android-35/com/android/internal/util/CallbackRegistry.java - platform/prebuilts/fullsdk/sources - Git at Google

 /*
  * Copyright (C) 2015 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 com.android.internal.util;

 import java.util.ArrayList;
 import java.util.List;

 /**
  * Tracks callbacks for the event. This class supports reentrant modification
  * of the callbacks during notification without adversely disrupting notifications.
  * A common pattern for callbacks is to receive a notification and then remove
  * themselves. This class handles this behavior with constant memory under
  * most circumstances.
  *
  * <p>A subclass of {@link CallbackRegistry.NotifierCallback} must be passed to
  * the constructor to define how notifications should be called. That implementation
  * does the actual notification on the listener.</p>
  *
  * <p>This class supports only callbacks with at most two parameters.
  * Typically, these are the notification originator and a parameter, but these may
  * be used as required. If more than two parameters are required or primitive types
  * must be used, <code>A</code> should be some kind of containing structure that
  * the subclass may reuse between notifications.</p>
  *
  * @param <C> The callback type.
  * @param <T> The notification sender type. Typically this is the containing class.
  * @param <A> Opaque argument used to pass additional data beyond an int.
  */
 @android.ravenwood.annotation.RavenwoodKeepWholeClass
 public class CallbackRegistry<C, T, A> implements Cloneable {
     private static final String TAG = "CallbackRegistry";

     /** An ordered collection of listeners waiting to be notified. */
     private List<C> mCallbacks = new ArrayList<C>();

     /**
      * A bit flag for the first 64 listeners that are removed during notification.
      * The lowest significant bit corresponds to the 0th index into mCallbacks.
      * For a small number of callbacks, no additional array of objects needs to
      * be allocated.
      */
     private long mFirst64Removed = 0x0;

     /**
      * Bit flags for the remaining callbacks that are removed during notification.
      * When there are more than 64 callbacks and one is marked for removal, a dynamic
      * array of bits are allocated for the callbacks.
      */
     private long[] mRemainderRemoved;

     /**
      * The reentrancy level of the notification. When we notify a callback, it may cause
      * further notifications. The reentrancy level must be tracked to let us clean up
      * the callback state when all notifications have been processed.
      */
     private int mNotificationLevel;

     /** The notification mechanism for notifying an event. */
     private final NotifierCallback<C, T, A> mNotifier;

     /**
      * Creates an EventRegistry that notifies the event with notifier.
      * @param notifier The class to use to notify events.
      */
     public CallbackRegistry(NotifierCallback<C, T, A> notifier) {
         mNotifier = notifier;
     }

     /**
      * Notify all callbacks.
      *
      * @param sender The originator. This is an opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg2 An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      */
     public synchronized void notifyCallbacks(T sender, int arg, A arg2) {
         mNotificationLevel++;
         notifyRecurseLocked(sender, arg, arg2);
         mNotificationLevel--;
         if (mNotificationLevel == 0) {
             if (mRemainderRemoved != null) {
                 for (int i = mRemainderRemoved.length - 1; i >= 0; i--) {
                     final long removedBits = mRemainderRemoved[i];
                     if (removedBits != 0) {
                         removeRemovedCallbacks((i + 1) * Long.SIZE, removedBits);
                         mRemainderRemoved[i] = 0;
                     }
                 }
             }
             if (mFirst64Removed != 0) {
                 removeRemovedCallbacks(0, mFirst64Removed);
                 mFirst64Removed = 0;
             }
         }
     }

     /**
      * Notify up to the first Long.SIZE callbacks that don't have a bit set in <code>removed</code>.
      *
      * @param sender The originator. This is an opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg2 An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      */
     private void notifyFirst64Locked(T sender, int arg, A arg2) {
         final int maxNotified = Math.min(Long.SIZE, mCallbacks.size());
         notifyCallbacksLocked(sender, arg, arg2, 0, maxNotified, mFirst64Removed);
     }

     /**
      * Notify all callbacks using a recursive algorithm to avoid allocating on the heap.
      * This part captures the callbacks beyond Long.SIZE that have no bits allocated for
      * removal before it recurses into {@link #notifyRemainderLocked(Object, int, A, int)}.
      * <p>
      * Recursion is used to avoid allocating temporary state on the heap. Each stack has one
      * long (64 callbacks) worth of information of which has been removed.
      *
      * @param sender The originator. This is an opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg2 An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      */
     private void notifyRecurseLocked(T sender, int arg, A arg2) {
         final int callbackCount = mCallbacks.size();
         final int remainderIndex = mRemainderRemoved == null ? -1 : mRemainderRemoved.length - 1;

         // Now we've got all callbacks that have no mRemainderRemoved value, so notify the
         // others.
         notifyRemainderLocked(sender, arg, arg2, remainderIndex);

         // notifyRemainderLocked notifies all at maxIndex, so we'd normally start at maxIndex + 1
         // However, we must also keep track of those in mFirst64Removed, so we add 2 instead:
         final int startCallbackIndex = (remainderIndex + 2) * Long.SIZE;

         // The remaining have no bit set
         notifyCallbacksLocked(sender, arg, arg2, startCallbackIndex, callbackCount, 0);
     }

     /**
      * Notify callbacks that have mRemainderRemoved bits set for remainderIndex. If
      * remainderIndex is -1, the first 64 will be notified instead.
      *
      * @param sender The originator. This is an opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg2 An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param remainderIndex The index into mRemainderRemoved that should be notified.
      */
     private void notifyRemainderLocked(T sender, int arg, A arg2, int remainderIndex) {
         if (remainderIndex < 0) {
             notifyFirst64Locked(sender, arg, arg2);
         } else {
             final long bits = mRemainderRemoved[remainderIndex];
             final int startIndex = (remainderIndex + 1) * Long.SIZE;
             final int endIndex = Math.min(mCallbacks.size(), startIndex + Long.SIZE);
             notifyRemainderLocked(sender, arg, arg2, remainderIndex - 1);
             notifyCallbacksLocked(sender, arg, arg2, startIndex, endIndex, bits);
         }
     }

     /**
      * Notify callbacks from startIndex to endIndex, using bits as the bit status
      * for whether they have been removed or not. bits should be from mRemainderRemoved or
      * mFirst64Removed. bits set to 0 indicates that all callbacks from startIndex to
      * endIndex should be notified.
      *
      * @param sender The originator. This is an opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param arg2 An opaque parameter passed to
      *      {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
      * @param startIndex The index into the mCallbacks to start notifying.
      * @param endIndex One past the last index into mCallbacks to notify.
      * @param bits A bit field indicating which callbacks have been removed and shouldn't
      *             be notified.
      */
     private void notifyCallbacksLocked(T sender, int arg, A arg2, final int startIndex,
             final int endIndex, final long bits) {
         long bitMask = 1;
         for (int i = startIndex; i < endIndex; i++) {
             if ((bits & bitMask) == 0) {
                 mNotifier.onNotifyCallback(mCallbacks.get(i), sender, arg, arg2);
             }
             bitMask <<= 1;
         }
     }

     /**
      * Add a callback to be notified. If the callback is already in the list, another won't
      * be added. This does not affect current notifications.
      * @param callback The callback to add.
      */
     public synchronized void add(C callback) {
         int index = mCallbacks.lastIndexOf(callback);
         if (index < 0 || isRemovedLocked(index)) {
             mCallbacks.add(callback);
         }
     }

     /**
      * Returns true if the callback at index has been marked for removal.
      *
      * @param index The index into mCallbacks to check.
      * @return true if the callback at index has been marked for removal.
      */
     private boolean isRemovedLocked(int index) {
         if (index < Long.SIZE) {
             // It is in the first 64 callbacks, just check the bit.
             final long bitMask = 1L << index;
             return (mFirst64Removed & bitMask) != 0;
         } else if (mRemainderRemoved == null) {
             // It is after the first 64 callbacks, but nothing else was marked for removal.
             return false;
         } else {
             final int maskIndex = (index / Long.SIZE) - 1;
             if (maskIndex >= mRemainderRemoved.length) {
                 // There are some items in mRemainderRemoved, but nothing at the given index.
                 return false;
             } else {
                 // There is something marked for removal, so we have to check the bit.
                 final long bits = mRemainderRemoved[maskIndex];
                 final long bitMask = 1L << (index % Long.SIZE);
                 return (bits & bitMask) != 0;
             }
         }
     }

     /**
      * Removes callbacks from startIndex to startIndex + Long.SIZE, based
      * on the bits set in removed.
      * @param startIndex The index into the mCallbacks to start removing callbacks.
      * @param removed The bits indicating removal, where each bit is set for one callback
      *                to be removed.
      */
     private void removeRemovedCallbacks(int startIndex, long removed) {
         // The naive approach should be fine. There may be a better bit-twiddling approach.
         final int endIndex = startIndex + Long.SIZE;

         long bitMask = 1L << (Long.SIZE - 1);
         for (int i = endIndex - 1; i >= startIndex; i--) {
             if ((removed & bitMask) != 0) {
                 mCallbacks.remove(i);
             }
             bitMask >>>= 1;
         }
     }

     /**
      * Remove a callback. This callback won't be notified after this call completes.
      * @param callback The callback to remove.
      */
     public synchronized void remove(C callback) {
         if (mNotificationLevel == 0) {
             mCallbacks.remove(callback);
         } else {
             int index = mCallbacks.lastIndexOf(callback);
             if (index >= 0) {
                 setRemovalBitLocked(index);
             }
         }
     }

     private void setRemovalBitLocked(int index) {
         if (index < Long.SIZE) {
             // It is in the first 64 callbacks, just check the bit.
             final long bitMask = 1L << index;
             mFirst64Removed |= bitMask;
         } else {
             final int remainderIndex = (index / Long.SIZE) - 1;
             if (mRemainderRemoved == null) {
                 mRemainderRemoved = new long[mCallbacks.size() / Long.SIZE];
             } else if (mRemainderRemoved.length < remainderIndex) {
                 // need to make it bigger
                 long[] newRemainders = new long[mCallbacks.size() / Long.SIZE];
                 System.arraycopy(mRemainderRemoved, 0, newRemainders, 0, mRemainderRemoved.length);
                 mRemainderRemoved = newRemainders;
             }
             final long bitMask = 1L << (index % Long.SIZE);
             mRemainderRemoved[remainderIndex] |= bitMask;
         }
     }

     /**
      * Makes a copy of the registered callbacks and returns it.
      *
      * @return a copy of the registered callbacks.
      */
     public synchronized ArrayList<C> copyListeners() {
         ArrayList<C> callbacks = new ArrayList<C>(mCallbacks.size());
         int numListeners = mCallbacks.size();
         for (int i = 0; i < numListeners; i++) {
             if (!isRemovedLocked(i)) {
                 callbacks.add(mCallbacks.get(i));
             }
         }
         return callbacks;
     }

     /**
      * Returns true if there are no registered callbacks or false otherwise.
      *
      * @return true if there are no registered callbacks or false otherwise.
      */
     public synchronized boolean isEmpty() {
         if (mCallbacks.isEmpty()) {
             return true;
         } else if (mNotificationLevel == 0) {
             return false;
         } else {
             int numListeners = mCallbacks.size();
             for (int i = 0; i < numListeners; i++) {
                 if (!isRemovedLocked(i)) {
                     return false;
                 }
             }
             return true;
         }
     }

     /**
      * Removes all callbacks from the list.
      */
     public synchronized void clear() {
         if (mNotificationLevel == 0) {
             mCallbacks.clear();
         } else if (!mCallbacks.isEmpty()) {
             for (int i = mCallbacks.size() - 1; i >= 0; i--) {
                 setRemovalBitLocked(i);
             }
         }
     }

     public synchronized CallbackRegistry<C, T, A> clone() {
         CallbackRegistry<C, T, A> clone = null;
         try {
             clone = (CallbackRegistry<C, T, A>) super.clone();
             clone.mFirst64Removed = 0;
             clone.mRemainderRemoved = null;
             clone.mNotificationLevel = 0;
             clone.mCallbacks = new ArrayList<C>();
             final int numListeners = mCallbacks.size();
             for (int i = 0; i < numListeners; i++) {
                 if (!isRemovedLocked(i)) {
                     clone.mCallbacks.add(mCallbacks.get(i));
                 }
             }
         } catch (CloneNotSupportedException e) {
             e.printStackTrace();
         }
         return clone;
     }

     /**
      * Class used to notify events from CallbackRegistry.
      *
      * @param <C> The callback type.
      * @param <T> The notification sender type. Typically this is the containing class.
      * @param <A> An opaque argument to pass to the notifier
      */
     public abstract static class NotifierCallback<C, T, A> {
         /**
          * Used to notify the callback.
          *
          * @param callback The callback to notify.
          * @param sender The opaque sender object.
          * @param arg The opaque notification parameter.
          * @param arg2 An opaque argument passed in
          *        {@link CallbackRegistry#notifyCallbacks}
          * @see CallbackRegistry#CallbackRegistry(CallbackRegistry.NotifierCallback)
          */
         public abstract void onNotifyCallback(C callback, T sender, int arg, A arg2);
     }
 }
	/*
	* Copyright (C) 2015 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 com.android.internal.util;

	import java.util.ArrayList;
	import java.util.List;

	/**
	* Tracks callbacks for the event. This class supports reentrant modification
	* of the callbacks during notification without adversely disrupting notifications.
	* A common pattern for callbacks is to receive a notification and then remove
	* themselves. This class handles this behavior with constant memory under
	* most circumstances.
	*
	* <p>A subclass of {@link CallbackRegistry.NotifierCallback} must be passed to
	* the constructor to define how notifications should be called. That implementation
	* does the actual notification on the listener.</p>
	*
	* <p>This class supports only callbacks with at most two parameters.
	* Typically, these are the notification originator and a parameter, but these may
	* be used as required. If more than two parameters are required or primitive types
	* must be used, <code>A</code> should be some kind of containing structure that
	* the subclass may reuse between notifications.</p>
	*
	* @param <C> The callback type.
	* @param <T> The notification sender type. Typically this is the containing class.
	* @param <A> Opaque argument used to pass additional data beyond an int.
	*/
	@android.ravenwood.annotation.RavenwoodKeepWholeClass
	public class CallbackRegistry<C, T, A> implements Cloneable {
	private static final String TAG = "CallbackRegistry";

	/** An ordered collection of listeners waiting to be notified. */
	private List<C> mCallbacks = new ArrayList<C>();

	/**
	* A bit flag for the first 64 listeners that are removed during notification.
	* The lowest significant bit corresponds to the 0th index into mCallbacks.
	* For a small number of callbacks, no additional array of objects needs to
	* be allocated.
	*/
	private long mFirst64Removed = 0x0;

	/**
	* Bit flags for the remaining callbacks that are removed during notification.
	* When there are more than 64 callbacks and one is marked for removal, a dynamic
	* array of bits are allocated for the callbacks.
	*/
	private long[] mRemainderRemoved;

	/**
	* The reentrancy level of the notification. When we notify a callback, it may cause
	* further notifications. The reentrancy level must be tracked to let us clean up
	* the callback state when all notifications have been processed.
	*/
	private int mNotificationLevel;

	/** The notification mechanism for notifying an event. */
	private final NotifierCallback<C, T, A> mNotifier;

	/**
	* Creates an EventRegistry that notifies the event with notifier.
	* @param notifier The class to use to notify events.
	*/
	public CallbackRegistry(NotifierCallback<C, T, A> notifier) {
	mNotifier = notifier;
	}

	/**
	* Notify all callbacks.
	*
	* @param sender The originator. This is an opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg2 An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	*/
	public synchronized void notifyCallbacks(T sender, int arg, A arg2) {
	mNotificationLevel++;
	notifyRecurseLocked(sender, arg, arg2);
	mNotificationLevel--;
	if (mNotificationLevel == 0) {
	if (mRemainderRemoved != null) {
	for (int i = mRemainderRemoved.length - 1; i >= 0; i--) {
	final long removedBits = mRemainderRemoved[i];
	if (removedBits != 0) {
	removeRemovedCallbacks((i + 1) * Long.SIZE, removedBits);
	mRemainderRemoved[i] = 0;
	}
	}
	}
	if (mFirst64Removed != 0) {
	removeRemovedCallbacks(0, mFirst64Removed);
	mFirst64Removed = 0;
	}
	}
	}

	/**
	* Notify up to the first Long.SIZE callbacks that don't have a bit set in <code>removed</code>.
	*
	* @param sender The originator. This is an opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg2 An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	*/
	private void notifyFirst64Locked(T sender, int arg, A arg2) {
	final int maxNotified = Math.min(Long.SIZE, mCallbacks.size());
	notifyCallbacksLocked(sender, arg, arg2, 0, maxNotified, mFirst64Removed);
	}

	/**
	* Notify all callbacks using a recursive algorithm to avoid allocating on the heap.
	* This part captures the callbacks beyond Long.SIZE that have no bits allocated for
	* removal before it recurses into {@link #notifyRemainderLocked(Object, int, A, int)}.
	* <p>
	* Recursion is used to avoid allocating temporary state on the heap. Each stack has one
	* long (64 callbacks) worth of information of which has been removed.
	*
	* @param sender The originator. This is an opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg2 An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	*/
	private void notifyRecurseLocked(T sender, int arg, A arg2) {
	final int callbackCount = mCallbacks.size();
	final int remainderIndex = mRemainderRemoved == null ? -1 : mRemainderRemoved.length - 1;

	// Now we've got all callbacks that have no mRemainderRemoved value, so notify the
	// others.
	notifyRemainderLocked(sender, arg, arg2, remainderIndex);

	// notifyRemainderLocked notifies all at maxIndex, so we'd normally start at maxIndex + 1
	// However, we must also keep track of those in mFirst64Removed, so we add 2 instead:
	final int startCallbackIndex = (remainderIndex + 2) * Long.SIZE;

	// The remaining have no bit set
	notifyCallbacksLocked(sender, arg, arg2, startCallbackIndex, callbackCount, 0);
	}

	/**
	* Notify callbacks that have mRemainderRemoved bits set for remainderIndex. If
	* remainderIndex is -1, the first 64 will be notified instead.
	*
	* @param sender The originator. This is an opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg2 An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param remainderIndex The index into mRemainderRemoved that should be notified.
	*/
	private void notifyRemainderLocked(T sender, int arg, A arg2, int remainderIndex) {
	if (remainderIndex < 0) {
	notifyFirst64Locked(sender, arg, arg2);
	} else {
	final long bits = mRemainderRemoved[remainderIndex];
	final int startIndex = (remainderIndex + 1) * Long.SIZE;
	final int endIndex = Math.min(mCallbacks.size(), startIndex + Long.SIZE);
	notifyRemainderLocked(sender, arg, arg2, remainderIndex - 1);
	notifyCallbacksLocked(sender, arg, arg2, startIndex, endIndex, bits);
	}
	}

	/**
	* Notify callbacks from startIndex to endIndex, using bits as the bit status
	* for whether they have been removed or not. bits should be from mRemainderRemoved or
	* mFirst64Removed. bits set to 0 indicates that all callbacks from startIndex to
	* endIndex should be notified.
	*
	* @param sender The originator. This is an opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param arg2 An opaque parameter passed to
	* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
	* @param startIndex The index into the mCallbacks to start notifying.
	* @param endIndex One past the last index into mCallbacks to notify.
	* @param bits A bit field indicating which callbacks have been removed and shouldn't
	* be notified.
	*/
	private void notifyCallbacksLocked(T sender, int arg, A arg2, final int startIndex,
	final int endIndex, final long bits) {
	long bitMask = 1;
	for (int i = startIndex; i < endIndex; i++) {
	if ((bits & bitMask) == 0) {
	mNotifier.onNotifyCallback(mCallbacks.get(i), sender, arg, arg2);
	}
	bitMask <<= 1;
	}
	}

	/**
	* Add a callback to be notified. If the callback is already in the list, another won't
	* be added. This does not affect current notifications.
	* @param callback The callback to add.
	*/
	public synchronized void add(C callback) {
	int index = mCallbacks.lastIndexOf(callback);
	if (index < 0 \|\| isRemovedLocked(index)) {
	mCallbacks.add(callback);
	}
	}

	/**
	* Returns true if the callback at index has been marked for removal.
	*
	* @param index The index into mCallbacks to check.
	* @return true if the callback at index has been marked for removal.
	*/
	private boolean isRemovedLocked(int index) {
	if (index < Long.SIZE) {
	// It is in the first 64 callbacks, just check the bit.
	final long bitMask = 1L << index;
	return (mFirst64Removed & bitMask) != 0;
	} else if (mRemainderRemoved == null) {
	// It is after the first 64 callbacks, but nothing else was marked for removal.
	return false;
	} else {
	final int maskIndex = (index / Long.SIZE) - 1;
	if (maskIndex >= mRemainderRemoved.length) {
	// There are some items in mRemainderRemoved, but nothing at the given index.
	return false;
	} else {
	// There is something marked for removal, so we have to check the bit.
	final long bits = mRemainderRemoved[maskIndex];
	final long bitMask = 1L << (index % Long.SIZE);
	return (bits & bitMask) != 0;
	}
	}
	}

	/**
	* Removes callbacks from startIndex to startIndex + Long.SIZE, based
	* on the bits set in removed.
	* @param startIndex The index into the mCallbacks to start removing callbacks.
	* @param removed The bits indicating removal, where each bit is set for one callback
	* to be removed.
	*/
	private void removeRemovedCallbacks(int startIndex, long removed) {
	// The naive approach should be fine. There may be a better bit-twiddling approach.
	final int endIndex = startIndex + Long.SIZE;

	long bitMask = 1L << (Long.SIZE - 1);
	for (int i = endIndex - 1; i >= startIndex; i--) {
	if ((removed & bitMask) != 0) {
	mCallbacks.remove(i);
	}
	bitMask >>>= 1;
	}
	}

	/**
	* Remove a callback. This callback won't be notified after this call completes.
	* @param callback The callback to remove.
	*/
	public synchronized void remove(C callback) {
	if (mNotificationLevel == 0) {
	mCallbacks.remove(callback);
	} else {
	int index = mCallbacks.lastIndexOf(callback);
	if (index >= 0) {
	setRemovalBitLocked(index);
	}
	}
	}

	private void setRemovalBitLocked(int index) {
	if (index < Long.SIZE) {
	// It is in the first 64 callbacks, just check the bit.
	final long bitMask = 1L << index;
	mFirst64Removed \|= bitMask;
	} else {
	final int remainderIndex = (index / Long.SIZE) - 1;
	if (mRemainderRemoved == null) {
	mRemainderRemoved = new long[mCallbacks.size() / Long.SIZE];
	} else if (mRemainderRemoved.length < remainderIndex) {
	// need to make it bigger
	long[] newRemainders = new long[mCallbacks.size() / Long.SIZE];
	System.arraycopy(mRemainderRemoved, 0, newRemainders, 0, mRemainderRemoved.length);
	mRemainderRemoved = newRemainders;
	}
	final long bitMask = 1L << (index % Long.SIZE);
	mRemainderRemoved[remainderIndex] \|= bitMask;
	}
	}

	/**
	* Makes a copy of the registered callbacks and returns it.
	*
	* @return a copy of the registered callbacks.
	*/
	public synchronized ArrayList<C> copyListeners() {
	ArrayList<C> callbacks = new ArrayList<C>(mCallbacks.size());
	int numListeners = mCallbacks.size();
	for (int i = 0; i < numListeners; i++) {
	if (!isRemovedLocked(i)) {
	callbacks.add(mCallbacks.get(i));
	}
	}
	return callbacks;
	}

	/**
	* Returns true if there are no registered callbacks or false otherwise.
	*
	* @return true if there are no registered callbacks or false otherwise.
	*/
	public synchronized boolean isEmpty() {
	if (mCallbacks.isEmpty()) {
	return true;
	} else if (mNotificationLevel == 0) {
	return false;
	} else {
	int numListeners = mCallbacks.size();
	for (int i = 0; i < numListeners; i++) {
	if (!isRemovedLocked(i)) {
	return false;
	}
	}
	return true;
	}
	}

	/**
	* Removes all callbacks from the list.
	*/
	public synchronized void clear() {
	if (mNotificationLevel == 0) {
	mCallbacks.clear();
	} else if (!mCallbacks.isEmpty()) {
	for (int i = mCallbacks.size() - 1; i >= 0; i--) {
	setRemovalBitLocked(i);
	}
	}
	}

	public synchronized CallbackRegistry<C, T, A> clone() {
	CallbackRegistry<C, T, A> clone = null;
	try {
	clone = (CallbackRegistry<C, T, A>) super.clone();
	clone.mFirst64Removed = 0;
	clone.mRemainderRemoved = null;
	clone.mNotificationLevel = 0;
	clone.mCallbacks = new ArrayList<C>();
	final int numListeners = mCallbacks.size();
	for (int i = 0; i < numListeners; i++) {
	if (!isRemovedLocked(i)) {
	clone.mCallbacks.add(mCallbacks.get(i));
	}
	}
	} catch (CloneNotSupportedException e) {
	e.printStackTrace();
	}
	return clone;
	}

	/**
	* Class used to notify events from CallbackRegistry.
	*
	* @param <C> The callback type.
	* @param <T> The notification sender type. Typically this is the containing class.
	* @param <A> An opaque argument to pass to the notifier
	*/
	public abstract static class NotifierCallback<C, T, A> {
	/**
	* Used to notify the callback.
	*
	* @param callback The callback to notify.
	* @param sender The opaque sender object.
	* @param arg The opaque notification parameter.
	* @param arg2 An opaque argument passed in
	* {@link CallbackRegistry#notifyCallbacks}
	* @see CallbackRegistry#CallbackRegistry(CallbackRegistry.NotifierCallback)
	*/
	public abstract void onNotifyCallback(C callback, T sender, int arg, A arg2);
	}
	}