/*
* 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.
*/
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);
}
}