/utils/src/com/google/marvin/utils/UserTask.java
http://eyes-free.googlecode.com/ · Java · 459 lines · 159 code · 39 blank · 261 comment · 4 complexity · 66d8a0c40f034b0feb5fc91f9e8b294d MD5 · raw file
- /*
- * Copyright (C) 2008 Google Inc.
- *
- * 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.
- */
- // Taken from the Photostream app by Romain Guy
- // at http://apps-for-android.googlecode.com
- package com.google.marvin.utils;
- import android.os.*;
- import android.os.Process;
- 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>UserTask 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>A user task is defined by a computation that runs on a background thread and
- * whose result is published on the UI thread. A user 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>UserTask must be subclassed to be used. The subclass will override at least
- * one method ({@link #doInBackground(Object[])}), and most often will override a
- * second one ({@link #onPostExecute(Object)}.)</p>
- *
- * <p>Here is an example of subclassing:</p>
- * <pre>
- * private class DownloadFilesTask extends UserTask<URL, Integer, Long> {
- * public File 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));
- * }
- * }
- *
- * public void onProgressUpdate(Integer... progress) {
- * setProgressPercent(progress[0]);
- * }
- *
- * public void onPostExecute(Long result) {
- * showDialog("Downloaded " + result + " bytes");
- * }
- * }
- * </pre>
- *
- * <p>Once created, a task is executed very simply:</p>
- * <pre>
- * new DownloadFilesTask().execute(new URL[] { ... });
- * </pre>
- *
- * <h2>User task's generic types</h2>
- * <p>The three types used by a user 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 a user task. To mark a type as unused,
- * simply use the type {@link Void}:</p>
- * <pre>
- * private class MyTask extends UserTask<Void, Void, Void) { ... }
- * </pre>
- *
- * <h2>The 4 steps</h2>
- * <p>When a user 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(Object[])}, 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 user 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(Object[])} to publish one or more units
- * of progress. These values are published on the UI thread, in the
- * {@link #onProgressUpdate(Object[])} step.</li>
- * <li>{@link # onProgressUpdate (Object[])}, invoked on the UI thread after a
- * call to {@link #publishProgress(Object[])}. 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 (Object)}, 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(Object[])} must be invoked on the UI thread.</li>
- * <li>Do not call {@link # onPreExecute ()}, {@link # onPostExecute (Object)},
- * {@link #doInBackground(Object[])}, {@link # onProgressUpdate (Object[])}
- * 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 UserTask<Params, Progress, Result> {
- private static final String LOG_TAG = "UserTask";
- private static final int CORE_POOL_SIZE = 1;
- private static final int MAXIMUM_POOL_SIZE = 10;
- private static final int KEEP_ALIVE = 10;
- private static final BlockingQueue<Runnable> sWorkQueue =
- new LinkedBlockingQueue<Runnable>(MAXIMUM_POOL_SIZE);
- private static final ThreadFactory sThreadFactory = new ThreadFactory() {
- private final AtomicInteger mCount = new AtomicInteger(1);
- public Thread newThread(Runnable r) {
- return new Thread(r, "UserTask #" + 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 UserTask#onPostExecute(Object)} has finished.
- */
- FINISHED,
- }
- /**
- * Creates a new user task. This constructor must be invoked on the UI thread.
- */
- public UserTask() {
- 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 UserTaskResult<Result>(UserTask.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 UserTaskResult<Result>(UserTask.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(Object[])}
- * by the caller of this task.
- *
- * This method can call {@link #publishProgress(Object[])} 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(Object)
- * @see #publishProgress(Object[])
- */
- public abstract Result doInBackground(Params... params);
- /**
- * Runs on the UI thread before {@link #doInBackground(Object[])}.
- *
- * @see #onPostExecute(Object)
- * @see #doInBackground(Object[])
- */
- public void onPreExecute() {
- }
- /**
- * Runs on the UI thread after {@link #doInBackground(Object[])}. The
- * specified result is the value returned by {@link #doInBackground(Object[])}
- * or null if the task was cancelled or an exception occured.
- *
- * @param result The result of the operation computed by {@link #doInBackground(Object[])}.
- *
- * @see #onPreExecute()
- * @see #doInBackground(Object[])
- */
- @SuppressWarnings({"UnusedDeclaration"})
- public void onPostExecute(Result result) {
- }
- /**
- * Runs on the UI thread after {@link #publishProgress(Object[])} is invoked.
- * The specified values are the values passed to {@link #publishProgress(Object[])}.
- *
- * @param values The values indicating progress.
- *
- * @see #publishProgress(Object[])
- * @see #doInBackground(Object[])
- */
- @SuppressWarnings({"UnusedDeclaration"})
- public void onProgressUpdate(Progress... values) {
- }
- /**
- * Runs on the UI thread after {@link #cancel(boolean)} is invoked.
- *
- * @see #cancel(boolean)
- * @see #isCancelled()
- */
- public 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 UserTask.
- *
- * @throws IllegalStateException If {@link #getStatus()} returns either
- * {@link UserTask.Status#RUNNING} or {@link UserTask.Status#FINISHED}.
- */
- public final UserTask<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(Object[])} 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(Object[])} on the UI thread.
- *
- * @param values The progress values to update the UI with.
- *
- * @see # onProgressUpdate (Object[])
- * @see #doInBackground(Object[])
- */
- protected final void publishProgress(Progress... values) {
- sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
- new UserTaskResult<Progress>(this, values)).sendToTarget();
- }
- private void finish(Result result) {
- onPostExecute(result);
- mStatus = Status.FINISHED;
- }
- private static class InternalHandler extends Handler {
- @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
- @Override
- public void handleMessage(Message msg) {
- UserTaskResult result = (UserTaskResult) 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 UserTaskResult<Data> {
- final UserTask mTask;
- final Data[] mData;
- UserTaskResult(UserTask task, Data... data) {
- mTask = task;
- mData = data;
- }
- }
- }