xref: /frameworks/base/media/java/android/media/MediaFocusControl.java

/*
 * Copyright (C) 2013 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.media;

import android.app.Activity;
import android.app.ActivityManager;
import android.app.AppOpsManager;
import android.app.KeyguardManager;
import android.app.PendingIntent;
import android.app.PendingIntent.CanceledException;
import android.app.PendingIntent.OnFinished;
import android.content.ActivityNotFoundException;
import android.content.BroadcastReceiver;
import android.content.ComponentName;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.pm.PackageManager;
import android.database.ContentObserver;
import android.media.PlayerRecord.RemotePlaybackState;
import android.media.audiopolicy.IAudioPolicyCallback;
import android.net.Uri;
import android.os.Binder;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;
import android.os.PowerManager;
import android.os.RemoteException;
import android.os.UserHandle;
import android.os.IBinder.DeathRecipient;
import android.provider.Settings;
import android.speech.RecognizerIntent;
import android.telephony.PhoneStateListener;
import android.telephony.TelephonyManager;
import android.util.Log;
import android.util.Slog;
import android.view.KeyEvent;

import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Stack;

/**
 * @hide
 *
 */
public class MediaFocusControl implements OnFinished {

    private static final String TAG = "MediaFocusControl";

    /** Debug remote control client/display feature */
    protected static final boolean DEBUG_RC = false;
    /** Debug volumes */
    protected static final boolean DEBUG_VOL = false;

    /** Used to alter media button redirection when the phone is ringing. */
    private boolean mIsRinging = false;

    private final PowerManager.WakeLock mMediaEventWakeLock;
    private final MediaEventHandler mEventHandler;
    private final Context mContext;
    private final ContentResolver mContentResolver;
    private final AudioService.VolumeController mVolumeController;
    private final AppOpsManager mAppOps;
    private final KeyguardManager mKeyguardManager;
    private final AudioService mAudioService;
    private final NotificationListenerObserver mNotifListenerObserver;

    protected MediaFocusControl(Looper looper, Context cntxt,
            AudioService.VolumeController volumeCtrl, AudioService as) {
        mEventHandler = new MediaEventHandler(looper);
        mContext = cntxt;
        mContentResolver = mContext.getContentResolver();
        mVolumeController = volumeCtrl;
        mAudioService = as;

        PowerManager pm = (PowerManager)mContext.getSystemService(Context.POWER_SERVICE);
        mMediaEventWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "handleMediaEvent");
        mMainRemote = new RemotePlaybackState(-1,
                AudioService.getMaxStreamVolume(AudioManager.STREAM_MUSIC),
                AudioService.getMaxStreamVolume(AudioManager.STREAM_MUSIC));

        // Register for phone state monitoring
        TelephonyManager tmgr = (TelephonyManager)
                mContext.getSystemService(Context.TELEPHONY_SERVICE);
        tmgr.listen(mPhoneStateListener, PhoneStateListener.LISTEN_CALL_STATE);

        mAppOps = (AppOpsManager)mContext.getSystemService(Context.APP_OPS_SERVICE);
        mKeyguardManager =
                (KeyguardManager) mContext.getSystemService(Context.KEYGUARD_SERVICE);
        mNotifListenerObserver = new NotificationListenerObserver();

        mHasRemotePlayback = false;
        mMainRemoteIsActive = false;

        PlayerRecord.setMediaFocusControl(this);

        postReevaluateRemote();
    }

    protected void dump(PrintWriter pw) {
        dumpFocusStack(pw);
        dumpRCStack(pw);
        dumpRCCStack(pw);
        dumpRCDList(pw);
    }

    //==========================================================================================
    // Management of RemoteControlDisplay registration permissions
    //==========================================================================================
    private final static Uri ENABLED_NOTIFICATION_LISTENERS_URI =
            Settings.Secure.getUriFor(Settings.Secure.ENABLED_NOTIFICATION_LISTENERS);

    private class NotificationListenerObserver extends ContentObserver {

        NotificationListenerObserver() {
            super(mEventHandler);
            mContentResolver.registerContentObserver(Settings.Secure.getUriFor(
                    Settings.Secure.ENABLED_NOTIFICATION_LISTENERS), false, this);
        }

        @Override
        public void onChange(boolean selfChange, Uri uri) {
            if (!ENABLED_NOTIFICATION_LISTENERS_URI.equals(uri) || selfChange) {
                return;
            }
            if (DEBUG_RC) { Log.d(TAG, "NotificationListenerObserver.onChange()"); }
            postReevaluateRemoteControlDisplays();
        }
    }

    private final static int RCD_REG_FAILURE = 0;
    private final static int RCD_REG_SUCCESS_PERMISSION = 1;
    private final static int RCD_REG_SUCCESS_ENABLED_NOTIF = 2;

    /**
     * Checks a caller's authorization to register an IRemoteControlDisplay.
     * Authorization is granted if one of the following is true:
     * <ul>
     * <li>the caller has android.Manifest.permission.MEDIA_CONTENT_CONTROL permission</li>
     * <li>the caller's listener is one of the enabled notification listeners</li>
     * </ul>
     * @return RCD_REG_FAILURE if it's not safe to proceed with the IRemoteControlDisplay
     *     registration.
     */
    private int checkRcdRegistrationAuthorization(ComponentName listenerComp) {
        // MEDIA_CONTENT_CONTROL permission check
        if (PackageManager.PERMISSION_GRANTED == mContext.checkCallingOrSelfPermission(
                android.Manifest.permission.MEDIA_CONTENT_CONTROL)) {
            if (DEBUG_RC) { Log.d(TAG, "ok to register Rcd: has MEDIA_CONTENT_CONTROL permission");}
            return RCD_REG_SUCCESS_PERMISSION;
        }

        // ENABLED_NOTIFICATION_LISTENERS settings check
        if (listenerComp != null) {
            // this call is coming from an app, can't use its identity to read secure settings
            final long ident = Binder.clearCallingIdentity();
            try {
                final int currentUser = ActivityManager.getCurrentUser();
                final String enabledNotifListeners = Settings.Secure.getStringForUser(
                        mContext.getContentResolver(),
                        Settings.Secure.ENABLED_NOTIFICATION_LISTENERS,
                        currentUser);
                if (enabledNotifListeners != null) {
                    final String[] components = enabledNotifListeners.split(":");
                    for (int i=0; i<components.length; i++) {
                        final ComponentName component =
                                ComponentName.unflattenFromString(components[i]);
                        if (component != null) {
                            if (listenerComp.equals(component)) {
                                if (DEBUG_RC) { Log.d(TAG, "ok to register RCC: " + component +
                                        " is authorized notification listener"); }
                                return RCD_REG_SUCCESS_ENABLED_NOTIF;
                            }
                        }
                    }
                }
                if (DEBUG_RC) { Log.d(TAG, "not ok to register RCD, " + listenerComp +
                        " is not in list of ENABLED_NOTIFICATION_LISTENERS"); }
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }

        return RCD_REG_FAILURE;
    }

    protected boolean registerRemoteController(IRemoteControlDisplay rcd, int w, int h,
            ComponentName listenerComp) {
        int reg = checkRcdRegistrationAuthorization(listenerComp);
        if (reg != RCD_REG_FAILURE) {
            registerRemoteControlDisplay_int(rcd, w, h, listenerComp);
            return true;
        } else {
            Slog.w(TAG, "Access denied to process: " + Binder.getCallingPid() +
                    ", must have permission " + android.Manifest.permission.MEDIA_CONTENT_CONTROL +
                    " or be an enabled NotificationListenerService for registerRemoteController");
            return false;
        }
    }

    protected boolean registerRemoteControlDisplay(IRemoteControlDisplay rcd, int w, int h) {
        int reg = checkRcdRegistrationAuthorization(null);
        if (reg != RCD_REG_FAILURE) {
            registerRemoteControlDisplay_int(rcd, w, h, null);
            return true;
        } else {
            Slog.w(TAG, "Access denied to process: " + Binder.getCallingPid() +
                    ", must have permission " + android.Manifest.permission.MEDIA_CONTENT_CONTROL +
                    " to register IRemoteControlDisplay");
            return false;
        }
    }

    private void postReevaluateRemoteControlDisplays() {
        sendMsg(mEventHandler, MSG_REEVALUATE_RCD, SENDMSG_QUEUE, 0, 0, null, 0);
    }

    private void onReevaluateRemoteControlDisplays() {
        if (DEBUG_RC) { Log.d(TAG, "onReevaluateRemoteControlDisplays()"); }
        // read which components are enabled notification listeners
        final int currentUser = ActivityManager.getCurrentUser();
        final String enabledNotifListeners = Settings.Secure.getStringForUser(
                mContext.getContentResolver(),
                Settings.Secure.ENABLED_NOTIFICATION_LISTENERS,
                currentUser);
        if (DEBUG_RC) { Log.d(TAG, " > enabled list: " + enabledNotifListeners); }
        synchronized(mAudioFocusLock) {
            synchronized(mPRStack) {
                // check whether the "enable" status of each RCD with a notification listener
                // has changed
                final String[] enabledComponents;
                if (enabledNotifListeners == null) {
                    enabledComponents = null;
                } else {
                    enabledComponents = enabledNotifListeners.split(":");
                }
                final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
                while (displayIterator.hasNext()) {
                    final DisplayInfoForServer di =
                            displayIterator.next();
                    if (di.mClientNotifListComp != null) {
                        boolean wasEnabled = di.mEnabled;
                        di.mEnabled = isComponentInStringArray(di.mClientNotifListComp,
                                enabledComponents);
                        if (wasEnabled != di.mEnabled){
                            try {
                                // tell the RCD whether it's enabled
                                di.mRcDisplay.setEnabled(di.mEnabled);
                                // tell the RCCs about the change for this RCD
                                enableRemoteControlDisplayForClient_syncRcStack(
                                        di.mRcDisplay, di.mEnabled);
                                // when enabling, refresh the information on the display
                                if (di.mEnabled) {
                                    sendMsg(mEventHandler, MSG_RCDISPLAY_INIT_INFO, SENDMSG_QUEUE,
                                            di.mArtworkExpectedWidth /*arg1*/,
                                            di.mArtworkExpectedHeight/*arg2*/,
                                            di.mRcDisplay /*obj*/, 0/*delay*/);
                                }
                            } catch (RemoteException e) {
                                Log.e(TAG, "Error en/disabling RCD: ", e);
                            }
                        }
                    }
                }
            }
        }
    }

    /**
     * @param comp a non-null ComponentName
     * @param enabledArray may be null
     * @return
     */
    private boolean isComponentInStringArray(ComponentName comp, String[] enabledArray) {
        if (enabledArray == null || enabledArray.length == 0) {
            if (DEBUG_RC) { Log.d(TAG, " > " + comp + " is NOT enabled"); }
            return false;
        }
        final String compString = comp.flattenToString();
        for (int i=0; i<enabledArray.length; i++) {
            if (compString.equals(enabledArray[i])) {
                if (DEBUG_RC) { Log.d(TAG, " > " + compString + " is enabled"); }
                return true;
            }
        }
        if (DEBUG_RC) { Log.d(TAG, " > " + compString + " is NOT enabled"); }
        return false;
    }

    //==========================================================================================
    // Internal event handling
    //==========================================================================================

    // event handler messages
    private static final int MSG_RCDISPLAY_CLEAR = 1;
    private static final int MSG_RCDISPLAY_UPDATE = 2;
    private static final int MSG_REEVALUATE_REMOTE = 3;
    private static final int MSG_RCC_NEW_PLAYBACK_INFO = 4;
    private static final int MSG_RCC_NEW_VOLUME_OBS = 5;
    private static final int MSG_RCC_NEW_PLAYBACK_STATE = 6;
    private static final int MSG_RCC_SEEK_REQUEST = 7;
    private static final int MSG_RCC_UPDATE_METADATA = 8;
    private static final int MSG_RCDISPLAY_INIT_INFO = 9;
    private static final int MSG_REEVALUATE_RCD = 10;
    private static final int MSG_UNREGISTER_MEDIABUTTONINTENT = 11;

    // sendMsg() flags
    /** If the msg is already queued, replace it with this one. */
    private static final int SENDMSG_REPLACE = 0;
    /** If the msg is already queued, ignore this one and leave the old. */
    private static final int SENDMSG_NOOP = 1;
    /** If the msg is already queued, queue this one and leave the old. */
    private static final int SENDMSG_QUEUE = 2;

    private static void sendMsg(Handler handler, int msg,
            int existingMsgPolicy, int arg1, int arg2, Object obj, int delay) {

        if (existingMsgPolicy == SENDMSG_REPLACE) {
            handler.removeMessages(msg);
        } else if (existingMsgPolicy == SENDMSG_NOOP && handler.hasMessages(msg)) {
            return;
        }

        handler.sendMessageDelayed(handler.obtainMessage(msg, arg1, arg2, obj), delay);
    }

    private class MediaEventHandler extends Handler {
        MediaEventHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            switch(msg.what) {
                case MSG_RCDISPLAY_CLEAR:
                    onRcDisplayClear();
                    break;

                case MSG_RCDISPLAY_UPDATE:
                    // msg.obj is guaranteed to be non null
                    onRcDisplayUpdate( (PlayerRecord) msg.obj, msg.arg1);
                    break;

                case MSG_REEVALUATE_REMOTE:
                    onReevaluateRemote();
                    break;

                case MSG_RCC_NEW_VOLUME_OBS:
                    onRegisterVolumeObserverForRcc(msg.arg1 /* rccId */,
                            (IRemoteVolumeObserver)msg.obj /* rvo */);
                    break;

                case MSG_RCDISPLAY_INIT_INFO:
                    // msg.obj is guaranteed to be non null
                    onRcDisplayInitInfo((IRemoteControlDisplay)msg.obj /*newRcd*/,
                            msg.arg1/*w*/, msg.arg2/*h*/);
                    break;

                case MSG_REEVALUATE_RCD:
                    onReevaluateRemoteControlDisplays();
                    break;

                case MSG_UNREGISTER_MEDIABUTTONINTENT:
                    unregisterMediaButtonIntent( (PendingIntent) msg.obj );
                    break;
            }
        }
    }


    //==========================================================================================
    // AudioFocus
    //==========================================================================================

    /**
     * Constant to identify a focus stack entry that is used to hold the focus while the phone
     * is ringing or during a call. Used by com.android.internal.telephony.CallManager when
     * entering and exiting calls.
     */
    protected final static String IN_VOICE_COMM_FOCUS_ID = "AudioFocus_For_Phone_Ring_And_Calls";

    private final static Object mAudioFocusLock = new Object();

    private final static Object mRingingLock = new Object();

    private PhoneStateListener mPhoneStateListener = new PhoneStateListener() {
        @Override
        public void onCallStateChanged(int state, String incomingNumber) {
            if (state == TelephonyManager.CALL_STATE_RINGING) {
                //Log.v(TAG, " CALL_STATE_RINGING");
                synchronized(mRingingLock) {
                    mIsRinging = true;
                }
            } else if ((state == TelephonyManager.CALL_STATE_OFFHOOK)
                    || (state == TelephonyManager.CALL_STATE_IDLE)) {
                synchronized(mRingingLock) {
                    mIsRinging = false;
                }
            }
        }
    };

    /**
     * Discard the current audio focus owner.
     * Notify top of audio focus stack that it lost focus (regardless of possibility to reassign
     * focus), remove it from the stack, and clear the remote control display.
     */
    protected void discardAudioFocusOwner() {
        synchronized(mAudioFocusLock) {
            if (!mFocusStack.empty()) {
                // notify the current focus owner it lost focus after removing it from stack
                final FocusRequester exFocusOwner = mFocusStack.pop();
                exFocusOwner.handleFocusLoss(AudioManager.AUDIOFOCUS_LOSS);
                exFocusOwner.release();
            }
        }
    }

    /**
     * Called synchronized on mAudioFocusLock
     */
    private void notifyTopOfAudioFocusStack() {
        // notify the top of the stack it gained focus
        if (!mFocusStack.empty()) {
            if (canReassignAudioFocus()) {
                mFocusStack.peek().handleFocusGain(AudioManager.AUDIOFOCUS_GAIN);
            }
        }
    }

    /**
     * Focus is requested, propagate the associated loss throughout the stack.
     * @param focusGain the new focus gain that will later be added at the top of the stack
     */
    private void propagateFocusLossFromGain_syncAf(int focusGain) {
        // going through the audio focus stack to signal new focus, traversing order doesn't
        // matter as all entries respond to the same external focus gain
        Iterator<FocusRequester> stackIterator = mFocusStack.iterator();
        while(stackIterator.hasNext()) {
            stackIterator.next().handleExternalFocusGain(focusGain);
        }
    }

    private final Stack<FocusRequester> mFocusStack = new Stack<FocusRequester>();

    /**
     * Helper function:
     * Display in the log the current entries in the audio focus stack
     */
    private void dumpFocusStack(PrintWriter pw) {
        pw.println("\nAudio Focus stack entries (last is top of stack):");
        synchronized(mAudioFocusLock) {
            Iterator<FocusRequester> stackIterator = mFocusStack.iterator();
            while(stackIterator.hasNext()) {
                stackIterator.next().dump(pw);
            }
        }
        pw.println("\n Notify on duck: " + mNotifyFocusOwnerOnDuck +"\n");
    }

    /**
     * Helper function:
     * Called synchronized on mAudioFocusLock
     * Remove a focus listener from the focus stack.
     * @param clientToRemove the focus listener
     * @param signal if true and the listener was at the top of the focus stack, i.e. it was holding
     *   focus, notify the next item in the stack it gained focus.
     */
    private void removeFocusStackEntry(String clientToRemove, boolean signal,
            boolean notifyFocusFollowers) {
        // is the current top of the focus stack abandoning focus? (because of request, not death)
        if (!mFocusStack.empty() && mFocusStack.peek().hasSameClient(clientToRemove))
        {
            //Log.i(TAG, "   removeFocusStackEntry() removing top of stack");
            FocusRequester fr = mFocusStack.pop();
            fr.release();
            if (notifyFocusFollowers) {
                final AudioFocusInfo afi = fr.toAudioFocusInfo();
                afi.clearLossReceived();
                notifyExtPolicyFocusLoss_syncAf(afi, false);
            }
            if (signal) {
                // notify the new top of the stack it gained focus
                notifyTopOfAudioFocusStack();
            }
        } else {
            // focus is abandoned by a client that's not at the top of the stack,
            // no need to update focus.
            // (using an iterator on the stack so we can safely remove an entry after having
            //  evaluated it, traversal order doesn't matter here)
            Iterator<FocusRequester> stackIterator = mFocusStack.iterator();
            while(stackIterator.hasNext()) {
                FocusRequester fr = stackIterator.next();
                if(fr.hasSameClient(clientToRemove)) {
                    Log.i(TAG, "AudioFocus  removeFocusStackEntry(): removing entry for "
                            + clientToRemove);
                    stackIterator.remove();
                    fr.release();
                }
            }
        }
    }

    /**
     * Helper function:
     * Called synchronized on mAudioFocusLock
     * Remove focus listeners from the focus stack for a particular client when it has died.
     */
    private void removeFocusStackEntryForClient(IBinder cb) {
        // is the owner of the audio focus part of the client to remove?
        boolean isTopOfStackForClientToRemove = !mFocusStack.isEmpty() &&
                mFocusStack.peek().hasSameBinder(cb);
        // (using an iterator on the stack so we can safely remove an entry after having
        //  evaluated it, traversal order doesn't matter here)
        Iterator<FocusRequester> stackIterator = mFocusStack.iterator();
        while(stackIterator.hasNext()) {
            FocusRequester fr = stackIterator.next();
            if(fr.hasSameBinder(cb)) {
                Log.i(TAG, "AudioFocus  removeFocusStackEntry(): removing entry for " + cb);
                stackIterator.remove();
                // the client just died, no need to unlink to its death
            }
        }
        if (isTopOfStackForClientToRemove) {
            // we removed an entry at the top of the stack:
            //  notify the new top of the stack it gained focus.
            notifyTopOfAudioFocusStack();
        }
    }

    /**
     * Helper function:
     * Returns true if the system is in a state where the focus can be reevaluated, false otherwise.
     * The implementation guarantees that a state where focus cannot be immediately reassigned
     * implies that an "locked" focus owner is at the top of the focus stack.
     * Modifications to the implementation that break this assumption will cause focus requests to
     * misbehave when honoring the AudioManager.AUDIOFOCUS_FLAG_DELAY_OK flag.
     */
    private boolean canReassignAudioFocus() {
        // focus requests are rejected during a phone call or when the phone is ringing
        // this is equivalent to IN_VOICE_COMM_FOCUS_ID having the focus
        if (!mFocusStack.isEmpty() && isLockedFocusOwner(mFocusStack.peek())) {
            return false;
        }
        return true;
    }

    private boolean isLockedFocusOwner(FocusRequester fr) {
        return (fr.hasSameClient(IN_VOICE_COMM_FOCUS_ID) || fr.isLockedFocusOwner());
    }

    /**
     * Helper function
     * Pre-conditions: focus stack is not empty, there is one or more locked focus owner
     *                 at the top of the focus stack
     * Push the focus requester onto the audio focus stack at the first position immediately
     * following the locked focus owners.
     * @return {@link AudioManager#AUDIOFOCUS_REQUEST_GRANTED} or
     *     {@link AudioManager#AUDIOFOCUS_REQUEST_DELAYED}
     */
    private int pushBelowLockedFocusOwners(FocusRequester nfr) {
        int lastLockedFocusOwnerIndex = mFocusStack.size();
        for (int index = mFocusStack.size()-1; index >= 0; index--) {
            if (isLockedFocusOwner(mFocusStack.elementAt(index))) {
                lastLockedFocusOwnerIndex = index;
            }
        }
        if (lastLockedFocusOwnerIndex == mFocusStack.size()) {
            // this should not happen, but handle it and log an error
            Log.e(TAG, "No exclusive focus owner found in propagateFocusLossFromGain_syncAf()",
                    new Exception());
            // no exclusive owner, push at top of stack, focus is granted, propagate change
            propagateFocusLossFromGain_syncAf(nfr.getGainRequest());
            mFocusStack.push(nfr);
            return AudioManager.AUDIOFOCUS_REQUEST_GRANTED;
        } else {
            mFocusStack.insertElementAt(nfr, lastLockedFocusOwnerIndex);
            return AudioManager.AUDIOFOCUS_REQUEST_DELAYED;
        }
    }

    /**
     * Inner class to monitor audio focus client deaths, and remove them from the audio focus
     * stack if necessary.
     */
    protected class AudioFocusDeathHandler implements IBinder.DeathRecipient {
        private IBinder mCb; // To be notified of client's death

        AudioFocusDeathHandler(IBinder cb) {
            mCb = cb;
        }

        public void binderDied() {
            synchronized(mAudioFocusLock) {
                Log.w(TAG, "  AudioFocus   audio focus client died");
                removeFocusStackEntryForClient(mCb);
            }
        }

        public IBinder getBinder() {
            return mCb;
        }
    }

    /**
     * Indicates whether to notify an audio focus owner when it loses focus
     * with {@link AudioManager#AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK} if it will only duck.
     * This variable being false indicates an AudioPolicy has been registered and has signaled
     * it will handle audio ducking.
     */
    private boolean mNotifyFocusOwnerOnDuck = true;

    protected void setDuckingInExtPolicyAvailable(boolean available) {
        mNotifyFocusOwnerOnDuck = !available;
    }

    boolean mustNotifyFocusOwnerOnDuck() { return mNotifyFocusOwnerOnDuck; }

    private ArrayList<IAudioPolicyCallback> mFocusFollowers = new ArrayList<IAudioPolicyCallback>();

    void addFocusFollower(IAudioPolicyCallback ff) {
        if (ff == null) {
            return;
        }
        synchronized(mAudioFocusLock) {
            boolean found = false;
            for (IAudioPolicyCallback pcb : mFocusFollowers) {
                if (pcb.asBinder().equals(ff.asBinder())) {
                    found = true;
                    break;
                }
            }
            if (found) {
                return;
            } else {
                mFocusFollowers.add(ff);
            }
        }
    }

    void removeFocusFollower(IAudioPolicyCallback ff) {
        if (ff == null) {
            return;
        }
        synchronized(mAudioFocusLock) {
            for (IAudioPolicyCallback pcb : mFocusFollowers) {
                if (pcb.asBinder().equals(ff.asBinder())) {
                    mFocusFollowers.remove(pcb);
                    break;
                }
            }
        }
    }

    /**
     * Called synchronized on mAudioFocusLock
     */
    void notifyExtPolicyFocusGrant_syncAf(AudioFocusInfo afi, int requestResult) {
        for (IAudioPolicyCallback pcb : mFocusFollowers) {
            try {
                // oneway
                pcb.notifyAudioFocusGrant(afi, requestResult);
            } catch (RemoteException e) {
                Log.e(TAG, "Can't call newAudioFocusLoser() on IAudioPolicyCallback "
                        + pcb.asBinder(), e);
            }
        }
    }

    /**
     * Called synchronized on mAudioFocusLock
     */
    void notifyExtPolicyFocusLoss_syncAf(AudioFocusInfo afi, boolean wasDispatched) {
        for (IAudioPolicyCallback pcb : mFocusFollowers) {
            try {
                // oneway
                pcb.notifyAudioFocusLoss(afi, wasDispatched);
            } catch (RemoteException e) {
                Log.e(TAG, "Can't call newAudioFocusLoser() on IAudioPolicyCallback "
                        + pcb.asBinder(), e);
            }
        }
    }

    protected int getCurrentAudioFocus() {
        synchronized(mAudioFocusLock) {
            if (mFocusStack.empty()) {
                return AudioManager.AUDIOFOCUS_NONE;
            } else {
                return mFocusStack.peek().getGainRequest();
            }
        }
    }

    /** @see AudioManager#requestAudioFocus(AudioManager.OnAudioFocusChangeListener, int, int, int) */
    protected int requestAudioFocus(AudioAttributes aa, int focusChangeHint, IBinder cb,
            IAudioFocusDispatcher fd, String clientId, String callingPackageName, int flags) {
        Log.i(TAG, " AudioFocus  requestAudioFocus() from " + clientId + " req=" + focusChangeHint +
                "flags=0x" + Integer.toHexString(flags));
        // we need a valid binder callback for clients
        if (!cb.pingBinder()) {
            Log.e(TAG, " AudioFocus DOA client for requestAudioFocus(), aborting.");
            return AudioManager.AUDIOFOCUS_REQUEST_FAILED;
        }

        if (mAppOps.noteOp(AppOpsManager.OP_TAKE_AUDIO_FOCUS, Binder.getCallingUid(),
                callingPackageName) != AppOpsManager.MODE_ALLOWED) {
            return AudioManager.AUDIOFOCUS_REQUEST_FAILED;
        }

        synchronized(mAudioFocusLock) {
            boolean focusGrantDelayed = false;
            if (!canReassignAudioFocus()) {
                if ((flags & AudioManager.AUDIOFOCUS_FLAG_DELAY_OK) == 0) {
                    return AudioManager.AUDIOFOCUS_REQUEST_FAILED;
                } else {
                    // request has AUDIOFOCUS_FLAG_DELAY_OK: focus can't be
                    // granted right now, so the requester will be inserted in the focus stack
                    // to receive focus later
                    focusGrantDelayed = true;
                }
            }

            // handle the potential premature death of the new holder of the focus
            // (premature death == death before abandoning focus)
            // Register for client death notification
            AudioFocusDeathHandler afdh = new AudioFocusDeathHandler(cb);
            try {
                cb.linkToDeath(afdh, 0);
            } catch (RemoteException e) {
                // client has already died!
                Log.w(TAG, "AudioFocus  requestAudioFocus() could not link to "+cb+" binder death");
                return AudioManager.AUDIOFOCUS_REQUEST_FAILED;
            }

            if (!mFocusStack.empty() && mFocusStack.peek().hasSameClient(clientId)) {
                // if focus is already owned by this client and the reason for acquiring the focus
                // hasn't changed, don't do anything
                final FocusRequester fr = mFocusStack.peek();
                if (fr.getGainRequest() == focusChangeHint && fr.getGrantFlags() == flags) {
                    // unlink death handler so it can be gc'ed.
                    // linkToDeath() creates a JNI global reference preventing collection.
                    cb.unlinkToDeath(afdh, 0);
                    notifyExtPolicyFocusGrant_syncAf(fr.toAudioFocusInfo(),
                            AudioManager.AUDIOFOCUS_REQUEST_GRANTED);
                    return AudioManager.AUDIOFOCUS_REQUEST_GRANTED;
                }
                // the reason for the audio focus request has changed: remove the current top of
                // stack and respond as if we had a new focus owner
                if (!focusGrantDelayed) {
                    mFocusStack.pop();
                    // the entry that was "popped" is the same that was "peeked" above
                    fr.release();
                }
            }

            // focus requester might already be somewhere below in the stack, remove it
            removeFocusStackEntry(clientId, false /* signal */, false /*notifyFocusFollowers*/);

            final FocusRequester nfr = new FocusRequester(aa, focusChangeHint, flags, fd, cb,
                    clientId, afdh, callingPackageName, Binder.getCallingUid(), this);
            if (focusGrantDelayed) {
                // focusGrantDelayed being true implies we can't reassign focus right now
                // which implies the focus stack is not empty.
                final int requestResult = pushBelowLockedFocusOwners(nfr);
                if (requestResult != AudioManager.AUDIOFOCUS_REQUEST_FAILED) {
                    notifyExtPolicyFocusGrant_syncAf(nfr.toAudioFocusInfo(), requestResult);
                }
                return requestResult;
            } else {
                // propagate the focus change through the stack
                if (!mFocusStack.empty()) {
                    propagateFocusLossFromGain_syncAf(focusChangeHint);
                }

                // push focus requester at the top of the audio focus stack
                mFocusStack.push(nfr);
            }
            notifyExtPolicyFocusGrant_syncAf(nfr.toAudioFocusInfo(),
                    AudioManager.AUDIOFOCUS_REQUEST_GRANTED);

        }//synchronized(mAudioFocusLock)

        return AudioManager.AUDIOFOCUS_REQUEST_GRANTED;
    }

    /**
     * @see AudioManager#abandonAudioFocus(AudioManager.OnAudioFocusChangeListener, AudioAttributes)
     * */
    protected int abandonAudioFocus(IAudioFocusDispatcher fl, String clientId, AudioAttributes aa) {
        // AudioAttributes are currently ignored, to be used for zones
        Log.i(TAG, " AudioFocus  abandonAudioFocus() from " + clientId);
        try {
            // this will take care of notifying the new focus owner if needed
            synchronized(mAudioFocusLock) {
                removeFocusStackEntry(clientId, true /*signal*/, true /*notifyFocusFollowers*/);
            }
        } catch (java.util.ConcurrentModificationException cme) {
            // Catching this exception here is temporary. It is here just to prevent
            // a crash seen when the "Silent" notification is played. This is believed to be fixed
            // but this try catch block is left just to be safe.
            Log.e(TAG, "FATAL EXCEPTION AudioFocus  abandonAudioFocus() caused " + cme);
            cme.printStackTrace();
        }

        return AudioManager.AUDIOFOCUS_REQUEST_GRANTED;
    }


    protected void unregisterAudioFocusClient(String clientId) {
        synchronized(mAudioFocusLock) {
            removeFocusStackEntry(clientId, false, true /*notifyFocusFollowers*/);
        }
    }


    //==========================================================================================
    // RemoteControl
    //==========================================================================================
    /**
     * No-op if the key code for keyEvent is not a valid media key
     * (see {@link #isValidMediaKeyEvent(KeyEvent)})
     * @param keyEvent the key event to send
     */
    protected void dispatchMediaKeyEvent(KeyEvent keyEvent) {
        filterMediaKeyEvent(keyEvent, false /*needWakeLock*/);
    }

    /**
     * No-op if the key code for keyEvent is not a valid media key
     * (see {@link #isValidMediaKeyEvent(KeyEvent)})
     * @param keyEvent the key event to send
     */
    protected void dispatchMediaKeyEventUnderWakelock(KeyEvent keyEvent) {
        filterMediaKeyEvent(keyEvent, true /*needWakeLock*/);
    }

    private void filterMediaKeyEvent(KeyEvent keyEvent, boolean needWakeLock) {
        // sanity check on the incoming key event
        if (!isValidMediaKeyEvent(keyEvent)) {
            Log.e(TAG, "not dispatching invalid media key event " + keyEvent);
            return;
        }
        // event filtering for telephony
        synchronized(mRingingLock) {
            synchronized(mPRStack) {
                if ((mMediaReceiverForCalls != null) &&
                        (mIsRinging || (mAudioService.getMode() == AudioSystem.MODE_IN_CALL))) {
                    dispatchMediaKeyEventForCalls(keyEvent, needWakeLock);
                    return;
                }
            }
        }
        // event filtering based on voice-based interactions
        if (isValidVoiceInputKeyCode(keyEvent.getKeyCode())) {
            filterVoiceInputKeyEvent(keyEvent, needWakeLock);
        } else {
            dispatchMediaKeyEvent(keyEvent, needWakeLock);
        }
    }

    /**
     * Handles the dispatching of the media button events to the telephony package.
     * Precondition: mMediaReceiverForCalls != null
     * @param keyEvent a non-null KeyEvent whose key code is one of the supported media buttons
     * @param needWakeLock true if a PARTIAL_WAKE_LOCK needs to be held while this key event
     *     is dispatched.
     */
    private void dispatchMediaKeyEventForCalls(KeyEvent keyEvent, boolean needWakeLock) {
        Intent keyIntent = new Intent(Intent.ACTION_MEDIA_BUTTON, null);
        keyIntent.putExtra(Intent.EXTRA_KEY_EVENT, keyEvent);
        keyIntent.setPackage(mMediaReceiverForCalls.getPackageName());
        if (needWakeLock) {
            mMediaEventWakeLock.acquire();
            keyIntent.putExtra(EXTRA_WAKELOCK_ACQUIRED, WAKELOCK_RELEASE_ON_FINISHED);
        }
        final long ident = Binder.clearCallingIdentity();
        try {
            mContext.sendOrderedBroadcastAsUser(keyIntent, UserHandle.ALL,
                    null, mKeyEventDone, mEventHandler, Activity.RESULT_OK, null, null);
        } finally {
            Binder.restoreCallingIdentity(ident);
        }
    }

    /**
     * Handles the dispatching of the media button events to one of the registered listeners,
     * or if there was none, broadcast an ACTION_MEDIA_BUTTON intent to the rest of the system.
     * @param keyEvent a non-null KeyEvent whose key code is one of the supported media buttons
     * @param needWakeLock true if a PARTIAL_WAKE_LOCK needs to be held while this key event
     *     is dispatched.
     */
    private void dispatchMediaKeyEvent(KeyEvent keyEvent, boolean needWakeLock) {
        if (needWakeLock) {
            mMediaEventWakeLock.acquire();
        }
        Intent keyIntent = new Intent(Intent.ACTION_MEDIA_BUTTON, null);
        keyIntent.putExtra(Intent.EXTRA_KEY_EVENT, keyEvent);
        synchronized(mPRStack) {
            if (!mPRStack.empty()) {
                // send the intent that was registered by the client
                try {
                    mPRStack.peek().getMediaButtonIntent().send(mContext,
                            needWakeLock ? WAKELOCK_RELEASE_ON_FINISHED : 0 /*code*/,
                            keyIntent, this, mEventHandler);
                } catch (CanceledException e) {
                    Log.e(TAG, "Error sending pending intent " + mPRStack.peek());
                    e.printStackTrace();
                }
            } else {
                // legacy behavior when nobody registered their media button event receiver
                //    through AudioManager
                if (needWakeLock) {
                    keyIntent.putExtra(EXTRA_WAKELOCK_ACQUIRED, WAKELOCK_RELEASE_ON_FINISHED);
                }
                final long ident = Binder.clearCallingIdentity();
                try {
                    mContext.sendOrderedBroadcastAsUser(keyIntent, UserHandle.ALL,
                            null, mKeyEventDone,
                            mEventHandler, Activity.RESULT_OK, null, null);
                } finally {
                    Binder.restoreCallingIdentity(ident);
                }
            }
        }
    }

    /**
     * The different actions performed in response to a voice button key event.
     */
    private final static int VOICEBUTTON_ACTION_DISCARD_CURRENT_KEY_PRESS = 1;
    private final static int VOICEBUTTON_ACTION_START_VOICE_INPUT = 2;
    private final static int VOICEBUTTON_ACTION_SIMULATE_KEY_PRESS = 3;

    private final Object mVoiceEventLock = new Object();
    private boolean mVoiceButtonDown;
    private boolean mVoiceButtonHandled;

    /**
     * Filter key events that may be used for voice-based interactions
     * @param keyEvent a non-null KeyEvent whose key code is that of one of the supported
     *    media buttons that can be used to trigger voice-based interactions.
     * @param needWakeLock true if a PARTIAL_WAKE_LOCK needs to be held while this key event
     *     is dispatched.
     */
    private void filterVoiceInputKeyEvent(KeyEvent keyEvent, boolean needWakeLock) {
        if (DEBUG_RC) {
            Log.v(TAG, "voice input key event: " + keyEvent + ", needWakeLock=" + needWakeLock);
        }

        int voiceButtonAction = VOICEBUTTON_ACTION_DISCARD_CURRENT_KEY_PRESS;
        int keyAction = keyEvent.getAction();
        synchronized (mVoiceEventLock) {
            if (keyAction == KeyEvent.ACTION_DOWN) {
                if (keyEvent.getRepeatCount() == 0) {
                    // initial down
                    mVoiceButtonDown = true;
                    mVoiceButtonHandled = false;
                } else if (mVoiceButtonDown && !mVoiceButtonHandled
                        && (keyEvent.getFlags() & KeyEvent.FLAG_LONG_PRESS) != 0) {
                    // long-press, start voice-based interactions
                    mVoiceButtonHandled = true;
                    voiceButtonAction = VOICEBUTTON_ACTION_START_VOICE_INPUT;
                }
            } else if (keyAction == KeyEvent.ACTION_UP) {
                if (mVoiceButtonDown) {
                    // voice button up
                    mVoiceButtonDown = false;
                    if (!mVoiceButtonHandled && !keyEvent.isCanceled()) {
                        voiceButtonAction = VOICEBUTTON_ACTION_SIMULATE_KEY_PRESS;
                    }
                }
            }
        }//synchronized (mVoiceEventLock)

        // take action after media button event filtering for voice-based interactions
        switch (voiceButtonAction) {
            case VOICEBUTTON_ACTION_DISCARD_CURRENT_KEY_PRESS:
                if (DEBUG_RC) Log.v(TAG, "   ignore key event");
                break;
            case VOICEBUTTON_ACTION_START_VOICE_INPUT:
                if (DEBUG_RC) Log.v(TAG, "   start voice-based interactions");
                // then start the voice-based interactions
                startVoiceBasedInteractions(needWakeLock);
                break;
            case VOICEBUTTON_ACTION_SIMULATE_KEY_PRESS:
                if (DEBUG_RC) Log.v(TAG, "   send simulated key event, wakelock=" + needWakeLock);
                sendSimulatedMediaButtonEvent(keyEvent, needWakeLock);
                break;
        }
    }

    private void sendSimulatedMediaButtonEvent(KeyEvent originalKeyEvent, boolean needWakeLock) {
        // send DOWN event
        KeyEvent keyEvent = KeyEvent.changeAction(originalKeyEvent, KeyEvent.ACTION_DOWN);
        dispatchMediaKeyEvent(keyEvent, needWakeLock);
        // send UP event
        keyEvent = KeyEvent.changeAction(originalKeyEvent, KeyEvent.ACTION_UP);
        dispatchMediaKeyEvent(keyEvent, needWakeLock);

    }

    private static boolean isValidMediaKeyEvent(KeyEvent keyEvent) {
        if (keyEvent == null) {
            return false;
        }
        return KeyEvent.isMediaKey(keyEvent.getKeyCode());
    }

    /**
     * Checks whether the given key code is one that can trigger the launch of voice-based
     *   interactions.
     * @param keyCode the key code associated with the key event
     * @return true if the key is one of the supported voice-based interaction triggers
     */
    private static boolean isValidVoiceInputKeyCode(int keyCode) {
        if (keyCode == KeyEvent.KEYCODE_HEADSETHOOK) {
            return true;
        } else {
            return false;
        }
    }

    /**
     * Tell the system to start voice-based interactions / voice commands
     */
    private void startVoiceBasedInteractions(boolean needWakeLock) {
        Intent voiceIntent = null;
        // select which type of search to launch:
        // - screen on and device unlocked: action is ACTION_WEB_SEARCH
        // - device locked or screen off: action is ACTION_VOICE_SEARCH_HANDS_FREE
        //    with EXTRA_SECURE set to true if the device is securely locked
        PowerManager pm = (PowerManager)mContext.getSystemService(Context.POWER_SERVICE);
        boolean isLocked = mKeyguardManager != null && mKeyguardManager.isKeyguardLocked();
        if (!isLocked && pm.isScreenOn()) {
            voiceIntent = new Intent(android.speech.RecognizerIntent.ACTION_WEB_SEARCH);
            Log.i(TAG, "voice-based interactions: about to use ACTION_WEB_SEARCH");
        } else {
            voiceIntent = new Intent(RecognizerIntent.ACTION_VOICE_SEARCH_HANDS_FREE);
            voiceIntent.putExtra(RecognizerIntent.EXTRA_SECURE,
                    isLocked && mKeyguardManager.isKeyguardSecure());
            Log.i(TAG, "voice-based interactions: about to use ACTION_VOICE_SEARCH_HANDS_FREE");
        }
        // start the search activity
        if (needWakeLock) {
            mMediaEventWakeLock.acquire();
        }
        final long identity = Binder.clearCallingIdentity();
        try {
            if (voiceIntent != null) {
                voiceIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                        | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
                mContext.startActivityAsUser(voiceIntent, UserHandle.CURRENT);
            }
        } catch (ActivityNotFoundException e) {
            Log.w(TAG, "No activity for search: " + e);
        } finally {
            Binder.restoreCallingIdentity(identity);
            if (needWakeLock) {
                mMediaEventWakeLock.release();
            }
        }
    }

    private static final int WAKELOCK_RELEASE_ON_FINISHED = 1980; //magic number

    // only set when wakelock was acquired, no need to check value when received
    private static final String EXTRA_WAKELOCK_ACQUIRED =
            "android.media.AudioService.WAKELOCK_ACQUIRED";

    public void onSendFinished(PendingIntent pendingIntent, Intent intent,
            int resultCode, String resultData, Bundle resultExtras) {
        if (resultCode == WAKELOCK_RELEASE_ON_FINISHED) {
            mMediaEventWakeLock.release();
        }
    }

    BroadcastReceiver mKeyEventDone = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            if (intent == null) {
                return;
            }
            Bundle extras = intent.getExtras();
            if (extras == null) {
                return;
            }
            if (extras.containsKey(EXTRA_WAKELOCK_ACQUIRED)) {
                mMediaEventWakeLock.release();
            }
        }
    };

    /**
     * Synchronization on mCurrentRcLock always inside a block synchronized on mPRStack
     */
    private final Object mCurrentRcLock = new Object();
    /**
     * The one remote control client which will receive a request for display information.
     * This object may be null.
     * Access protected by mCurrentRcLock.
     */
    private IRemoteControlClient mCurrentRcClient = null;
    /**
     * The PendingIntent associated with mCurrentRcClient. Its value is irrelevant
     * if mCurrentRcClient is null
     */
    private PendingIntent mCurrentRcClientIntent = null;

    private final static int RC_INFO_NONE = 0;
    private final static int RC_INFO_ALL =
        RemoteControlClient.FLAG_INFORMATION_REQUEST_ALBUM_ART |
        RemoteControlClient.FLAG_INFORMATION_REQUEST_KEY_MEDIA |
        RemoteControlClient.FLAG_INFORMATION_REQUEST_METADATA |
        RemoteControlClient.FLAG_INFORMATION_REQUEST_PLAYSTATE;

    /**
     * A monotonically increasing generation counter for mCurrentRcClient.
     * Only accessed with a lock on mCurrentRcLock.
     * No value wrap-around issues as we only act on equal values.
     */
    private int mCurrentRcClientGen = 0;


    /**
     * Internal cache for the playback information of the RemoteControlClient whose volume gets to
     * be controlled by the volume keys ("main"), so we don't have to iterate over the RC stack
     * every time we need this info.
     */
    private RemotePlaybackState mMainRemote;
    /**
     * Indicates whether the "main" RemoteControlClient is considered active.
     * Use synchronized on mMainRemote.
     */
    private boolean mMainRemoteIsActive;
    /**
     * Indicates whether there is remote playback going on. True even if there is no "active"
     * remote playback (mMainRemoteIsActive is false), but a RemoteControlClient has declared it
     * handles remote playback.
     * Use synchronized on mMainRemote.
     */
    private boolean mHasRemotePlayback;

    /**
     * The stack of remote control event receivers.
     * All read and write operations on mPRStack are synchronized.
     */
    private final Stack<PlayerRecord> mPRStack = new Stack<PlayerRecord>();

    /**
     * The component the telephony package can register so telephony calls have priority to
     * handle media button events
     */
    private ComponentName mMediaReceiverForCalls = null;

    /**
     * Helper function:
     * Display in the log the current entries in the remote control focus stack
     */
    private void dumpRCStack(PrintWriter pw) {
        pw.println("\nRemote Control stack entries (last is top of stack):");
        synchronized(mPRStack) {
            Iterator<PlayerRecord> stackIterator = mPRStack.iterator();
            while(stackIterator.hasNext()) {
                stackIterator.next().dump(pw, true);
            }
        }
    }

    /**
     * Helper function:
     * Display in the log the current entries in the remote control stack, focusing
     * on RemoteControlClient data
     */
    private void dumpRCCStack(PrintWriter pw) {
        pw.println("\nRemote Control Client stack entries (last is top of stack):");
        synchronized(mPRStack) {
            Iterator<PlayerRecord> stackIterator = mPRStack.iterator();
            while(stackIterator.hasNext()) {
                stackIterator.next().dump(pw, false);
            }
            synchronized(mCurrentRcLock) {
                pw.println("\nCurrent remote control generation ID = " + mCurrentRcClientGen);
            }
        }
        synchronized (mMainRemote) {
            pw.println("\nRemote Volume State:");
            pw.println("  has remote: " + mHasRemotePlayback);
            pw.println("  is remote active: " + mMainRemoteIsActive);
            pw.println("  rccId: " + mMainRemote.mRccId);
            pw.println("  volume handling: "
                    + ((mMainRemote.mVolumeHandling == RemoteControlClient.PLAYBACK_VOLUME_FIXED) ?
                            "PLAYBACK_VOLUME_FIXED(0)" : "PLAYBACK_VOLUME_VARIABLE(1)"));
            pw.println("  volume: " + mMainRemote.mVolume);
            pw.println("  volume steps: " + mMainRemote.mVolumeMax);
        }
    }

    /**
     * Helper function:
     * Display in the log the current entries in the list of remote control displays
     */
    private void dumpRCDList(PrintWriter pw) {
        pw.println("\nRemote Control Display list entries:");
        synchronized(mPRStack) {
            final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
            while (displayIterator.hasNext()) {
                final DisplayInfoForServer di = displayIterator.next();
                pw.println("  IRCD: " + di.mRcDisplay +
                        "  -- w:" + di.mArtworkExpectedWidth +
                        "  -- h:" + di.mArtworkExpectedHeight +
                        "  -- wantsPosSync:" + di.mWantsPositionSync +
                        "  -- " + (di.mEnabled ? "enabled" : "disabled"));
            }
        }
    }

    /**
     * Helper function:
     * Push the new media button receiver "near" the top of the PlayerRecord stack.
     * "Near the top" is defined as:
     *   - at the top if the current PlayerRecord at the top is not playing
     *   - below the entries at the top of the stack that correspond to the playing PlayerRecord
     *     otherwise
     * Called synchronized on mPRStack
     * precondition: mediaIntent != null
     * @return true if the top of mPRStack was changed, false otherwise
     */
    private boolean pushMediaButtonReceiver_syncPrs(PendingIntent mediaIntent,
            ComponentName target, IBinder token) {
        if (mPRStack.empty()) {
            mPRStack.push(new PlayerRecord(mediaIntent, target, token));
            return true;
        } else if (mPRStack.peek().hasMatchingMediaButtonIntent(mediaIntent)) {
            // already at top of stack
            return false;
        }
        if (mAppOps.noteOp(AppOpsManager.OP_TAKE_MEDIA_BUTTONS, Binder.getCallingUid(),
                mediaIntent.getCreatorPackage()) != AppOpsManager.MODE_ALLOWED) {
            return false;
        }
        PlayerRecord oldTopPrse = mPRStack.lastElement(); // top of the stack before any changes
        boolean topChanged = false;
        PlayerRecord prse = null;
        int lastPlayingIndex = mPRStack.size();
        int inStackIndex = -1;
        try {
            // go through the stack from the top to figure out who's playing, and the position
            // of this media button receiver (note that it may not be in the stack)
            for (int index = mPRStack.size()-1; index >= 0; index--) {
                prse = mPRStack.elementAt(index);
                if (prse.isPlaybackActive()) {
                    lastPlayingIndex = index;
                }
                if (prse.hasMatchingMediaButtonIntent(mediaIntent)) {
                    inStackIndex = index;
                }
            }

            if (inStackIndex == -1) {
                // is not in stack
                prse = new PlayerRecord(mediaIntent, target, token);
                // it's new so it's not playing (no RemoteControlClient to give a playstate),
                // therefore it goes after the ones with active playback
                mPRStack.add(lastPlayingIndex, prse);
            } else {
                // is in the stack
                if (mPRStack.size() > 1) { // no need to remove and add if stack contains only 1
                    prse = mPRStack.elementAt(inStackIndex);
                    // remove it from its old location in the stack
                    mPRStack.removeElementAt(inStackIndex);
                    if (prse.isPlaybackActive()) {
                        // and put it at the top
                        mPRStack.push(prse);
                    } else {
                        // and put it after the ones with active playback
                        if (inStackIndex > lastPlayingIndex) {
                            mPRStack.add(lastPlayingIndex, prse);
                        } else {
                            mPRStack.add(lastPlayingIndex - 1, prse);
                        }
                    }
                }
            }

        } catch (ArrayIndexOutOfBoundsException e) {
            // not expected to happen, indicates improper concurrent modification or bad index
            Log.e(TAG, "Wrong index (inStack=" + inStackIndex + " lastPlaying=" + lastPlayingIndex
                    + " size=" + mPRStack.size()
                    + " accessing media button stack", e);
        }

        return (topChanged);
    }

    /**
     * Helper function:
     * Remove the remote control receiver from the RC focus stack.
     * Called synchronized on mPRStack
     * precondition: pi != null
     */
    private void removeMediaButtonReceiver_syncPrs(PendingIntent pi) {
        try {
            for (int index = mPRStack.size()-1; index >= 0; index--) {
                final PlayerRecord prse = mPRStack.elementAt(index);
                if (prse.hasMatchingMediaButtonIntent(pi)) {
                    prse.destroy();
                    // ok to remove element while traversing the stack since we're leaving the loop
                    mPRStack.removeElementAt(index);
                    break;
                }
            }
        } catch (ArrayIndexOutOfBoundsException e) {
            // not expected to happen, indicates improper concurrent modification
            Log.e(TAG, "Wrong index accessing media button stack, lock error? ", e);
        }
    }

    /**
     * Helper function:
     * Called synchronized on mPRStack
     */
    private boolean isCurrentRcController(PendingIntent pi) {
        if (!mPRStack.empty() && mPRStack.peek().hasMatchingMediaButtonIntent(pi)) {
            return true;
        }
        return false;
    }

    //==========================================================================================
    // Remote control display / client
    //==========================================================================================
    /**
     * Update the remote control displays with the new "focused" client generation
     */
    private void setNewRcClientOnDisplays_syncRcsCurrc(int newClientGeneration,
            PendingIntent newMediaIntent, boolean clearing) {
        synchronized(mPRStack) {
            if (mRcDisplays.size() > 0) {
                final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
                while (displayIterator.hasNext()) {
                    final DisplayInfoForServer di = displayIterator.next();
                    try {
                        di.mRcDisplay.setCurrentClientId(
                                newClientGeneration, newMediaIntent, clearing);
                    } catch (RemoteException e) {
                        Log.e(TAG, "Dead display in setNewRcClientOnDisplays_syncRcsCurrc()",e);
                        di.release();
                        displayIterator.remove();
                    }
                }
            }
        }
    }

    /**
     * Update the remote control clients with the new "focused" client generation
     */
    private void setNewRcClientGenerationOnClients_syncRcsCurrc(int newClientGeneration) {
        // (using an iterator on the stack so we can safely remove an entry if needed,
        //  traversal order doesn't matter here as we update all entries)
        Iterator<PlayerRecord> stackIterator = mPRStack.iterator();
        while(stackIterator.hasNext()) {
            PlayerRecord se = stackIterator.next();
            if ((se != null) && (se.getRcc() != null)) {
                try {
                    se.getRcc().setCurrentClientGenerationId(newClientGeneration);
                } catch (RemoteException e) {
                    Log.w(TAG, "Dead client in setNewRcClientGenerationOnClients_syncRcsCurrc()",e);
                    stackIterator.remove();
                    se.unlinkToRcClientDeath();
                }
            }
        }
    }

    /**
     * Update the displays and clients with the new "focused" client generation and name
     * @param newClientGeneration the new generation value matching a client update
     * @param newMediaIntent the media button event receiver associated with the client.
     *    May be null, which implies there is no registered media button event receiver.
     * @param clearing true if the new client generation value maps to a remote control update
     *    where the display should be cleared.
     */
    private void setNewRcClient_syncRcsCurrc(int newClientGeneration,
            PendingIntent newMediaIntent, boolean clearing) {
        // send the new valid client generation ID to all displays
        setNewRcClientOnDisplays_syncRcsCurrc(newClientGeneration, newMediaIntent, clearing);
        // send the new valid client generation ID to all clients
        setNewRcClientGenerationOnClients_syncRcsCurrc(newClientGeneration);
    }

    /**
     * Called when processing MSG_RCDISPLAY_CLEAR event
     */
    private void onRcDisplayClear() {
        if (DEBUG_RC) Log.i(TAG, "Clear remote control display");

        synchronized(mPRStack) {
            synchronized(mCurrentRcLock) {
                mCurrentRcClientGen++;
                // synchronously update the displays and clients with the new client generation
                setNewRcClient_syncRcsCurrc(mCurrentRcClientGen,
                        null /*newMediaIntent*/, true /*clearing*/);
            }
        }
    }

    /**
     * Called when processing MSG_RCDISPLAY_UPDATE event
     */
    private void onRcDisplayUpdate(PlayerRecord prse, int flags /* USED ?*/) {
        synchronized(mPRStack) {
            synchronized(mCurrentRcLock) {
                if ((mCurrentRcClient != null) && (mCurrentRcClient.equals(prse.getRcc()))) {
                    if (DEBUG_RC) Log.i(TAG, "Display/update remote control ");

                    mCurrentRcClientGen++;
                    // synchronously update the displays and clients with
                    //      the new client generation
                    setNewRcClient_syncRcsCurrc(mCurrentRcClientGen,
                            prse.getMediaButtonIntent() /*newMediaIntent*/,
                            false /*clearing*/);

                    // tell the current client that it needs to send info
                    try {
                        //TODO change name to informationRequestForAllDisplays()
                        mCurrentRcClient.onInformationRequested(mCurrentRcClientGen, flags);
                    } catch (RemoteException e) {
                        Log.e(TAG, "Current valid remote client is dead: "+e);
                        mCurrentRcClient = null;
                    }
                } else {
                    // the remote control display owner has changed between the
                    // the message to update the display was sent, and the time it
                    // gets to be processed (now)
                }
            }
        }
    }

    /**
     * Called when processing MSG_RCDISPLAY_INIT_INFO event
     * Causes the current RemoteControlClient to send its info (metadata, playstate...) to
     *   a single RemoteControlDisplay, NOT all of them, as with MSG_RCDISPLAY_UPDATE.
     */
    private void onRcDisplayInitInfo(IRemoteControlDisplay newRcd, int w, int h) {
        synchronized(mPRStack) {
            synchronized(mCurrentRcLock) {
                if (mCurrentRcClient != null) {
                    if (DEBUG_RC) { Log.i(TAG, "Init RCD with current info"); }
                    try {
                        // synchronously update the new RCD with the current client generation
                        // and matching PendingIntent
                        newRcd.setCurrentClientId(mCurrentRcClientGen, mCurrentRcClientIntent,
                                false);

                        // tell the current RCC that it needs to send info, but only to the new RCD
                        try {
                            mCurrentRcClient.informationRequestForDisplay(newRcd, w, h);
                        } catch (RemoteException e) {
                            Log.e(TAG, "Current valid remote client is dead: ", e);
                            mCurrentRcClient = null;
                        }
                    } catch (RemoteException e) {
                        Log.e(TAG, "Dead display in onRcDisplayInitInfo()", e);
                    }
                }
            }
        }
    }

    /**
     * Helper function:
     * Called synchronized on mPRStack
     */
    private void clearRemoteControlDisplay_syncPrs() {
        synchronized(mCurrentRcLock) {
            mCurrentRcClient = null;
        }
        // will cause onRcDisplayClear() to be called in AudioService's handler thread
        mEventHandler.sendMessage( mEventHandler.obtainMessage(MSG_RCDISPLAY_CLEAR) );
    }

    /**
     * Helper function for code readability: only to be called from
     *    checkUpdateRemoteControlDisplay_syncPrs() which checks the preconditions for
     *    this method.
     * Preconditions:
     *    - called synchronized on mPRStack
     *    - mPRStack.isEmpty() is false
     */
    private void updateRemoteControlDisplay_syncPrs(int infoChangedFlags) {
        PlayerRecord prse = mPRStack.peek();
        int infoFlagsAboutToBeUsed = infoChangedFlags;
        // this is where we enforce opt-in for information display on the remote controls
        //   with the new AudioManager.registerRemoteControlClient() API
        if (prse.getRcc() == null) {
            //Log.w(TAG, "Can't update remote control display with null remote control client");
            clearRemoteControlDisplay_syncPrs();
            return;
        }
        synchronized(mCurrentRcLock) {
            if (!prse.getRcc().equals(mCurrentRcClient)) {
                // new RC client, assume every type of information shall be queried
                infoFlagsAboutToBeUsed = RC_INFO_ALL;
            }
            mCurrentRcClient = prse.getRcc();
            mCurrentRcClientIntent = prse.getMediaButtonIntent();
        }
        // will cause onRcDisplayUpdate() to be called in AudioService's handler thread
        mEventHandler.sendMessage( mEventHandler.obtainMessage(MSG_RCDISPLAY_UPDATE,
                infoFlagsAboutToBeUsed /* arg1 */, 0, prse /* obj, != null */) );
    }

    /**
     * Helper function:
     * Called synchronized on mPRStack
     * Check whether the remote control display should be updated, triggers the update if required
     * @param infoChangedFlags the flags corresponding to the remote control client information
     *     that has changed, if applicable (checking for the update conditions might trigger a
     *     clear, rather than an update event).
     */
    private void checkUpdateRemoteControlDisplay_syncPrs(int infoChangedFlags) {
        // determine whether the remote control display should be refreshed
        // if the player record stack is empty, there is nothing to display, so clear the RC display
        if (mPRStack.isEmpty()) {
            clearRemoteControlDisplay_syncPrs();
            return;
        }

        // this is where more rules for refresh go

        // refresh conditions were verified: update the remote controls
        // ok to call: synchronized on mPRStack, mPRStack is not empty
        updateRemoteControlDisplay_syncPrs(infoChangedFlags);
    }

    /**
     * see AudioManager.registerMediaButtonIntent(PendingIntent pi, ComponentName c)
     * precondition: mediaIntent != null
     */
    protected void registerMediaButtonIntent(PendingIntent mediaIntent, ComponentName eventReceiver,
            IBinder token) {
        Log.i(TAG, "  Remote Control   registerMediaButtonIntent() for " + mediaIntent);

        synchronized(mPRStack) {
            if (pushMediaButtonReceiver_syncPrs(mediaIntent, eventReceiver, token)) {
                // new RC client, assume every type of information shall be queried
                checkUpdateRemoteControlDisplay_syncPrs(RC_INFO_ALL);
            }
        }
    }

    /**
     * see AudioManager.unregisterMediaButtonIntent(PendingIntent mediaIntent)
     * precondition: mediaIntent != null, eventReceiver != null
     */
    protected void unregisterMediaButtonIntent(PendingIntent mediaIntent)
    {
        Log.i(TAG, "  Remote Control   unregisterMediaButtonIntent() for " + mediaIntent);

        synchronized(mPRStack) {
            boolean topOfStackWillChange = isCurrentRcController(mediaIntent);
            removeMediaButtonReceiver_syncPrs(mediaIntent);
            if (topOfStackWillChange) {
                // current RC client will change, assume every type of info needs to be queried
                checkUpdateRemoteControlDisplay_syncPrs(RC_INFO_ALL);
            }
        }
    }

    protected void unregisterMediaButtonIntentAsync(final PendingIntent mediaIntent) {
        mEventHandler.sendMessage(
                mEventHandler.obtainMessage(MSG_UNREGISTER_MEDIABUTTONINTENT, 0, 0,
                        mediaIntent));
    }

    /**
     * see AudioManager.registerMediaButtonEventReceiverForCalls(ComponentName c)
     * precondition: c != null
     */
    protected void registerMediaButtonEventReceiverForCalls(ComponentName c) {
        if (mContext.checkCallingPermission("android.permission.MODIFY_PHONE_STATE")
                != PackageManager.PERMISSION_GRANTED) {
            Log.e(TAG, "Invalid permissions to register media button receiver for calls");
            return;
        }
        synchronized(mPRStack) {
            mMediaReceiverForCalls = c;
        }
    }

    /**
     * see AudioManager.unregisterMediaButtonEventReceiverForCalls()
     */
    protected void unregisterMediaButtonEventReceiverForCalls() {
        if (mContext.checkCallingPermission("android.permission.MODIFY_PHONE_STATE")
                != PackageManager.PERMISSION_GRANTED) {
            Log.e(TAG, "Invalid permissions to unregister media button receiver for calls");
            return;
        }
        synchronized(mPRStack) {
            mMediaReceiverForCalls = null;
        }
    }

    /**
     * see AudioManager.registerRemoteControlClient(ComponentName eventReceiver, ...)
     * @return the unique ID of the PlayerRecord associated with the RemoteControlClient
     * Note: using this method with rcClient == null is a way to "disable" the IRemoteControlClient
     *     without modifying the RC stack, but while still causing the display to refresh (will
     *     become blank as a result of this)
     */
    protected int registerRemoteControlClient(PendingIntent mediaIntent,
            IRemoteControlClient rcClient, String callingPackageName) {
        if (DEBUG_RC) Log.i(TAG, "Register remote control client rcClient="+rcClient);
        int rccId = RemoteControlClient.RCSE_ID_UNREGISTERED;
        synchronized(mPRStack) {
            // store the new display information
            try {
                for (int index = mPRStack.size()-1; index >= 0; index--) {
                    final PlayerRecord prse = mPRStack.elementAt(index);
                    if(prse.hasMatchingMediaButtonIntent(mediaIntent)) {
                        prse.resetControllerInfoForRcc(rcClient, callingPackageName,
                                Binder.getCallingUid());

                        if (rcClient == null) {
                            break;
                        }

                        rccId = prse.getRccId();

                        // there is a new (non-null) client:
                        //     give the new client the displays (if any)
                        if (mRcDisplays.size() > 0) {
                            plugRemoteControlDisplaysIntoClient_syncPrs(prse.getRcc());
                        }
                        break;
                    }
                }//for
            } catch (ArrayIndexOutOfBoundsException e) {
                // not expected to happen, indicates improper concurrent modification
                Log.e(TAG, "Wrong index accessing RC stack, lock error? ", e);
            }

            // if the eventReceiver is at the top of the stack
            // then check for potential refresh of the remote controls
            if (isCurrentRcController(mediaIntent)) {
                checkUpdateRemoteControlDisplay_syncPrs(RC_INFO_ALL);
            }
        }//synchronized(mPRStack)
        return rccId;
    }

    /**
     * see AudioManager.unregisterRemoteControlClient(PendingIntent pi, ...)
     * rcClient is guaranteed non-null
     */
    protected void unregisterRemoteControlClient(PendingIntent mediaIntent,
            IRemoteControlClient rcClient) {
        if (DEBUG_RC) Log.i(TAG, "Unregister remote control client rcClient="+rcClient);
        synchronized(mPRStack) {
            boolean topRccChange = false;
            try {
                for (int index = mPRStack.size()-1; index >= 0; index--) {
                    final PlayerRecord prse = mPRStack.elementAt(index);
                    if ((prse.hasMatchingMediaButtonIntent(mediaIntent))
                            && rcClient.equals(prse.getRcc())) {
                        // we found the IRemoteControlClient to unregister
                        prse.resetControllerInfoForNoRcc();
                        topRccChange = (index == mPRStack.size()-1);
                        // there can only be one matching RCC in the RC stack, we're done
                        break;
                    }
                }
            } catch (ArrayIndexOutOfBoundsException e) {
                // not expected to happen, indicates improper concurrent modification
                Log.e(TAG, "Wrong index accessing RC stack, lock error? ", e);
            }
            if (topRccChange) {
                // no more RCC for the RCD, check for potential refresh of the remote controls
                checkUpdateRemoteControlDisplay_syncPrs(RC_INFO_ALL);
            }
        }
    }


    /**
     * A class to encapsulate all the information about a remote control display.
     * After instanciation, init() must always be called before the object is added in the list
     * of displays.
     * Before being removed from the list of displays, release() must always be called (otherwise
     * it will leak death handlers).
     */
    private class DisplayInfoForServer implements IBinder.DeathRecipient {
        /** may never be null */
        private final IRemoteControlDisplay mRcDisplay;
        private final IBinder mRcDisplayBinder;
        private int mArtworkExpectedWidth = -1;
        private int mArtworkExpectedHeight = -1;
        private boolean mWantsPositionSync = false;
        private ComponentName mClientNotifListComp;
        private boolean mEnabled = true;

        public DisplayInfoForServer(IRemoteControlDisplay rcd, int w, int h) {
            if (DEBUG_RC) Log.i(TAG, "new DisplayInfoForServer for " + rcd + " w=" + w + " h=" + h);
            mRcDisplay = rcd;
            mRcDisplayBinder = rcd.asBinder();
            mArtworkExpectedWidth = w;
            mArtworkExpectedHeight = h;
        }

        public boolean init() {
            try {
                mRcDisplayBinder.linkToDeath(this, 0);
            } catch (RemoteException e) {
                // remote control display is DOA, disqualify it
                Log.w(TAG, "registerRemoteControlDisplay() has a dead client " + mRcDisplayBinder);
                return false;
            }
            return true;
        }

        public void release() {
            try {
                mRcDisplayBinder.unlinkToDeath(this, 0);
            } catch (java.util.NoSuchElementException e) {
                // not much we can do here, the display should have been unregistered anyway
                Log.e(TAG, "Error in DisplaInfoForServer.relase()", e);
            }
        }

        public void binderDied() {
            synchronized(mPRStack) {
                Log.w(TAG, "RemoteControl: display " + mRcDisplay + " died");
                // remove the display from the list
                final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
                while (displayIterator.hasNext()) {
                    final DisplayInfoForServer di = displayIterator.next();
                    if (di.mRcDisplay == mRcDisplay) {
                        if (DEBUG_RC) Log.w(TAG, " RCD removed from list");
                        displayIterator.remove();
                        return;
                    }
                }
            }
        }
    }

    /**
     * The remote control displays.
     * Access synchronized on mPRStack
     */
    private ArrayList<DisplayInfoForServer> mRcDisplays = new ArrayList<DisplayInfoForServer>(1);

    /**
     * Plug each registered display into the specified client
     * @param rcc, guaranteed non null
     */
    private void plugRemoteControlDisplaysIntoClient_syncPrs(IRemoteControlClient rcc) {
        final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
        while (displayIterator.hasNext()) {
            final DisplayInfoForServer di = displayIterator.next();
            try {
                rcc.plugRemoteControlDisplay(di.mRcDisplay, di.mArtworkExpectedWidth,
                        di.mArtworkExpectedHeight);
                if (di.mWantsPositionSync) {
                    rcc.setWantsSyncForDisplay(di.mRcDisplay, true);
                }
            } catch (RemoteException e) {
                Log.e(TAG, "Error connecting RCD to RCC in RCC registration",e);
            }
        }
    }

    private void enableRemoteControlDisplayForClient_syncRcStack(IRemoteControlDisplay rcd,
            boolean enabled) {
        // let all the remote control clients know whether the given display is enabled
        //   (so the remote control stack traversal order doesn't matter).
        final Iterator<PlayerRecord> stackIterator = mPRStack.iterator();
        while(stackIterator.hasNext()) {
            PlayerRecord prse = stackIterator.next();
            if(prse.getRcc() != null) {
                try {
                    prse.getRcc().enableRemoteControlDisplay(rcd, enabled);
                } catch (RemoteException e) {
                    Log.e(TAG, "Error connecting RCD to client: ", e);
                }
            }
        }
    }

    /**
     * Is the remote control display interface already registered
     * @param rcd
     * @return true if the IRemoteControlDisplay is already in the list of displays
     */
    private boolean rcDisplayIsPluggedIn_syncRcStack(IRemoteControlDisplay rcd) {
        final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
        while (displayIterator.hasNext()) {
            final DisplayInfoForServer di = displayIterator.next();
            if (di.mRcDisplay.asBinder().equals(rcd.asBinder())) {
                return true;
            }
        }
        return false;
    }

    /**
     * Register an IRemoteControlDisplay.
     * Notify all IRemoteControlClient of the new display and cause the RemoteControlClient
     * at the top of the stack to update the new display with its information.
     * @see android.media.IAudioService#registerRemoteControlDisplay(android.media.IRemoteControlDisplay, int, int)
     * @param rcd the IRemoteControlDisplay to register. No effect if null.
     * @param w the maximum width of the expected bitmap. Negative or zero values indicate this
     *   display doesn't need to receive artwork.
     * @param h the maximum height of the expected bitmap. Negative or zero values indicate this
     *   display doesn't need to receive artwork.
     * @param listenerComp the component for the listener interface, may be null if it's not needed
     *   to verify it belongs to one of the enabled notification listeners
     */
    private void registerRemoteControlDisplay_int(IRemoteControlDisplay rcd, int w, int h,
            ComponentName listenerComp) {
        if (DEBUG_RC) Log.d(TAG, ">>> registerRemoteControlDisplay("+rcd+")");
        synchronized(mAudioFocusLock) {
            synchronized(mPRStack) {
                if ((rcd == null) || rcDisplayIsPluggedIn_syncRcStack(rcd)) {
                    return;
                }
                DisplayInfoForServer di = new DisplayInfoForServer(rcd, w, h);
                di.mEnabled = true;
                di.mClientNotifListComp = listenerComp;
                if (!di.init()) {
                    if (DEBUG_RC) Log.e(TAG, " error registering RCD");
                    return;
                }
                // add RCD to list of displays
                mRcDisplays.add(di);

                // let all the remote control clients know there is a new display (so the remote
                //   control stack traversal order doesn't matter).
                Iterator<PlayerRecord> stackIterator = mPRStack.iterator();
                while(stackIterator.hasNext()) {
                    PlayerRecord prse = stackIterator.next();
                    if(prse.getRcc() != null) {
                        try {
                            prse.getRcc().plugRemoteControlDisplay(rcd, w, h);
                        } catch (RemoteException e) {
                            Log.e(TAG, "Error connecting RCD to client: ", e);
                        }
                    }
                }

                // we have a new display, of which all the clients are now aware: have it be
                // initialized wih the current gen ID and the current client info, do not
                // reset the information for the other (existing) displays
                sendMsg(mEventHandler, MSG_RCDISPLAY_INIT_INFO, SENDMSG_QUEUE,
                        w /*arg1*/, h /*arg2*/,
                        rcd /*obj*/, 0/*delay*/);
            }
        }
    }

    /**
     * Unregister an IRemoteControlDisplay.
     * No effect if the IRemoteControlDisplay hasn't been successfully registered.
     * @see android.media.IAudioService#unregisterRemoteControlDisplay(android.media.IRemoteControlDisplay)
     * @param rcd the IRemoteControlDisplay to unregister. No effect if null.
     */
    protected void unregisterRemoteControlDisplay(IRemoteControlDisplay rcd) {
        if (DEBUG_RC) Log.d(TAG, "<<< unregisterRemoteControlDisplay("+rcd+")");
        synchronized(mPRStack) {
            if (rcd == null) {
                return;
            }

            boolean displayWasPluggedIn = false;
            final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
            while (displayIterator.hasNext() && !displayWasPluggedIn) {
                final DisplayInfoForServer di = displayIterator.next();
                if (di.mRcDisplay.asBinder().equals(rcd.asBinder())) {
                    displayWasPluggedIn = true;
                    di.release();
                    displayIterator.remove();
                }
            }

            if (displayWasPluggedIn) {
                // disconnect this remote control display from all the clients, so the remote
                //   control stack traversal order doesn't matter
                final Iterator<PlayerRecord> stackIterator = mPRStack.iterator();
                while(stackIterator.hasNext()) {
                    final PlayerRecord prse = stackIterator.next();
                    if(prse.getRcc() != null) {
                        try {
                            prse.getRcc().unplugRemoteControlDisplay(rcd);
                        } catch (RemoteException e) {
                            Log.e(TAG, "Error disconnecting remote control display to client: ", e);
                        }
                    }
                }
            } else {
                if (DEBUG_RC) Log.w(TAG, "  trying to unregister unregistered RCD");
            }
        }
    }

    /**
     * Update the size of the artwork used by an IRemoteControlDisplay.
     * @see android.media.IAudioService#remoteControlDisplayUsesBitmapSize(android.media.IRemoteControlDisplay, int, int)
     * @param rcd the IRemoteControlDisplay with the new artwork size requirement
     * @param w the maximum width of the expected bitmap. Negative or zero values indicate this
     *   display doesn't need to receive artwork.
     * @param h the maximum height of the expected bitmap. Negative or zero values indicate this
     *   display doesn't need to receive artwork.
     */
    protected void remoteControlDisplayUsesBitmapSize(IRemoteControlDisplay rcd, int w, int h) {
        synchronized(mPRStack) {
            final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
            boolean artworkSizeUpdate = false;
            while (displayIterator.hasNext() && !artworkSizeUpdate) {
                final DisplayInfoForServer di = displayIterator.next();
                if (di.mRcDisplay.asBinder().equals(rcd.asBinder())) {
                    if ((di.mArtworkExpectedWidth != w) || (di.mArtworkExpectedHeight != h)) {
                        di.mArtworkExpectedWidth = w;
                        di.mArtworkExpectedHeight = h;
                        artworkSizeUpdate = true;
                    }
                }
            }
            if (artworkSizeUpdate) {
                // RCD is currently plugged in and its artwork size has changed, notify all RCCs,
                // stack traversal order doesn't matter
                final Iterator<PlayerRecord> stackIterator = mPRStack.iterator();
                while(stackIterator.hasNext()) {
                    final PlayerRecord prse = stackIterator.next();
                    if(prse.getRcc() != null) {
                        try {
                            prse.getRcc().setBitmapSizeForDisplay(rcd, w, h);
                        } catch (RemoteException e) {
                            Log.e(TAG, "Error setting bitmap size for RCD on RCC: ", e);
                        }
                    }
                }
            }
        }
    }

    /**
     * Controls whether a remote control display needs periodic checks of the RemoteControlClient
     * playback position to verify that the estimated position has not drifted from the actual
     * position. By default the check is not performed.
     * The IRemoteControlDisplay must have been previously registered for this to have any effect.
     * @param rcd the IRemoteControlDisplay for which the anti-drift mechanism will be enabled
     *     or disabled. Not null.
     * @param wantsSync if true, RemoteControlClient instances which expose their playback position
     *     to the framework will regularly compare the estimated playback position with the actual
     *     position, and will update the IRemoteControlDisplay implementation whenever a drift is
     *     detected.
     */
    protected void remoteControlDisplayWantsPlaybackPositionSync(IRemoteControlDisplay rcd,
            boolean wantsSync) {
        synchronized(mPRStack) {
            boolean rcdRegistered = false;
            // store the information about this display
            // (display stack traversal order doesn't matter).
            final Iterator<DisplayInfoForServer> displayIterator = mRcDisplays.iterator();
            while (displayIterator.hasNext()) {
                final DisplayInfoForServer di = displayIterator.next();
                if (di.mRcDisplay.asBinder().equals(rcd.asBinder())) {
                    di.mWantsPositionSync = wantsSync;
                    rcdRegistered = true;
                    break;
                }
            }
            if (!rcdRegistered) {
                return;
            }
            // notify all current RemoteControlClients
            // (stack traversal order doesn't matter as we notify all RCCs)
            final Iterator<PlayerRecord> stackIterator = mPRStack.iterator();
            while (stackIterator.hasNext()) {
                final PlayerRecord prse = stackIterator.next();
                if (prse.getRcc() != null) {
                    try {
                        prse.getRcc().setWantsSyncForDisplay(rcd, wantsSync);
                    } catch (RemoteException e) {
                        Log.e(TAG, "Error setting position sync flag for RCD on RCC: ", e);
                    }
                }
            }
        }
    }

    // handler for MSG_RCC_NEW_VOLUME_OBS
    private void onRegisterVolumeObserverForRcc(int rccId, IRemoteVolumeObserver rvo) {
        synchronized(mPRStack) {
            // The stack traversal order doesn't matter because there is only one stack entry
            //  with this RCC ID, but the matching ID is more likely at the top of the stack, so
            //  start iterating from the top.
            try {
                for (int index = mPRStack.size()-1; index >= 0; index--) {
                    final PlayerRecord prse = mPRStack.elementAt(index);
                    if (prse.getRccId() == rccId) {
                        prse.mRemoteVolumeObs = rvo;
                        break;
                    }
                }
            } catch (ArrayIndexOutOfBoundsException e) {
                // not expected to happen, indicates improper concurrent modification
                Log.e(TAG, "Wrong index accessing media button stack, lock error? ", e);
            }
        }
    }

    /**
     * Checks if a remote client is active on the supplied stream type. Update the remote stream
     * volume state if found and playing
     * @param streamType
     * @return false if no remote playing is currently playing
     */
    protected boolean checkUpdateRemoteStateIfActive(int streamType) {
        synchronized(mPRStack) {
            // iterating from top of stack as active playback is more likely on entries at the top
            try {
                for (int index = mPRStack.size()-1; index >= 0; index--) {
                    final PlayerRecord prse = mPRStack.elementAt(index);
                    if ((prse.mPlaybackType == RemoteControlClient.PLAYBACK_TYPE_REMOTE)
                            && isPlaystateActive(prse.mPlaybackState.mState)
                            && (prse.mPlaybackStream == streamType)) {
                        if (DEBUG_RC) Log.d(TAG, "remote playback active on stream " + streamType
                                + ", vol =" + prse.mPlaybackVolume);
                        synchronized (mMainRemote) {
                            mMainRemote.mRccId = prse.getRccId();
                            mMainRemote.mVolume = prse.mPlaybackVolume;
                            mMainRemote.mVolumeMax = prse.mPlaybackVolumeMax;
                            mMainRemote.mVolumeHandling = prse.mPlaybackVolumeHandling;
                            mMainRemoteIsActive = true;
                        }
                        return true;
                    }
                }
            } catch (ArrayIndexOutOfBoundsException e) {
                // not expected to happen, indicates improper concurrent modification
                Log.e(TAG, "Wrong index accessing RC stack, lock error? ", e);
            }
        }
        synchronized (mMainRemote) {
            mMainRemoteIsActive = false;
        }
        return false;
    }

    /**
     * Returns true if the given playback state is considered "active", i.e. it describes a state
     * where playback is happening, or about to
     * @param playState the playback state to evaluate
     * @return true if active, false otherwise (inactive or unknown)
     */
    protected static boolean isPlaystateActive(int playState) {
        switch (playState) {
            case RemoteControlClient.PLAYSTATE_PLAYING:
            case RemoteControlClient.PLAYSTATE_BUFFERING:
            case RemoteControlClient.PLAYSTATE_FAST_FORWARDING:
            case RemoteControlClient.PLAYSTATE_REWINDING:
            case RemoteControlClient.PLAYSTATE_SKIPPING_BACKWARDS:
            case RemoteControlClient.PLAYSTATE_SKIPPING_FORWARDS:
                return true;
            default:
                return false;
        }
    }

    private void sendVolumeUpdateToRemote(int rccId, int direction) {
        if (DEBUG_VOL) { Log.d(TAG, "sendVolumeUpdateToRemote(rccId="+rccId+" , dir="+direction); }
        if (direction == 0) {
            // only handling discrete events
            return;
        }
        IRemoteVolumeObserver rvo = null;
        synchronized (mPRStack) {
            // The stack traversal order doesn't matter because there is only one stack entry
            //  with this RCC ID, but the matching ID is more likely at the top of the stack, so
            //  start iterating from the top.
            try {
                for (int index = mPRStack.size()-1; index >= 0; index--) {
                    final PlayerRecord prse = mPRStack.elementAt(index);
                    //FIXME OPTIMIZE store this info in mMainRemote so we don't have to iterate?
                    if (prse.getRccId() == rccId) {
                        rvo = prse.mRemoteVolumeObs;
                        break;
                    }
                }
            } catch (ArrayIndexOutOfBoundsException e) {
                // not expected to happen, indicates improper concurrent modification
                Log.e(TAG, "Wrong index accessing media button stack, lock error? ", e);
            }
        }
        if (rvo != null) {
            try {
                rvo.dispatchRemoteVolumeUpdate(direction, -1);
            } catch (RemoteException e) {
                Log.e(TAG, "Error dispatching relative volume update", e);
            }
        }
    }

    protected int getRemoteStreamMaxVolume() {
        synchronized (mMainRemote) {
            if (mMainRemote.mRccId == RemoteControlClient.RCSE_ID_UNREGISTERED) {
                return 0;
            }
            return mMainRemote.mVolumeMax;
        }
    }

    protected int getRemoteStreamVolume() {
        synchronized (mMainRemote) {
            if (mMainRemote.mRccId == RemoteControlClient.RCSE_ID_UNREGISTERED) {
                return 0;
            }
            return mMainRemote.mVolume;
        }
    }

    protected void setRemoteStreamVolume(int vol) {
        if (DEBUG_VOL) { Log.d(TAG, "setRemoteStreamVolume(vol="+vol+")"); }
        int rccId = RemoteControlClient.RCSE_ID_UNREGISTERED;
        synchronized (mMainRemote) {
            if (mMainRemote.mRccId == RemoteControlClient.RCSE_ID_UNREGISTERED) {
                return;
            }
            rccId = mMainRemote.mRccId;
        }
        IRemoteVolumeObserver rvo = null;
        synchronized (mPRStack) {
            // The stack traversal order doesn't matter because there is only one stack entry
            //  with this RCC ID, but the matching ID is more likely at the top of the stack, so
            //  start iterating from the top.
            try {
                for (int index = mPRStack.size()-1; index >= 0; index--) {
                    final PlayerRecord prse = mPRStack.elementAt(index);
                    //FIXME OPTIMIZE store this info in mMainRemote so we don't have to iterate?
                    if (prse.getRccId() == rccId) {
                        rvo = prse.mRemoteVolumeObs;
                        break;
                    }
                }
            } catch (ArrayIndexOutOfBoundsException e) {
                // not expected to happen, indicates improper concurrent modification
                Log.e(TAG, "Wrong index accessing media button stack, lock error? ", e);
            }
        }
        if (rvo != null) {
            try {
                rvo.dispatchRemoteVolumeUpdate(0, vol);
            } catch (RemoteException e) {
                Log.e(TAG, "Error dispatching absolute volume update", e);
            }
        }
    }

    /**
     * Call to make AudioService reevaluate whether it's in a mode where remote players should
     * have their volume controlled. In this implementation this is only to reset whether
     * VolumePanel should display remote volumes
     */
    protected void postReevaluateRemote() {
        sendMsg(mEventHandler, MSG_REEVALUATE_REMOTE, SENDMSG_QUEUE, 0, 0, null, 0);
    }

    private void onReevaluateRemote() {
        // TODO This was used to notify VolumePanel if there was remote playback
        // in the stack. This is now in MediaSessionService. More code should be
        // removed.
    }

}