Android example source code file (TokenWatcher.java)

This example Android source code file (TokenWatcher.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, death, handler, ibinder, remoteexception, runnable, set, string, throwable, tokenwatcher, util, utilities, utils, weakhashmap

The TokenWatcher.java Android example source code

/*
 * Copyright (C) 2007 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.os;

import java.util.WeakHashMap;
import java.util.Set;
import android.util.Log;

/**
 * Helper class that helps you use IBinder objects as reference counted
 * tokens.  IBinders make good tokens because we find out when they are
 * removed
 *
 */
public abstract class TokenWatcher
{
    /**
     * Construct the TokenWatcher
     *
     * @param h A handler to call {@link #acquired} and {@link #released}
     * on.  If you don't care, just call it like this, although your thread
     * will have to be a Looper thread.
     * <code>new TokenWatcher(new Handler())
     * @param tag A debugging tag for this TokenWatcher
     */
    public TokenWatcher(Handler h, String tag)
    {
        mHandler = h;
        mTag = tag != null ? tag : "TokenWatcher";
    }

    /**
     * Called when the number of active tokens goes from 0 to 1.
     */
    public abstract void acquired();

    /**
     * Called when the number of active tokens goes from 1 to 0.
     */
    public abstract void released();

    /**
     * Record that this token has been acquired.  When acquire is called, and
     * the current count is 0, the acquired method is called on the given
     * handler.
     * 
     * @param token An IBinder object.  If this token has already been acquired,
     *              no action is taken.
     * @param tag   A string used by the {@link #dump} method for debugging,
     *              to see who has references.
     */
    public void acquire(IBinder token, String tag)
    {
        synchronized (mTokens) {
            // explicitly checked to avoid bogus sendNotification calls because
            // of the WeakHashMap and the GC
            int oldSize = mTokens.size();

            Death d = new Death(token, tag);
            try {
                token.linkToDeath(d, 0);
            } catch (RemoteException e) {
                return;
            }
            mTokens.put(token, d);

            if (oldSize == 0 && !mAcquired) {
                sendNotificationLocked(true);
                mAcquired = true;
            }
        }
    }

    public void cleanup(IBinder token, boolean unlink)
    {
        synchronized (mTokens) {
            Death d = mTokens.remove(token);
            if (unlink && d != null) {
                d.token.unlinkToDeath(d, 0);
                d.token = null;
            }

            if (mTokens.size() == 0 && mAcquired) {
                sendNotificationLocked(false);
                mAcquired = false;
            }
        }
    }

    public void release(IBinder token)
    {
        cleanup(token, true);
    }

    public boolean isAcquired()
    {
        synchronized (mTokens) {
            return mAcquired;
        }
    }

    public void dump()
    {
        synchronized (mTokens) {
            Set<IBinder> keys = mTokens.keySet();
            Log.i(mTag, "Token count: " + mTokens.size());
            int i = 0;
            for (IBinder b: keys) {
                Log.i(mTag, "[" + i + "] " + mTokens.get(b).tag + " - " + b);
                i++;
            }
        }
    }

    private Runnable mNotificationTask = new Runnable() {
        public void run()
        {
            int value;
            synchronized (mTokens) {
                value = mNotificationQueue;
                mNotificationQueue = -1;
            }
            if (value == 1) {
                acquired();
            }
            else if (value == 0) {
                released();
            }
        }
    };

    private void sendNotificationLocked(boolean on)
    {
        int value = on ? 1 : 0;
        if (mNotificationQueue == -1) {
            // empty
            mNotificationQueue = value;
            mHandler.post(mNotificationTask);
        }
        else if (mNotificationQueue != value) {
            // it's a pair, so cancel it
            mNotificationQueue = -1;
            mHandler.removeCallbacks(mNotificationTask);
        }
        // else, same so do nothing -- maybe we should warn?
    }

    private class Death implements IBinder.DeathRecipient
    {
        IBinder token;
        String tag;

        Death(IBinder token, String tag)
        {
            this.token = token;
            this.tag = tag;
        }

        public void binderDied()
        {
            cleanup(token, false);
        }

        protected void finalize() throws Throwable
        {
            try {
                if (token != null) {
                    Log.w(mTag, "cleaning up leaked reference: " + tag);
                    release(token);
                }
            }
            finally {
                super.finalize();
            }
        }
    }

    private WeakHashMap<IBinder,Death> mTokens = new WeakHashMap();
    private Handler mHandler;
    private String mTag;
    private int mNotificationQueue = -1;
    private volatile boolean mAcquired = false;
}