APIレベル11より前のAsyncTask.executeOnExecutor（）
AndroidでAsyncTaskを行う通常の方法は、from Android API：
private class DoIntenseTask extends AsyncTask<Object, Object, Void> {
protected Void doInBackground(Object... params) {
for (Object param : params) {
Object rtnObj = doIntenseJob(param);
publishProgress(rtnObj);
}
return null;
}
protected void onProgressUpdate(Object... progress) {
for (Object rtnObj : progress) {
updateActivityUI(rtnObj);
}
}
}
私の集中的なタスクは疎結合であり、実行順序は重要ではありません。このようにすることで、集中的なタスクのリストを実行するために単一のスレッドが割り当てられます。個人的には、これは一種の中間的な解決策だと思います。はい、強烈なジョブはUIスレッドでもう実行されていませんが、1つずつ実行する必要があります（多くの場合、強烈なジョブのリストに直面しています。これがAsyncTaskのメソッドがマルチパラメーター化される理由でもあると思います）。 Googleは、さまざまな種類のシナリオを解決するためにAPIをより再利用可能にする必要があります。
私が本当に好きなのは、スレッドプールによって管理された多数のdoIntenseJob（）を並行して実行することです（例：poolSize = 5）。グーグルはAsyncTask.executeOnExecutor（）によって解決策を提供するようですが、残念ながらAPIレベル11以降でのみ利用可能です。モバイルでアプリを開発していますが、APIレベル11で同じ動作を達成できる回避策があるかどうか疑問に思います。
前もって感謝します
Y
私の集中的なタスクは疎結合であり、実行順序は重要ではありません。このようにすることで、集中的なタスクのリストを実行するために単一のスレッドが割り当てられます。
AsyncTaskは現在、複数のスレッドでスレッドプールを使用しています。将来的には、単一のスレッドに制限される可能性があります-Googleはこれが事実であることを示唆しています。
aPIレベル11で同じ動作を実現できる回避策があるかどうか疑問に思います。
デフォルトの動作は、必要な動作です。 AsyncTaskへのソースコード を調べると、Gingerbreadの時点で、最小5スレッド、最大128のスレッドプールを使用していることがわかります。
ここで、vastAndroid現在使用されているデバイスの大部分はシングルコアであることに注意してください。 「強力なタスク」は非常に多くのことを行うのではなく、ネットワークI/Oでブロックします。スレッド間でコンテキストを切り替えると単純に速度が低下するため、それらを並行して行いたくありません。
ビルドターゲットがAPIレベル11以上に設定されており、特に並列タスクを使用する場合は、コード内で次のような明示的な記述を開始します。
if (Build.VERSION.SDK_INT>=Build.VERSION_CODES.HONEYCOMB) {
myTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, (Void[]) null);
}
else {
myTask.execute((Void) null);
}
http://commonsware.com/blog/2012/04/20/asynctask-threading-regression-confirmed.html
この質問をしてからかなりの時間が経ちましたが、StackOverflowで同様の質問が終わることもありますが、しっかりした答えはありません。
最初に指摘しなければならないことは、ほとんどの一般的な場合です。AsyncTaskAPIに付属する基本的なスレッドプール実装のデフォルトの動作で十分であり、特にHoneyCombより前の以前のバージョンを対象とする場合はAsyncTask.executeOnExecutor（）を使用して変更する必要はありません、CommonsWareの回答で既に述べています。ただし、AsyncTask.executeOnExecutor（）を使用して、SDKの以前のバージョンの元になるスレッドプールを細かく制御する必要がある場合は、次の回答を参考にしてください。
一般的に言えば、私のソリューションは、AsyncTaskの新しいバージョン（APIレベル11から）を独自のAsyncTask実装にコピーし、以前のAndroid SDK（APIレベル3まで）で動作するようにすることです。 、AsyncTaskのソースコードを読んでください こちら そして、それがどのように実装されているかについての基本的なアイデアを得ることを確認してください。
ソースコードから、APIレベル1以降、AsyncTaskによってインポートおよび使用されるほぼすべてのクラス、つまりJava.util.concurrent。*のすべてのクラスに加え、Android.osの他の3つ（ハンドラー、メッセージ、プロセス）が導入されていることがわかります。*、唯一の例外は Java.util.ArrayDeque で、これはAndroid SDKに導入されています。APIレベル9以降です。ArrayDequeはデフォルトのExecutorの1つを実装するためにのみ使用されます SERIAL_EXECUTOR AsyncTaskに付属しており、AsyncTask.executeOnExecutor（）を古いAndroid SDK、SERIAL_EXECUTOR実装をソースコードから簡単に削除します。 singleThreadPoolExecutorを使用します。
変更されたソースコードは最後に添付されます（Gingerbreadでテスト済み）。ここで必要なことは、AsyncTask.executeOnExecutor（）をサポートするAndroid.os.AsyncTaskではなく、このcom.example.AsyncTaskからAsyncTaskをAPIレベル3まで拡張することです。
package com.example;
/*
* 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.
*/
//import Java.util.ArrayDeque;
import Java.util.concurrent.BlockingQueue;
import Java.util.concurrent.Callable;
import Java.util.concurrent.CancellationException;
import Java.util.concurrent.Executor;
import Java.util.concurrent.ExecutionException;
import Java.util.concurrent.FutureTask;
import Java.util.concurrent.LinkedBlockingQueue;
import Java.util.concurrent.ThreadFactory;
import Java.util.concurrent.ThreadPoolExecutor;
import Java.util.concurrent.TimeUnit;
import Java.util.concurrent.TimeoutException;
import Java.util.concurrent.atomic.AtomicBoolean;
import Java.util.concurrent.atomic.AtomicInteger;
import Android.os.Handler;
import Android.os.Message;
import Android.os.Process;
/**
* ### I delete this comments as it make the answer too long to submit ###
*/
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 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 BlockingQueue<Runnable> sPoolWorkQueue =
new LinkedBlockingQueue<Runnable>(10);
/**
* An {@link Executor} that can be used to execute tasks in parallel.
*/
public static final Executor THREAD_POOL_EXECUTOR
= new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);
/**
* An {@link Executor} that executes tasks one at a time in serial
* order. This serialization is global to a particular process.
*/
// public static final Executor SERIAL_EXECUTOR = new SerialExecutor();
private static final int MESSAGE_POST_RESULT = 0x1;
private static final int MESSAGE_POST_PROGRESS = 0x2;
private static final InternalHandler sHandler = new InternalHandler();
// private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
private static volatile Executor sDefaultExecutor = THREAD_POOL_EXECUTOR;
private final WorkerRunnable<Params, Result> mWorker;
private final FutureTask<Result> mFuture;
private volatile Status mStatus = Status.PENDING;
private final AtomicBoolean mTaskInvoked = new AtomicBoolean();
// private static class SerialExecutor implements Executor {
// final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
// Runnable mActive;
//
// public synchronized void execute(final Runnable r) {
// mTasks.offer(new Runnable() {
// public void run() {
// try {
// r.run();
// } finally {
// scheduleNext();
// }
// }
// });
// if (mActive == null) {
// scheduleNext();
// }
// }
//
// protected synchronized void scheduleNext() {
// if ((mActive = mTasks.poll()) != null) {
// THREAD_POOL_EXECUTOR.execute(mActive);
// }
// }
// }
/**
* 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,
}
/** @hide Used to force static handler to be created. */
public static void init() {
sHandler.getLooper();
}
/** @hide */
public static void setDefaultExecutor(Executor exec) {
sDefaultExecutor = exec;
}
/**
* 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 {
mTaskInvoked.set(true);
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
return postResult(doInBackground(mParams));
}
};
mFuture = new FutureTask<Result>(mWorker) {
@Override
protected void done() {
try {
final Result result = get();
postResultIfNotInvoked(result);
} 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) {
postResultIfNotInvoked(null);
} catch (Throwable t) {
throw new RuntimeException("An error occured while executing "
+ "doInBackground()", t);
}
}
};
}
private void postResultIfNotInvoked(Result result) {
final boolean wasTaskInvoked = mTaskInvoked.get();
if (!wasTaskInvoked) {
postResult(result);
}
}
private Result postResult(Result result) {
Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
new AsyncTaskResult<Result>(this, result));
message.sendToTarget();
return result;
}
/**
* 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() {
}
/**
* <p>Runs on the UI thread after {@link #doInBackground}. The
* specified result is the value returned by {@link #doInBackground}.</p>
*
* <p>This method won't be invoked if the task was cancelled.</p>
*
* @param result The result of the operation computed by {@link #doInBackground}.
*
* @see #onPreExecute
* @see #doInBackground
* @see #onCancelled(Object)
*/
@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) {
}
/**
* <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
* {@link #doInBackground(Object[])} has finished.</p>
*
* <p>The default implementation simply invokes {@link #onCancelled()} and
* ignores the result. If you write your own implementation, do not call
* <code>super.onCancelled(result)</code>.</p>
*
* @param result The result, if any, computed in
* {@link #doInBackground(Object[])}, can be null
*
* @see #cancel(boolean)
* @see #isCancelled()
*/
@SuppressWarnings({"UnusedParameters"})
protected void onCancelled(Result result) {
onCancelled();
}
/**
* <p>Applications should preferably override {@link #onCancelled(Object)}.
* This method is invoked by the default implementation of
* {@link #onCancelled(Object)}.</p>
*
* <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
* {@link #doInBackground(Object[])} has finished.</p>
*
* @see #onCancelled(Object)
* @see #cancel(boolean)
* @see #isCancelled()
*/
protected void onCancelled() {
}
/**
* Returns <tt>true</tt> if this task was cancelled before it completed
* normally. If you are calling {@link #cancel(boolean)} on the task,
* the value returned by this method should be checked periodically from
* {@link #doInBackground(Object[])} to end the task as soon as possible.
*
* @return <tt>true</tt> if task was cancelled before it completed
*
* @see #cancel(boolean)
*/
public final boolean isCancelled() {
return mFuture.isCancelled();
}
/**
* <p>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.</p>
*
* <p>Calling this method will result in {@link #onCancelled(Object)} being
* invoked on the UI thread after {@link #doInBackground(Object[])}
* returns. Calling this method guarantees that {@link #onPostExecute(Object)}
* is never invoked. After invoking this method, you should check the
* value returned by {@link #isCancelled()} periodically from
* {@link #doInBackground(Object[])} to finish the task as early as
* possible.</p>
*
* @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(Object)
*/
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.
*
* <p>Note: this function schedules the task on a queue for a single background
* thread or pool of threads depending on the platform version. When first
* introduced, AsyncTasks were executed serially on a single background thread.
* Starting with {@link Android.os.Build.VERSION_CODES#DONUT}, this was changed
* to a pool of threads allowing multiple tasks to operate in parallel. After
* {@link Android.os.Build.VERSION_CODES#HONEYCOMB}, it is planned to change this
* back to a single thread to avoid common application errors caused
* by parallel execution. If you truly want parallel execution, you can use
* the {@link #executeOnExecutor} version of this method
* with {@link #THREAD_POOL_EXECUTOR}; however, see commentary there for warnings on
* its use.
*
* <p>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) {
return executeOnExecutor(sDefaultExecutor, params);
}
/**
* Executes the task with the specified parameters. The task returns
* itself (this) so that the caller can keep a reference to it.
*
* <p>This method is typically used with {@link #THREAD_POOL_EXECUTOR} to
* allow multiple tasks to run in parallel on a pool of threads managed by
* AsyncTask, however you can also use your own {@link Executor} for custom
* behavior.
*
* <p><em>Warning:</em> Allowing multiple tasks to run in parallel from
* a thread pool is generally <em>not</em> what one wants, because the order
* of their operation is not defined. For example, if these tasks are used
* to modify any state in common (such as writing a file due to a button click),
* there are no guarantees on the order of the modifications.
* Without careful work it is possible in rare cases for the newer version
* of the data to be over-written by an older one, leading to obscure data
* loss and stability issues. Such changes are best
* executed in serial; to guarantee such work is serialized regardless of
* platform version you can use this function with {@link #SERIAL_EXECUTOR}.
*
* <p>This method must be invoked on the UI thread.
*
* @param exec The executor to use. {@link #THREAD_POOL_EXECUTOR} is available as a
* convenient process-wide thread pool for tasks that are loosely coupled.
* @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> executeOnExecutor(Executor exec,
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;
exec.execute(mFuture);
return this;
}
/**
* Convenience version of {@link #execute(Object...)} for use with
* a simple Runnable object.
*/
public static void execute(Runnable runnable) {
sDefaultExecutor.execute(runnable);
}
/**
* 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.
*
* {@link #onProgressUpdate} will note be called if the task has been
* canceled.
*
* @param values The progress values to update the UI with.
*
* @see #onProgressUpdate
* @see #doInBackground
*/
protected final void publishProgress(Progress... values) {
if (!isCancelled()) {
sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
new AsyncTaskResult<Progress>(this, values)).sendToTarget();
}
}
private void finish(Result result) {
if (isCancelled()) {
onCancelled(result);
} else {
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;
}
}
}
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;
}
}
}
抽象ヘルパークラスを作成して、ビルド番号を決定し、executeまたはexecuteOnExecutorを適切に選択します。かなりうまくいくようです
public abstract class MyAsyncTask<T, V, Q> extends AsyncTask<T, V, Q> {
public void executeContent(T... content) {
if (Build.VERSION.SDK_INT>=Build.VERSION_CODES.HONEYCOMB) {
this.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, content);
}
else {
this.execute(content);
}
}
}
抽象クラスの実装例：
public class MyTask extends MyAsyncTask<String, Void, Void> {
@Override
protected Void doInBackground(String... params) {
//do work
return null;
}
}
クラスのインスタンスを作成する
new MyTask().executeContent("go");
互換性ライブラリには、AsyncTaskCompatが存在します。このクラスには、静的メソッドexecuteInParallelが含まれています。
このメソッドはメソッドexecuteOrExecutorと同じです。このメソッドはAPI 4で使用できます
これの使用例を参照してください。
AsyncTaskCompat.executeParallel(new AsyncTask<Void, Void, Bitmap>() {
@Override
protected Bitmap doInBackground(Void... params) {
return MediaStore.Images.Thumbnails.getThumbnail(
imageView.getContext().getContentResolver(),
id,
MediaStore.Images.Thumbnails.MINI_KIND,
null);
}
@Override
protected void onPostExecute(Bitmap bitmap) {
imageView.setImageBitmap(bitmap);
if (bitmap != null) {
// Add the image to the memory cache first
CACHE.put(id, bitmap);
if (listener != null) {
listener.onImageLoaded(bitmap);
}
}
}
});
楽しい