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 (at) 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 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
