include/apr-1/apr_thread_cond.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_COND_H
  18 #define APR_THREAD_COND_H
  19
  20 /**
  21  * @file apr_thread_cond.h
  22  * @brief APR Condition Variable Routines
  23  */
  24
  25 #include "apr.h"
  26 #include "apr_pools.h"
  27 #include "apr_errno.h"
  28 #include "apr_time.h"
  29 #include "apr_thread_mutex.h"
  30
  31 #ifdef __cplusplus
  32 extern "C" {
  33 #endif /* __cplusplus */
  34
  35 #if APR_HAS_THREADS || defined(DOXYGEN)
  36
  37 /**
  38  * @defgroup apr_thread_cond Condition Variable Routines
  39  * @ingroup APR
  40  * @{
  41  */
  42
  43 /** Opaque structure for thread condition variables */
  44 typedef struct apr_thread_cond_t apr_thread_cond_t;
  45
  46 /**
  47  * Note: destroying a condition variable (or likewise, destroying or
  48  * clearing the pool from which a condition variable was allocated) if
  49  * any threads are blocked waiting on it gives undefined results.
  50  */
  51
  52 /**
  53  * Create and initialize a condition variable that can be used to signal
  54  * and schedule threads in a single process.
  55  * @param cond the memory address where the newly created condition variable
  56  *        will be stored.
  57  * @param pool the pool from which to allocate the condition.
  58  */
  59 APR_DECLARE(apr_status_t) apr_thread_cond_create(apr_thread_cond_t **cond,
  60                                                  apr_pool_t *pool);
  61
  62 /**
  63  * Put the active calling thread to sleep until signaled to wake up. Each
  64  * condition variable must be associated with a mutex, and that mutex must
  65  * be locked before  calling this function, or the behavior will be
  66  * undefined. As the calling thread is put to sleep, the given mutex
  67  * will be simultaneously released; and as this thread wakes up the lock
  68  * is again simultaneously acquired.
  69  * @param cond the condition variable on which to block.
  70  * @param mutex the mutex that must be locked upon entering this function,
  71  *        is released while the thread is asleep, and is again acquired before
  72  *        returning from this function.
  73  * @remark Spurious wakeups may occur. Before and after every call to wait on
  74  * a condition variable, the caller should test whether the condition is already
  75  * met.
  76  */
  77 APR_DECLARE(apr_status_t) apr_thread_cond_wait(apr_thread_cond_t *cond,
  78                                                apr_thread_mutex_t *mutex);
  79
  80 /**
  81  * Put the active calling thread to sleep until signaled to wake up or
  82  * the timeout is reached. Each condition variable must be associated
  83  * with a mutex, and that mutex must be locked before calling this
  84  * function, or the behavior will be undefined. As the calling thread
  85  * is put to sleep, the given mutex will be simultaneously released;
  86  * and as this thread wakes up the lock is again simultaneously acquired.
  87  * @param cond the condition variable on which to block.
  88  * @param mutex the mutex that must be locked upon entering this function,
  89  *        is released while the thread is asleep, and is again acquired before
  90  *        returning from this function.
  91  * @param timeout The amount of time in microseconds to wait. This is
  92  *        a maximum, not a minimum. If the condition is signaled, we
  93  *        will wake up before this time, otherwise the error APR_TIMEUP
  94  *        is returned.
  95  */
  96 APR_DECLARE(apr_status_t) apr_thread_cond_timedwait(apr_thread_cond_t *cond,
  97                                                     apr_thread_mutex_t *mutex,
  98                                                     apr_interval_time_t timeout);
  99
 100 /**
 101  * Signals a single thread, if one exists, that is blocking on the given
 102  * condition variable. That thread is then scheduled to wake up and acquire
 103  * the associated mutex. Although it is not required, if predictable scheduling
 104  * is desired, that mutex must be locked while calling this function.
 105  * @param cond the condition variable on which to produce the signal.
 106  * @remark If no threads are waiting on the condition variable, nothing happens.
 107  */
 108 APR_DECLARE(apr_status_t) apr_thread_cond_signal(apr_thread_cond_t *cond);
 109
 110 /**
 111  * Signals all threads blocking on the given condition variable.
 112  * Each thread that was signaled is then scheduled to wake up and acquire
 113  * the associated mutex. This will happen in a serialized manner.
 114  * @param cond the condition variable on which to produce the broadcast.
 115  * @remark If no threads are waiting on the condition variable, nothing happens.
 116  */
 117 APR_DECLARE(apr_status_t) apr_thread_cond_broadcast(apr_thread_cond_t *cond);
 118
 119 /**
 120  * Destroy the condition variable and free the associated memory.
 121  * @param cond the condition variable to destroy.
 122  */
 123 APR_DECLARE(apr_status_t) apr_thread_cond_destroy(apr_thread_cond_t *cond);
 124
 125 /**
 126  * Get the pool used by this thread_cond.
 127  * @return apr_pool_t the pool
 128  */
 129 APR_POOL_DECLARE_ACCESSOR(thread_cond);
 130
 131 #endif /* APR_HAS_THREADS */
 132
 133 /** @} */
 134
 135 #ifdef __cplusplus
 136 }
 137 #endif
 138
 139 #endif  /* ! APR_THREAD_COND_H */