// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
package org.chromium.base.task;
import android.os.Binder;
import androidx.annotation.IntDef;
import androidx.annotation.MainThread;
import androidx.annotation.WorkerThread;
import org.chromium.base.Log;
import org.chromium.base.ThreadUtils;
import org.chromium.base.TraceEvent;
import org.chromium.base.metrics.RecordHistogram;
import org.chromium.build.annotations.DoNotInline;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.concurrent.Callable;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.FutureTask;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* A Chromium version of android.os.AsyncTask.
*
* The API is quite close to Android's Oreo version, but with a number of things removed.
* @param <Result> Return type of the background task.
*/
public abstract class AsyncTask<Result> {
private static final String TAG = "AsyncTask";
private static final String GET_STATUS_UMA_HISTOGRAM =
"Android.Jank.AsyncTaskGetOnUiThreadStatus";
/**
* An {@link Executor} that can be used to execute tasks in parallel.
* We use the lowest task priority, and mayBlock = true since any user of this could
* block.
*/
public static final Executor THREAD_POOL_EXECUTOR =
(Runnable r) -> PostTask.postTask(TaskTraits.BEST_EFFORT_MAY_BLOCK, r);
/**
* 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 StealRunnableHandler STEAL_RUNNABLE_HANDLER = new StealRunnableHandler();
private final Callable<Result> mWorker;
private final NamedFutureTask mFuture;
private volatile @Status int mStatus = Status.PENDING;
private final AtomicBoolean mCancelled = new AtomicBoolean();
private final AtomicBoolean mTaskInvoked = new AtomicBoolean();
private int mIterationIdForTesting = PostTask.sTestIterationForTesting;
private static class StealRunnableHandler implements RejectedExecutionHandler {
@Override
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
THREAD_POOL_EXECUTOR.execute(r);
}
}
/**
* Indicates the current status of the task. Each status will be set only once during the
* lifetime of a task. AsyncTaskStatus corresponding to this is defined in
* tools/metrics/histograms/enums.xml. Entries should not be renumbered and numeric values
* should never be reused.
*/
@IntDef({Status.PENDING, Status.RUNNING, Status.FINISHED})
@Retention(RetentionPolicy.SOURCE)
public @interface Status {
/** Indicates that the task has not been executed yet. */
int PENDING = 0;
/** Indicates that the task is running. */
int RUNNING = 1;
/** Indicates that {@link AsyncTask#onPostExecute} has finished. */
int FINISHED = 2;
/** Just used for reporting this status to UMA. */
int NUM_ENTRIES = 3;
}
@SuppressWarnings("NoAndroidAsyncTaskCheck")
public static void takeOverAndroidThreadPool() {
ThreadPoolExecutor exec = (ThreadPoolExecutor) android.os.AsyncTask.THREAD_POOL_EXECUTOR;
exec.setRejectedExecutionHandler(STEAL_RUNNABLE_HANDLER);
exec.shutdown();
}
/** Creates a new asynchronous task. This constructor must be invoked on the UI thread. */
public AsyncTask() {
mWorker =
() -> {
mTaskInvoked.set(true);
Result result = null;
try {
result = doInBackground();
Binder.flushPendingCommands();
} catch (Throwable tr) {
mCancelled.set(true);
throw tr;
} finally {
postResult(result);
}
return result;
};
mFuture = new NamedFutureTask(mWorker);
}
private void postResultIfNotInvoked(Result result) {
final boolean wasTaskInvoked = mTaskInvoked.get();
if (!wasTaskInvoked) {
postResult(result);
}
}
private void postResult(Result result) {
// We check if this task is of a type which does not require post-execution.
if (this instanceof BackgroundOnlyAsyncTask) {
mStatus = Status.FINISHED;
} else if (mIterationIdForTesting == PostTask.sTestIterationForTesting) {
ThreadUtils.postOnUiThread(
() -> {
finish(result);
});
}
}
/**
* Returns the current status of this task.
*
* @return The current status.
*/
public final @Status int getStatus() {
return mStatus;
}
/**
* Returns the current status of this task, with adjustments made to make UMA more useful.
* Namely, we are going to return "PENDING" until the asynctask actually starts running. Right
* now, as soon as you try to schedule the AsyncTask, it gets set to "RUNNING" which doesn't
* make sense. However, we aren't fixing this globally as this is the well-defined API
* AsyncTasks have, so we are just fixing this for our UMA reporting.
*
* @return The current status.
*/
public final @Status int getUmaStatus() {
if (mStatus == Status.RUNNING && !mTaskInvoked.get()) return Status.PENDING;
return mStatus;
}
/**
* Override this method to perform a computation on a background thread.
*
* @return A result, defined by the subclass of this task.
*
* @see #onPreExecute()
* @see #onPostExecute
*/
@WorkerThread
protected abstract Result doInBackground();
/**
* Runs on the UI thread before {@link #doInBackground}.
*
* @see #onPostExecute
* @see #doInBackground
*/
@MainThread
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>
*
* <p> Must be overridden by subclasses. If a subclass doesn't need
* post-execution, is should extend BackgroundOnlyAsyncTask instead.
*
* @param result The result of the operation computed by {@link #doInBackground}.
*
* @see #onPreExecute
* @see #doInBackground
* @see #onCancelled(Object)
*/
@SuppressWarnings({"UnusedDeclaration"})
@MainThread
protected abstract void onPostExecute(Result result);
/**
* <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and
* {@link #doInBackground()} 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()}, can be null
*
* @see #cancel(boolean)
* @see #isCancelled()
*/
@SuppressWarnings({"UnusedParameters"})
@MainThread
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()} has finished.</p>
*
* @see #onCancelled(Object)
* @see #cancel(boolean)
* @see #isCancelled()
*/
@MainThread
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()} 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 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>Calling this method will result in {@link #onCancelled(Object)} being
* invoked on the UI thread after {@link #doInBackground()}
* 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()} 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) {
mCancelled.set(true);
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.
*/
@DoNotInline
// The string passed is safe since it is class and method name.
@SuppressWarnings("NoDynamicStringsInTraceEventCheck")
public final Result get() throws InterruptedException, ExecutionException {
Result r;
int status = getUmaStatus();
if (status != Status.FINISHED && ThreadUtils.runningOnUiThread()) {
RecordHistogram.recordEnumeratedHistogram(
GET_STATUS_UMA_HISTOGRAM, status, Status.NUM_ENTRIES);
StackTraceElement[] stackTrace = new Exception().getStackTrace();
String caller = "";
if (stackTrace.length > 1) {
caller = stackTrace[1].getClassName() + '.' + stackTrace[1].getMethodName() + '.';
}
try (TraceEvent e = TraceEvent.scoped(caller + "AsyncTask.get")) {
r = mFuture.get();
}
} else {
r = mFuture.get();
}
return r;
}
/**
* 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.
*/
@DoNotInline
// The string passed is safe since it is class and method name.
@SuppressWarnings("NoDynamicStringsInTraceEventCheck")
public final Result get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
Result r;
int status = getUmaStatus();
if (status != Status.FINISHED && ThreadUtils.runningOnUiThread()) {
RecordHistogram.recordEnumeratedHistogram(
GET_STATUS_UMA_HISTOGRAM, status, Status.NUM_ENTRIES);
StackTraceElement[] stackTrace = new Exception().getStackTrace();
String caller = "";
if (stackTrace.length > 1) {
caller = stackTrace[1].getClassName() + '.' + stackTrace[1].getMethodName() + '.';
}
try (TraceEvent e = TraceEvent.scoped(caller + "AsyncTask.get")) {
r = mFuture.get(timeout, unit);
}
} else {
r = mFuture.get(timeout, unit);
}
return r;
}
@SuppressWarnings({"MissingCasesInEnumSwitch"})
private void executionPreamble() {
if (mStatus != Status.PENDING) {
switch (mStatus) {
case Status.RUNNING:
throw new IllegalStateException(
"Cannot execute task:" + " the task is already running.");
case Status.FINISHED:
throw new IllegalStateException(
"Cannot execute task:"
+ " the task has already been executed "
+ "(a task can be executed only once)");
}
}
mStatus = Status.RUNNING;
onPreExecute();
}
/**
* 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.
*
* @return This instance of AsyncTask.
*
* @throws IllegalStateException If {@link #getStatus()} returns either
* {@link AsyncTask.Status#RUNNING} or {@link AsyncTask.Status#FINISHED}.
*/
@MainThread
public final AsyncTask<Result> executeOnExecutor(Executor exec) {
executionPreamble();
exec.execute(mFuture);
return this;
}
/**
* Executes an AsyncTask on the given TaskRunner.
*
* @param taskRunner taskRunner to run this AsyncTask on.
* @return This instance of AsyncTask.
*/
@MainThread
public final AsyncTask<Result> executeOnTaskRunner(TaskRunner taskRunner) {
executionPreamble();
taskRunner.postTask(mFuture);
return this;
}
/**
* Executes an AsyncTask with the given task traits. Provides no guarantees about sequencing or
* which thread it runs on.
*
* @param taskTraits traits which describe this AsyncTask.
* @return This instance of AsyncTask.
*/
@MainThread
public final AsyncTask<Result> executeWithTaskTraits(@TaskTraits int taskTraits) {
executionPreamble();
PostTask.postTask(taskTraits, mFuture);
return this;
}
private void finish(Result result) {
if (isCancelled()) {
onCancelled(result);
} else {
onPostExecute(result);
}
mStatus = Status.FINISHED;
}
class NamedFutureTask extends FutureTask<Result> {
NamedFutureTask(Callable<Result> c) {
super(c);
}
Class getBlamedClass() {
return AsyncTask.this.getClass();
}
@Override
@SuppressWarnings("NoDynamicStringsInTraceEventCheck")
public void run() {
try (TraceEvent e =
TraceEvent.scoped("AsyncTask.run: " + mFuture.getBlamedClass().getName())) {
super.run();
} finally {
// Clear the interrupt on this background thread, if there is one, as it likely
// came from cancelling the FutureTask. It is possible this was already cleared
// in run() if something was listening for an interrupt; however, if it wasn't
// then the interrupt may still be around. By clearing it here the thread is in
// a clean state for the next task. See: crbug/1473731.
// This is safe and prevents future leaks because the state of the FutureTask
// should now be >= COMPLETING. Any future calls to cancel() will not trigger
// an interrupt.
Thread.interrupted();
}
}
@Override
protected void done() {
try {
postResultIfNotInvoked(get());
} catch (InterruptedException e) {
Log.w(TAG, e.toString());
} catch (ExecutionException e) {
throw new RuntimeException(
"An error occurred while executing doInBackground()", e.getCause());
} catch (CancellationException e) {
postResultIfNotInvoked(null);
}
}
}
}
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