/*
* Copyright (C) 2010 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.app;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.Message;
import android.os.Process;
import android.os.StrictMode;
import android.util.Log;
import com.android.internal.annotations.GuardedBy;
import com.android.internal.util.ExponentiallyBucketedHistogram;
import java.util.LinkedList;
/**
* Internal utility class to keep track of process-global work that's outstanding and hasn't been
* finished yet.
*
* New work will be {@link #queue queued}.
*
* It is possible to add 'finisher'-runnables that are {@link #waitToFinish guaranteed to be run}.
* This is used to make sure the work has been finished.
*
* This was created for writing SharedPreference edits out asynchronously so we'd have a mechanism
* to wait for the writes in Activity.onPause and similar places, but we may use this mechanism for
* other things in the future.
*
* The queued asynchronous work is performed on a separate, dedicated thread.
*
* @hide
*/
public class QueuedWork {
private static final String LOG_TAG = QueuedWork.class.getSimpleName();
private static final boolean DEBUG = false;
/** Delay for delayed runnables, as big as possible but low enough to be barely perceivable */
private static final long DELAY = 100;
/** If a {@link #waitToFinish()} takes more than {@value #MAX_WAIT_TIME_MILLIS} ms, warn */
private static final long MAX_WAIT_TIME_MILLIS = 512;
/** Lock for this class */
private static final Object sLock = new Object();
/**
* Used to make sure that only one thread is processing work items at a time. This means that
* they are processed in the order added.
*
* This is separate from {@link #sLock} as this is held the whole time while work is processed
* and we do not want to stall the whole class.
*/
private static Object sProcessingWork = new Object();
/** Finishers {@link #addFinisher added} and not yet {@link #removeFinisher removed} */
@GuardedBy("sLock")
private static final LinkedList<Runnable> sFinishers = new LinkedList<>();
/** {@link #getHandler() Lazily} created handler */
@GuardedBy("sLock")
private static Handler sHandler = null;
/** Work queued via {@link #queue} */
@GuardedBy("sLock")
private static final LinkedList<Runnable> sWork = new LinkedList<>();
/** If new work can be delayed or not */
@GuardedBy("sLock")
private static boolean sCanDelay = true;
/** Time (and number of instances) waited for work to get processed */
@GuardedBy("sLock")
private final static ExponentiallyBucketedHistogram
mWaitTimes = new ExponentiallyBucketedHistogram(
16);
private static int mNumWaits = 0;
/**
* Lazily create a handler on a separate thread.
*
* @return the handler
*/
private static Handler getHandler() {
synchronized (sLock) {
if (sHandler == null) {
HandlerThread handlerThread = new HandlerThread("queued-work-looper",
Process.THREAD_PRIORITY_FOREGROUND);
handlerThread.start();
sHandler = new QueuedWorkHandler(handlerThread.getLooper());
}
return sHandler;
}
}
/**
* Add a finisher-runnable to wait for {@link #queue asynchronously processed work}.
*
* Used by SharedPreferences$Editor#startCommit().
*
* Note that this doesn't actually start it running. This is just a scratch set for callers
* doing async work to keep updated with what's in-flight. In the common case, caller code
* (e.g. SharedPreferences) will pretty quickly call remove() after an add(). The only time
* these Runnables are run is from {@link #waitToFinish}.
*
* @param finisher The runnable to add as finisher
*/
public static void addFinisher(Runnable finisher) {
synchronized (sLock) {
sFinishers.add(finisher);
}
}
/**
* Remove a previously {@link #addFinisher added} finisher-runnable.
*
* @param finisher The runnable to remove.
*/
public static void removeFinisher(Runnable finisher) {
synchronized (sLock) {
sFinishers.remove(finisher);
}
}
/**
* Trigger queued work to be processed immediately. The queued work is processed on a separate
* thread asynchronous. While doing that run and process all finishers on this thread. The
* finishers can be implemented in a way to check weather the queued work is finished.
*
* Is called from the Activity base class's onPause(), after BroadcastReceiver's onReceive,
* after Service command handling, etc. (so async work is never lost)
*/
public static void waitToFinish() {
long startTime = System.currentTimeMillis();
boolean hadMessages = false;
Handler handler = getHandler();
synchronized (sLock) {
if (handler.hasMessages(QueuedWorkHandler.MSG_RUN)) {
// Delayed work will be processed at processPendingWork() below
handler.removeMessages(QueuedWorkHandler.MSG_RUN);
if (DEBUG) {
hadMessages = true;
Log.d(LOG_TAG, "waiting");
}
}
// We should not delay any work as this might delay the finishers
sCanDelay = false;
}
StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskWrites();
try {
processPendingWork();
} finally {
StrictMode.setThreadPolicy(oldPolicy);
}
try {
while (true) {
Runnable finisher;
synchronized (sLock) {
finisher = sFinishers.poll();
}
if (finisher == null) {
break;
}
finisher.run();
}
} finally {
sCanDelay = true;
}
synchronized (sLock) {
long waitTime = System.currentTimeMillis() - startTime;
if (waitTime > 0 || hadMessages) {
mWaitTimes.add(Long.valueOf(waitTime).intValue());
mNumWaits++;
if (DEBUG || mNumWaits % 1024 == 0 || waitTime > MAX_WAIT_TIME_MILLIS) {
mWaitTimes.log(LOG_TAG, "waited: ");
}
}
}
}
/**
* Queue a work-runnable for processing asynchronously.
*
* @param work The new runnable to process
* @param shouldDelay If the message should be delayed
*/
public static void queue(Runnable work, boolean shouldDelay) {
Handler handler = getHandler();
synchronized (sLock) {
sWork.add(work);
if (shouldDelay && sCanDelay) {
handler.sendEmptyMessageDelayed(QueuedWorkHandler.MSG_RUN, DELAY);
} else {
handler.sendEmptyMessage(QueuedWorkHandler.MSG_RUN);
}
}
}
/**
* @return True iff there is any {@link #queue async work queued}.
*/
public static boolean hasPendingWork() {
synchronized (sLock) {
return !sWork.isEmpty();
}
}
private static void processPendingWork() {
long startTime = 0;
if (DEBUG) {
startTime = System.currentTimeMillis();
}
synchronized (sProcessingWork) {
LinkedList<Runnable> work;
synchronized (sLock) {
work = (LinkedList<Runnable>) sWork.clone();
sWork.clear();
// Remove all msg-s as all work will be processed now
getHandler().removeMessages(QueuedWorkHandler.MSG_RUN);
}
if (work.size() > 0) {
for (Runnable w : work) {
w.run();
}
if (DEBUG) {
Log.d(LOG_TAG, "processing " + work.size() + " items took " +
+(System.currentTimeMillis() - startTime) + " ms");
}
}
}
}
private static class QueuedWorkHandler extends Handler {
static final int MSG_RUN = 1;
QueuedWorkHandler(Looper looper) {
super(looper);
}
public void handleMessage(Message msg) {
if (msg.what == MSG_RUN) {
processPendingWork();
}
}
}
}