ModernAsyncTask.java revision ea85d97d6a7eed3aedbde96bbeb40690599ef071
1/* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * 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 17package android.support.v4.content; 18 19import java.util.concurrent.BlockingQueue; 20import java.util.concurrent.Callable; 21import java.util.concurrent.CancellationException; 22import java.util.concurrent.ExecutionException; 23import java.util.concurrent.Executor; 24import java.util.concurrent.FutureTask; 25import java.util.concurrent.LinkedBlockingQueue; 26import java.util.concurrent.ThreadFactory; 27import java.util.concurrent.ThreadPoolExecutor; 28import java.util.concurrent.TimeUnit; 29import java.util.concurrent.TimeoutException; 30import java.util.concurrent.atomic.AtomicBoolean; 31import java.util.concurrent.atomic.AtomicInteger; 32 33import android.os.AsyncTask; 34import android.os.Handler; 35import android.os.Looper; 36import android.os.Message; 37import android.os.Process; 38 39/** 40 * Copy of the required parts of {@link android.os.AsyncTask} from Android 3.0 that is 41 * needed to support AsyncTaskLoader. We use this rather than the one from the platform 42 * because we rely on some subtle behavior of AsyncTask that is not reliable on 43 * older platforms. 44 * 45 * <p>Note that for now this is not publicly available because it is not a 46 * complete implementation, only sufficient for the needs of 47 * {@link AsyncTaskLoader}. 48 */ 49abstract class ModernAsyncTask<Params, Progress, Result> { 50 private static final String LOG_TAG = "AsyncTask"; 51 52 private static final int CORE_POOL_SIZE = 5; 53 private static final int MAXIMUM_POOL_SIZE = 128; 54 private static final int KEEP_ALIVE = 1; 55 56 private static final ThreadFactory sThreadFactory = new ThreadFactory() { 57 private final AtomicInteger mCount = new AtomicInteger(1); 58 59 public Thread newThread(Runnable r) { 60 return new Thread(r, "ModernAsyncTask #" + mCount.getAndIncrement()); 61 } 62 }; 63 64 private static final BlockingQueue<Runnable> sPoolWorkQueue = 65 new LinkedBlockingQueue<Runnable>(10); 66 67 /** 68 * An {@link Executor} that can be used to execute tasks in parallel. 69 */ 70 public static final Executor THREAD_POOL_EXECUTOR 71 = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE, 72 TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory); 73 74 private static final int MESSAGE_POST_RESULT = 0x1; 75 private static final int MESSAGE_POST_PROGRESS = 0x2; 76 77 private static InternalHandler sHandler; 78 79 private static volatile Executor sDefaultExecutor = THREAD_POOL_EXECUTOR; 80 private final WorkerRunnable<Params, Result> mWorker; 81 private final FutureTask<Result> mFuture; 82 83 private volatile Status mStatus = Status.PENDING; 84 85 private final AtomicBoolean mTaskInvoked = new AtomicBoolean(); 86 87 /** 88 * Indicates the current status of the task. Each status will be set only once 89 * during the lifetime of a task. 90 */ 91 public enum Status { 92 /** 93 * Indicates that the task has not been executed yet. 94 */ 95 PENDING, 96 /** 97 * Indicates that the task is running. 98 */ 99 RUNNING, 100 /** 101 * Indicates that {@link android.os.AsyncTask#onPostExecute(Object)} has finished. 102 */ 103 FINISHED, 104 } 105 106 private static Handler getHandler() { 107 synchronized (AsyncTask.class) { 108 if (sHandler == null) { 109 sHandler = new InternalHandler(); 110 } 111 return sHandler; 112 } 113 } 114 115 /** @hide */ 116 public static void setDefaultExecutor(Executor exec) { 117 sDefaultExecutor = exec; 118 } 119 120 /** 121 * Creates a new asynchronous task. This constructor must be invoked on the UI thread. 122 */ 123 public ModernAsyncTask() { 124 mWorker = new WorkerRunnable<Params, Result>() { 125 public Result call() throws Exception { 126 mTaskInvoked.set(true); 127 128 Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); 129 return postResult(doInBackground(mParams)); 130 } 131 }; 132 133 mFuture = new FutureTask<Result>(mWorker) { 134 @Override 135 protected void done() { 136 try { 137 final Result result = get(); 138 139 postResultIfNotInvoked(result); 140 } catch (InterruptedException e) { 141 android.util.Log.w(LOG_TAG, e); 142 } catch (ExecutionException e) { 143 throw new RuntimeException( 144 "An error occurred while executing doInBackground()", e.getCause()); 145 } catch (CancellationException e) { 146 postResultIfNotInvoked(null); 147 } catch (Throwable t) { 148 throw new RuntimeException( 149 "An error occurred while executing doInBackground()", t); 150 } 151 } 152 }; 153 } 154 155 private void postResultIfNotInvoked(Result result) { 156 final boolean wasTaskInvoked = mTaskInvoked.get(); 157 if (!wasTaskInvoked) { 158 postResult(result); 159 } 160 } 161 162 private Result postResult(Result result) { 163 Message message = getHandler().obtainMessage(MESSAGE_POST_RESULT, 164 new AsyncTaskResult<Result>(this, result)); 165 message.sendToTarget(); 166 return result; 167 } 168 169 /** 170 * Returns the current status of this task. 171 * 172 * @return The current status. 173 */ 174 public final Status getStatus() { 175 return mStatus; 176 } 177 178 /** 179 * Override this method to perform a computation on a background thread. The 180 * specified parameters are the parameters passed to {@link #execute} 181 * by the caller of this task. 182 * 183 * This method can call {@link #publishProgress} to publish updates 184 * on the UI thread. 185 * 186 * @param params The parameters of the task. 187 * 188 * @return A result, defined by the subclass of this task. 189 * 190 * @see #onPreExecute() 191 * @see #onPostExecute 192 * @see #publishProgress 193 */ 194 protected abstract Result doInBackground(Params... params); 195 196 /** 197 * Runs on the UI thread before {@link #doInBackground}. 198 * 199 * @see #onPostExecute 200 * @see #doInBackground 201 */ 202 protected void onPreExecute() { 203 } 204 205 /** 206 * <p>Runs on the UI thread after {@link #doInBackground}. The 207 * specified result is the value returned by {@link #doInBackground}.</p> 208 * 209 * <p>This method won't be invoked if the task was cancelled.</p> 210 * 211 * @param result The result of the operation computed by {@link #doInBackground}. 212 * 213 * @see #onPreExecute 214 * @see #doInBackground 215 * @see #onCancelled(Object) 216 */ 217 @SuppressWarnings({"UnusedDeclaration"}) 218 protected void onPostExecute(Result result) { 219 } 220 221 /** 222 * Runs on the UI thread after {@link #publishProgress} is invoked. 223 * The specified values are the values passed to {@link #publishProgress}. 224 * 225 * @param values The values indicating progress. 226 * 227 * @see #publishProgress 228 * @see #doInBackground 229 */ 230 @SuppressWarnings({"UnusedDeclaration"}) 231 protected void onProgressUpdate(Progress... values) { 232 } 233 234 /** 235 * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and 236 * {@link #doInBackground(Object[])} has finished.</p> 237 * 238 * <p>The default implementation simply invokes {@link #onCancelled()} and 239 * ignores the result. If you write your own implementation, do not call 240 * <code>super.onCancelled(result)</code>.</p> 241 * 242 * @param result The result, if any, computed in 243 * {@link #doInBackground(Object[])}, can be null 244 * 245 * @see #cancel(boolean) 246 * @see #isCancelled() 247 */ 248 @SuppressWarnings({"UnusedParameters"}) 249 protected void onCancelled(Result result) { 250 onCancelled(); 251 } 252 253 /** 254 * <p>Applications should preferably override {@link #onCancelled(Object)}. 255 * This method is invoked by the default implementation of 256 * {@link #onCancelled(Object)}.</p> 257 * 258 * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and 259 * {@link #doInBackground(Object[])} has finished.</p> 260 * 261 * @see #onCancelled(Object) 262 * @see #cancel(boolean) 263 * @see #isCancelled() 264 */ 265 protected void onCancelled() { 266 } 267 268 /** 269 * Returns <tt>true</tt> if this task was cancelled before it completed 270 * normally. If you are calling {@link #cancel(boolean)} on the task, 271 * the value returned by this method should be checked periodically from 272 * {@link #doInBackground(Object[])} to end the task as soon as possible. 273 * 274 * @return <tt>true</tt> if task was cancelled before it completed 275 * 276 * @see #cancel(boolean) 277 */ 278 public final boolean isCancelled() { 279 return mFuture.isCancelled(); 280 } 281 282 /** 283 * <p>Attempts to cancel execution of this task. This attempt will 284 * fail if the task has already completed, already been cancelled, 285 * or could not be cancelled for some other reason. If successful, 286 * and this task has not started when <tt>cancel</tt> is called, 287 * this task should never run. If the task has already started, 288 * then the <tt>mayInterruptIfRunning</tt> parameter determines 289 * whether the thread executing this task should be interrupted in 290 * an attempt to stop the task.</p> 291 * 292 * <p>Calling this method will result in {@link #onCancelled(Object)} being 293 * invoked on the UI thread after {@link #doInBackground(Object[])} 294 * returns. Calling this method guarantees that {@link #onPostExecute(Object)} 295 * is never invoked. After invoking this method, you should check the 296 * value returned by {@link #isCancelled()} periodically from 297 * {@link #doInBackground(Object[])} to finish the task as early as 298 * possible.</p> 299 * 300 * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this 301 * task should be interrupted; otherwise, in-progress tasks are allowed 302 * to complete. 303 * 304 * @return <tt>false</tt> if the task could not be cancelled, 305 * typically because it has already completed normally; 306 * <tt>true</tt> otherwise 307 * 308 * @see #isCancelled() 309 * @see #onCancelled(Object) 310 */ 311 public final boolean cancel(boolean mayInterruptIfRunning) { 312 return mFuture.cancel(mayInterruptIfRunning); 313 } 314 315 /** 316 * Waits if necessary for the computation to complete, and then 317 * retrieves its result. 318 * 319 * @return The computed result. 320 * 321 * @throws CancellationException If the computation was cancelled. 322 * @throws ExecutionException If the computation threw an exception. 323 * @throws InterruptedException If the current thread was interrupted 324 * while waiting. 325 */ 326 public final Result get() throws InterruptedException, ExecutionException { 327 return mFuture.get(); 328 } 329 330 /** 331 * Waits if necessary for at most the given time for the computation 332 * to complete, and then retrieves its result. 333 * 334 * @param timeout Time to wait before cancelling the operation. 335 * @param unit The time unit for the timeout. 336 * 337 * @return The computed result. 338 * 339 * @throws CancellationException If the computation was cancelled. 340 * @throws ExecutionException If the computation threw an exception. 341 * @throws InterruptedException If the current thread was interrupted 342 * while waiting. 343 * @throws TimeoutException If the wait timed out. 344 */ 345 public final Result get(long timeout, TimeUnit unit) throws InterruptedException, 346 ExecutionException, TimeoutException { 347 return mFuture.get(timeout, unit); 348 } 349 350 /** 351 * Executes the task with the specified parameters. The task returns 352 * itself (this) so that the caller can keep a reference to it. 353 * 354 * <p>Note: this function schedules the task on a queue for a single background 355 * thread or pool of threads depending on the platform version. When first 356 * introduced, AsyncTasks were executed serially on a single background thread. 357 * Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed 358 * to a pool of threads allowing multiple tasks to operate in parallel. After 359 * {@link android.os.Build.VERSION_CODES#HONEYCOMB}, it is planned to change this 360 * back to a single thread to avoid common application errors caused 361 * by parallel execution. If you truly want parallel execution, you can use 362 * the {@link #executeOnExecutor} version of this method 363 * with {@link #THREAD_POOL_EXECUTOR}; however, see commentary there for warnings on 364 * its use. 365 * 366 * <p>This method must be invoked on the UI thread. 367 * 368 * @param params The parameters of the task. 369 * 370 * @return This instance of AsyncTask. 371 * 372 * @throws IllegalStateException If {@link #getStatus()} returns either 373 * {@link android.os.AsyncTask.Status#RUNNING} or 374 * {@link android.os.AsyncTask.Status#FINISHED}. 375 */ 376 public final ModernAsyncTask<Params, Progress, Result> execute(Params... params) { 377 return executeOnExecutor(sDefaultExecutor, params); 378 } 379 380 /** 381 * Executes the task with the specified parameters. The task returns 382 * itself (this) so that the caller can keep a reference to it. 383 * 384 * <p>This method is typically used with {@link #THREAD_POOL_EXECUTOR} to 385 * allow multiple tasks to run in parallel on a pool of threads managed by 386 * AsyncTask, however you can also use your own {@link Executor} for custom 387 * behavior. 388 * 389 * <p><em>Warning:</em> Allowing multiple tasks to run in parallel from 390 * a thread pool is generally <em>not</em> what one wants, because the order 391 * of their operation is not defined. For example, if these tasks are used 392 * to modify any state in common (such as writing a file due to a button click), 393 * there are no guarantees on the order of the modifications. 394 * Without careful work it is possible in rare cases for the newer version 395 * of the data to be over-written by an older one, leading to obscure data 396 * loss and stability issues. 397 * 398 * <p>This method must be invoked on the UI thread. 399 * 400 * @param exec The executor to use. {@link #THREAD_POOL_EXECUTOR} is available as a 401 * convenient process-wide thread pool for tasks that are loosely coupled. 402 * @param params The parameters of the task. 403 * 404 * @return This instance of AsyncTask. 405 * 406 * @throws IllegalStateException If {@link #getStatus()} returns either 407 * {@link android.os.AsyncTask.Status#RUNNING} 408 * or {@link android.os.AsyncTask.Status#FINISHED}. 409 */ 410 public final ModernAsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec, 411 Params... params) { 412 if (mStatus != Status.PENDING) { 413 switch (mStatus) { 414 case RUNNING: 415 throw new IllegalStateException("Cannot execute task:" 416 + " the task is already running."); 417 case FINISHED: 418 throw new IllegalStateException("Cannot execute task:" 419 + " the task has already been executed " 420 + "(a task can be executed only once)"); 421 } 422 } 423 424 mStatus = Status.RUNNING; 425 426 onPreExecute(); 427 428 mWorker.mParams = params; 429 exec.execute(mFuture); 430 431 return this; 432 } 433 434 /** 435 * Convenience version of {@link #execute(Object...)} for use with 436 * a simple Runnable object. 437 */ 438 public static void execute(Runnable runnable) { 439 sDefaultExecutor.execute(runnable); 440 } 441 442 /** 443 * This method can be invoked from {@link #doInBackground} to 444 * publish updates on the UI thread while the background computation is 445 * still running. Each call to this method will trigger the execution of 446 * {@link #onProgressUpdate} on the UI thread. 447 * 448 * {@link #onProgressUpdate} will note be called if the task has been 449 * canceled. 450 * 451 * @param values The progress values to update the UI with. 452 * 453 * @see #onProgressUpdate 454 * @see #doInBackground 455 */ 456 protected final void publishProgress(Progress... values) { 457 if (!isCancelled()) { 458 getHandler().obtainMessage(MESSAGE_POST_PROGRESS, 459 new AsyncTaskResult<Progress>(this, values)).sendToTarget(); 460 } 461 } 462 463 private void finish(Result result) { 464 if (isCancelled()) { 465 onCancelled(result); 466 } else { 467 onPostExecute(result); 468 } 469 mStatus = Status.FINISHED; 470 } 471 472 private static class InternalHandler extends Handler { 473 public InternalHandler() { 474 super(Looper.getMainLooper()); 475 } 476 477 @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"}) 478 @Override 479 public void handleMessage(Message msg) { 480 AsyncTaskResult result = (AsyncTaskResult) msg.obj; 481 switch (msg.what) { 482 case MESSAGE_POST_RESULT: 483 // There is only one result 484 result.mTask.finish(result.mData[0]); 485 break; 486 case MESSAGE_POST_PROGRESS: 487 result.mTask.onProgressUpdate(result.mData); 488 break; 489 } 490 } 491 } 492 493 private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> { 494 Params[] mParams; 495 } 496 497 @SuppressWarnings({"RawUseOfParameterizedType"}) 498 private static class AsyncTaskResult<Data> { 499 final ModernAsyncTask mTask; 500 final Data[] mData; 501 502 AsyncTaskResult(ModernAsyncTask task, Data... data) { 503 mTask = task; 504 mData = data; 505 } 506 } 507} 508