (at your option) any later version.
32 *
33 * This library is distributed in the hope that it will be useful,
34 * but WITHOUT ANY WARRANTY; without even the implied warranty of
35 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
36 * Lesser General Public License for more details.
37 *
38 * You should have received a copy of the GNU Lesser General Public
39 * License along with this library in the file COPYING.LIB;
40 * if not, write to the Free Software Foundation, Inc.,
41 * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
42 */
43
44 #include "pthread.h"
45 #include "semaphore.h"
46 #include "implement.h"
47
48
49 int
sem_trywait(sem_t * sem)50 sem_trywait (sem_t * sem)
51 /*
52 * ------------------------------------------------------
53 * DOCPUBLIC
54 * This function tries to wait on a semaphore.
55 *
56 * PARAMETERS
57 * sem
58 * pointer to an instance of sem_t
59 *
60 * DESCRIPTION
61 * This function tries to wait on a semaphore. If the
62 * semaphore value is greater than zero, it decreases
63 * its value by one. If the semaphore value is zero, then
64 * this function returns immediately with the error EAGAIN
65 *
66 * RESULTS
67 * 0 successfully decreased semaphore,
68 * -1 failed, error in errno
69 * ERRNO
70 * EAGAIN the semaphore was already locked,
71 * EINVAL 'sem' is not a valid semaphore,
72 * ENOTSUP sem_trywait is not supported,
73 * EINTR the function was interrupted by a signal,
74 * EDEADLK a deadlock condition was detected.
75 *
76 * ------------------------------------------------------
77 */
78 {
79 int result = 0;
80 sem_t s = *sem;
81
82 if (s == NULL)
83 {
84 result = EINVAL;
85 }
86 else if ((result = pthread_mutex_lock (&s->lock)) == 0)
87 {
88 /* See sem_destroy.c
89 */
90 if (*sem == NULL)
91 {
92 (void) pthread_mutex_unlock (&s->lock);
93 errno = EINVAL;
94 return -1;
95 }
96
97 if (s->value > 0)
98 {
99 s->value--;
100 }
101 else
102 {
103 result = EAGAIN;
104 }
105
106 (void) pthread_mutex_unlock (&s->lock);
107 }
108
109 if (result != 0)
110 {
111 errno = result;
112 return -1;
113 }
114
115 return 0;
116
117 } /* sem_trywait */
118