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 27static 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 53APR_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 83APR_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 103APR_DECLARE(apr_status_t) apr_thread_rwlock_tryrdlock(apr_thread_rwlock_t *rwlock) 104{ 105 return APR_ENOTIMPL; 106} 107 108APR_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 139APR_DECLARE(apr_status_t) apr_thread_rwlock_trywrlock(apr_thread_rwlock_t *rwlock) 140{ 141 return APR_ENOTIMPL; 142} 143 144APR_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 179APR_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 189APR_POOL_IMPLEMENT_ACCESSOR(thread_rwlock) 190 191