1 /* Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 * Use of this source code is governed by a BSD-style license that can be 3 * found in the LICENSE file. 4 */ 5 6 /** 7 * Defines the PPB_MessageLoop interface. 8 */ 9 label Chrome { 10 M25 = 1.0 11 }; 12 13 /** 14 * A message loop allows PPAPI calls to be issued on a thread. You may not 15 * issue any API calls on a thread without creating a message loop. It also 16 * allows you to post work to the message loop for a thread. 17 * 18 * To process work posted to the message loop, as well as completion callbacks 19 * for asynchronous operations, you must run the message loop via Run(). 20 * 21 * Note the system manages the lifetime of the instance (and all associated 22 * resources). If the instance is deleted from the page, background threads may 23 * suddenly see their PP_Resource handles become invalid. In this case, calls 24 * will fail with PP_ERROR_BADRESOURCE. If you need to access data associated 25 * with your instance, you will probably want to create some kind of threadsafe 26 * proxy object that can handle asynchronous destruction of the instance object. 27 * 28 * Typical usage: 29 * On the main thread: 30 * - Create the thread yourself (using pthreads). 31 * - Create the message loop resource. 32 * - Pass the message loop resource to your thread's main function. 33 * - Call PostWork() on the message loop to run functions on the thread. 34 * 35 * From the background thread's main function: 36 * - Call AttachToCurrentThread() with the message loop resource. 37 * - Call Run() with the message loop resource. 38 * 39 * Your callbacks should look like this: 40 * @code 41 * void DoMyWork(void* user_data, int32_t status) { 42 * if (status != PP_OK) { 43 * Cleanup(); // e.g. free user_data. 44 * return; 45 * } 46 * ... do your work... 47 * } 48 * @endcode 49 * For a C++ example, see ppapi/utility/threading/simple_thread.h 50 * 51 * (You can also create the message loop resource on the background thread, 52 * but then the main thread will have no reference to it should you want to 53 * call PostWork()). 54 * 55 * 56 * THREAD HANDLING 57 * 58 * The main thread has an implicitly created message loop. The main thread is 59 * the thread where PPP_InitializeModule and PPP_Instance functions are called. 60 * You can retrieve a reference to this message loop by calling 61 * GetForMainThread() or, if your code is on the main thread, GetCurrent() will 62 * also work. 63 * 64 * Some special threads created by the system can not have message loops. In 65 * particular, the background thread created for audio processing has this 66 * requirement because it's intended to be highly responsive to keep up with 67 * the realtime requirements of audio processing. You can not make PPAPI calls 68 * from these threads. 69 * 70 * Once you associate a message loop with a thread, you don't have to keep a 71 * reference to it. The system will hold a reference to the message loop for as 72 * long as the thread is running. The current message loop can be retrieved 73 * using the GetCurrent() function. 74 * 75 * It is legal to create threads in your plugin without message loops, but 76 * PPAPI calls will fail unless explicitly noted in the documentation. 77 * 78 * You can create a message loop object on a thread and never actually run the 79 * message loop. This will allow you to call blocking PPAPI calls (via 80 * PP_BlockUntilComplete()). If you make any asynchronous calls, the callbacks 81 * from those calls will be queued in the message loop and never run. The same 82 * thing will happen if work is scheduled after the message loop exits and 83 * the message loop is not run again. 84 * 85 * 86 * DESTRUCTION AND ERROR HANDLING 87 * 88 * Often, your application will associate memory with completion callbacks. For 89 * example, the C++ CompletionCallbackFactory has a small amount of 90 * heap-allocated memory for each callback. This memory will be leaked if the 91 * callback is never run. To avoid this memory leak, you need to be careful 92 * about error handling and shutdown. 93 * 94 * There are a number of cases where posted callbacks will never be run: 95 * 96 * - You tear down the thread (via pthreads) without "destroying" the message 97 * loop (via PostQuit with should_destroy = PP_TRUE). In this case, any 98 * tasks in the message queue will be lost. 99 * 100 * - You create a message loop, post callbacks to it, and never run it. 101 * 102 * - You quit the message loop via PostQuit with should_destroy set to 103 * PP_FALSE. In this case, the system will assume the message loop will be 104 * run again later and keep your tasks. 105 * 106 * To do proper shutdown, call PostQuit with should_destroy = PP_TRUE. This 107 * will prohibit future work from being posted, and will allow the message loop 108 * to run until all pending tasks are run. 109 * 110 * If you post a callback to a message loop that's been destroyed, or to an 111 * invalid message loop, PostWork will return an error and will not run the 112 * callback. This is true even for callbacks with the "required" flag set, 113 * since the system may not even know what thread to issue the error callback 114 * on. 115 * 116 * Therefore, you should check for errors from PostWork and destroy any 117 * associated memory to avoid leaks. If you're using the C++ 118 * CompletionCallbackFactory, use the following pattern: 119 * @code 120 * pp::CompletionCallback callback = factory_.NewOptionalCallback(...); 121 * int32_t result = message_loop.PostWork(callback); 122 * if (result != PP_OK) 123 * callback.Run(result); 124 * @endcode 125 * This will run the callback with an error value, and assumes that the 126 * implementation of your callback checks the "result" argument and returns 127 * immediately on error. 128 */ 129 interface PPB_MessageLoop { 130 /** 131 * Creates a message loop resource. 132 * 133 * This may be called from any thread. After your thread starts but before 134 * issuing any other PPAPI calls on it, you must associate it with a message 135 * loop by calling AttachToCurrentThread. 136 */ 137 PP_Resource Create(PP_Instance instance); 138 139 /** 140 * Returns a resource identifying the message loop for the main thread. The 141 * main thread always has a message loop created by the system. 142 */ 143 PP_Resource GetForMainThread(); 144 145 /** 146 * Returns a reference to the PPB_MessageLoop object attached to the current 147 * thread. If there is no attached message loop, the return value will be 0. 148 */ 149 PP_Resource GetCurrent(); 150 151 /** 152 * Sets the given message loop resource as being the associated message loop 153 * for the currently running thread. 154 * 155 * You must call this function exactly once on a thread before making any 156 * PPAPI calls. A message loop can only be attached to one thread, and the 157 * message loop can not be changed later. The message loop will be attached 158 * as long as the thread is running or until you quit with should_destroy 159 * set to PP_TRUE. 160 * 161 * If this function fails, attempting to run the message loop will fail. 162 * Note that you can still post work to the message loop: it will get queued 163 * up should the message loop eventually be successfully attached and run. 164 * 165 * @return 166 * - PP_OK: The message loop was successfully attached to the thread and is 167 * ready to use. 168 * - PP_ERROR_BADRESOURCE: The given message loop resource is invalid. 169 * - PP_ERROR_INPROGRESS: The current thread already has a message loop 170 * attached. This will always be the case for the main thread, which has 171 * an implicit system-created message loop attached. 172 * - PP_ERROR_WRONG_THREAD: The current thread type can not have a message 173 * loop attached to it. See the interface level discussion about these 174 * special threads, which include realtime audio threads. 175 */ 176 int32_t AttachToCurrentThread([in] PP_Resource message_loop); 177 178 /** 179 * Runs the thread message loop. Running the message loop is required for you 180 * to get issued completion callbacks on the thread. 181 * 182 * The message loop identified by the argument must have been previously 183 * successfully attached to the current thread. 184 * 185 * You may not run nested message loops. Since the main thread has an 186 * implicit message loop that the system runs, you may not call Run on the 187 * main thread. 188 * 189 * @return 190 * - PP_OK: The message loop was successfully run. Note that on 191 * success, the message loop will only exit when you call PostQuit(). 192 * - PP_ERROR_BADRESOURCE: The given message loop resource is invalid. 193 * - PP_ERROR_WRONG_THREAD: You are attempting to run a message loop that 194 * has not been successfully attached to the current thread. Call 195 * AttachToCurrentThread(). 196 * - PP_ERROR_INPROGRESS: You are attempting to call Run in a nested 197 * fashion (Run is already on the stack). This will occur if you attempt 198 * to call run on the main thread's message loop (see above). 199 */ 200 int32_t Run([in] PP_Resource message_loop); 201 202 /** 203 * Schedules work to run on the given message loop. This may be called from 204 * any thread. Posted work will be executed in the order it was posted when 205 * the message loop is Run(). 206 * 207 * @param message_loop The message loop resource. 208 * 209 * @param callback The completion callback to execute from the message loop. 210 * 211 * @param delay_ms The number of milliseconds to delay execution of the given 212 * completion callback. Passing 0 means it will get queued normally and 213 * executed in order. 214 * 215 * 216 * The completion callback will be called with PP_OK as the "result" parameter 217 * if it is run normally. It is good practice to check for PP_OK and return 218 * early otherwise. 219 * 220 * The "required" flag on the completion callback is ignored. If there is an 221 * error posting your callback, the error will be returned from PostWork and 222 * the callback will never be run (because there is no appropriate place to 223 * run your callback with an error without causing unexpected threading 224 * problems). If you associate memory with the completion callback (for 225 * example, you're using the C++ CompletionCallbackFactory), you will need to 226 * free this or manually run the callback. See "Destruction and error 227 * handling" above. 228 * 229 * 230 * You can call this function before the message loop has started and the 231 * work will get queued until the message loop is run. You can also post 232 * work after the message loop has exited as long as should_destroy was 233 * PP_FALSE. It will be queued until the next invocation of Run(). 234 * 235 * @return 236 * - PP_OK: The work was posted to the message loop's queue. As described 237 * above, this does not mean that the work has been or will be executed 238 * (if you never run the message loop after posting). 239 * - PP_ERROR_BADRESOURCE: The given message loop resource is invalid. 240 * - PP_ERROR_BADARGUMENT: The function pointer for the completion callback 241 * is null (this will be the case if you pass PP_BlockUntilComplete()). 242 * - PP_ERROR_FAILED: The message loop has been destroyed. 243 */ 244 int32_t PostWork([in] PP_Resource message_loop, 245 [in] PP_CompletionCallback callback, 246 [in] int64_t delay_ms); 247 248 /** 249 * Posts a quit message to the given message loop's work queue. Work posted 250 * before that point will be processed before quitting. 251 * 252 * This may be called on the message loop registered for the current thread, 253 * or it may be called on the message loop registered for another thread. It 254 * is an error to attempt to PostQuit() the main thread loop. 255 * 256 * @param should_destroy Marks the message loop as being in a destroyed state 257 * and prevents further posting of messages. 258 * 259 * If you quit a message loop without setting should_destroy, it will still 260 * be attached to the thread and you can still run it again by calling Run() 261 * again. If you destroy it, it will be detached from the current thread. 262 * 263 * @return 264 * - PP_OK: The request to quit was successfully posted. 265 * - PP_ERROR_BADRESOURCE: The message loop was invalid. 266 * - PP_ERROR_WRONG_THREAD: You are attempting to quit the main thread. 267 * The main thread's message loop is managed by the system and can't be 268 * quit. 269 */ 270 int32_t PostQuit([in] PP_Resource message_loop, PP_Bool should_destroy); 271 }; 272
