include/apr-0/apr_thread_rwlock.h

   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 #ifndef APR_THREAD_RWLOCK_H
  18 #define APR_THREAD_RWLOCK_H
  19
  20 /**
  21  * @file apr_thread_rwlock.h
  22  * @brief APR Reader/Writer Lock Routines
  23  */
  24
  25 #include "apr.h"
  26 #include "apr_pools.h"
  27 #include "apr_errno.h"
  28
  29 #ifdef __cplusplus
  30 extern "C" {
  31 #endif /* __cplusplus */
  32
  33 #if APR_HAS_THREADS
  34
  35 /**
  36  * @defgroup apr_thread_rwlock Reader/Writer Lock Routines
  37  * @ingroup APR
  38  * @{
  39  */
  40
  41 /** Opaque read-write thread-safe lock. */
  42 typedef struct apr_thread_rwlock_t apr_thread_rwlock_t;
  43
  44 /**
  45  * Create and initialize a read-write lock that can be used to synchronize
  46  * threads.
  47  * @param rwlock the memory address where the newly created readwrite lock
  48  *        will be stored.
  49  * @param pool the pool from which to allocate the mutex.
  50  */
  51 APR_DECLARE(apr_status_t) apr_thread_rwlock_create(apr_thread_rwlock_t **rwlock,
  52                                                    apr_pool_t *pool);
  53 /**
  54  * Acquire a shared-read lock on the given read-write lock. This will allow
  55  * multiple threads to enter the same critical section while they have acquired
  56  * the read lock.
  57  * @param rwlock the read-write lock on which to acquire the shared read.
  58  */
  59 APR_DECLARE(apr_status_t) apr_thread_rwlock_rdlock(apr_thread_rwlock_t *rwlock);
  60
  61 /**
  62  * Attempt to acquire the shread-read lock on the given read-write lock. This
  63  * is the same as apr_thread_rwlock_rdlock(), only that the funtion fails
  64  * if there is another thread holding the write lock, or if there are any
  65  * write threads blocking on the lock. If the function failes for this case,
  66  * APR_EBUSY will be returned. Note: it is important that the
  67  * APR_STATUS_IS_EBUSY(s) macro be used to determine if the return value was
  68  * APR_EBUSY, for portability reasons.
  69  * @param rwlock the rwlock on which to attempt the shared read.
  70  */
  71 APR_DECLARE(apr_status_t) apr_thread_rwlock_tryrdlock(apr_thread_rwlock_t *rwlock);
  72
  73 /**
  74  * Acquire an exclusive-write lock on the given read-write lock. This will
  75  * allow only one single thread to enter the critical sections. If there
  76  * are any threads currently holding thee read-lock, this thread is put to
  77  * sleep until it can have exclusive access to the lock.
  78  * @param rwlock the read-write lock on which to acquire the exclusive write.
  79  */
  80 APR_DECLARE(apr_status_t) apr_thread_rwlock_wrlock(apr_thread_rwlock_t *rwlock);
  81
  82 /**
  83  * Attempt to acquire the exclusive-write lock on the given read-write lock.
  84  * This is the same as apr_thread_rwlock_wrlock(), only that the funtion fails
  85  * if there is any other thread holding the lock (for reading or writing),
  86  * in which case the function will return APR_EBUSY. Note: it is important
  87  * that the APR_STATUS_IS_EBUSY(s) macro be used to determine if the return
  88  * value was APR_EBUSY, for portability reasons.
  89  * @param rwlock the rwlock on which to attempt the exclusive write.
  90  */
  91 APR_DECLARE(apr_status_t) apr_thread_rwlock_trywrlock(apr_thread_rwlock_t *rwlock);
  92
  93 /**
  94  * Release either the read or write lock currently held by the calling thread
  95  * associated with the given read-write lock.
  96  * @param rwlock the read-write lock to be released (unlocked).
  97  */
  98 APR_DECLARE(apr_status_t) apr_thread_rwlock_unlock(apr_thread_rwlock_t *rwlock);
  99
 100 /**
 101  * Destroy the read-write lock and free the associated memory.
 102  * @param rwlock the rwlock to destroy.
 103  */
 104 APR_DECLARE(apr_status_t) apr_thread_rwlock_destroy(apr_thread_rwlock_t *rwlock);
 105
 106 /**
 107  * Get the pool used by this thread_rwlock.
 108  * @return apr_pool_t the pool
 109  */
 110 APR_POOL_DECLARE_ACCESSOR(thread_rwlock);
 111
 112 #endif  /* APR_HAS_THREADS */
 113
 114 /** @} */
 115
 116 #ifdef __cplusplus
 117 }
 118 #endif
 119
 120 #endif  /* ! APR_THREAD_RWLOCK_H */