// Copyright 2012 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.android_webview;
import android.annotation.SuppressLint;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import org.chromium.base.Log;
import org.chromium.base.ThreadUtils;
import org.chromium.base.TraceEvent;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.HashSet;
import java.util.Set;
/**
* Handles running cleanup tasks when an object becomes eligible for GC. Cleanup tasks
* are always executed on the main thread. In general, classes should not have
* finalizers and likewise should not use this class for the same reasons. The
* exception is where public APIs exist that require native side resources to be
* cleaned up in response to java side GC of API objects. (Private/internal
* interfaces should always favor explicit resource releases / destroy()
* protocol for this rather than depend on GC to trigger native cleanup).
* NOTE this uses WeakReference rather than PhantomReference, to avoid delaying the
* cleanup processing until after finalizers (if any) have run. In general usage of
* this class indicates the client does NOT use finalizers anyway (Good), so this should
* not be a visible difference in practice.
*/
public class CleanupReference extends WeakReference<Object> {
private static final String TAG = "CleanupReference";
private static final boolean DEBUG = false; // Always check in as false!
// The VM will enqueue CleanupReference instance onto sGcQueue when it becomes eligible for
// garbage collection (i.e. when all references to the underlying object are nullified).
// |sReaperThread| processes this queue by forwarding the references on to the UI thread
// (via REMOVE_REF message) to perform cleanup.
private static ReferenceQueue<Object> sGcQueue = new ReferenceQueue<Object>();
private static Object sCleanupMonitor = new Object();
private static final Thread sReaperThread =
new Thread(TAG) {
@Override
@SuppressWarnings("WaitNotInLoop")
public void run() {
while (true) {
try {
CleanupReference ref = (CleanupReference) sGcQueue.remove();
if (DEBUG) Log.d(TAG, "removed one ref from GC queue");
synchronized (sCleanupMonitor) {
Message.obtain(LazyHolder.sHandler, REMOVE_REF, ref).sendToTarget();
// Give the UI thread chance to run cleanup before looping around
// and taking the next item from the queue, to avoid Message
// bombing it.
sCleanupMonitor.wait(500);
}
} catch (Exception e) {
Log.e(TAG, "Queue remove exception:", e);
}
}
}
};
static {
sReaperThread.setDaemon(true);
sReaperThread.start();
}
// Message's sent in the |what| field to |sHandler|.
// Add a new reference to sRefs. |msg.obj| is the CleanupReference to add.
private static final int ADD_REF = 1;
// Remove reference from sRefs. |msg.obj| is the CleanupReference to remove.
private static final int REMOVE_REF = 2;
/**
* This {@link Handler} polls {@link #sRefs}, looking for cleanup tasks that
* are ready to run.
* This is lazily initialized as ThreadUtils.getUiThreadLooper() may not be
* set yet early in startup.
*/
@SuppressLint("HandlerLeak")
private static class LazyHolder {
static final Handler sHandler =
new Handler(ThreadUtils.getUiThreadLooper()) {
@Override
public void handleMessage(Message msg) {
try {
TraceEvent.begin("CleanupReference.LazyHolder.handleMessage");
CleanupReference ref = (CleanupReference) msg.obj;
switch (msg.what) {
case ADD_REF:
sRefs.add(ref);
break;
case REMOVE_REF:
ref.runCleanupTaskInternal();
break;
default:
Log.e(TAG, "Bad message=%d", msg.what);
break;
}
if (DEBUG) Log.d(TAG, "will try and cleanup; max = %d", sRefs.size());
synchronized (sCleanupMonitor) {
// Always run the cleanup loop here even when adding or removing
// refs, to avoid falling behind on rapid garbage allocation inner
// loops.
while ((ref = (CleanupReference) sGcQueue.poll()) != null) {
ref.runCleanupTaskInternal();
}
sCleanupMonitor.notifyAll();
}
} finally {
TraceEvent.end("CleanupReference.LazyHolder.handleMessage");
}
}
};
}
/**
* Keep a strong reference to {@link CleanupReference} so that it will
* actually get enqueued.
* Only accessed on the UI thread.
*/
private static Set<CleanupReference> sRefs = new HashSet<CleanupReference>();
private Runnable mCleanupTask;
/**
* @param obj the object whose loss of reachability should trigger the
* cleanup task.
* @param cleanupTask the task to run once obj loses reachability.
*/
public CleanupReference(Object obj, Runnable cleanupTask) {
super(obj, sGcQueue);
if (DEBUG) Log.d(TAG, "+++ CREATED ONE REF");
mCleanupTask = cleanupTask;
handleOnUiThread(ADD_REF);
}
/**
* Clear the cleanup task {@link Runnable} so that nothing will be done
* after garbage collection.
*/
public void cleanupNow() {
handleOnUiThread(REMOVE_REF);
}
public boolean hasCleanedUp() {
return mCleanupTask == null;
}
private void handleOnUiThread(int what) {
Message msg = Message.obtain(LazyHolder.sHandler, what, this);
if (Looper.myLooper() == msg.getTarget().getLooper()) {
msg.getTarget().handleMessage(msg);
msg.recycle();
} else {
msg.sendToTarget();
}
}
private void runCleanupTaskInternal() {
if (DEBUG) Log.d(TAG, "runCleanupTaskInternal");
sRefs.remove(this);
Runnable cleanupTask = mCleanupTask;
mCleanupTask = null;
if (cleanupTask != null) {
if (DEBUG) Log.i(TAG, "--- CLEANING ONE REF");
cleanupTask.run();
}
clear();
}
}
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