| // Copyright 2012 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| package org.chromium.content.common; |
| |
| import android.os.Handler; |
| import android.os.Looper; |
| import android.os.Message; |
| import android.util.Log; |
| |
| import org.chromium.base.ThreadUtils; |
| |
| 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 |
| 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. |
| */ |
| private static class LazyHolder { |
| static final Handler sHandler = new Handler(ThreadUtils.getUiThreadLooper()) { |
| @Override |
| public void handleMessage(Message msg) { |
| TraceEvent.begin(); |
| 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=" + msg.what); |
| break; |
| } |
| |
| if (DEBUG) Log.d(TAG, "will try and cleanup; max = " + 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(); |
| } |
| TraceEvent.end(); |
| } |
| }; |
| } |
| |
| /** |
| * 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); |
| } |
| |
| 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); |
| if (mCleanupTask != null) { |
| if (DEBUG) Log.i(TAG, "--- CLEANING ONE REF"); |
| mCleanupTask.run(); |
| mCleanupTask = null; |
| } |
| clear(); |
| } |
| } |