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comparison org.eclipse.equinox.common/src/org/eclipse/core/runtime/ListenerList.d @ 12:bc29606a740c

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Added dwt-addons in original directory structure of eclipse.org
author Frank Benoit <benoit@tionex.de>
date Sat, 14 Mar 2009 18:23:29 +0100
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11:43904fec5dca 12:bc29606a740c
1 /*******************************************************************************
2 * Copyright (c) 2004, 2006 IBM Corporation and others.
3 * All rights reserved. This program and the accompanying materials
4 * are made available under the terms of the Eclipse Public License v1.0
5 * which accompanies this distribution, and is available at
6 * http://www.eclipse.org/legal/epl-v10.html
7 *
8 * Contributors:
9 * IBM Corporation - initial API and implementation
10 * Port to the D programming language:
11 * Frank Benoit <benoit@tionex.de>
12 *******************************************************************************/
13 module org.eclipse.core.runtime.ListenerList;
14
15 import java.lang.all;
16
17 /**
18 * This class is a thread safe list that is designed for storing lists of listeners.
19 * The implementation is optimized for minimal memory footprint, frequent reads
20 * and infrequent writes. Modification of the list is synchronized and relatively
21 * expensive, while accessing the listeners is very fast. Readers are given access
22 * to the underlying array data structure for reading, with the trust that they will
23 * not modify the underlying array.
24 * <p>
25 * <a name="same">A listener list handles the <i>same</i> listener being added
26 * multiple times, and tolerates removal of listeners that are the same as other
27 * listeners in the list. For this purpose, listeners can be compared with each other
28 * using either equality or identity, as specified in the list constructor.
29 * </p>
30 * <p>
31 * Use the <code>getListeners</code> method when notifying listeners. The recommended
32 * code sequence for notifying all registered listeners of say,
33 * <code>FooListener.eventHappened</code>, is:
34 *
35 * <pre>
36 * Object[] listeners = myListenerList.getListeners();
37 * for (int i = 0; i &lt; listeners.length; ++i) {
38 * ((FooListener) listeners[i]).eventHappened(event);
39 * }
40 * </pre>
41 *
42 * </p><p>
43 * This class can be used without OSGi running.
44 * </p>
45 * @since org.eclipse.equinox.common 3.2
46 */
47 public class ListenerList {
48
49 /**
50 * The empty array singleton instance.
51 */
52 private static const Object[] EmptyArray;
53
54 /**
55 * Mode constant (value 0) indicating that listeners should be considered
56 * the <a href="#same">same</a> if they are equal.
57 */
58 public static const int EQUALITY = 0;
59
60 /**
61 * Mode constant (value 1) indicating that listeners should be considered
62 * the <a href="#same">same</a> if they are identical.
63 */
64 public static const int IDENTITY = 1;
65
66 /**
67 * Indicates the comparison mode used to determine if two
68 * listeners are equivalent
69 */
70 private final bool identity;
71
72 /**
73 * The list of listeners. Initially empty but initialized
74 * to an array of size capacity the first time a listener is added.
75 * Maintains invariant: listeners !is null
76 */
77 private Object[] listeners;
78
79 /**
80 * Creates a listener list in which listeners are compared using equality.
81 */
82 public this() {
83 this(EQUALITY);
84 }
85
86 /**
87 * Creates a listener list using the provided comparison mode.
88 *
89 * @param mode The mode used to determine if listeners are the <a href="#same">same</a>.
90 */
91 public this(int mode) {
92 if (mode !is EQUALITY && mode !is IDENTITY)
93 throw new IllegalArgumentException( null );
94 this.identity = mode is IDENTITY;
95 }
96
97 /**
98 * Adds a listener to this list. This method has no effect if the <a href="#same">same</a>
99 * listener is already registered.
100 *
101 * @param listener the non-<code>null</code> listener to add
102 */
103 public synchronized void add(Object listener) {
104 // This method is synchronized to protect against multiple threads adding
105 // or removing listeners concurrently. This does not block concurrent readers.
106 if (listener is null)
107 throw new IllegalArgumentException( null );
108 // check for duplicates
109 final int oldSize = listeners.length;
110 for (int i = 0; i < oldSize; ++i) {
111 Object listener2 = listeners[i];
112 if (identity ? listener is listener2 : listener.opEquals(listener2))
113 return;
114 }
115 // Thread safety: create new array to avoid affecting concurrent readers
116 Object[] newListeners = new Object[oldSize + 1];
117 System.arraycopy(listeners, 0, newListeners, 0, oldSize);
118 newListeners[oldSize] = listener;
119 //atomic assignment
120 this.listeners = newListeners;
121 }
122
123 /**
124 * Returns an array containing all the registered listeners.
125 * The resulting array is unaffected by subsequent adds or removes.
126 * If there are no listeners registered, the result is an empty array.
127 * Use this method when notifying listeners, so that any modifications
128 * to the listener list during the notification will have no effect on
129 * the notification itself.
130 * <p>
131 * Note: Callers of this method <b>must not</b> modify the returned array.
132 *
133 * @return the list of registered listeners
134 */
135 public Object[] getListeners() {
136 return listeners;
137 }
138
139 /**
140 * Returns whether this listener list is empty.
141 *
142 * @return <code>true</code> if there are no registered listeners, and
143 * <code>false</code> otherwise
144 */
145 public bool isEmpty() {
146 return listeners.length is 0;
147 }
148
149 /**
150 * Removes a listener from this list. Has no effect if the <a href="#same">same</a>
151 * listener was not already registered.
152 *
153 * @param listener the non-<code>null</code> listener to remove
154 */
155 public synchronized void remove(Object listener) {
156 // This method is synchronized to protect against multiple threads adding
157 // or removing listeners concurrently. This does not block concurrent readers.
158 if (listener is null)
159 throw new IllegalArgumentException( null );
160 int oldSize = listeners.length;
161 for (int i = 0; i < oldSize; ++i) {
162 Object listener2 = listeners[i];
163 if (identity ? listener is listener2 : listener.opEquals(listener2)) {
164 if (oldSize is 1) {
165 listeners = EmptyArray;
166 } else {
167 // Thread safety: create new array to avoid affecting concurrent readers
168 Object[] newListeners = new Object[oldSize - 1];
169 System.arraycopy(listeners, 0, newListeners, 0, i);
170 System.arraycopy(listeners, i + 1, newListeners, i, oldSize - i - 1);
171 //atomic assignment to field
172 this.listeners = newListeners;
173 }
174 return;
175 }
176 }
177 }
178
179 /**
180 * Returns the number of registered listeners.
181 *
182 * @return the number of registered listeners
183 */
184 public int size() {
185 return listeners.length;
186 }
187
188 /**
189 * Removes all listeners from this list.
190 */
191 public synchronized void clear() {
192 listeners = EmptyArray;
193 }
194 }