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/*******************************************************************************
* Copyright (c) 2003, 2004 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Common Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/cpl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.osgi.framework.eventmgr;
/**
* This class manages a list of listeners.
* Listeners may be added or removed as necessary.
*/
public class EventListeners {
/**
* The empty array singleton instance, returned by getListeners()
* when size == 0.
*/
private static final ListElement[] emptyArray = new ListElement[0];
/**
* The initial capacity of the list. Always >= 1.
*/
private final int initialCapacity;
/**
* The list of elements. Initially <code>null</code> but initialized
* to an array of size initialCapacity the first time an element is added.
* Maintains invariants:
* list != null IFF size != 0
* list[size] == null
* for all i < size: list[i] != null
* Access to this field must be protected by a synchronized region.
*/
private ListElement[] list = null;
/**
* The current number of elements.
* Maintains invariant: 0 <= size <= list.length.
* Access to this field must be protected by a synchronized region.
*/
private int size = 0;
/**
* If true and about to modify the list,
* then the list must be copied first.
* Access to this field must be protected by a synchronized region.
*/
private boolean copyOnWrite = false;
/**
* Creates a listener list with an initial capacity of 10.
*
*/
public EventListeners() {
this(10);
}
/**
* Creates a listener list with the given initial capacity.
*
* @param capacity The number of listeners which this list can initially
* accept without growing its internal representation; must be at
* least 1
* @throws IllegalArgumentException If capacity is less than 1.
*/
public EventListeners(int capacity) {
if (capacity < 1)
throw new IllegalArgumentException();
this.initialCapacity = capacity;
}
/**
* Add a listener to the list.
* If a listener object is already in the list, then it is replaced.
*
* @param listener This is the listener object to be added to the list.
* @param listenerObject This is an optional listener-specific object.
* This object will be passed to the EventDispatcher along with the listener
* when the listener is to be called. This may be null
* @throws IllegalArgumentException If listener is null.
*/
public synchronized void addListener(Object listener, Object listenerObject) {
if (listener == null) {
throw new IllegalArgumentException();
}
if (size == 0) {
list = new ListElement[initialCapacity];
}
else {
// copy array if necessary
if (copyOnWrite) {
copyList(size);
copyOnWrite = false;
}
// check for duplicates using identity
for (int i = 0; i < size; i++) {
if (list[i].primary == listener) {
list[i] = new ListElement(listener, listenerObject); /* use the most recent companion */
return;
}
}
// grow array if necessary
// This wont recopy list if copy on write occured above since that
// would have grown the list.
if (size == list.length) {
copyList(size);
}
}
list[size] = new ListElement(listener, listenerObject);
size++;
}
/**
* Remove a listener from the list.
*
* @param listener This is the listener object to be removed from the list.
* @throws IllegalArgumentException If listener is null.
*/
public synchronized void removeListener(Object listener) {
if (listener == null) {
throw new IllegalArgumentException();
}
for (int i = 0; i < size; i++) {
if (list[i].primary == listener) {
size--;
if (size == 0) {
list = null; /* invariant: list must be null iff size is zero */
return;
}
if (copyOnWrite) {
copyList(i);
copyOnWrite = false;
}
else {
System.arraycopy(list, i + 1, list, i, size - i);
list[size] = null; /* invariant: end of list must be null */
}
return;
}
}
}
/**
* Remove all listeners from the list.
*/
public synchronized void removeAllListeners() {
/* invariant: list must be null iff size is zero */
list = null;
size = 0;
}
/**
* Return the list of (listener, listenerObject) pairs.
* Package private method.
* The array may be longer than the number of pairs in the array.
* The end of the pairs is signalled by a null element or
* end of array.
* This array must not be modified by anyone and should not be
* exposed outside of this package.
* To reduce memory allocations, the internal array is shared
* with the rest of this package. However an array returned by this method
* must not be modified in anyway.
*
* @return A shared array that must not be modified by anyone.
*/
synchronized ListElement[] getListeners() {
if (size == 0) {
return emptyArray;
}
copyOnWrite = true;
return list;
}
/**
* Copy the array.
* @param i Index of element to remove from array. Must be equal to size to
* copy entire array.
* @throws IndexOutOfBoundsException If i < 0 or i > size.
*/
private void copyList(int i) {
if (i > size) {
throw new IndexOutOfBoundsException();
}
int capacity = (size * 3) / 2 + 1;
if (capacity < initialCapacity) {
capacity = initialCapacity;
}
ListElement[] newList = new ListElement[capacity];
System.arraycopy(list, 0, newList, 0, i);
if (i < size) {
System.arraycopy(list, i + 1, newList, i, size - i);
}
list = newList;
}
}
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