/* Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #ifndef APR_THREAD_RWLOCK_H #define APR_THREAD_RWLOCK_H /** * @file apr_thread_rwlock.h * @brief APR Reader/Writer Lock Routines */ #include "apr.h" #include "apr_pools.h" #include "apr_errno.h" #ifdef __cplusplus extern "C" { #endif /* __cplusplus */ #if APR_HAS_THREADS /** * @defgroup apr_thread_rwlock Reader/Writer Lock Routines * @ingroup APR * @{ */ /** Opaque read-write thread-safe lock. */ typedef struct apr_thread_rwlock_t apr_thread_rwlock_t; /** * Note: The following operations have undefined results: unlocking a * read-write lock which is not locked in the calling thread; write * locking a read-write lock which is already locked by the calling * thread; destroying a read-write lock more than once; clearing or * destroying the pool from which a <b>locked</b> read-write lock is * allocated. */ /** * Create and initialize a read-write lock that can be used to synchronize * threads. * @param rwlock the memory address where the newly created readwrite lock * will be stored. * @param pool the pool from which to allocate the mutex. */ APR_DECLARE(apr_status_t) apr_thread_rwlock_create(apr_thread_rwlock_t **rwlock, apr_pool_t *pool); /** * Acquire a shared-read lock on the given read-write lock. This will allow * multiple threads to enter the same critical section while they have acquired * the read lock. * @param rwlock the read-write lock on which to acquire the shared read. */ APR_DECLARE(apr_status_t) apr_thread_rwlock_rdlock(apr_thread_rwlock_t *rwlock); /** * Attempt to acquire the shared-read lock on the given read-write lock. This * is the same as apr_thread_rwlock_rdlock(), only that the function fails * if there is another thread holding the write lock, or if there are any * write threads blocking on the lock. If the function fails for this case, * APR_EBUSY will be returned. Note: it is important that the * APR_STATUS_IS_EBUSY(s) macro be used to determine if the return value was * APR_EBUSY, for portability reasons. * @param rwlock the rwlock on which to attempt the shared read. */ APR_DECLARE(apr_status_t) apr_thread_rwlock_tryrdlock(apr_thread_rwlock_t *rwlock); /** * Acquire an exclusive-write lock on the given read-write lock. This will * allow only one single thread to enter the critical sections. If there * are any threads currently holding the read-lock, this thread is put to * sleep until it can have exclusive access to the lock. * @param rwlock the read-write lock on which to acquire the exclusive write. */ APR_DECLARE(apr_status_t) apr_thread_rwlock_wrlock(apr_thread_rwlock_t *rwlock); /** * Attempt to acquire the exclusive-write lock on the given read-write lock. * This is the same as apr_thread_rwlock_wrlock(), only that the function fails * if there is any other thread holding the lock (for reading or writing), * in which case the function will return APR_EBUSY. Note: it is important * that the APR_STATUS_IS_EBUSY(s) macro be used to determine if the return * value was APR_EBUSY, for portability reasons. * @param rwlock the rwlock on which to attempt the exclusive write. */ APR_DECLARE(apr_status_t) apr_thread_rwlock_trywrlock(apr_thread_rwlock_t *rwlock); /** * Release either the read or write lock currently held by the calling thread * associated with the given read-write lock. * @param rwlock the read-write lock to be released (unlocked). */ APR_DECLARE(apr_status_t) apr_thread_rwlock_unlock(apr_thread_rwlock_t *rwlock); /** * Destroy the read-write lock and free the associated memory. * @param rwlock the rwlock to destroy. */ APR_DECLARE(apr_status_t) apr_thread_rwlock_destroy(apr_thread_rwlock_t *rwlock); /** * Get the pool used by this thread_rwlock. * @return apr_pool_t the pool */ APR_POOL_DECLARE_ACCESSOR(thread_rwlock); #endif /* APR_HAS_THREADS */ /** @} */ #ifdef __cplusplus } #endif #endif /* ! APR_THREAD_RWLOCK_H */