1 #ifndef foothreadmainloophfoo 2 #define foothreadmainloophfoo 3 4 /*** 5 This file is part of PulseAudio. 6 7 Copyright 2006 Lennart Poettering 8 Copyright 2006 Pierre Ossman <ossman (at) cendio.se> for Cendio AB 9 10 PulseAudio is free software; you can redistribute it and/or modify 11 it under the terms of the GNU Lesser General Public License as published 12 by the Free Software Foundation; either version 2.1 of the License, 13 or (at your option) any later version. 14 15 PulseAudio is distributed in the hope that it will be useful, but 16 WITHOUT ANY WARRANTY; without even the implied warranty of 17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 18 General Public License for more details. 19 20 You should have received a copy of the GNU Lesser General Public License 21 along with PulseAudio; if not, write to the Free Software 22 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 23 USA. 24 ***/ 25 26 #include <pulse/mainloop-api.h> 27 #include <pulse/cdecl.h> 28 #include <pulse/version.h> 29 30 PA_C_DECL_BEGIN 31 32 /** \page threaded_mainloop Threaded Main Loop 33 * 34 * \section overv_sec Overview 35 * 36 * The threaded main loop implementation is a special version of the primary 37 * main loop implementation (see \ref mainloop). For the basic design, see 38 * its documentation. 39 * 40 * The added feature in the threaded main loop is that it spawns a new thread 41 * that runs the real main loop. This allows a synchronous application to use 42 * the asynchronous API without risking to stall the PulseAudio library. 43 * 44 * \section creat_sec Creation 45 * 46 * A pa_threaded_mainloop object is created using pa_threaded_mainloop_new(). 47 * This will only allocate the required structures though, so to use it the 48 * thread must also be started. This is done through 49 * pa_threaded_mainloop_start(), after which you can start using the main loop. 50 * 51 * \section destr_sec Destruction 52 * 53 * When the PulseAudio connection has been terminated, the thread must be 54 * stopped and the resources freed. Stopping the thread is done using 55 * pa_threaded_mainloop_stop(), which must be called without the lock (see 56 * below) held. When that function returns, the thread is stopped and the 57 * pa_threaded_mainloop object can be freed using pa_threaded_mainloop_free(). 58 * 59 * \section lock_sec Locking 60 * 61 * Since the PulseAudio API doesn't allow concurrent accesses to objects, 62 * a locking scheme must be used to guarantee safe usage. The threaded main 63 * loop API provides such a scheme through the functions 64 * pa_threaded_mainloop_lock() and pa_threaded_mainloop_unlock(). 65 * 66 * The lock is recursive, so it's safe to use it multiple times from the same 67 * thread. Just make sure you call pa_threaded_mainloop_unlock() the same 68 * number of times you called pa_threaded_mainloop_lock(). 69 * 70 * The lock needs to be held whenever you call any PulseAudio function that 71 * uses an object associated with this main loop. Make sure you do not hold 72 * on to the lock more than necessary though, as the threaded main loop stops 73 * while the lock is held. 74 * 75 * Example: 76 * 77 * \code 78 * void my_check_stream_func(pa_threaded_mainloop *m, pa_stream *s) { 79 * pa_stream_state_t state; 80 * 81 * pa_threaded_mainloop_lock(m); 82 * 83 * state = pa_stream_get_state(s); 84 * 85 * pa_threaded_mainloop_unlock(m); 86 * 87 * if (state == PA_STREAM_READY) 88 * printf("Stream is ready!"); 89 * else 90 * printf("Stream is not ready!"); 91 * } 92 * \endcode 93 * 94 * \section cb_sec Callbacks 95 * 96 * Callbacks in PulseAudio are asynchronous, so they require extra care when 97 * using them together with a threaded main loop. 98 * 99 * The easiest way to turn the callback based operations into synchronous 100 * ones, is to simply wait for the callback to be called and continue from 101 * there. This is the approach chosen in PulseAudio's threaded API. 102 * 103 * \subsection basic_subsec Basic callbacks 104 * 105 * For the basic case, where all that is required is to wait for the callback 106 * to be invoked, the code should look something like this: 107 * 108 * Example: 109 * 110 * \code 111 * static void my_drain_callback(pa_stream *s, int success, void *userdata) { 112 * pa_threaded_mainloop *m; 113 * 114 * m = userdata; 115 * assert(m); 116 * 117 * pa_threaded_mainloop_signal(m, 0); 118 * } 119 * 120 * void my_drain_stream_func(pa_threaded_mainloop *m, pa_stream *s) { 121 * pa_operation *o; 122 * 123 * pa_threaded_mainloop_lock(m); 124 * 125 * o = pa_stream_drain(s, my_drain_callback, m); 126 * assert(o); 127 * 128 * while (pa_operation_get_state(o) == PA_OPERATION_RUNNING) 129 * pa_threaded_mainloop_wait(m); 130 * 131 * pa_operation_unref(o); 132 * 133 * pa_threaded_mainloop_unlock(m); 134 * } 135 * \endcode 136 * 137 * The main function, my_drain_stream_func(), will wait for the callback to 138 * be called using pa_threaded_mainloop_wait(). 139 * 140 * If your application is multi-threaded, then this waiting must be 141 * done inside a while loop. The reason for this is that multiple 142 * threads might be using pa_threaded_mainloop_wait() at the same 143 * time. Each thread must therefore verify that it was its callback 144 * that was invoked. Also the underlying OS synchronization primitives 145 * are usually not free of spurious wake-ups, so a 146 * pa_threaded_mainloop_wait() must be called within a loop even if 147 * you have only one thread waiting. 148 * 149 * The callback, my_drain_callback(), indicates to the main function that it 150 * has been called using pa_threaded_mainloop_signal(). 151 * 152 * As you can see, pa_threaded_mainloop_wait() may only be called with 153 * the lock held. The same thing is true for pa_threaded_mainloop_signal(), 154 * but as the lock is held before the callback is invoked, you do not have to 155 * deal with that. 156 * 157 * The functions will not dead lock because the wait function will release 158 * the lock before waiting and then regrab it once it has been signaled. 159 * For those of you familiar with threads, the behaviour is that of a 160 * condition variable. 161 * 162 * \subsection data_subsec Data callbacks 163 * 164 * For many callbacks, simply knowing that they have been called is 165 * insufficient. The callback also receives some data that is desired. To 166 * access this data safely, we must extend our example a bit: 167 * 168 * \code 169 * static int *drain_result; 170 * 171 * static void my_drain_callback(pa_stream*s, int success, void *userdata) { 172 * pa_threaded_mainloop *m; 173 * 174 * m = userdata; 175 * assert(m); 176 * 177 * drain_result = &success; 178 * 179 * pa_threaded_mainloop_signal(m, 1); 180 * } 181 * 182 * void my_drain_stream_func(pa_threaded_mainloop *m, pa_stream *s) { 183 * pa_operation *o; 184 * 185 * pa_threaded_mainloop_lock(m); 186 * 187 * o = pa_stream_drain(s, my_drain_callback, m); 188 * assert(o); 189 * 190 * while (pa_operation_get_state(o) == PA_OPERATION_RUNNING) 191 * pa_threaded_mainloop_wait(m); 192 * 193 * pa_operation_unref(o); 194 * 195 * if (*drain_result) 196 * printf("Success!"); 197 * else 198 * printf("Bitter defeat..."); 199 * 200 * pa_threaded_mainloop_accept(m); 201 * 202 * pa_threaded_mainloop_unlock(m); 203 * } 204 * \endcode 205 * 206 * The example is a bit silly as it would probably have been easier to just 207 * copy the contents of success, but for larger data structures this can be 208 * wasteful. 209 * 210 * The difference here compared to the basic callback is the 1 sent to 211 * pa_threaded_mainloop_signal() and the call to 212 * pa_threaded_mainloop_accept(). What will happen is that 213 * pa_threaded_mainloop_signal() will signal the main function and then stop. 214 * The main function is then free to use the data in the callback until 215 * pa_threaded_mainloop_accept() is called, which will allow the callback 216 * to continue. 217 * 218 * Note that pa_threaded_mainloop_accept() must be called some time between 219 * exiting the while loop and unlocking the main loop! Failure to do so will 220 * result in a race condition. I.e. it is not ok to release the lock and 221 * regrab it before calling pa_threaded_mainloop_accept(). 222 * 223 * \subsection async_subsec Asynchronous callbacks 224 * 225 * PulseAudio also has callbacks that are completely asynchronous, meaning 226 * that they can be called at any time. The threading main loop API provides 227 * the locking mechanism to handle concurrent accesses, but nothing else. 228 * Applications will have to handle communication from the callback to the 229 * main program through some own system. 230 * 231 * The callbacks that are completely asynchronous are: 232 * 233 * \li State callbacks for contexts, streams, etc. 234 * \li Subscription notifications 235 */ 236 237 /** \file 238 * 239 * A thread based event loop implementation based on pa_mainloop. The 240 * event loop is run in a helper thread in the background. A few 241 * synchronization primitives are available to access the objects 242 * attached to the event loop safely. 243 * 244 * See also \subpage threaded_mainloop 245 */ 246 247 /** An opaque threaded main loop object */ 248 typedef struct pa_threaded_mainloop pa_threaded_mainloop; 249 250 /** Allocate a new threaded main loop object. You have to call 251 * pa_threaded_mainloop_start() before the event loop thread starts 252 * running. */ 253 pa_threaded_mainloop *pa_threaded_mainloop_new(void); 254 255 /** Free a threaded main loop object. If the event loop thread is 256 * still running, terminate it with pa_threaded_mainloop_stop() 257 * first. */ 258 void pa_threaded_mainloop_free(pa_threaded_mainloop* m); 259 260 /** Start the event loop thread. */ 261 int pa_threaded_mainloop_start(pa_threaded_mainloop *m); 262 263 /** Terminate the event loop thread cleanly. Make sure to unlock the 264 * mainloop object before calling this function. */ 265 void pa_threaded_mainloop_stop(pa_threaded_mainloop *m); 266 267 /** Lock the event loop object, effectively blocking the event loop 268 * thread from processing events. You can use this to enforce 269 * exclusive access to all objects attached to the event loop. This 270 * lock is recursive. This function may not be called inside the event 271 * loop thread. Events that are dispatched from the event loop thread 272 * are executed with this lock held. */ 273 void pa_threaded_mainloop_lock(pa_threaded_mainloop *m); 274 275 /** Unlock the event loop object, inverse of pa_threaded_mainloop_lock() */ 276 void pa_threaded_mainloop_unlock(pa_threaded_mainloop *m); 277 278 /** Wait for an event to be signalled by the event loop thread. You 279 * can use this to pass data from the event loop thread to the main 280 * thread in synchronized fashion. This function may not be called 281 * inside the event loop thread. Prior to this call the event loop 282 * object needs to be locked using pa_threaded_mainloop_lock(). While 283 * waiting the lock will be released, immediately before returning it 284 * will be acquired again. This function may spuriously wake up even 285 * without _signal() being called. You need to make sure to handle 286 * that! */ 287 void pa_threaded_mainloop_wait(pa_threaded_mainloop *m); 288 289 /** Signal all threads waiting for a signalling event in 290 * pa_threaded_mainloop_wait(). If wait_for_release is non-zero, do 291 * not return before the signal was accepted by a 292 * pa_threaded_mainloop_accept() call. While waiting for that condition 293 * the event loop object is unlocked. */ 294 void pa_threaded_mainloop_signal(pa_threaded_mainloop *m, int wait_for_accept); 295 296 /** Accept a signal from the event thread issued with 297 * pa_threaded_mainloop_signal(). This call should only be used in 298 * conjunction with pa_threaded_mainloop_signal() with a non-zero 299 * wait_for_accept value. */ 300 void pa_threaded_mainloop_accept(pa_threaded_mainloop *m); 301 302 /** Return the return value as specified with the main loop's quit() routine. */ 303 int pa_threaded_mainloop_get_retval(pa_threaded_mainloop *m); 304 305 /** Return the abstract main loop abstraction layer vtable for this 306 main loop. No need to free the API as it is owned by the loop 307 and is destroyed when the loop is freed. */ 308 pa_mainloop_api* pa_threaded_mainloop_get_api(pa_threaded_mainloop*m); 309 310 /** Returns non-zero when called from withing the event loop thread. \since 0.9.7 */ 311 int pa_threaded_mainloop_in_thread(pa_threaded_mainloop *m); 312 313 PA_C_DECL_END 314 315 #endif 316
