1 /* Licensed to the Apache Software Foundation (ASF) under one or more
2 * contributor license agreements. See the NOTICE file distributed with
3 * this work for additional information regarding copyright ownership.
4 * The ASF licenses this file to You under the Apache License, Version 2.0
5 * (the "License"); you may not use this file except in compliance with
6 * the License. You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 /*Read/Write locking implementation based on the MultiLock code from
18 * Stephen Beaulieu <hippo@be.com>
19 */
20
21 #include "apr_arch_thread_rwlock.h"
22 #include "apr_strings.h"
23 #include "apr_portable.h"
24
25 #define BIG_NUM 100000
26
_thread_rw_cleanup(void * data)27 static apr_status_t _thread_rw_cleanup(void * data)
28 {
29 apr_thread_rwlock_t *mutex = (apr_thread_rwlock_t*)data;
30
31 if (mutex->ReadCount != 0) {
32 while (atomic_add(&mutex->ReadCount , -1) > 1){
33 release_sem (mutex->Read);
34 }
35 }
36 if (mutex->WriteCount != 0) {
37 while (atomic_add(&mutex->WriteCount , -1) > 1){
38 release_sem (mutex->Write);
39 }
40 }
41 if (mutex->LockCount != 0) {
42 while (atomic_add(&mutex->LockCount , -1) > 1){
43 release_sem (mutex->Lock);
44 }
45 }
46
47 delete_sem(mutex->Read);
48 delete_sem(mutex->Write);
49 delete_sem(mutex->Lock);
50 return APR_SUCCESS;
51 }
52
apr_thread_rwlock_create(apr_thread_rwlock_t ** rwlock,apr_pool_t * pool)53 APR_DECLARE(apr_status_t) apr_thread_rwlock_create(apr_thread_rwlock_t **rwlock,
54 apr_pool_t *pool)
55 {
56 apr_thread_rwlock_t *new;
57
58 new = (apr_thread_rwlock_t *)apr_pcalloc(pool, sizeof(apr_thread_rwlock_t));
59 if (new == NULL){
60 return APR_ENOMEM;
61 }
62
63 new->pool = pool;
64 /* we need to make 3 locks... */
65 new->ReadCount = 0;
66 new->WriteCount = 0;
67 new->LockCount = 0;
68 new->Read = create_sem(0, "APR_ReadLock");
69 new->Write = create_sem(0, "APR_WriteLock");
70 new->Lock = create_sem(0, "APR_Lock");
71
72 if (new->Lock < 0 || new->Read < 0 || new->Write < 0) {
73 _thread_rw_cleanup(new);
74 return -1;
75 }
76
77 apr_pool_cleanup_register(new->pool, (void *)new, _thread_rw_cleanup,
78 apr_pool_cleanup_null);
79 (*rwlock) = new;
80 return APR_SUCCESS;
81 }
82
apr_thread_rwlock_rdlock(apr_thread_rwlock_t * rwlock)83 APR_DECLARE(apr_status_t) apr_thread_rwlock_rdlock(apr_thread_rwlock_t *rwlock)
84 {
85 int32 rv = APR_SUCCESS;
86
87 if (find_thread(NULL) == rwlock->writer) {
88 /* we're the writer - no problem */
89 rwlock->Nested++;
90 } else {
91 /* we're not the writer */
92 int32 r = atomic_add(&rwlock->ReadCount, 1);
93 if (r < 0) {
94 /* Oh dear, writer holds lock, wait for sem */
95 rv = acquire_sem_etc(rwlock->Read, 1, B_DO_NOT_RESCHEDULE,
96 B_INFINITE_TIMEOUT);
97 }
98 }
99
100 return rv;
101 }
102
apr_thread_rwlock_tryrdlock(apr_thread_rwlock_t * rwlock)103 APR_DECLARE(apr_status_t) apr_thread_rwlock_tryrdlock(apr_thread_rwlock_t *rwlock)
104 {
105 return APR_ENOTIMPL;
106 }
107
apr_thread_rwlock_wrlock(apr_thread_rwlock_t * rwlock)108 APR_DECLARE(apr_status_t) apr_thread_rwlock_wrlock(apr_thread_rwlock_t *rwlock)
109 {
110 int rv = APR_SUCCESS;
111
112 if (find_thread(NULL) == rwlock->writer) {
113 rwlock->Nested++;
114 } else {
115 /* we're not the writer... */
116 if (atomic_add(&rwlock->LockCount, 1) >= 1) {
117 /* we're locked - acquire the sem */
118 rv = acquire_sem_etc(rwlock->Lock, 1, B_DO_NOT_RESCHEDULE,
119 B_INFINITE_TIMEOUT);
120 }
121 if (rv == APR_SUCCESS) {
122 /* decrement the ReadCount to a large -ve number so that
123 * we block on new readers...
124 */
125 int32 readers = atomic_add(&rwlock->ReadCount, -BIG_NUM);
126 if (readers > 0) {
127 /* readers are holding the lock */
128 rv = acquire_sem_etc(rwlock->Write, readers, B_DO_NOT_RESCHEDULE,
129 B_INFINITE_TIMEOUT);
130 }
131 if (rv == APR_SUCCESS)
132 rwlock->writer = find_thread(NULL);
133 }
134 }
135
136 return rv;
137 }
138
apr_thread_rwlock_trywrlock(apr_thread_rwlock_t * rwlock)139 APR_DECLARE(apr_status_t) apr_thread_rwlock_trywrlock(apr_thread_rwlock_t *rwlock)
140 {
141 return APR_ENOTIMPL;
142 }
143
apr_thread_rwlock_unlock(apr_thread_rwlock_t * rwlock)144 APR_DECLARE(apr_status_t) apr_thread_rwlock_unlock(apr_thread_rwlock_t *rwlock)
145 {
146 apr_status_t rv = APR_SUCCESS;
147 int32 readers;
148
149 /* we know we hold the lock, so don't check it :) */
150 if (find_thread(NULL) == rwlock->writer) {
151 /* we know we hold the lock, so don't check it :) */
152 if (rwlock->Nested > 1) {
153 /* we're recursively locked */
154 rwlock->Nested--;
155 return APR_SUCCESS;
156 }
157 /* OK so we need to release the sem if we have it :) */
158 readers = atomic_add(&rwlock->ReadCount, BIG_NUM) + BIG_NUM;
159 if (readers > 0) {
160 rv = release_sem_etc(rwlock->Read, readers, B_DO_NOT_RESCHEDULE);
161 }
162 if (rv == APR_SUCCESS) {
163 rwlock->writer = -1;
164 if (atomic_add(&rwlock->LockCount, -1) > 1) {
165 rv = release_sem_etc(rwlock->Lock, 1, B_DO_NOT_RESCHEDULE);
166 }
167 }
168 } else {
169 /* We weren't the Writer, so just release the ReadCount... */
170 if (atomic_add(&rwlock->ReadCount, -1) < 0) {
171 /* we have a writer waiting for the lock, so release it */
172 rv = release_sem_etc(rwlock->Write, 1, B_DO_NOT_RESCHEDULE);
173 }
174 }
175
176 return rv;
177 }
178
apr_thread_rwlock_destroy(apr_thread_rwlock_t * rwlock)179 APR_DECLARE(apr_status_t) apr_thread_rwlock_destroy(apr_thread_rwlock_t *rwlock)
180 {
181 apr_status_t stat;
182 if ((stat = _thread_rw_cleanup(rwlock)) == APR_SUCCESS) {
183 apr_pool_cleanup_kill(rwlock->pool, rwlock, _thread_rw_cleanup);
184 return APR_SUCCESS;
185 }
186 return stat;
187 }
188
189 APR_POOL_IMPLEMENT_ACCESSOR(thread_rwlock)
190
191