[10824] | 1 | // License: GPL. For details, see LICENSE file.
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| 2 | package org.openstreetmap.josm.tools;
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| 3 |
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| 4 | import java.lang.ref.WeakReference;
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| 5 | import java.text.MessageFormat;
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| 6 | import java.util.HashMap;
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| 7 | import java.util.Iterator;
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| 8 | import java.util.Objects;
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| 9 | import java.util.concurrent.CopyOnWriteArrayList;
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| 10 | import java.util.stream.Stream;
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| 11 |
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| 12 | /**
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| 13 | * This is a list of listeners. It does error checking and allows you to fire all listeners.
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| 14 | *
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| 15 | * @author Michael Zangl
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| 16 | * @param <T> The type of listener contained in this list.
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| 17 | * @since 10824
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| 18 | */
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| 19 | public class ListenerList<T> {
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| 20 | /**
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| 21 | * This is a function that can be invoked for every listener.
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| 22 | * @param <T> the listener type.
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| 23 | */
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| 24 | @FunctionalInterface
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| 25 | public interface EventFirerer<T> {
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| 26 | /**
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| 27 | * Should fire the event for the given listener.
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| 28 | * @param listener The listener to fire the event for.
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| 29 | */
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| 30 | void fire(T listener);
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| 31 | }
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| 32 |
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| 33 | private static final class WeakListener<T> {
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| 34 |
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[10939] | 35 | private final WeakReference<T> listener;
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[10824] | 36 |
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| 37 | WeakListener(T listener) {
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| 38 | this.listener = new WeakReference<>(listener);
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| 39 | }
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| 40 |
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| 41 | @Override
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| 42 | public boolean equals(Object obj) {
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| 43 | if (obj != null && obj.getClass() == WeakListener.class) {
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| 44 | return Objects.equals(listener.get(), ((WeakListener<?>) obj).listener.get());
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| 45 | } else {
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| 46 | return false;
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| 47 | }
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| 48 | }
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| 49 |
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| 50 | @Override
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| 51 | public int hashCode() {
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| 52 | T l = listener.get();
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| 53 | if (l == null) {
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| 54 | return 0;
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| 55 | } else {
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| 56 | return l.hashCode();
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| 57 | }
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| 58 | }
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| 59 |
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| 60 | @Override
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| 61 | public String toString() {
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[10939] | 62 | return "WeakListener [listener=" + listener + ']';
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[10824] | 63 | }
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| 64 | }
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| 65 |
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| 66 | private final CopyOnWriteArrayList<T> listeners = new CopyOnWriteArrayList<>();
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| 67 | private final CopyOnWriteArrayList<WeakListener<T>> weakListeners = new CopyOnWriteArrayList<>();
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| 68 |
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| 69 | protected ListenerList() {
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| 70 | // hide
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| 71 | }
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| 72 |
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| 73 | /**
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| 74 | * Adds a listener. The listener will not prevent the object from being garbage collected.
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| 75 | *
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| 76 | * This should be used with care. It is better to add good cleanup code.
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| 77 | * @param listener The listener.
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| 78 | */
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| 79 | public synchronized void addWeakListener(T listener) {
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[11224] | 80 | if (ensureNotInList(listener)) {
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| 81 | // clean the weak listeners, just to be sure...
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| 82 | while (weakListeners.remove(new WeakListener<T>(null))) {
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| 83 | // continue
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| 84 | }
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| 85 | weakListeners.add(new WeakListener<>(listener));
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[10824] | 86 | }
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| 87 | }
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| 88 |
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| 89 | /**
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| 90 | * Adds a listener.
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| 91 | * @param listener The listener to add.
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| 92 | */
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| 93 | public synchronized void addListener(T listener) {
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[11224] | 94 | if (ensureNotInList(listener)) {
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| 95 | listeners.add(listener);
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| 96 | }
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[10824] | 97 | }
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| 98 |
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[11224] | 99 | private boolean ensureNotInList(T listener) {
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[10824] | 100 | CheckParameterUtil.ensureParameterNotNull(listener, "listener");
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| 101 | if (containsListener(listener)) {
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| 102 | failAdd(listener);
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[11224] | 103 | return false;
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| 104 | } else {
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| 105 | return true;
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[10824] | 106 | }
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| 107 | }
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| 108 |
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| 109 | protected void failAdd(T listener) {
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| 110 | throw new IllegalArgumentException(
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[10936] | 111 | MessageFormat.format("Listener {0} (instance of {1}) was already registered.", listener,
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[10824] | 112 | listener.getClass().getName()));
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| 113 | }
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| 114 |
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| 115 | private boolean containsListener(T listener) {
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| 116 | return listeners.contains(listener) || weakListeners.contains(new WeakListener<>(listener));
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| 117 | }
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| 118 |
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| 119 | /**
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| 120 | * Removes a listener.
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| 121 | * @param listener The listener to remove.
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| 122 | * @throws IllegalArgumentException if the listener was not registered before
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| 123 | */
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| 124 | public synchronized void removeListener(T listener) {
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| 125 | if (!listeners.remove(listener) && !weakListeners.remove(new WeakListener<>(listener))) {
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| 126 | failRemove(listener);
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| 127 | }
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| 128 | }
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| 129 |
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| 130 | protected void failRemove(T listener) {
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| 131 | throw new IllegalArgumentException(
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| 132 | MessageFormat.format("Listener {0} (instance of {1}) was not registered before or already removed.",
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[10936] | 133 | listener, listener.getClass().getName()));
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[10824] | 134 | }
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| 135 |
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| 136 | /**
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| 137 | * Check if any listeners are registered.
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| 138 | * @return <code>true</code> if any are registered.
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| 139 | */
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| 140 | public boolean hasListeners() {
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| 141 | return !listeners.isEmpty();
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| 142 | }
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| 143 |
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| 144 | /**
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| 145 | * Fires an event to every listener.
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| 146 | * @param eventFirerer The firerer to invoke the event method of the listener.
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| 147 | */
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| 148 | public void fireEvent(EventFirerer<T> eventFirerer) {
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| 149 | for (T l : listeners) {
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| 150 | eventFirerer.fire(l);
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| 151 | }
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| 152 | for (Iterator<WeakListener<T>> iterator = weakListeners.iterator(); iterator.hasNext();) {
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| 153 | WeakListener<T> weakLink = iterator.next();
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| 154 | T l = weakLink.listener.get();
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[10894] | 155 | if (l != null) {
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| 156 | // cleanup during add() should be enough to not cause memory leaks
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| 157 | // therefore, we ignore null listeners.
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[10824] | 158 | eventFirerer.fire(l);
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| 159 | }
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| 160 | }
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| 161 | }
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| 162 |
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| 163 | /**
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| 164 | * This is a special {@link ListenerList} that traces calls to the add/remove methods. This may cause memory leaks.
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| 165 | * @author Michael Zangl
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| 166 | *
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| 167 | * @param <T> The type of listener contained in this list
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| 168 | */
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| 169 | public static class TracingListenerList<T> extends ListenerList<T> {
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[10939] | 170 | private final HashMap<T, StackTraceElement[]> listenersAdded = new HashMap<>();
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| 171 | private final HashMap<T, StackTraceElement[]> listenersRemoved = new HashMap<>();
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[10824] | 172 |
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| 173 | protected TracingListenerList() {
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| 174 | // hidden
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| 175 | }
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| 176 |
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| 177 | @Override
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| 178 | public synchronized void addListener(T listener) {
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| 179 | super.addListener(listener);
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| 180 | listenersRemoved.remove(listener);
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| 181 | listenersAdded.put(listener, Thread.currentThread().getStackTrace());
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| 182 | }
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| 183 |
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| 184 | @Override
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| 185 | public synchronized void addWeakListener(T listener) {
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| 186 | super.addWeakListener(listener);
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| 187 | listenersRemoved.remove(listener);
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| 188 | listenersAdded.put(listener, Thread.currentThread().getStackTrace());
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| 189 | }
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| 190 |
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| 191 | @Override
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| 192 | public synchronized void removeListener(T listener) {
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| 193 | super.removeListener(listener);
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| 194 | listenersAdded.remove(listener);
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| 195 | listenersRemoved.put(listener, Thread.currentThread().getStackTrace());
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| 196 | }
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| 197 |
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| 198 | @Override
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| 199 | protected void failAdd(T listener) {
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[12620] | 200 | Logging.trace("Previous addition of the listener");
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[10824] | 201 | dumpStack(listenersAdded.get(listener));
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| 202 | super.failAdd(listener);
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| 203 | }
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| 204 |
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| 205 | @Override
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| 206 | protected void failRemove(T listener) {
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[12620] | 207 | Logging.trace("Previous removal of the listener");
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[10824] | 208 | dumpStack(listenersRemoved.get(listener));
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| 209 | super.failRemove(listener);
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| 210 | }
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| 211 |
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[12798] | 212 | private static void dumpStack(StackTraceElement... stackTraceElements) {
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[10824] | 213 | if (stackTraceElements == null) {
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[12620] | 214 | Logging.trace(" - (no trace recorded)");
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[10824] | 215 | } else {
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| 216 | Stream.of(stackTraceElements).limit(20).forEach(
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[12620] | 217 | e -> Logging.trace(e.getClassName() + "." + e.getMethodName() + " line " + e.getLineNumber()));
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[10824] | 218 | }
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| 219 | }
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| 220 | }
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| 221 |
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[11224] | 222 | private static class UncheckedListenerList<T> extends ListenerList<T> {
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| 223 | @Override
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| 224 | protected void failAdd(T listener) {
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| 225 | Logging.warn("Listener was alreaady added: {0}", listener);
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| 226 | // ignore
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| 227 | }
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| 228 |
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| 229 | @Override
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| 230 | protected void failRemove(T listener) {
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| 231 | Logging.warn("Listener was removed twice or not added: {0}", listener);
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| 232 | // ignore
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| 233 | }
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| 234 | }
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| 235 |
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[10824] | 236 | /**
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| 237 | * Create a new listener list
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| 238 | * @param <T> The listener type the list should hold.
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| 239 | * @return A new list. A tracing list is created if trace is enabled.
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| 240 | */
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| 241 | public static <T> ListenerList<T> create() {
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[12620] | 242 | if (Logging.isTraceEnabled()) {
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[10824] | 243 | return new TracingListenerList<>();
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| 244 | } else {
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| 245 | return new ListenerList<>();
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| 246 | }
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| 247 | }
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[11224] | 248 |
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| 249 | /**
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[13203] | 250 | * Creates a new listener list that does not fail if listeners are added or removed twice.
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[11224] | 251 | * <p>
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| 252 | * Use of this list is discouraged. You should always use {@link #create()} in new implementations and check your listeners.
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| 253 | * @param <T> The listener type
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| 254 | * @return A new list.
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| 255 | * @since 11224
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| 256 | */
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| 257 | public static <T> ListenerList<T> createUnchecked() {
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| 258 | return new UncheckedListenerList<>();
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| 259 | }
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[10824] | 260 | }
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