397 lines
16 KiB
Java
397 lines
16 KiB
Java
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.internal.util;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* Tracks callbacks for the event. This class supports reentrant modification
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* of the callbacks during notification without adversely disrupting notifications.
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* A common pattern for callbacks is to receive a notification and then remove
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* themselves. This class handles this behavior with constant memory under
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* most circumstances.
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*
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* <p>A subclass of {@link CallbackRegistry.NotifierCallback} must be passed to
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* the constructor to define how notifications should be called. That implementation
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* does the actual notification on the listener.</p>
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*
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* <p>This class supports only callbacks with at most two parameters.
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* Typically, these are the notification originator and a parameter, but these may
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* be used as required. If more than two parameters are required or primitive types
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* must be used, <code>A</code> should be some kind of containing structure that
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* the subclass may reuse between notifications.</p>
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*
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* @param <C> The callback type.
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* @param <T> The notification sender type. Typically this is the containing class.
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* @param <A> Opaque argument used to pass additional data beyond an int.
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*/
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@android.ravenwood.annotation.RavenwoodKeepWholeClass
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public class CallbackRegistry<C, T, A> implements Cloneable {
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private static final String TAG = "CallbackRegistry";
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/** An ordered collection of listeners waiting to be notified. */
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private List<C> mCallbacks = new ArrayList<C>();
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/**
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* A bit flag for the first 64 listeners that are removed during notification.
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* The lowest significant bit corresponds to the 0th index into mCallbacks.
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* For a small number of callbacks, no additional array of objects needs to
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* be allocated.
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*/
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private long mFirst64Removed = 0x0;
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/**
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* Bit flags for the remaining callbacks that are removed during notification.
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* When there are more than 64 callbacks and one is marked for removal, a dynamic
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* array of bits are allocated for the callbacks.
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*/
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private long[] mRemainderRemoved;
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/**
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* The reentrancy level of the notification. When we notify a callback, it may cause
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* further notifications. The reentrancy level must be tracked to let us clean up
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* the callback state when all notifications have been processed.
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*/
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private int mNotificationLevel;
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/** The notification mechanism for notifying an event. */
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private final NotifierCallback<C, T, A> mNotifier;
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/**
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* Creates an EventRegistry that notifies the event with notifier.
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* @param notifier The class to use to notify events.
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*/
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public CallbackRegistry(NotifierCallback<C, T, A> notifier) {
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mNotifier = notifier;
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}
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/**
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* Notify all callbacks.
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*
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* @param sender The originator. This is an opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg2 An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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*/
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public synchronized void notifyCallbacks(T sender, int arg, A arg2) {
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mNotificationLevel++;
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notifyRecurseLocked(sender, arg, arg2);
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mNotificationLevel--;
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if (mNotificationLevel == 0) {
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if (mRemainderRemoved != null) {
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for (int i = mRemainderRemoved.length - 1; i >= 0; i--) {
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final long removedBits = mRemainderRemoved[i];
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if (removedBits != 0) {
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removeRemovedCallbacks((i + 1) * Long.SIZE, removedBits);
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mRemainderRemoved[i] = 0;
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}
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}
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}
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if (mFirst64Removed != 0) {
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removeRemovedCallbacks(0, mFirst64Removed);
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mFirst64Removed = 0;
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}
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}
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}
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/**
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* Notify up to the first Long.SIZE callbacks that don't have a bit set in <code>removed</code>.
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*
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* @param sender The originator. This is an opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg2 An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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*/
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private void notifyFirst64Locked(T sender, int arg, A arg2) {
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final int maxNotified = Math.min(Long.SIZE, mCallbacks.size());
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notifyCallbacksLocked(sender, arg, arg2, 0, maxNotified, mFirst64Removed);
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}
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/**
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* Notify all callbacks using a recursive algorithm to avoid allocating on the heap.
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* This part captures the callbacks beyond Long.SIZE that have no bits allocated for
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* removal before it recurses into {@link #notifyRemainderLocked(Object, int, A, int)}.
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* <p>
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* Recursion is used to avoid allocating temporary state on the heap. Each stack has one
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* long (64 callbacks) worth of information of which has been removed.
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*
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* @param sender The originator. This is an opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg2 An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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*/
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private void notifyRecurseLocked(T sender, int arg, A arg2) {
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final int callbackCount = mCallbacks.size();
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final int remainderIndex = mRemainderRemoved == null ? -1 : mRemainderRemoved.length - 1;
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// Now we've got all callbacks that have no mRemainderRemoved value, so notify the
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// others.
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notifyRemainderLocked(sender, arg, arg2, remainderIndex);
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// notifyRemainderLocked notifies all at maxIndex, so we'd normally start at maxIndex + 1
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// However, we must also keep track of those in mFirst64Removed, so we add 2 instead:
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final int startCallbackIndex = (remainderIndex + 2) * Long.SIZE;
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// The remaining have no bit set
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notifyCallbacksLocked(sender, arg, arg2, startCallbackIndex, callbackCount, 0);
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}
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/**
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* Notify callbacks that have mRemainderRemoved bits set for remainderIndex. If
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* remainderIndex is -1, the first 64 will be notified instead.
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*
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* @param sender The originator. This is an opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg2 An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param remainderIndex The index into mRemainderRemoved that should be notified.
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*/
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private void notifyRemainderLocked(T sender, int arg, A arg2, int remainderIndex) {
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if (remainderIndex < 0) {
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notifyFirst64Locked(sender, arg, arg2);
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} else {
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final long bits = mRemainderRemoved[remainderIndex];
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final int startIndex = (remainderIndex + 1) * Long.SIZE;
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final int endIndex = Math.min(mCallbacks.size(), startIndex + Long.SIZE);
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notifyRemainderLocked(sender, arg, arg2, remainderIndex - 1);
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notifyCallbacksLocked(sender, arg, arg2, startIndex, endIndex, bits);
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}
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}
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/**
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* Notify callbacks from startIndex to endIndex, using bits as the bit status
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* for whether they have been removed or not. bits should be from mRemainderRemoved or
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* mFirst64Removed. bits set to 0 indicates that all callbacks from startIndex to
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* endIndex should be notified.
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*
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* @param sender The originator. This is an opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param arg2 An opaque parameter passed to
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* {@link CallbackRegistry.NotifierCallback#onNotifyCallback(Object, Object, int, A)}
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* @param startIndex The index into the mCallbacks to start notifying.
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* @param endIndex One past the last index into mCallbacks to notify.
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* @param bits A bit field indicating which callbacks have been removed and shouldn't
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* be notified.
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*/
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private void notifyCallbacksLocked(T sender, int arg, A arg2, final int startIndex,
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final int endIndex, final long bits) {
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long bitMask = 1;
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for (int i = startIndex; i < endIndex; i++) {
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if ((bits & bitMask) == 0) {
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mNotifier.onNotifyCallback(mCallbacks.get(i), sender, arg, arg2);
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}
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bitMask <<= 1;
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}
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}
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/**
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* Add a callback to be notified. If the callback is already in the list, another won't
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* be added. This does not affect current notifications.
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* @param callback The callback to add.
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*/
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public synchronized void add(C callback) {
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int index = mCallbacks.lastIndexOf(callback);
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if (index < 0 || isRemovedLocked(index)) {
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mCallbacks.add(callback);
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}
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}
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/**
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* Returns true if the callback at index has been marked for removal.
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*
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* @param index The index into mCallbacks to check.
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* @return true if the callback at index has been marked for removal.
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*/
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private boolean isRemovedLocked(int index) {
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if (index < Long.SIZE) {
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// It is in the first 64 callbacks, just check the bit.
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final long bitMask = 1L << index;
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return (mFirst64Removed & bitMask) != 0;
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} else if (mRemainderRemoved == null) {
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// It is after the first 64 callbacks, but nothing else was marked for removal.
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return false;
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} else {
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final int maskIndex = (index / Long.SIZE) - 1;
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if (maskIndex >= mRemainderRemoved.length) {
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// There are some items in mRemainderRemoved, but nothing at the given index.
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return false;
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} else {
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// There is something marked for removal, so we have to check the bit.
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final long bits = mRemainderRemoved[maskIndex];
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final long bitMask = 1L << (index % Long.SIZE);
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return (bits & bitMask) != 0;
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}
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}
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}
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/**
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* Removes callbacks from startIndex to startIndex + Long.SIZE, based
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* on the bits set in removed.
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* @param startIndex The index into the mCallbacks to start removing callbacks.
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* @param removed The bits indicating removal, where each bit is set for one callback
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* to be removed.
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*/
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private void removeRemovedCallbacks(int startIndex, long removed) {
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// The naive approach should be fine. There may be a better bit-twiddling approach.
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final int endIndex = startIndex + Long.SIZE;
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long bitMask = 1L << (Long.SIZE - 1);
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for (int i = endIndex - 1; i >= startIndex; i--) {
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if ((removed & bitMask) != 0) {
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mCallbacks.remove(i);
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}
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bitMask >>>= 1;
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}
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}
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/**
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* Remove a callback. This callback won't be notified after this call completes.
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* @param callback The callback to remove.
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*/
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public synchronized void remove(C callback) {
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if (mNotificationLevel == 0) {
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mCallbacks.remove(callback);
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} else {
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int index = mCallbacks.lastIndexOf(callback);
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if (index >= 0) {
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setRemovalBitLocked(index);
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}
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}
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}
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private void setRemovalBitLocked(int index) {
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if (index < Long.SIZE) {
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// It is in the first 64 callbacks, just check the bit.
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final long bitMask = 1L << index;
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mFirst64Removed |= bitMask;
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} else {
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final int remainderIndex = (index / Long.SIZE) - 1;
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if (mRemainderRemoved == null) {
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mRemainderRemoved = new long[mCallbacks.size() / Long.SIZE];
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} else if (mRemainderRemoved.length < remainderIndex) {
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// need to make it bigger
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long[] newRemainders = new long[mCallbacks.size() / Long.SIZE];
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System.arraycopy(mRemainderRemoved, 0, newRemainders, 0, mRemainderRemoved.length);
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mRemainderRemoved = newRemainders;
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}
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final long bitMask = 1L << (index % Long.SIZE);
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mRemainderRemoved[remainderIndex] |= bitMask;
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}
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}
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/**
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* Makes a copy of the registered callbacks and returns it.
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*
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* @return a copy of the registered callbacks.
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*/
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public synchronized ArrayList<C> copyListeners() {
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ArrayList<C> callbacks = new ArrayList<C>(mCallbacks.size());
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int numListeners = mCallbacks.size();
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for (int i = 0; i < numListeners; i++) {
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if (!isRemovedLocked(i)) {
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callbacks.add(mCallbacks.get(i));
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}
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}
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return callbacks;
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}
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/**
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* Returns true if there are no registered callbacks or false otherwise.
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*
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* @return true if there are no registered callbacks or false otherwise.
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*/
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public synchronized boolean isEmpty() {
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if (mCallbacks.isEmpty()) {
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return true;
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} else if (mNotificationLevel == 0) {
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return false;
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} else {
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int numListeners = mCallbacks.size();
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for (int i = 0; i < numListeners; i++) {
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if (!isRemovedLocked(i)) {
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return false;
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}
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}
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return true;
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}
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}
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/**
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* Removes all callbacks from the list.
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*/
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public synchronized void clear() {
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if (mNotificationLevel == 0) {
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mCallbacks.clear();
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} else if (!mCallbacks.isEmpty()) {
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for (int i = mCallbacks.size() - 1; i >= 0; i--) {
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setRemovalBitLocked(i);
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}
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}
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}
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public synchronized CallbackRegistry<C, T, A> clone() {
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CallbackRegistry<C, T, A> clone = null;
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try {
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clone = (CallbackRegistry<C, T, A>) super.clone();
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clone.mFirst64Removed = 0;
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clone.mRemainderRemoved = null;
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clone.mNotificationLevel = 0;
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clone.mCallbacks = new ArrayList<C>();
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final int numListeners = mCallbacks.size();
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for (int i = 0; i < numListeners; i++) {
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if (!isRemovedLocked(i)) {
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clone.mCallbacks.add(mCallbacks.get(i));
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}
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}
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} catch (CloneNotSupportedException e) {
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e.printStackTrace();
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}
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return clone;
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}
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/**
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* Class used to notify events from CallbackRegistry.
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*
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* @param <C> The callback type.
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* @param <T> The notification sender type. Typically this is the containing class.
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* @param <A> An opaque argument to pass to the notifier
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*/
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public abstract static class NotifierCallback<C, T, A> {
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/**
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* Used to notify the callback.
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*
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* @param callback The callback to notify.
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* @param sender The opaque sender object.
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* @param arg The opaque notification parameter.
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* @param arg2 An opaque argument passed in
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* {@link CallbackRegistry#notifyCallbacks}
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* @see CallbackRegistry#CallbackRegistry(CallbackRegistry.NotifierCallback)
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*/
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public abstract void onNotifyCallback(C callback, T sender, int arg, A arg2);
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}
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}
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