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 static android.support.annotation.RestrictTo.Scope.LIBRARY_GROUP; 20 21import android.os.Binder; 22import android.os.Handler; 23import android.os.Looper; 24import android.os.Message; 25import android.os.Process; 26import android.support.annotation.RestrictTo; 27 28import java.util.concurrent.BlockingQueue; 29import java.util.concurrent.Callable; 30import java.util.concurrent.CancellationException; 31import java.util.concurrent.ExecutionException; 32import java.util.concurrent.Executor; 33import java.util.concurrent.FutureTask; 34import java.util.concurrent.LinkedBlockingQueue; 35import java.util.concurrent.ThreadFactory; 36import java.util.concurrent.ThreadPoolExecutor; 37import java.util.concurrent.TimeUnit; 38import java.util.concurrent.TimeoutException; 39import java.util.concurrent.atomic.AtomicBoolean; 40import java.util.concurrent.atomic.AtomicInteger; 41 42/** 43 * Copy of the required parts of {@link android.os.AsyncTask} from Android 3.0 that is 44 * needed to support AsyncTaskLoader. We use this rather than the one from the platform 45 * because we rely on some subtle behavior of AsyncTask that is not reliable on 46 * older platforms. 47 * 48 * <p>Note that for now this is not publicly available because it is not a 49 * complete implementation, only sufficient for the needs of 50 * {@link android.content.AsyncTaskLoader}. 51 */ 52abstract class ModernAsyncTask<Params, Progress, Result> { 53 private static final String LOG_TAG = "AsyncTask"; 54 55 private static final int CORE_POOL_SIZE = 5; 56 private static final int MAXIMUM_POOL_SIZE = 128; 57 private static final int KEEP_ALIVE = 1; 58 59 private static final ThreadFactory sThreadFactory = new ThreadFactory() { 60 private final AtomicInteger mCount = new AtomicInteger(1); 61 62 @Override 63 public Thread newThread(Runnable r) { 64 return new Thread(r, "ModernAsyncTask #" + mCount.getAndIncrement()); 65 } 66 }; 67 68 private static final BlockingQueue<Runnable> sPoolWorkQueue = 69 new LinkedBlockingQueue<Runnable>(10); 70 71 /** 72 * An {@link Executor} that can be used to execute tasks in parallel. 73 */ 74 public static final Executor THREAD_POOL_EXECUTOR = 75 new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE, 76 TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory); 77 78 private static final int MESSAGE_POST_RESULT = 0x1; 79 private static final int MESSAGE_POST_PROGRESS = 0x2; 80 81 private static InternalHandler sHandler; 82 83 private static volatile Executor sDefaultExecutor = THREAD_POOL_EXECUTOR; 84 private final WorkerRunnable<Params, Result> mWorker; 85 private final FutureTask<Result> mFuture; 86 87 private volatile Status mStatus = Status.PENDING; 88 89 private final AtomicBoolean mCancelled = new AtomicBoolean(); 90 private final AtomicBoolean mTaskInvoked = new AtomicBoolean(); 91 92 /** 93 * Indicates the current status of the task. Each status will be set only once 94 * during the lifetime of a task. 95 */ 96 public enum Status { 97 /** 98 * Indicates that the task has not been executed yet. 99 */ 100 PENDING, 101 /** 102 * Indicates that the task is running. 103 */ 104 RUNNING, 105 /** 106 * Indicates that {@link android.os.AsyncTask#onPostExecute(Object)} has finished. 107 */ 108 FINISHED, 109 } 110 111 private static Handler getHandler() { 112 synchronized (ModernAsyncTask.class) { 113 if (sHandler == null) { 114 sHandler = new InternalHandler(); 115 } 116 return sHandler; 117 } 118 } 119 120 /** @hide */ 121 @RestrictTo(LIBRARY_GROUP) 122 public static void setDefaultExecutor(Executor exec) { 123 sDefaultExecutor = exec; 124 } 125 126 /** 127 * Creates a new asynchronous task. This constructor must be invoked on the UI thread. 128 */ 129 ModernAsyncTask() { 130 mWorker = new WorkerRunnable<Params, Result>() { 131 @Override 132 public Result call() throws Exception { 133 mTaskInvoked.set(true); 134 Result result = null; 135 try { 136 Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); 137 //noinspection unchecked 138 result = doInBackground(mParams); 139 Binder.flushPendingCommands(); 140 } catch (Throwable tr) { 141 mCancelled.set(true); 142 throw tr; 143 } finally { 144 postResult(result); 145 } 146 return result; 147 } 148 }; 149 150 mFuture = new FutureTask<Result>(mWorker) { 151 @Override 152 protected void done() { 153 try { 154 final Result result = get(); 155 156 postResultIfNotInvoked(result); 157 } catch (InterruptedException e) { 158 android.util.Log.w(LOG_TAG, e); 159 } catch (ExecutionException e) { 160 throw new RuntimeException( 161 "An error occurred while executing doInBackground()", e.getCause()); 162 } catch (CancellationException e) { 163 postResultIfNotInvoked(null); 164 } catch (Throwable t) { 165 throw new RuntimeException( 166 "An error occurred while executing doInBackground()", t); 167 } 168 } 169 }; 170 } 171 172 void postResultIfNotInvoked(Result result) { 173 final boolean wasTaskInvoked = mTaskInvoked.get(); 174 if (!wasTaskInvoked) { 175 postResult(result); 176 } 177 } 178 179 Result postResult(Result result) { 180 Message message = getHandler().obtainMessage(MESSAGE_POST_RESULT, 181 new AsyncTaskResult<>(this, result)); 182 message.sendToTarget(); 183 return result; 184 } 185 186 /** 187 * Returns the current status of this task. 188 * 189 * @return The current status. 190 */ 191 public final Status getStatus() { 192 return mStatus; 193 } 194 195 /** 196 * Override this method to perform a computation on a background thread. The 197 * specified parameters are the parameters passed to {@link #execute} 198 * by the caller of this task. 199 * 200 * This method can call {@link #publishProgress} to publish updates 201 * on the UI thread. 202 * 203 * @param params The parameters of the task. 204 * 205 * @return A result, defined by the subclass of this task. 206 * 207 * @see #onPreExecute() 208 * @see #onPostExecute 209 * @see #publishProgress 210 */ 211 protected abstract Result doInBackground(Params... params); 212 213 /** 214 * Runs on the UI thread before {@link #doInBackground}. 215 * 216 * @see #onPostExecute 217 * @see #doInBackground 218 */ 219 protected void onPreExecute() { 220 } 221 222 /** 223 * <p>Runs on the UI thread after {@link #doInBackground}. The 224 * specified result is the value returned by {@link #doInBackground}.</p> 225 * 226 * <p>This method won't be invoked if the task was cancelled.</p> 227 * 228 * @param result The result of the operation computed by {@link #doInBackground}. 229 * 230 * @see #onPreExecute 231 * @see #doInBackground 232 * @see #onCancelled(Object) 233 */ 234 @SuppressWarnings({"UnusedDeclaration"}) 235 protected void onPostExecute(Result result) { 236 } 237 238 /** 239 * Runs on the UI thread after {@link #publishProgress} is invoked. 240 * The specified values are the values passed to {@link #publishProgress}. 241 * 242 * @param values The values indicating progress. 243 * 244 * @see #publishProgress 245 * @see #doInBackground 246 */ 247 @SuppressWarnings({"UnusedDeclaration"}) 248 protected void onProgressUpdate(Progress... values) { 249 } 250 251 /** 252 * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and 253 * {@link #doInBackground(Object[])} has finished.</p> 254 * 255 * <p>The default implementation simply invokes {@link #onCancelled()} and 256 * ignores the result. If you write your own implementation, do not call 257 * <code>super.onCancelled(result)</code>.</p> 258 * 259 * @param result The result, if any, computed in 260 * {@link #doInBackground(Object[])}, can be null 261 * 262 * @see #cancel(boolean) 263 * @see #isCancelled() 264 */ 265 @SuppressWarnings({"UnusedParameters"}) 266 protected void onCancelled(Result result) { 267 onCancelled(); 268 } 269 270 /** 271 * <p>Applications should preferably override {@link #onCancelled(Object)}. 272 * This method is invoked by the default implementation of 273 * {@link #onCancelled(Object)}.</p> 274 * 275 * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and 276 * {@link #doInBackground(Object[])} has finished.</p> 277 * 278 * @see #onCancelled(Object) 279 * @see #cancel(boolean) 280 * @see #isCancelled() 281 */ 282 protected void onCancelled() { 283 } 284 285 /** 286 * Returns <tt>true</tt> if this task was cancelled before it completed 287 * normally. If you are calling {@link #cancel(boolean)} on the task, 288 * the value returned by this method should be checked periodically from 289 * {@link #doInBackground(Object[])} to end the task as soon as possible. 290 * 291 * @return <tt>true</tt> if task was cancelled before it completed 292 * 293 * @see #cancel(boolean) 294 */ 295 public final boolean isCancelled() { 296 return mCancelled.get(); 297 } 298 299 /** 300 * <p>Attempts to cancel execution of this task. This attempt will 301 * fail if the task has already completed, already been cancelled, 302 * or could not be cancelled for some other reason. If successful, 303 * and this task has not started when <tt>cancel</tt> is called, 304 * this task should never run. If the task has already started, 305 * then the <tt>mayInterruptIfRunning</tt> parameter determines 306 * whether the thread executing this task should be interrupted in 307 * an attempt to stop the task.</p> 308 * 309 * <p>Calling this method will result in {@link #onCancelled(Object)} being 310 * invoked on the UI thread after {@link #doInBackground(Object[])} 311 * returns. Calling this method guarantees that {@link #onPostExecute(Object)} 312 * is never invoked. After invoking this method, you should check the 313 * value returned by {@link #isCancelled()} periodically from 314 * {@link #doInBackground(Object[])} to finish the task as early as 315 * possible.</p> 316 * 317 * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this 318 * task should be interrupted; otherwise, in-progress tasks are allowed 319 * to complete. 320 * 321 * @return <tt>false</tt> if the task could not be cancelled, 322 * typically because it has already completed normally; 323 * <tt>true</tt> otherwise 324 * 325 * @see #isCancelled() 326 * @see #onCancelled(Object) 327 */ 328 public final boolean cancel(boolean mayInterruptIfRunning) { 329 mCancelled.set(true); 330 return mFuture.cancel(mayInterruptIfRunning); 331 } 332 333 /** 334 * Waits if necessary for the computation to complete, and then 335 * retrieves its result. 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 */ 344 public final Result get() throws InterruptedException, ExecutionException { 345 return mFuture.get(); 346 } 347 348 /** 349 * Waits if necessary for at most the given time for the computation 350 * to complete, and then retrieves its result. 351 * 352 * @param timeout Time to wait before cancelling the operation. 353 * @param unit The time unit for the timeout. 354 * 355 * @return The computed result. 356 * 357 * @throws CancellationException If the computation was cancelled. 358 * @throws ExecutionException If the computation threw an exception. 359 * @throws InterruptedException If the current thread was interrupted 360 * while waiting. 361 * @throws TimeoutException If the wait timed out. 362 */ 363 public final Result get(long timeout, TimeUnit unit) throws InterruptedException, 364 ExecutionException, TimeoutException { 365 return mFuture.get(timeout, unit); 366 } 367 368 /** 369 * Executes the task with the specified parameters. The task returns 370 * itself (this) so that the caller can keep a reference to it. 371 * 372 * <p>Note: this function schedules the task on a queue for a single background 373 * thread or pool of threads depending on the platform version. When first 374 * introduced, AsyncTasks were executed serially on a single background thread. 375 * Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed 376 * to a pool of threads allowing multiple tasks to operate in parallel. After 377 * {@link android.os.Build.VERSION_CODES#HONEYCOMB}, it is planned to change this 378 * back to a single thread to avoid common application errors caused 379 * by parallel execution. If you truly want parallel execution, you can use 380 * the {@link #executeOnExecutor} version of this method 381 * with {@link #THREAD_POOL_EXECUTOR}; however, see commentary there for warnings on 382 * its use. 383 * 384 * <p>This method must be invoked on the UI thread. 385 * 386 * @param params The parameters of the task. 387 * 388 * @return This instance of AsyncTask. 389 * 390 * @throws IllegalStateException If {@link #getStatus()} returns either 391 * {@link android.os.AsyncTask.Status#RUNNING} or 392 * {@link android.os.AsyncTask.Status#FINISHED}. 393 */ 394 public final ModernAsyncTask<Params, Progress, Result> execute(Params... params) { 395 return executeOnExecutor(sDefaultExecutor, params); 396 } 397 398 /** 399 * Executes the task with the specified parameters. The task returns 400 * itself (this) so that the caller can keep a reference to it. 401 * 402 * <p>This method is typically used with {@link #THREAD_POOL_EXECUTOR} to 403 * allow multiple tasks to run in parallel on a pool of threads managed by 404 * AsyncTask, however you can also use your own {@link Executor} for custom 405 * behavior. 406 * 407 * <p><em>Warning:</em> Allowing multiple tasks to run in parallel from 408 * a thread pool is generally <em>not</em> what one wants, because the order 409 * of their operation is not defined. For example, if these tasks are used 410 * to modify any state in common (such as writing a file due to a button click), 411 * there are no guarantees on the order of the modifications. 412 * Without careful work it is possible in rare cases for the newer version 413 * of the data to be over-written by an older one, leading to obscure data 414 * loss and stability issues. 415 * 416 * <p>This method must be invoked on the UI thread. 417 * 418 * @param exec The executor to use. {@link #THREAD_POOL_EXECUTOR} is available as a 419 * convenient process-wide thread pool for tasks that are loosely coupled. 420 * @param params The parameters of the task. 421 * 422 * @return This instance of AsyncTask. 423 * 424 * @throws IllegalStateException If {@link #getStatus()} returns either 425 * {@link android.os.AsyncTask.Status#RUNNING} 426 * or {@link android.os.AsyncTask.Status#FINISHED}. 427 */ 428 public final ModernAsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec, 429 Params... params) { 430 if (mStatus != Status.PENDING) { 431 switch (mStatus) { 432 case RUNNING: 433 throw new IllegalStateException("Cannot execute task:" 434 + " the task is already running."); 435 case FINISHED: 436 throw new IllegalStateException("Cannot execute task:" 437 + " the task has already been executed " 438 + "(a task can be executed only once)"); 439 default: 440 throw new IllegalStateException("We should never reach this state"); 441 } 442 } 443 444 mStatus = Status.RUNNING; 445 446 onPreExecute(); 447 448 mWorker.mParams = params; 449 exec.execute(mFuture); 450 451 return this; 452 } 453 454 /** 455 * Convenience version of {@link #execute(Object...)} for use with 456 * a simple Runnable object. 457 */ 458 public static void execute(Runnable runnable) { 459 sDefaultExecutor.execute(runnable); 460 } 461 462 /** 463 * This method can be invoked from {@link #doInBackground} to 464 * publish updates on the UI thread while the background computation is 465 * still running. Each call to this method will trigger the execution of 466 * {@link #onProgressUpdate} on the UI thread. 467 * 468 * {@link #onProgressUpdate} will note be called if the task has been 469 * canceled. 470 * 471 * @param values The progress values to update the UI with. 472 * 473 * @see #onProgressUpdate 474 * @see #doInBackground 475 */ 476 protected final void publishProgress(Progress... values) { 477 if (!isCancelled()) { 478 getHandler().obtainMessage(MESSAGE_POST_PROGRESS, 479 new AsyncTaskResult<Progress>(this, values)).sendToTarget(); 480 } 481 } 482 483 void finish(Result result) { 484 if (isCancelled()) { 485 onCancelled(result); 486 } else { 487 onPostExecute(result); 488 } 489 mStatus = Status.FINISHED; 490 } 491 492 private static class InternalHandler extends Handler { 493 InternalHandler() { 494 super(Looper.getMainLooper()); 495 } 496 497 @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"}) 498 @Override 499 public void handleMessage(Message msg) { 500 AsyncTaskResult result = (AsyncTaskResult) msg.obj; 501 switch (msg.what) { 502 case MESSAGE_POST_RESULT: 503 // There is only one result 504 result.mTask.finish(result.mData[0]); 505 break; 506 case MESSAGE_POST_PROGRESS: 507 result.mTask.onProgressUpdate(result.mData); 508 break; 509 } 510 } 511 } 512 513 private abstract static class WorkerRunnable<Params, Result> implements Callable<Result> { 514 Params[] mParams; 515 516 WorkerRunnable() { 517 } 518 } 519 520 @SuppressWarnings({"RawUseOfParameterizedType"}) 521 private static class AsyncTaskResult<Data> { 522 final ModernAsyncTask mTask; 523 final Data[] mData; 524 525 AsyncTaskResult(ModernAsyncTask task, Data... data) { 526 mTask = task; 527 mData = data; 528 } 529 } 530} 531