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     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 */