1 /* 2 * pthread_rwlock_tryrdlock.c 3 * 4 * Description: 5 * This translation unit implements read/write lock primitives. 6 * 7 * -------------------------------------------------------------------------- 8 * 9 * Pthreads-win32 - POSIX Threads Library for Win32 10 * Copyright(C) 1998 John E. Bossom 11 * Copyright(C) 1999,2005 Pthreads-win32 contributors 12 * 13 * Contact Email: rpj (at) callisto.canberra.edu.au 14 * 15 * The current list of contributors is contained 16 * in the file CONTRIBUTORS included with the source 17 * code distribution. The list can also be seen at the 18 * following World Wide Web location: 19 * http://sources.redhat.com/pthreads-win32/contributors.html 20 * 21 * This library is free software; you can redistribute it and/or 22 * modify it under the terms of the GNU Lesser General Public 23 * License as published by the Free Software Foundation; either 24 * version 2 of the License, or (at your option) any later version. 25 * 26 * This library is distributed in the hope that it will be useful, 27 * but WITHOUT ANY WARRANTY; without even the implied warranty of 28 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 29 * Lesser General Public License for more details. 30 * 31 * You should have received a copy of the GNU Lesser General Public 32 * License along with this library in the file COPYING.LIB; 33 * if not, write to the Free Software Foundation, Inc., 34 * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA 35 */ 36 37 #include <limits.h> 38 39 #include "pthread.h" 40 #include "implement.h" 41 42 int 43 pthread_rwlock_tryrdlock (pthread_rwlock_t * rwlock) 44 { 45 int result; 46 pthread_rwlock_t rwl; 47 48 if (rwlock == NULL || *rwlock == NULL) 49 { 50 return EINVAL; 51 } 52 53 /* 54 * We do a quick check to see if we need to do more work 55 * to initialise a static rwlock. We check 56 * again inside the guarded section of ptw32_rwlock_check_need_init() 57 * to avoid race conditions. 58 */ 59 if (*rwlock == PTHREAD_RWLOCK_INITIALIZER) 60 { 61 result = ptw32_rwlock_check_need_init (rwlock); 62 63 if (result != 0 && result != EBUSY) 64 { 65 return result; 66 } 67 } 68 69 rwl = *rwlock; 70 71 if (rwl->nMagic != PTW32_RWLOCK_MAGIC) 72 { 73 return EINVAL; 74 } 75 76 if ((result = pthread_mutex_trylock (&(rwl->mtxExclusiveAccess))) != 0) 77 { 78 return result; 79 } 80 81 if (++rwl->nSharedAccessCount == INT_MAX) 82 { 83 if ((result = 84 pthread_mutex_lock (&(rwl->mtxSharedAccessCompleted))) != 0) 85 { 86 (void) pthread_mutex_unlock (&(rwl->mtxExclusiveAccess)); 87 return result; 88 } 89 90 rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount; 91 rwl->nCompletedSharedAccessCount = 0; 92 93 if ((result = 94 pthread_mutex_unlock (&(rwl->mtxSharedAccessCompleted))) != 0) 95 { 96 (void) pthread_mutex_unlock (&(rwl->mtxExclusiveAccess)); 97 return result; 98 } 99 } 100 101 return (pthread_mutex_unlock (&rwl->mtxExclusiveAccess)); 102 } 103