1 /*
2  * Copyright (C) 2008 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 
17 package com.example.android.displayingbitmaps.util;
18 
19 import android.annotation.TargetApi;
20 import android.os.Handler;
21 import android.os.Message;
22 import android.os.Process;
23 
24 import java.util.ArrayDeque;
25 import java.util.concurrent.BlockingQueue;
26 import java.util.concurrent.Callable;
27 import java.util.concurrent.CancellationException;
28 import java.util.concurrent.ExecutionException;
29 import java.util.concurrent.Executor;
30 import java.util.concurrent.Executors;
31 import java.util.concurrent.FutureTask;
32 import java.util.concurrent.LinkedBlockingQueue;
33 import java.util.concurrent.ThreadFactory;
34 import java.util.concurrent.ThreadPoolExecutor;
35 import java.util.concurrent.TimeUnit;
36 import java.util.concurrent.TimeoutException;
37 import java.util.concurrent.atomic.AtomicBoolean;
38 import java.util.concurrent.atomic.AtomicInteger;
39 
40 /**
41  * *************************************
42  * Copied from JB release framework:
43  * https://android.googlesource.com/platform/frameworks/base/+/jb-release/core/java/android/os/AsyncTask.java
44  *
45  * so that threading behavior on all OS versions is the same and we can tweak behavior by using
46  * executeOnExecutor() if needed.
47  *
48  * There are 3 changes in this copy of AsyncTask:
49  *    -pre-HC a single thread executor is used for serial operation
50  *    (Executors.newSingleThreadExecutor) and is the default
51  *    -the default THREAD_POOL_EXECUTOR was changed to use DiscardOldestPolicy
52  *    -a new fixed thread pool called DUAL_THREAD_EXECUTOR was added
53  * *************************************
54  *
55  * <p>AsyncTask enables proper and easy use of the UI thread. This class allows to
56  * perform background operations and publish results on the UI thread without
57  * having to manipulate threads and/or handlers.</p>
58  *
59  * <p>AsyncTask is designed to be a helper class around {@link Thread} and {@link android.os.Handler}
60  * and does not constitute a generic threading framework. AsyncTasks should ideally be
61  * used for short operations (a few seconds at the most.) If you need to keep threads
62  * running for long periods of time, it is highly recommended you use the various APIs
63  * provided by the <code>java.util.concurrent</code> pacakge such as {@link java.util.concurrent.Executor},
64  * {@link java.util.concurrent.ThreadPoolExecutor} and {@link java.util.concurrent.FutureTask}.</p>
65  *
66  * <p>An asynchronous task is defined by a computation that runs on a background thread and
67  * whose result is published on the UI thread. An asynchronous task is defined by 3 generic
68  * types, called <code>Params</code>, <code>Progress</code> and <code>Result</code>,
69  * and 4 steps, called <code>onPreExecute</code>, <code>doInBackground</code>,
70  * <code>onProgressUpdate</code> and <code>onPostExecute</code>.</p>
71  *
72  * <div class="special reference">
73  * <h3>Developer Guides</h3>
74  * <p>For more information about using tasks and threads, read the
75  * <a href="{@docRoot}guide/topics/fundamentals/processes-and-threads.html">Processes and
76  * Threads</a> developer guide.</p>
77  * </div>
78  *
79  * <h2>Usage</h2>
80  * <p>AsyncTask must be subclassed to be used. The subclass will override at least
81  * one method ({@link #doInBackground}), and most often will override a
82  * second one ({@link #onPostExecute}.)</p>
83  *
84  * <p>Here is an example of subclassing:</p>
85  * <pre class="prettyprint">
86  * private class DownloadFilesTask extends AsyncTask&lt;URL, Integer, Long&gt; {
87  *     protected Long doInBackground(URL... urls) {
88  *         int count = urls.length;
89  *         long totalSize = 0;
90  *         for (int i = 0; i < count; i++) {
91  *             totalSize += Downloader.downloadFile(urls[i]);
92  *             publishProgress((int) ((i / (float) count) * 100));
93  *             // Escape early if cancel() is called
94  *             if (isCancelled()) break;
95  *         }
96  *         return totalSize;
97  *     }
98  *
99  *     protected void onProgressUpdate(Integer... progress) {
100  *         setProgressPercent(progress[0]);
101  *     }
102  *
103  *     protected void onPostExecute(Long result) {
104  *         showDialog("Downloaded " + result + " bytes");
105  *     }
106  * }
107  * </pre>
108  *
109  * <p>Once created, a task is executed very simply:</p>
110  * <pre class="prettyprint">
111  * new DownloadFilesTask().execute(url1, url2, url3);
112  * </pre>
113  *
114  * <h2>AsyncTask's generic types</h2>
115  * <p>The three types used by an asynchronous task are the following:</p>
116  * <ol>
117  *     <li><code>Params</code>, the type of the parameters sent to the task upon
118  *     execution.</li>
119  *     <li><code>Progress</code>, the type of the progress units published during
120  *     the background computation.</li>
121  *     <li><code>Result</code>, the type of the result of the background
122  *     computation.</li>
123  * </ol>
124  * <p>Not all types are always used by an asynchronous task. To mark a type as unused,
125  * simply use the type {@link Void}:</p>
126  * <pre>
127  * private class MyTask extends AsyncTask&lt;Void, Void, Void&gt; { ... }
128  * </pre>
129  *
130  * <h2>The 4 steps</h2>
131  * <p>When an asynchronous task is executed, the task goes through 4 steps:</p>
132  * <ol>
133  *     <li>{@link #onPreExecute()}, invoked on the UI thread immediately after the task
134  *     is executed. This step is normally used to setup the task, for instance by
135  *     showing a progress bar in the user interface.</li>
136  *     <li>{@link #doInBackground}, invoked on the background thread
137  *     immediately after {@link #onPreExecute()} finishes executing. This step is used
138  *     to perform background computation that can take a long time. The parameters
139  *     of the asynchronous task are passed to this step. The result of the computation must
140  *     be returned by this step and will be passed back to the last step. This step
141  *     can also use {@link #publishProgress} to publish one or more units
142  *     of progress. These values are published on the UI thread, in the
143  *     {@link #onProgressUpdate} step.</li>
144  *     <li>{@link #onProgressUpdate}, invoked on the UI thread after a
145  *     call to {@link #publishProgress}. The timing of the execution is
146  *     undefined. This method is used to display any form of progress in the user
147  *     interface while the background computation is still executing. For instance,
148  *     it can be used to animate a progress bar or show logs in a text field.</li>
149  *     <li>{@link #onPostExecute}, invoked on the UI thread after the background
150  *     computation finishes. The result of the background computation is passed to
151  *     this step as a parameter.</li>
152  * </ol>
153  *
154  * <h2>Cancelling a task</h2>
155  * <p>A task can be cancelled at any time by invoking {@link #cancel(boolean)}. Invoking
156  * this method will cause subsequent calls to {@link #isCancelled()} to return true.
157  * After invoking this method, {@link #onCancelled(Object)}, instead of
158  * {@link #onPostExecute(Object)} will be invoked after {@link #doInBackground(Object[])}
159  * returns. To ensure that a task is cancelled as quickly as possible, you should always
160  * check the return value of {@link #isCancelled()} periodically from
161  * {@link #doInBackground(Object[])}, if possible (inside a loop for instance.)</p>
162  *
163  * <h2>Threading rules</h2>
164  * <p>There are a few threading rules that must be followed for this class to
165  * work properly:</p>
166  * <ul>
167  *     <li>The AsyncTask class must be loaded on the UI thread. This is done
168  *     automatically as of {@link android.os.Build.VERSION_CODES#JELLY_BEAN}.</li>
169  *     <li>The task instance must be created on the UI thread.</li>
170  *     <li>{@link #execute} must be invoked on the UI thread.</li>
171  *     <li>Do not call {@link #onPreExecute()}, {@link #onPostExecute},
172  *     {@link #doInBackground}, {@link #onProgressUpdate} manually.</li>
173  *     <li>The task can be executed only once (an exception will be thrown if
174  *     a second execution is attempted.)</li>
175  * </ul>
176  *
177  * <h2>Memory observability</h2>
178  * <p>AsyncTask guarantees that all callback calls are synchronized in such a way that the following
179  * operations are safe without explicit synchronizations.</p>
180  * <ul>
181  *     <li>Set member fields in the constructor or {@link #onPreExecute}, and refer to them
182  *     in {@link #doInBackground}.
183  *     <li>Set member fields in {@link #doInBackground}, and refer to them in
184  *     {@link #onProgressUpdate} and {@link #onPostExecute}.
185  * </ul>
186  *
187  * <h2>Order of execution</h2>
188  * <p>When first introduced, AsyncTasks were executed serially on a single background
189  * thread. Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed
190  * to a pool of threads allowing multiple tasks to operate in parallel. Starting with
191  * {@link android.os.Build.VERSION_CODES#HONEYCOMB}, tasks are executed on a single
192  * thread to avoid common application errors caused by parallel execution.</p>
193  * <p>If you truly want parallel execution, you can invoke
194  * {@link #executeOnExecutor(java.util.concurrent.Executor, Object[])} with
195  * {@link #THREAD_POOL_EXECUTOR}.</p>
196  */
197 public abstract class AsyncTask<Params, Progress, Result> {
198     private static final String LOG_TAG = "AsyncTask";
199 
200     private static final int CORE_POOL_SIZE = 5;
201     private static final int MAXIMUM_POOL_SIZE = 128;
202     private static final int KEEP_ALIVE = 1;
203 
204     private static final ThreadFactory  sThreadFactory = new ThreadFactory() {
205         private final AtomicInteger mCount = new AtomicInteger(1);
206 
207         public Thread newThread(Runnable r) {
208             return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
209         }
210     };
211 
212     private static final BlockingQueue<Runnable> sPoolWorkQueue =
213             new LinkedBlockingQueue<Runnable>(10);
214 
215     /**
216      * An {@link java.util.concurrent.Executor} that can be used to execute tasks in parallel.
217      */
218     public static final Executor THREAD_POOL_EXECUTOR
219             = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
220             TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory,
221             new ThreadPoolExecutor.DiscardOldestPolicy());
222 
223     /**
224      * An {@link java.util.concurrent.Executor} that executes tasks one at a time in serial
225      * order.  This serialization is global to a particular process.
226      */
227     public static final Executor SERIAL_EXECUTOR = Utils.hasHoneycomb() ? new SerialExecutor() :
228             Executors.newSingleThreadExecutor(sThreadFactory);
229 
230     public static final Executor DUAL_THREAD_EXECUTOR =
231             Executors.newFixedThreadPool(2, sThreadFactory);
232 
233     private static final int MESSAGE_POST_RESULT = 0x1;
234     private static final int MESSAGE_POST_PROGRESS = 0x2;
235 
236     private static final InternalHandler sHandler = new InternalHandler();
237 
238     private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
239     private final WorkerRunnable<Params, Result> mWorker;
240     private final FutureTask<Result> mFuture;
241 
242     private volatile Status mStatus = Status.PENDING;
243 
244     private final AtomicBoolean mCancelled = new AtomicBoolean();
245     private final AtomicBoolean mTaskInvoked = new AtomicBoolean();
246 
247     @TargetApi(11)
248     private static class SerialExecutor implements Executor {
249         final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
250         Runnable mActive;
251 
execute(final Runnable r)252         public synchronized void execute(final Runnable r) {
253             mTasks.offer(new Runnable() {
254                 public void run() {
255                     try {
256                         r.run();
257                     } finally {
258                         scheduleNext();
259                     }
260                 }
261             });
262             if (mActive == null) {
263                 scheduleNext();
264             }
265         }
266 
scheduleNext()267         protected synchronized void scheduleNext() {
268             if ((mActive = mTasks.poll()) != null) {
269                 THREAD_POOL_EXECUTOR.execute(mActive);
270             }
271         }
272     }
273 
274     /**
275      * Indicates the current status of the task. Each status will be set only once
276      * during the lifetime of a task.
277      */
278     public enum Status {
279         /**
280          * Indicates that the task has not been executed yet.
281          */
282         PENDING,
283         /**
284          * Indicates that the task is running.
285          */
286         RUNNING,
287         /**
288          * Indicates that {@link AsyncTask#onPostExecute} has finished.
289          */
290         FINISHED,
291     }
292 
293     /** @hide Used to force static handler to be created. */
init()294     public static void init() {
295         sHandler.getLooper();
296     }
297 
298     /** @hide */
setDefaultExecutor(Executor exec)299     public static void setDefaultExecutor(Executor exec) {
300         sDefaultExecutor = exec;
301     }
302 
303     /**
304      * Creates a new asynchronous task. This constructor must be invoked on the UI thread.
305      */
AsyncTask()306     public AsyncTask() {
307         mWorker = new WorkerRunnable<Params, Result>() {
308             public Result call() throws Exception {
309                 mTaskInvoked.set(true);
310 
311                 Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
312                 //noinspection unchecked
313                 return postResult(doInBackground(mParams));
314             }
315         };
316 
317         mFuture = new FutureTask<Result>(mWorker) {
318             @Override
319             protected void done() {
320                 try {
321                     postResultIfNotInvoked(get());
322                 } catch (InterruptedException e) {
323                     android.util.Log.w(LOG_TAG, e);
324                 } catch (ExecutionException e) {
325                     throw new RuntimeException("An error occured while executing doInBackground()",
326                             e.getCause());
327                 } catch (CancellationException e) {
328                     postResultIfNotInvoked(null);
329                 }
330             }
331         };
332     }
333 
postResultIfNotInvoked(Result result)334     private void postResultIfNotInvoked(Result result) {
335         final boolean wasTaskInvoked = mTaskInvoked.get();
336         if (!wasTaskInvoked) {
337             postResult(result);
338         }
339     }
340 
postResult(Result result)341     private Result postResult(Result result) {
342         @SuppressWarnings("unchecked")
343         Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
344                 new AsyncTaskResult<Result>(this, result));
345         message.sendToTarget();
346         return result;
347     }
348 
349     /**
350      * Returns the current status of this task.
351      *
352      * @return The current status.
353      */
getStatus()354     public final Status getStatus() {
355         return mStatus;
356     }
357 
358     /**
359      * Override this method to perform a computation on a background thread. The
360      * specified parameters are the parameters passed to {@link #execute}
361      * by the caller of this task.
362      *
363      * This method can call {@link #publishProgress} to publish updates
364      * on the UI thread.
365      *
366      * @param params The parameters of the task.
367      *
368      * @return A result, defined by the subclass of this task.
369      *
370      * @see #onPreExecute()
371      * @see #onPostExecute
372      * @see #publishProgress
373      */
doInBackground(Params... params)374     protected abstract Result doInBackground(Params... params);
375 
376     /**
377      * Runs on the UI thread before {@link #doInBackground}.
378      *
379      * @see #onPostExecute
380      * @see #doInBackground
381      */
onPreExecute()382     protected void onPreExecute() {
383     }
384 
385     /**
386      * <p>Runs on the UI thread after {@link #doInBackground}. The
387      * specified result is the value returned by {@link #doInBackground}.</p>
388      *
389      * <p>This method won't be invoked if the task was cancelled.</p>
390      *
391      * @param result The result of the operation computed by {@link #doInBackground}.
392      *
393      * @see #onPreExecute
394      * @see #doInBackground
395      * @see #onCancelled(Object)
396      */
397     @SuppressWarnings({"UnusedDeclaration"})
onPostExecute(Result result)398     protected void onPostExecute(Result result) {
399     }
400 
401     /**
402      * Runs on the UI thread after {@link #publishProgress} is invoked.
403      * The specified values are the values passed to {@link #publishProgress}.
404      *
405      * @param values The values indicating progress.
406      *
407      * @see #publishProgress
408      * @see #doInBackground
409      */
410     @SuppressWarnings({"UnusedDeclaration"})
onProgressUpdate(Progress... values)411     protected void onProgressUpdate(Progress... values) {
412     }
413 
414     /**
415      * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
416      * {@link #doInBackground(Object[])} has finished.</p>
417      *
418      * <p>The default implementation simply invokes {@link #onCancelled()} and
419      * ignores the result. If you write your own implementation, do not call
420      * <code>super.onCancelled(result)</code>.</p>
421      *
422      * @param result The result, if any, computed in
423      *               {@link #doInBackground(Object[])}, can be null
424      *
425      * @see #cancel(boolean)
426      * @see #isCancelled()
427      */
428     @SuppressWarnings({"UnusedParameters"})
onCancelled(Result result)429     protected void onCancelled(Result result) {
430         onCancelled();
431     }
432 
433     /**
434      * <p>Applications should preferably override {@link #onCancelled(Object)}.
435      * This method is invoked by the default implementation of
436      * {@link #onCancelled(Object)}.</p>
437      *
438      * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
439      * {@link #doInBackground(Object[])} has finished.</p>
440      *
441      * @see #onCancelled(Object)
442      * @see #cancel(boolean)
443      * @see #isCancelled()
444      */
onCancelled()445     protected void onCancelled() {
446     }
447 
448     /**
449      * Returns <tt>true</tt> if this task was cancelled before it completed
450      * normally. If you are calling {@link #cancel(boolean)} on the task,
451      * the value returned by this method should be checked periodically from
452      * {@link #doInBackground(Object[])} to end the task as soon as possible.
453      *
454      * @return <tt>true</tt> if task was cancelled before it completed
455      *
456      * @see #cancel(boolean)
457      */
isCancelled()458     public final boolean isCancelled() {
459         return mCancelled.get();
460     }
461 
462     /**
463      * <p>Attempts to cancel execution of this task.  This attempt will
464      * fail if the task has already completed, already been cancelled,
465      * or could not be cancelled for some other reason. If successful,
466      * and this task has not started when <tt>cancel</tt> is called,
467      * this task should never run. If the task has already started,
468      * then the <tt>mayInterruptIfRunning</tt> parameter determines
469      * whether the thread executing this task should be interrupted in
470      * an attempt to stop the task.</p>
471      *
472      * <p>Calling this method will result in {@link #onCancelled(Object)} being
473      * invoked on the UI thread after {@link #doInBackground(Object[])}
474      * returns. Calling this method guarantees that {@link #onPostExecute(Object)}
475      * is never invoked. After invoking this method, you should check the
476      * value returned by {@link #isCancelled()} periodically from
477      * {@link #doInBackground(Object[])} to finish the task as early as
478      * possible.</p>
479      *
480      * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
481      *        task should be interrupted; otherwise, in-progress tasks are allowed
482      *        to complete.
483      *
484      * @return <tt>false</tt> if the task could not be cancelled,
485      *         typically because it has already completed normally;
486      *         <tt>true</tt> otherwise
487      *
488      * @see #isCancelled()
489      * @see #onCancelled(Object)
490      */
cancel(boolean mayInterruptIfRunning)491     public final boolean cancel(boolean mayInterruptIfRunning) {
492         mCancelled.set(true);
493         return mFuture.cancel(mayInterruptIfRunning);
494     }
495 
496     /**
497      * Waits if necessary for the computation to complete, and then
498      * retrieves its result.
499      *
500      * @return The computed result.
501      *
502      * @throws java.util.concurrent.CancellationException If the computation was cancelled.
503      * @throws java.util.concurrent.ExecutionException If the computation threw an exception.
504      * @throws InterruptedException If the current thread was interrupted
505      *         while waiting.
506      */
get()507     public final Result get() throws InterruptedException, ExecutionException {
508         return mFuture.get();
509     }
510 
511     /**
512      * Waits if necessary for at most the given time for the computation
513      * to complete, and then retrieves its result.
514      *
515      * @param timeout Time to wait before cancelling the operation.
516      * @param unit The time unit for the timeout.
517      *
518      * @return The computed result.
519      *
520      * @throws java.util.concurrent.CancellationException If the computation was cancelled.
521      * @throws java.util.concurrent.ExecutionException If the computation threw an exception.
522      * @throws InterruptedException If the current thread was interrupted
523      *         while waiting.
524      * @throws java.util.concurrent.TimeoutException If the wait timed out.
525      */
get(long timeout, TimeUnit unit)526     public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
527             ExecutionException, TimeoutException {
528         return mFuture.get(timeout, unit);
529     }
530 
531     /**
532      * Executes the task with the specified parameters. The task returns
533      * itself (this) so that the caller can keep a reference to it.
534      *
535      * <p>Note: this function schedules the task on a queue for a single background
536      * thread or pool of threads depending on the platform version.  When first
537      * introduced, AsyncTasks were executed serially on a single background thread.
538      * Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed
539      * to a pool of threads allowing multiple tasks to operate in parallel. Starting
540      * {@link android.os.Build.VERSION_CODES#HONEYCOMB}, tasks are back to being
541      * executed on a single thread to avoid common application errors caused
542      * by parallel execution.  If you truly want parallel execution, you can use
543      * the {@link #executeOnExecutor} version of this method
544      * with {@link #THREAD_POOL_EXECUTOR}; however, see commentary there for warnings
545      * on its use.
546      *
547      * <p>This method must be invoked on the UI thread.
548      *
549      * @param params The parameters of the task.
550      *
551      * @return This instance of AsyncTask.
552      *
553      * @throws IllegalStateException If {@link #getStatus()} returns either
554      *         {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
555      *
556      * @see #executeOnExecutor(java.util.concurrent.Executor, Object[])
557      * @see #execute(Runnable)
558      */
execute(Params... params)559     public final AsyncTask<Params, Progress, Result> execute(Params... params) {
560         return executeOnExecutor(sDefaultExecutor, params);
561     }
562 
563     /**
564      * Executes the task with the specified parameters. The task returns
565      * itself (this) so that the caller can keep a reference to it.
566      *
567      * <p>This method is typically used with {@link #THREAD_POOL_EXECUTOR} to
568      * allow multiple tasks to run in parallel on a pool of threads managed by
569      * AsyncTask, however you can also use your own {@link java.util.concurrent.Executor} for custom
570      * behavior.
571      *
572      * <p><em>Warning:</em> Allowing multiple tasks to run in parallel from
573      * a thread pool is generally <em>not</em> what one wants, because the order
574      * of their operation is not defined.  For example, if these tasks are used
575      * to modify any state in common (such as writing a file due to a button click),
576      * there are no guarantees on the order of the modifications.
577      * Without careful work it is possible in rare cases for the newer version
578      * of the data to be over-written by an older one, leading to obscure data
579      * loss and stability issues.  Such changes are best
580      * executed in serial; to guarantee such work is serialized regardless of
581      * platform version you can use this function with {@link #SERIAL_EXECUTOR}.
582      *
583      * <p>This method must be invoked on the UI thread.
584      *
585      * @param exec The executor to use.  {@link #THREAD_POOL_EXECUTOR} is available as a
586      *              convenient process-wide thread pool for tasks that are loosely coupled.
587      * @param params The parameters of the task.
588      *
589      * @return This instance of AsyncTask.
590      *
591      * @throws IllegalStateException If {@link #getStatus()} returns either
592      *         {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
593      *
594      * @see #execute(Object[])
595      */
executeOnExecutor(Executor exec, Params... params)596     public final AsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec,
597             Params... params) {
598         if (mStatus != Status.PENDING) {
599             switch (mStatus) {
600                 case RUNNING:
601                     throw new IllegalStateException("Cannot execute task:"
602                             + " the task is already running.");
603                 case FINISHED:
604                     throw new IllegalStateException("Cannot execute task:"
605                             + " the task has already been executed "
606                             + "(a task can be executed only once)");
607             }
608         }
609 
610         mStatus = Status.RUNNING;
611 
612         onPreExecute();
613 
614         mWorker.mParams = params;
615         exec.execute(mFuture);
616 
617         return this;
618     }
619 
620     /**
621      * Convenience version of {@link #execute(Object...)} for use with
622      * a simple Runnable object. See {@link #execute(Object[])} for more
623      * information on the order of execution.
624      *
625      * @see #execute(Object[])
626      * @see #executeOnExecutor(java.util.concurrent.Executor, Object[])
627      */
execute(Runnable runnable)628     public static void execute(Runnable runnable) {
629         sDefaultExecutor.execute(runnable);
630     }
631 
632     /**
633      * This method can be invoked from {@link #doInBackground} to
634      * publish updates on the UI thread while the background computation is
635      * still running. Each call to this method will trigger the execution of
636      * {@link #onProgressUpdate} on the UI thread.
637      *
638      * {@link #onProgressUpdate} will note be called if the task has been
639      * canceled.
640      *
641      * @param values The progress values to update the UI with.
642      *
643      * @see #onProgressUpdate
644      * @see #doInBackground
645      */
publishProgress(Progress... values)646     protected final void publishProgress(Progress... values) {
647         if (!isCancelled()) {
648             sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
649                     new AsyncTaskResult<Progress>(this, values)).sendToTarget();
650         }
651     }
652 
finish(Result result)653     private void finish(Result result) {
654         if (isCancelled()) {
655             onCancelled(result);
656         } else {
657             onPostExecute(result);
658         }
659         mStatus = Status.FINISHED;
660     }
661 
662     private static class InternalHandler extends Handler {
663         @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
664         @Override
handleMessage(Message msg)665         public void handleMessage(Message msg) {
666             AsyncTaskResult result = (AsyncTaskResult) msg.obj;
667             switch (msg.what) {
668                 case MESSAGE_POST_RESULT:
669                     // There is only one result
670                     result.mTask.finish(result.mData[0]);
671                     break;
672                 case MESSAGE_POST_PROGRESS:
673                     result.mTask.onProgressUpdate(result.mData);
674                     break;
675             }
676         }
677     }
678 
679     private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
680         Params[] mParams;
681     }
682 
683     @SuppressWarnings({"RawUseOfParameterizedType"})
684     private static class AsyncTaskResult<Data> {
685         final AsyncTask mTask;
686         final Data[] mData;
687 
AsyncTaskResult(AsyncTask task, Data... data)688         AsyncTaskResult(AsyncTask task, Data... data) {
689             mTask = task;
690             mData = data;
691         }
692     }
693 }