core/java/android/os/AsyncTask.java - platform/frameworks/base - Git at Google

 /*
  * Copyright (C) 2008 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package android.os;

 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.Callable;
 import java.util.concurrent.FutureTask;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.CancellationException;
 import java.util.concurrent.atomic.AtomicInteger;

 /**
  * <p>AsyncTask enables proper and easy use of the UI thread. This class allows to
  * perform background operations and publish results on the UI thread without
  * having to manipulate threads and/or handlers.</p>
  *
  * <p>An asynchronous task is defined by a computation that runs on a background thread and
  * whose result is published on the UI thread. An asynchronous task is defined by 3 generic
  * types, called <code>Params</code>, <code>Progress</code> and <code>Result</code>,
  * and 4 steps, called <code>begin</code>, <code>doInBackground</code>,
  * <code>processProgress</code> and <code>end</code>.</p>
  *
  * <h2>Usage</h2>
  * <p>AsyncTask must be subclassed to be used. The subclass will override at least
  * one method ({@link #doInBackground}), and most often will override a
  * second one ({@link #onPostExecute}.)</p>
  *
  * <p>Here is an example of subclassing:</p>
  * <pre class="prettyprint">
  * private class DownloadFilesTask extends AsyncTask&lt;URL, Integer, Long&gt; {
  *     protected Long doInBackground(URL... urls) {
  *         int count = urls.length;
  *         long totalSize = 0;
  *         for (int i = 0; i < count; i++) {
  *             totalSize += Downloader.downloadFile(urls[i]);
  *             publishProgress((int) ((i / (float) count) * 100));
  *         }
  *         return totalSize;
  *     }
  *
  *     protected void onProgressUpdate(Integer... progress) {
  *         setProgressPercent(progress[0]);
  *     }
  *
  *     protected void onPostExecute(Long result) {
  *         showDialog("Downloaded " + result + " bytes");
  *     }
  * }
  * </pre>
  *
  * <p>Once created, a task is executed very simply:</p>
  * <pre class="prettyprint">
  * new DownloadFilesTask().execute(url1, url2, url3);
  * </pre>
  *
  * <h2>AsyncTask's generic types</h2>
  * <p>The three types used by an asynchronous task are the following:</p>
  * <ol>
  *     <li><code>Params</code>, the type of the parameters sent to the task upon
  *     execution.</li>
  *     <li><code>Progress</code>, the type of the progress units published during
  *     the background computation.</li>
  *     <li><code>Result</code>, the type of the result of the background
  *     computation.</li>
  * </ol>
  * <p>Not all types are always used by an asynchronous task. To mark a type as unused,
  * simply use the type {@link Void}:</p>
  * <pre>
  * private class MyTask extends AsyncTask&lt;Void, Void, Void&gt; { ... }
  * </pre>
  *
  * <h2>The 4 steps</h2>
  * <p>When an asynchronous task is executed, the task goes through 4 steps:</p>
  * <ol>
  *     <li>{@link #onPreExecute()}, invoked on the UI thread immediately after the task
  *     is executed. This step is normally used to setup the task, for instance by
  *     showing a progress bar in the user interface.</li>
  *     <li>{@link #doInBackground}, invoked on the background thread
  *     immediately after {@link #onPreExecute()} finishes executing. This step is used
  *     to perform background computation that can take a long time. The parameters
  *     of the asynchronous task are passed to this step. The result of the computation must
  *     be returned by this step and will be passed back to the last step. This step
  *     can also use {@link #publishProgress} to publish one or more units
  *     of progress. These values are published on the UI thread, in the
  *     {@link #onProgressUpdate} step.</li>
  *     <li>{@link #onProgressUpdate}, invoked on the UI thread after a
  *     call to {@link #publishProgress}. The timing of the execution is
  *     undefined. This method is used to display any form of progress in the user
  *     interface while the background computation is still executing. For instance,
  *     it can be used to animate a progress bar or show logs in a text field.</li>
  *     <li>{@link #onPostExecute}, invoked on the UI thread after the background
  *     computation finishes. The result of the background computation is passed to
  *     this step as a parameter.</li>
  * </ol>
  *
  * <h2>Threading rules</h2>
  * <p>There are a few threading rules that must be followed for this class to
  * work properly:</p>
  * <ul>
  *     <li>The task instance must be created on the UI thread.</li>
  *     <li>{@link #execute} must be invoked on the UI thread.</li>
  *     <li>Do not call {@link #onPreExecute()}, {@link #onPostExecute},
  *     {@link #doInBackground}, {@link #onProgressUpdate} manually.</li>
  *     <li>The task can be executed only once (an exception will be thrown if
  *     a second execution is attempted.)</li>
  * </ul>
  */
 public abstract class AsyncTask<Params, Progress, Result> {
     private static final String LOG_TAG = "AsyncTask";

     private static final int CORE_POOL_SIZE = 5;
     private static final int MAXIMUM_POOL_SIZE = 128;
     private static final int KEEP_ALIVE = 1;

     private static final BlockingQueue<Runnable> sWorkQueue =
             new LinkedBlockingQueue<Runnable>(10);

     private static final ThreadFactory sThreadFactory = new ThreadFactory() {
         private final AtomicInteger mCount = new AtomicInteger(1);

         public Thread newThread(Runnable r) {
             return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
         }
     };

     private static final ThreadPoolExecutor sExecutor = new ThreadPoolExecutor(CORE_POOL_SIZE,
             MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, sWorkQueue, sThreadFactory);

     private static final int MESSAGE_POST_RESULT = 0x1;
     private static final int MESSAGE_POST_PROGRESS = 0x2;
     private static final int MESSAGE_POST_CANCEL = 0x3;

     private static final InternalHandler sHandler = new InternalHandler();

     private final WorkerRunnable<Params, Result> mWorker;
     private final FutureTask<Result> mFuture;

     private volatile Status mStatus = Status.PENDING;

     /**
      * Indicates the current status of the task. Each status will be set only once
      * during the lifetime of a task.
      */
     public enum Status {
         /**
          * Indicates that the task has not been executed yet.
          */
         PENDING,
         /**
          * Indicates that the task is running.
          */
         RUNNING,
         /**
          * Indicates that {@link AsyncTask#onPostExecute} has finished.
          */
         FINISHED,
     }

     /**
      * Creates a new asynchronous task. This constructor must be invoked on the UI thread.
      */
     public AsyncTask() {
         mWorker = new WorkerRunnable<Params, Result>() {
             public Result call() throws Exception {
                 Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
                 return doInBackground(mParams);
             }
         };

         mFuture = new FutureTask<Result>(mWorker) {
             @Override
             protected void done() {
                 Message message;
                 Result result = null;

                 try {
                     result = get();
                 } catch (InterruptedException e) {
                     android.util.Log.w(LOG_TAG, e);
                 } catch (ExecutionException e) {
                     throw new RuntimeException("An error occured while executing doInBackground()",
                             e.getCause());
                 } catch (CancellationException e) {
                     message = sHandler.obtainMessage(MESSAGE_POST_CANCEL,
                             new AsyncTaskResult<Result>(AsyncTask.this, (Result[]) null));
                     message.sendToTarget();
                     return;
                 } catch (Throwable t) {
                     throw new RuntimeException("An error occured while executing "
                             + "doInBackground()", t);
                 }

                 message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
                         new AsyncTaskResult<Result>(AsyncTask.this, result));
                 message.sendToTarget();
             }
         };
     }

     /**
      * Returns the current status of this task.
      *
      * @return The current status.
      */
     public final Status getStatus() {
         return mStatus;
     }

     /**
      * Override this method to perform a computation on a background thread. The
      * specified parameters are the parameters passed to {@link #execute}
      * by the caller of this task.
      *
      * This method can call {@link #publishProgress} to publish updates
      * on the UI thread.
      *
      * @param params The parameters of the task.
      *
      * @return A result, defined by the subclass of this task.
      *
      * @see #onPreExecute()
      * @see #onPostExecute
      * @see #publishProgress
      */
     protected abstract Result doInBackground(Params... params);

     /**
      * Runs on the UI thread before {@link #doInBackground}.
      *
      * @see #onPostExecute
      * @see #doInBackground
      */
     protected void onPreExecute() {
     }

     /**
      * Runs on the UI thread after {@link #doInBackground}. The
      * specified result is the value returned by {@link #doInBackground}
      * or null if the task was cancelled or an exception occured.
      *
      * @param result The result of the operation computed by {@link #doInBackground}.
      *
      * @see #onPreExecute
      * @see #doInBackground
      */
     @SuppressWarnings({"UnusedDeclaration"})
     protected void onPostExecute(Result result) {
     }

     /**
      * Runs on the UI thread after {@link #publishProgress} is invoked.
      * The specified values are the values passed to {@link #publishProgress}.
      *
      * @param values The values indicating progress.
      *
      * @see #publishProgress
      * @see #doInBackground
      */
     @SuppressWarnings({"UnusedDeclaration"})
     protected void onProgressUpdate(Progress... values) {
     }

     /**
      * Runs on the UI thread after {@link #cancel(boolean)} is invoked.
      *
      * @see #cancel(boolean)
      * @see #isCancelled()
      */
     protected void onCancelled() {
     }

     /**
      * Returns <tt>true</tt> if this task was cancelled before it completed
      * normally.
      *
      * @return <tt>true</tt> if task was cancelled before it completed
      *
      * @see #cancel(boolean)
      */
     public final boolean isCancelled() {
         return mFuture.isCancelled();
     }

     /**
      * Attempts to cancel execution of this task.  This attempt will
      * fail if the task has already completed, already been cancelled,
      * or could not be cancelled for some other reason. If successful,
      * and this task has not started when <tt>cancel</tt> is called,
      * this task should never run.  If the task has already started,
      * then the <tt>mayInterruptIfRunning</tt> parameter determines
      * whether the thread executing this task should be interrupted in
      * an attempt to stop the task.
      *
      * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
      *        task should be interrupted; otherwise, in-progress tasks are allowed
      *        to complete.
      *
      * @return <tt>false</tt> if the task could not be cancelled,
      *         typically because it has already completed normally;
      *         <tt>true</tt> otherwise
      *
      * @see #isCancelled()
      * @see #onCancelled()
      */
     public final boolean cancel(boolean mayInterruptIfRunning) {
         return mFuture.cancel(mayInterruptIfRunning);
     }

     /**
      * Waits if necessary for the computation to complete, and then
      * retrieves its result.
      *
      * @return The computed result.
      *
      * @throws CancellationException If the computation was cancelled.
      * @throws ExecutionException If the computation threw an exception.
      * @throws InterruptedException If the current thread was interrupted
      *         while waiting.
      */
     public final Result get() throws InterruptedException, ExecutionException {
         return mFuture.get();
     }

     /**
      * Waits if necessary for at most the given time for the computation
      * to complete, and then retrieves its result.
      *
      * @param timeout Time to wait before cancelling the operation.
      * @param unit The time unit for the timeout.
      *
      * @return The computed result.
      *
      * @throws CancellationException If the computation was cancelled.
      * @throws ExecutionException If the computation threw an exception.
      * @throws InterruptedException If the current thread was interrupted
      *         while waiting.
      * @throws TimeoutException If the wait timed out.
      */
     public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
             ExecutionException, TimeoutException {
         return mFuture.get(timeout, unit);
     }

     /**
      * Executes the task with the specified parameters. The task returns
      * itself (this) so that the caller can keep a reference to it.
      *
      * This method must be invoked on the UI thread.
      *
      * @param params The parameters of the task.
      *
      * @return This instance of AsyncTask.
      *
      * @throws IllegalStateException If {@link #getStatus()} returns either
      *         {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
      */
     public final AsyncTask<Params, Progress, Result> execute(Params... params) {
         if (mStatus != Status.PENDING) {
             switch (mStatus) {
                 case RUNNING:
                     throw new IllegalStateException("Cannot execute task:"
                             + " the task is already running.");
                 case FINISHED:
                     throw new IllegalStateException("Cannot execute task:"
                             + " the task has already been executed "
                             + "(a task can be executed only once)");
             }
         }

         mStatus = Status.RUNNING;

         onPreExecute();

         mWorker.mParams = params;
         sExecutor.execute(mFuture);

         return this;
     }

     /**
      * This method can be invoked from {@link #doInBackground} to
      * publish updates on the UI thread while the background computation is
      * still running. Each call to this method will trigger the execution of
      * {@link #onProgressUpdate} on the UI thread.
      *
      * @param values The progress values to update the UI with.
      *
      * @see #onProgressUpdate
      * @see #doInBackground
      */
     protected final void publishProgress(Progress... values) {
         sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
                 new AsyncTaskResult<Progress>(this, values)).sendToTarget();
     }

     private void finish(Result result) {
         if (isCancelled()) result = null;
         onPostExecute(result);
         mStatus = Status.FINISHED;
     }

     private static class InternalHandler extends Handler {
         @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
         @Override
         public void handleMessage(Message msg) {
             AsyncTaskResult result = (AsyncTaskResult) msg.obj;
             switch (msg.what) {
                 case MESSAGE_POST_RESULT:
                     // There is only one result
                     result.mTask.finish(result.mData[0]);
                     break;
                 case MESSAGE_POST_PROGRESS:
                     result.mTask.onProgressUpdate(result.mData);
                     break;
                 case MESSAGE_POST_CANCEL:
                     result.mTask.onCancelled();
                     break;
             }
         }
     }

     private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
         Params[] mParams;
     }

     @SuppressWarnings({"RawUseOfParameterizedType"})
     private static class AsyncTaskResult<Data> {
         final AsyncTask mTask;
         final Data[] mData;

         AsyncTaskResult(AsyncTask task, Data... data) {
             mTask = task;
             mData = data;
         }
     }
 }
	/*
	* Copyright (C) 2008 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package android.os;

	import java.util.concurrent.ThreadPoolExecutor;
	import java.util.concurrent.TimeUnit;
	import java.util.concurrent.BlockingQueue;
	import java.util.concurrent.LinkedBlockingQueue;
	import java.util.concurrent.ThreadFactory;
	import java.util.concurrent.Callable;
	import java.util.concurrent.FutureTask;
	import java.util.concurrent.ExecutionException;
	import java.util.concurrent.TimeoutException;
	import java.util.concurrent.CancellationException;
	import java.util.concurrent.atomic.AtomicInteger;

	/**
	* <p>AsyncTask enables proper and easy use of the UI thread. This class allows to
	* perform background operations and publish results on the UI thread without
	* having to manipulate threads and/or handlers.</p>
	*
	* <p>An asynchronous task is defined by a computation that runs on a background thread and
	* whose result is published on the UI thread. An asynchronous task is defined by 3 generic
	* types, called <code>Params</code>, <code>Progress</code> and <code>Result</code>,
	* and 4 steps, called <code>begin</code>, <code>doInBackground</code>,
	* <code>processProgress</code> and <code>end</code>.</p>
	*
	* <h2>Usage</h2>
	* <p>AsyncTask must be subclassed to be used. The subclass will override at least
	* one method ({@link #doInBackground}), and most often will override a
	* second one ({@link #onPostExecute}.)</p>
	*
	* <p>Here is an example of subclassing:</p>
	* <pre class="prettyprint">
	* private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
	* protected Long doInBackground(URL... urls) {
	* int count = urls.length;
	* long totalSize = 0;
	* for (int i = 0; i < count; i++) {
	* totalSize += Downloader.downloadFile(urls[i]);
	* publishProgress((int) ((i / (float) count) * 100));
	* }
	* return totalSize;
	* }
	*
	* protected void onProgressUpdate(Integer... progress) {
	* setProgressPercent(progress[0]);
	* }
	*
	* protected void onPostExecute(Long result) {
	* showDialog("Downloaded " + result + " bytes");
	* }
	* }
	* </pre>
	*
	* <p>Once created, a task is executed very simply:</p>
	* <pre class="prettyprint">
	* new DownloadFilesTask().execute(url1, url2, url3);
	* </pre>
	*
	* <h2>AsyncTask's generic types</h2>
	* <p>The three types used by an asynchronous task are the following:</p>
	* <ol>
	* <li><code>Params</code>, the type of the parameters sent to the task upon
	* execution.</li>
	* <li><code>Progress</code>, the type of the progress units published during
	* the background computation.</li>
	* <li><code>Result</code>, the type of the result of the background
	* computation.</li>
	* </ol>
	* <p>Not all types are always used by an asynchronous task. To mark a type as unused,
	* simply use the type {@link Void}:</p>
	* <pre>
	* private class MyTask extends AsyncTask<Void, Void, Void> { ... }
	* </pre>
	*
	* <h2>The 4 steps</h2>
	* <p>When an asynchronous task is executed, the task goes through 4 steps:</p>
	* <ol>
	* <li>{@link #onPreExecute()}, invoked on the UI thread immediately after the task
	* is executed. This step is normally used to setup the task, for instance by
	* showing a progress bar in the user interface.</li>
	* <li>{@link #doInBackground}, invoked on the background thread
	* immediately after {@link #onPreExecute()} finishes executing. This step is used
	* to perform background computation that can take a long time. The parameters
	* of the asynchronous task are passed to this step. The result of the computation must
	* be returned by this step and will be passed back to the last step. This step
	* can also use {@link #publishProgress} to publish one or more units
	* of progress. These values are published on the UI thread, in the
	* {@link #onProgressUpdate} step.</li>
	* <li>{@link #onProgressUpdate}, invoked on the UI thread after a
	* call to {@link #publishProgress}. The timing of the execution is
	* undefined. This method is used to display any form of progress in the user
	* interface while the background computation is still executing. For instance,
	* it can be used to animate a progress bar or show logs in a text field.</li>
	* <li>{@link #onPostExecute}, invoked on the UI thread after the background
	* computation finishes. The result of the background computation is passed to
	* this step as a parameter.</li>
	* </ol>
	*
	* <h2>Threading rules</h2>
	* <p>There are a few threading rules that must be followed for this class to
	* work properly:</p>
	* <ul>
	* <li>The task instance must be created on the UI thread.</li>
	* <li>{@link #execute} must be invoked on the UI thread.</li>
	* <li>Do not call {@link #onPreExecute()}, {@link #onPostExecute},
	* {@link #doInBackground}, {@link #onProgressUpdate} manually.</li>
	* <li>The task can be executed only once (an exception will be thrown if
	* a second execution is attempted.)</li>
	* </ul>
	*/
	public abstract class AsyncTask<Params, Progress, Result> {
	private static final String LOG_TAG = "AsyncTask";

	private static final int CORE_POOL_SIZE = 5;
	private static final int MAXIMUM_POOL_SIZE = 128;
	private static final int KEEP_ALIVE = 1;

	private static final BlockingQueue<Runnable> sWorkQueue =
	new LinkedBlockingQueue<Runnable>(10);

	private static final ThreadFactory sThreadFactory = new ThreadFactory() {
	private final AtomicInteger mCount = new AtomicInteger(1);

	public Thread newThread(Runnable r) {
	return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
	}
	};

	private static final ThreadPoolExecutor sExecutor = new ThreadPoolExecutor(CORE_POOL_SIZE,
	MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, sWorkQueue, sThreadFactory);

	private static final int MESSAGE_POST_RESULT = 0x1;
	private static final int MESSAGE_POST_PROGRESS = 0x2;
	private static final int MESSAGE_POST_CANCEL = 0x3;

	private static final InternalHandler sHandler = new InternalHandler();

	private final WorkerRunnable<Params, Result> mWorker;
	private final FutureTask<Result> mFuture;

	private volatile Status mStatus = Status.PENDING;

	/**
	* Indicates the current status of the task. Each status will be set only once
	* during the lifetime of a task.
	*/
	public enum Status {
	/**
	* Indicates that the task has not been executed yet.
	*/
	PENDING,
	/**
	* Indicates that the task is running.
	*/
	RUNNING,
	/**
	* Indicates that {@link AsyncTask#onPostExecute} has finished.
	*/
	FINISHED,
	}

	/**
	* Creates a new asynchronous task. This constructor must be invoked on the UI thread.
	*/
	public AsyncTask() {
	mWorker = new WorkerRunnable<Params, Result>() {
	public Result call() throws Exception {
	Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
	return doInBackground(mParams);
	}
	};

	mFuture = new FutureTask<Result>(mWorker) {
	@Override
	protected void done() {
	Message message;
	Result result = null;

	try {
	result = get();
	} catch (InterruptedException e) {
	android.util.Log.w(LOG_TAG, e);
	} catch (ExecutionException e) {
	throw new RuntimeException("An error occured while executing doInBackground()",
	e.getCause());
	} catch (CancellationException e) {
	message = sHandler.obtainMessage(MESSAGE_POST_CANCEL,
	new AsyncTaskResult<Result>(AsyncTask.this, (Result[]) null));
	message.sendToTarget();
	return;
	} catch (Throwable t) {
	throw new RuntimeException("An error occured while executing "
	+ "doInBackground()", t);
	}

	message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
	new AsyncTaskResult<Result>(AsyncTask.this, result));
	message.sendToTarget();
	}
	};
	}

	/**
	* Returns the current status of this task.
	*
	* @return The current status.
	*/
	public final Status getStatus() {
	return mStatus;
	}

	/**
	* Override this method to perform a computation on a background thread. The
	* specified parameters are the parameters passed to {@link #execute}
	* by the caller of this task.
	*
	* This method can call {@link #publishProgress} to publish updates
	* on the UI thread.
	*
	* @param params The parameters of the task.
	*
	* @return A result, defined by the subclass of this task.
	*
	* @see #onPreExecute()
	* @see #onPostExecute
	* @see #publishProgress
	*/
	protected abstract Result doInBackground(Params... params);

	/**
	* Runs on the UI thread before {@link #doInBackground}.
	*
	* @see #onPostExecute
	* @see #doInBackground
	*/
	protected void onPreExecute() {
	}

	/**
	* Runs on the UI thread after {@link #doInBackground}. The
	* specified result is the value returned by {@link #doInBackground}
	* or null if the task was cancelled or an exception occured.
	*
	* @param result The result of the operation computed by {@link #doInBackground}.
	*
	* @see #onPreExecute
	* @see #doInBackground
	*/
	@SuppressWarnings({"UnusedDeclaration"})
	protected void onPostExecute(Result result) {
	}

	/**
	* Runs on the UI thread after {@link #publishProgress} is invoked.
	* The specified values are the values passed to {@link #publishProgress}.
	*
	* @param values The values indicating progress.
	*
	* @see #publishProgress
	* @see #doInBackground
	*/
	@SuppressWarnings({"UnusedDeclaration"})
	protected void onProgressUpdate(Progress... values) {
	}

	/**
	* Runs on the UI thread after {@link #cancel(boolean)} is invoked.
	*
	* @see #cancel(boolean)
	* @see #isCancelled()
	*/
	protected void onCancelled() {
	}

	/**
	* Returns <tt>true</tt> if this task was cancelled before it completed
	* normally.
	*
	* @return <tt>true</tt> if task was cancelled before it completed
	*
	* @see #cancel(boolean)
	*/
	public final boolean isCancelled() {
	return mFuture.isCancelled();
	}

	/**
	* Attempts to cancel execution of this task. This attempt will
	* fail if the task has already completed, already been cancelled,
	* or could not be cancelled for some other reason. If successful,
	* and this task has not started when <tt>cancel</tt> is called,
	* this task should never run. If the task has already started,
	* then the <tt>mayInterruptIfRunning</tt> parameter determines
	* whether the thread executing this task should be interrupted in
	* an attempt to stop the task.
	*
	* @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
	* task should be interrupted; otherwise, in-progress tasks are allowed
	* to complete.
	*
	* @return <tt>false</tt> if the task could not be cancelled,
	* typically because it has already completed normally;
	* <tt>true</tt> otherwise
	*
	* @see #isCancelled()
	* @see #onCancelled()
	*/
	public final boolean cancel(boolean mayInterruptIfRunning) {
	return mFuture.cancel(mayInterruptIfRunning);
	}

	/**
	* Waits if necessary for the computation to complete, and then
	* retrieves its result.
	*
	* @return The computed result.
	*
	* @throws CancellationException If the computation was cancelled.
	* @throws ExecutionException If the computation threw an exception.
	* @throws InterruptedException If the current thread was interrupted
	* while waiting.
	*/
	public final Result get() throws InterruptedException, ExecutionException {
	return mFuture.get();
	}

	/**
	* Waits if necessary for at most the given time for the computation
	* to complete, and then retrieves its result.
	*
	* @param timeout Time to wait before cancelling the operation.
	* @param unit The time unit for the timeout.
	*
	* @return The computed result.
	*
	* @throws CancellationException If the computation was cancelled.
	* @throws ExecutionException If the computation threw an exception.
	* @throws InterruptedException If the current thread was interrupted
	* while waiting.
	* @throws TimeoutException If the wait timed out.
	*/
	public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
	ExecutionException, TimeoutException {
	return mFuture.get(timeout, unit);
	}

	/**
	* Executes the task with the specified parameters. The task returns
	* itself (this) so that the caller can keep a reference to it.
	*
	* This method must be invoked on the UI thread.
	*
	* @param params The parameters of the task.
	*
	* @return This instance of AsyncTask.
	*
	* @throws IllegalStateException If {@link #getStatus()} returns either
	* {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
	*/
	public final AsyncTask<Params, Progress, Result> execute(Params... params) {
	if (mStatus != Status.PENDING) {
	switch (mStatus) {
	case RUNNING:
	throw new IllegalStateException("Cannot execute task:"
	+ " the task is already running.");
	case FINISHED:
	throw new IllegalStateException("Cannot execute task:"
	+ " the task has already been executed "
	+ "(a task can be executed only once)");
	}
	}

	mStatus = Status.RUNNING;

	onPreExecute();

	mWorker.mParams = params;
	sExecutor.execute(mFuture);

	return this;
	}

	/**
	* This method can be invoked from {@link #doInBackground} to
	* publish updates on the UI thread while the background computation is
	* still running. Each call to this method will trigger the execution of
	* {@link #onProgressUpdate} on the UI thread.
	*
	* @param values The progress values to update the UI with.
	*
	* @see #onProgressUpdate
	* @see #doInBackground
	*/
	protected final void publishProgress(Progress... values) {
	sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
	new AsyncTaskResult<Progress>(this, values)).sendToTarget();
	}

	private void finish(Result result) {
	if (isCancelled()) result = null;
	onPostExecute(result);
	mStatus = Status.FINISHED;
	}

	private static class InternalHandler extends Handler {
	@SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
	@Override
	public void handleMessage(Message msg) {
	AsyncTaskResult result = (AsyncTaskResult) msg.obj;
	switch (msg.what) {
	case MESSAGE_POST_RESULT:
	// There is only one result
	result.mTask.finish(result.mData[0]);
	break;
	case MESSAGE_POST_PROGRESS:
	result.mTask.onProgressUpdate(result.mData);
	break;
	case MESSAGE_POST_CANCEL:
	result.mTask.onCancelled();
	break;
	}
	}
	}

	private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
	Params[] mParams;
	}

	@SuppressWarnings({"RawUseOfParameterizedType"})
	private static class AsyncTaskResult<Data> {
	final AsyncTask mTask;
	final Data[] mData;

	AsyncTaskResult(AsyncTask task, Data... data) {
	mTask = task;
	mData = data;
	}
	}
	}