src/misc/background_worker.h

   1 /*****************************************************************************
   2  * Copyright (C) 2017 VLC authors and VideoLAN
   3  *
   4  * This program is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU Lesser General Public License as published by
   6  * the Free Software Foundation; either version 2.1 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  12  * GNU Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public License
  15  * along with this program; if not, write to the Free Software Foundation,
  16  * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  17  *****************************************************************************/
  18
  19 #ifndef BACKGROUND_WORKER_H__
  20 #define BACKGROUND_WORKER_H__
  21
  22 struct background_worker_config {
  23     /**
  24      * Default timeout for completing a task
  25      *
  26      * If less-than 0 a task can run indefinitely without being killed, whereas
  27      * a positive value denotes the maximum number of milliseconds a task can
  28      * run before \ref pf_stop is called to kill it.
  29      **/
  30     vlc_tick_t default_timeout;
  31
  32     /**
  33      * Release an entity
  34      *
  35      * This callback will be called in order to decrement the ref-count of a
  36      * entity within the background-worker. It will happen either when \ref
  37      * pf_stop has finished executing, or if the entity is removed from the
  38      * queue (through \ref background_worker_Cancel)
  39      *
  40      * \param entity the entity to release
  41      **/
  42     void( *pf_release )( void* entity );
  43
  44     /**
  45      * Hold a queued item
  46      *
  47      * This callback will be called in order to increment the ref-count of an
  48      * entity. It will happen when the entity is pushed into the queue of
  49      * pending tasks as part of \ref background_worker_Push.
  50      *
  51      * \param entity the entity to hold
  52      **/
  53     void( *pf_hold )( void* entity );
  54
  55     /**
  56      * Start a new task
  57      *
  58      * This callback is called in order to construct a new background task. In
  59      * order for the background-worker to be able to continue processing
  60      * incoming requests, \ref pf_start is meant to start a task (such as a
  61      * thread), and then store the associated handle in `*out`.
  62      *
  63      * The value of `*out` will then be the value of the argument named `handle`
  64      * in terms of \ref pf_probe and \ref pf_stop.
  65      *
  66      * \param owner the owner of the background-worker
  67      * \param entity the entity for which a task is to be created
  68      * \param out [out] `*out` shall, on success, refer to the handle associated
  69      *                   with the running task.
  70      * \return VLC_SUCCESS if a task was created, an error-code on failure.
  71      **/
  72     int( *pf_start )( void* owner, void* entity, void** out );
  73
  74     /**
  75      * Probe a running task
  76      *
  77      * This callback is called in order to see whether or not a running task has
  78      * finished or not. It can be called anytime between a successful call to
  79      * \ref pf_start, and the corresponding call to \ref pf_stop.
  80      *
  81      * \param owner the owner of the background-worker
  82      * \param handle the handle associated with the running task
  83      * \return 0 if the task is still running, any other value if finished.
  84      **/
  85     int( *pf_probe )( void* owner, void* handle );
  86
  87     /**
  88      * Stop a running task
  89      *
  90      * This callback is called in order to stop a running task. If \ref pf_start
  91      * has created a non-detached thread, \ref pf_stop is where you would
  92      * interrupt and then join it.
  93      *
  94      * \warning This function is called either after \ref pf_probe has stated
  95      *          that the task has finished, or if the timeout (if any) for the
  96      *          task has been reached.
  97      *
  98      * \param owner the owner of the background-worker
  99      * \parma handle the handle associated with the task to be stopped
 100      **/
 101     void( *pf_stop )( void* owner, void* handle );
 102 };
 103
 104 /**
 105  * Create a background-worker
 106  *
 107  * This function creates a new background-worker using the passed configuration.
 108  *
 109  * \warning all members of `config` shall have been set by the caller.
 110  * \warning the returned resource must be destroyed using \ref
 111  *          background_worker_Delete on success.
 112  *
 113  * \param owner the owner of the background-worker
 114  * \param config the background-worker's configuration
 115  * \return a pointer-to the created background-worker on success,
 116  *         `NULL` on failure.
 117  **/
 118 struct background_worker* background_worker_New( void* owner,
 119     struct background_worker_config* config );
 120
 121 /**
 122  * Request the background-worker to probe the current task
 123  *
 124  * This function is used to signal the background-worker that it should do
 125  * another probe to see whether the current task is still alive.
 126  *
 127  * \warning Note that the function will not wait for the probing to finish, it
 128  *          will simply ask the background worker to recheck it as soon as
 129  *          possible.
 130  *
 131  * \param worker the background-worker
 132  **/
 133 void background_worker_RequestProbe( struct background_worker* worker );
 134
 135 /**
 136  * Push an entity into the background-worker
 137  *
 138  * This function is used to push an entity into the queue of pending work. The
 139  * entities will be processed in the order in which they are received (in terms
 140  * of the order of invocations in a single-threaded environment).
 141  *
 142  * \param worker the background-worker
 143  * \param entity the entity which is to be queued
 144  * \param id a value suitable for identifying the entity, or `NULL`
 145  * \param timeout the timeout of the entity in milliseconds, `0` denotes no
 146  *                timeout, a negative value will use the default timeout
 147  *                associated with the background-worker.
 148  * \return VLC_SUCCESS if the entity was successfully queued, an error-code on
 149  *         failure.
 150  **/
 151 int background_worker_Push( struct background_worker* worker, void* entity,
 152     void* id, int timeout );
 153
 154 /**
 155  * Remove entities from the background-worker
 156  *
 157  * This function is used to remove processing of a certain entity given its
 158  * associated id, or to remove all queued (including currently running)
 159  * entities.
 160  *
 161  * \warning if the `id` passed refers to an entity that is currently being
 162  *          processed, the call will block until the task has been terminated.
 163  *
 164  * \param worker the background-worker
 165  * \param id NULL if every entity shall be removed, and the currently running
 166  *        task (if any) shall be cancelled.
 167  **/
 168 void background_worker_Cancel( struct background_worker* worker, void* id );
 169
 170 /**
 171  * Delete a background-worker
 172  *
 173  * This function will destroy a background-worker created through \ref
 174  * background_worker_New. It will effectively stop the currently running task,
 175  * if any, and empty the queue of pending entities.
 176  *
 177  * \warning If there is a currently running task, the function will block until
 178  *          it has been stopped.
 179  *
 180  * \param worker the background-worker
 181  **/
 182 void background_worker_Delete( struct background_worker* worker );
 183 #endif