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@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 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
35 */
36
37 #include <limits.h>
38
39 #include "pthread.h"
40 #include "implement.h"
41
42 int
pthread_rwlock_tryrdlock(pthread_rwlock_t * rwlock)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