/*
* 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 com.nf2m.util;
import android.annotation.TargetApi;
import android.os.Handler;
import android.os.Message;
import android.os.Process;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import java.util.ArrayDeque;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
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;
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);
@NonNull
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.
*/
private static final Executor THREAD_POOL_EXECUTOR
= new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory,
new ThreadPoolExecutor.DiscardOldestPolicy());
/**
* An {@link Executor} that executes tasks one at UriObserver time in serial
* order. This serialization is global to UriObserver particular process.
*/
private static final Executor SERIAL_EXECUTOR = Utils.hasHoneycomb() ? new SerialExecutor() :
Executors.newSingleThreadExecutor(sThreadFactory);
static final Executor DUAL_THREAD_EXECUTOR =
Executors.newFixedThreadPool(2, sThreadFactory);
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;
@NonNull
private final WorkerRunnable<Params, Result> mWorker;
@NonNull
private final FutureTask<Result> mFuture;
@NonNull
private volatile Status mStatus = Status.PENDING;
private final AtomicBoolean mCancelled = new AtomicBoolean();
private final AtomicBoolean mTaskInvoked = new AtomicBoolean();
@TargetApi(11)
private static class SerialExecutor implements Executor {
final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
Runnable mActive;
public synchronized void execute(@NonNull final Runnable r) {
mTasks.offer(new Runnable() {
public void run() {
try {
r.run();
} finally {
scheduleNext();
}
}
});
if (mActive == null) {
scheduleNext();
}
}
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 UriObserver task.
*/
private 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 UriObserver new asynchronous task. This constructor must be invoked on the UI thread.
*/
AsyncTask() {
mWorker = new WorkerRunnable<Params, Result>() {
public Result call() throws Exception {
mTaskInvoked.set(true);
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
//noinspection unchecked
return postResult(doInBackground(mParams));
}
};
mFuture = new FutureTask<Result>(mWorker) {
@Override
protected void done() {
try {
postResultIfNotInvoked(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) {
postResultIfNotInvoked(null);
}
}
};
}
private void postResultIfNotInvoked(Result result) {
final boolean wasTaskInvoked = mTaskInvoked.get();
if (!wasTaskInvoked) {
postResult(result);
}
}
private Result postResult(Result result) {
@SuppressWarnings("unchecked")
Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
new AsyncTaskResult<>(this, result));
message.sendToTarget();
return result;
}
/**
* Returns the current status of this task.
*
* @return The current status.
*/
@NonNull
private Status getStatus() {
return mStatus;
}
/**
* Override this method to perform UriObserver computation on UriObserver background thread. The
* specified parameters are the parameters passed to {@link #execute}
* by the caller of this task.
* <p/>
* on the UI thread.
*
* @param params The parameters of the task.
* @return A result, defined by the subclass of this task.
* @see #onPostExecute
*/
@Nullable
protected abstract Result doInBackground(Params... params);
/**
* <p>Runs on the UI thread after {@link #doInBackground}. The
* specified result is the value returned by {@link #doInBackground}.</p>
* <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 #doInBackground
*/
@SuppressWarnings({"UnusedDeclaration"})
protected void onPostExecute(Result result) {
}
/**
* 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)
*/
final boolean isCancelled() {
return mCancelled.get();
}
/**
* <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>
* 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()
*/
final void cancel(boolean mayInterruptIfRunning) {
mCancelled.set(true);
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, @NonNull 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 UriObserver reference to it.
* <p/>
* <p>Note: this function schedules the task on UriObserver queue for UriObserver single background
* thread or pool of threads depending on the platform version. When first
* introduced, AsyncTasks were executed serially on UriObserver single background thread.
* Starting with {@link android.os.Build.VERSION_CODES#DONUT}, this was changed
* to UriObserver pool of threads allowing multiple tasks to operate in parallel. Starting
* {@link android.os.Build.VERSION_CODES#HONEYCOMB}, tasks are back to being
* executed on UriObserver 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/>
* <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}.
* @see #executeOnExecutor(Executor, Object[])
*/
@NonNull
final void execute(Params... params) {
executeOnExecutor(sDefaultExecutor, params);
}
/**
* Executes the task with the specified parameters. The task returns
* itself (this) so that the caller can keep UriObserver reference to it.
* <p/>
* <p>This method is typically used with {@link #THREAD_POOL_EXECUTOR} to
* allow multiple tasks to run in parallel on UriObserver pool of threads managed by
* AsyncTask, however you can also use your own {@link Executor} for custom
* behavior.
* <p/>
* <p><em>Warning:</em> Allowing multiple tasks to run in parallel from
* UriObserver 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 UriObserver file due to UriObserver 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/>
* <p>This method must be invoked on the UI thread.
*
* @param exec The executor to use. {@link #THREAD_POOL_EXECUTOR} is available as UriObserver
* 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}.
* @see #execute(Object[])
*/
@NonNull
final AsyncTask<Params, Progress, Result> executeOnExecutor(@NonNull 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 "
+ "(UriObserver task can be executed only once)");
}
}
mStatus = Status.RUNNING;
mWorker.mParams = params;
exec.execute(mFuture);
return this;
}
private void finish(Result result) {
onPostExecute(result);
mStatus = Status.FINISHED;
}
private static class InternalHandler extends Handler {
@SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
@Override
public void handleMessage(@NonNull 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:
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;
}
}
}