1*062c5bc4SJason Schmidlapp /*
2*062c5bc4SJason Schmidlapp * -------------------------------------------------------------
3*062c5bc4SJason Schmidlapp *
4*062c5bc4SJason Schmidlapp * Module: sem_trywait.c
5*062c5bc4SJason Schmidlapp *
6*062c5bc4SJason Schmidlapp * Purpose:
7*062c5bc4SJason Schmidlapp * Semaphores aren't actually part of the PThreads standard.
8*062c5bc4SJason Schmidlapp * They are defined by the POSIX Standard:
9*062c5bc4SJason Schmidlapp *
10*062c5bc4SJason Schmidlapp * POSIX 1003.1b-1993 (POSIX.1b)
11*062c5bc4SJason Schmidlapp *
12*062c5bc4SJason Schmidlapp * -------------------------------------------------------------
13*062c5bc4SJason Schmidlapp *
14*062c5bc4SJason Schmidlapp * --------------------------------------------------------------------------
15*062c5bc4SJason Schmidlapp *
16*062c5bc4SJason Schmidlapp * Pthreads-embedded (PTE) - POSIX Threads Library for embedded systems
17*062c5bc4SJason Schmidlapp * Copyright(C) 2008 Jason Schmidlapp
18*062c5bc4SJason Schmidlapp *
19*062c5bc4SJason Schmidlapp * Contact Email: jschmidlapp@users.sourceforge.net
20*062c5bc4SJason Schmidlapp *
21*062c5bc4SJason Schmidlapp *
22*062c5bc4SJason Schmidlapp * Based upon Pthreads-win32 - POSIX Threads Library for Win32
23*062c5bc4SJason Schmidlapp * Copyright(C) 1998 John E. Bossom
24*062c5bc4SJason Schmidlapp * Copyright(C) 1999,2005 Pthreads-win32 contributors
25*062c5bc4SJason Schmidlapp *
26*062c5bc4SJason Schmidlapp * Contact Email: rpj@callisto.canberra.edu.au
27*062c5bc4SJason Schmidlapp *
28*062c5bc4SJason Schmidlapp * The original list of contributors to the Pthreads-win32 project
29*062c5bc4SJason Schmidlapp * is contained in the file CONTRIBUTORS.ptw32 included with the
30*062c5bc4SJason Schmidlapp * source code distribution. The list can also be seen at the
31*062c5bc4SJason Schmidlapp * following World Wide Web location:
32*062c5bc4SJason Schmidlapp * http://sources.redhat.com/pthreads-win32/contributors.html
33*062c5bc4SJason Schmidlapp *
34*062c5bc4SJason Schmidlapp * This library is free software; you can redistribute it and/or
35*062c5bc4SJason Schmidlapp * modify it under the terms of the GNU Lesser General Public
36*062c5bc4SJason Schmidlapp * License as published by the Free Software Foundation; either
37*062c5bc4SJason Schmidlapp * version 2 of the License, or (at your option) any later version.
38*062c5bc4SJason Schmidlapp *
39*062c5bc4SJason Schmidlapp * This library is distributed in the hope that it will be useful,
40*062c5bc4SJason Schmidlapp * but WITHOUT ANY WARRANTY; without even the implied warranty of
41*062c5bc4SJason Schmidlapp * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
42*062c5bc4SJason Schmidlapp * Lesser General Public License for more details.
43*062c5bc4SJason Schmidlapp *
44*062c5bc4SJason Schmidlapp * You should have received a copy of the GNU Lesser General Public
45*062c5bc4SJason Schmidlapp * License along with this library in the file COPYING.LIB;
46*062c5bc4SJason Schmidlapp * if not, write to the Free Software Foundation, Inc.,
47*062c5bc4SJason Schmidlapp * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
48*062c5bc4SJason Schmidlapp */
49*062c5bc4SJason Schmidlapp
50*062c5bc4SJason Schmidlapp #include "pthread.h"
51*062c5bc4SJason Schmidlapp #include "semaphore.h"
52*062c5bc4SJason Schmidlapp #include "implement.h"
53*062c5bc4SJason Schmidlapp
54*062c5bc4SJason Schmidlapp
55*062c5bc4SJason Schmidlapp int
sem_trywait(sem_t * sem)56*062c5bc4SJason Schmidlapp sem_trywait (sem_t * sem)
57*062c5bc4SJason Schmidlapp /*
58*062c5bc4SJason Schmidlapp * ------------------------------------------------------
59*062c5bc4SJason Schmidlapp * DOCPUBLIC
60*062c5bc4SJason Schmidlapp * This function tries to wait on a semaphore.
61*062c5bc4SJason Schmidlapp *
62*062c5bc4SJason Schmidlapp * PARAMETERS
63*062c5bc4SJason Schmidlapp * sem
64*062c5bc4SJason Schmidlapp * pointer to an instance of sem_t
65*062c5bc4SJason Schmidlapp *
66*062c5bc4SJason Schmidlapp * DESCRIPTION
67*062c5bc4SJason Schmidlapp * This function tries to wait on a semaphore. If the
68*062c5bc4SJason Schmidlapp * semaphore value is greater than zero, it decreases
69*062c5bc4SJason Schmidlapp * its value by one. If the semaphore value is zero, then
70*062c5bc4SJason Schmidlapp * this function returns immediately with the error EAGAIN
71*062c5bc4SJason Schmidlapp *
72*062c5bc4SJason Schmidlapp * RESULTS
73*062c5bc4SJason Schmidlapp * 0 successfully decreased semaphore,
74*062c5bc4SJason Schmidlapp * -1 failed, error in errno
75*062c5bc4SJason Schmidlapp * ERRNO
76*062c5bc4SJason Schmidlapp * EAGAIN the semaphore was already locked,
77*062c5bc4SJason Schmidlapp * EINVAL 'sem' is not a valid semaphore,
78*062c5bc4SJason Schmidlapp * ENOTSUP sem_trywait is not supported,
79*062c5bc4SJason Schmidlapp * EINTR the function was interrupted by a signal,
80*062c5bc4SJason Schmidlapp * EDEADLK a deadlock condition was detected.
81*062c5bc4SJason Schmidlapp *
82*062c5bc4SJason Schmidlapp * ------------------------------------------------------
83*062c5bc4SJason Schmidlapp */
84*062c5bc4SJason Schmidlapp {
85*062c5bc4SJason Schmidlapp int result = 0;
86*062c5bc4SJason Schmidlapp sem_t s = *sem;
87*062c5bc4SJason Schmidlapp
88*062c5bc4SJason Schmidlapp if (s == NULL)
89*062c5bc4SJason Schmidlapp {
90*062c5bc4SJason Schmidlapp result = EINVAL;
91*062c5bc4SJason Schmidlapp }
92*062c5bc4SJason Schmidlapp else if ((result = pthread_mutex_lock (&s->lock)) == 0)
93*062c5bc4SJason Schmidlapp {
94*062c5bc4SJason Schmidlapp /* See sem_destroy.c
95*062c5bc4SJason Schmidlapp */
96*062c5bc4SJason Schmidlapp if (*sem == NULL)
97*062c5bc4SJason Schmidlapp {
98*062c5bc4SJason Schmidlapp (void) pthread_mutex_unlock (&s->lock);
99*062c5bc4SJason Schmidlapp errno = EINVAL;
100*062c5bc4SJason Schmidlapp return -1;
101*062c5bc4SJason Schmidlapp }
102*062c5bc4SJason Schmidlapp
103*062c5bc4SJason Schmidlapp if (s->value > 0)
104*062c5bc4SJason Schmidlapp {
105*062c5bc4SJason Schmidlapp s->value--;
106*062c5bc4SJason Schmidlapp }
107*062c5bc4SJason Schmidlapp else
108*062c5bc4SJason Schmidlapp {
109*062c5bc4SJason Schmidlapp result = EAGAIN;
110*062c5bc4SJason Schmidlapp }
111*062c5bc4SJason Schmidlapp
112*062c5bc4SJason Schmidlapp (void) pthread_mutex_unlock (&s->lock);
113*062c5bc4SJason Schmidlapp }
114*062c5bc4SJason Schmidlapp
115*062c5bc4SJason Schmidlapp if (result != 0)
116*062c5bc4SJason Schmidlapp {
117*062c5bc4SJason Schmidlapp errno = result;
118*062c5bc4SJason Schmidlapp return -1;
119*062c5bc4SJason Schmidlapp }
120*062c5bc4SJason Schmidlapp
121*062c5bc4SJason Schmidlapp return 0;
122*062c5bc4SJason Schmidlapp
123*062c5bc4SJason Schmidlapp } /* sem_trywait */
124