| /******************************************************************************* |
| * Copyright (c) 2000, 2008 IBM Corporation and others. |
| * |
| * This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License 2.0 |
| * which accompanies this distribution, and is available at |
| * https://www.eclipse.org/legal/epl-2.0/ |
| * |
| * SPDX-License-Identifier: EPL-2.0 |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| *******************************************************************************/ |
| package org.eclipse.core.internal.events; |
| |
| import org.eclipse.core.resources.IResourceChangeListener; |
| import org.eclipse.core.runtime.Assert; |
| |
| /** |
| * This class is used to maintain a list of listeners. It is a fairly lightweight object, |
| * occupying minimal space when no listeners are registered. |
| * <p> |
| * Note that the <code>add</code> method checks for and eliminates |
| * duplicates based on identity (not equality). Likewise, the |
| * <code>remove</code> method compares based on identity. |
| * </p> |
| * <p> |
| * This implementation is thread safe. The listener list is copied every time |
| * it is modified, so readers do not need to copy or synchronize. This optimizes |
| * for frequent reads and infrequent writes, and assumes that readers can |
| * be trusted not to modify the returned array. |
| */ |
| public class ResourceChangeListenerList { |
| |
| static class ListenerEntry { |
| int eventMask; |
| IResourceChangeListener listener; |
| |
| ListenerEntry(IResourceChangeListener listener, int eventMask) { |
| this.listener = listener; |
| this.eventMask = eventMask; |
| } |
| } |
| |
| /** |
| * The empty array singleton instance. |
| */ |
| private static final ListenerEntry[] EMPTY_ARRAY = new ListenerEntry[0]; |
| |
| private int count1 = 0; |
| private int count2 = 0; |
| private int count4 = 0; |
| private int count8 = 0; |
| private int count16 = 0; |
| private int count32 = 0; |
| |
| /** |
| * The list of listeners. Maintains invariant: listeners != null. |
| */ |
| private volatile ListenerEntry[] listeners = EMPTY_ARRAY; |
| |
| /** |
| * Adds the given listener to this list. Has no effect if an identical listener |
| * is already registered. |
| * |
| * @param listener the listener |
| * @param mask event types |
| */ |
| public synchronized void add(IResourceChangeListener listener, int mask) { |
| Assert.isNotNull(listener); |
| if (mask == 0) { |
| remove(listener); |
| return; |
| } |
| ResourceChangeListenerList.ListenerEntry entry = new ResourceChangeListenerList.ListenerEntry(listener, mask); |
| final int oldSize = listeners.length; |
| // check for duplicates using identity |
| for (int i = 0; i < oldSize; ++i) { |
| if (listeners[i].listener == listener) { |
| removing(listeners[i].eventMask); |
| adding(mask); |
| listeners[i] = entry; |
| return; |
| } |
| } |
| adding(mask); |
| // Thread safety: copy on write to protect concurrent readers. |
| ListenerEntry[] newListeners = new ListenerEntry[oldSize + 1]; |
| System.arraycopy(listeners, 0, newListeners, 0, oldSize); |
| newListeners[oldSize] = entry; |
| //atomic assignment |
| this.listeners = newListeners; |
| } |
| |
| private void adding(int mask) { |
| if ((mask & 1) != 0) |
| count1++; |
| if ((mask & 2) != 0) |
| count2++; |
| if ((mask & 4) != 0) |
| count4++; |
| if ((mask & 8) != 0) |
| count8++; |
| if ((mask & 16) != 0) |
| count16++; |
| if ((mask & 32) != 0) |
| count32++; |
| } |
| |
| /** |
| * Returns an array containing all the registered listeners. |
| * The resulting array is unaffected by subsequent adds or removes. |
| * If there are no listeners registered, the result is an empty array |
| * singleton instance (no garbage is created). |
| * Use this method when notifying listeners, so that any modifications |
| * to the listener list during the notification will have no effect on the |
| * notification itself. |
| * <p> |
| * Note: Clients must not modify the returned list |
| * @return the list of registered listeners that must not be modified |
| */ |
| public ListenerEntry[] getListeners() { |
| return listeners; |
| } |
| |
| public boolean hasListenerFor(int event) { |
| if (event == 1) |
| return count1 > 0; |
| if (event == 2) |
| return count2 > 0; |
| if (event == 4) |
| return count4 > 0; |
| if (event == 8) |
| return count8 > 0; |
| if (event == 16) |
| return count16 > 0; |
| if (event == 32) |
| return count32 > 0; |
| return false; |
| } |
| |
| /** |
| * Removes the given listener from this list. Has no effect if an identical |
| * listener was not already registered. |
| * |
| * @param listener the listener to remove |
| */ |
| public synchronized void remove(IResourceChangeListener listener) { |
| Assert.isNotNull(listener); |
| final int oldSize = listeners.length; |
| for (int i = 0; i < oldSize; ++i) { |
| if (listeners[i].listener == listener) { |
| removing(listeners[i].eventMask); |
| if (oldSize == 1) { |
| listeners = EMPTY_ARRAY; |
| } else { |
| // Thread safety: create new array to avoid affecting concurrent readers |
| ListenerEntry[] newListeners = new ListenerEntry[oldSize - 1]; |
| System.arraycopy(listeners, 0, newListeners, 0, i); |
| System.arraycopy(listeners, i + 1, newListeners, i, oldSize - i - 1); |
| //atomic assignment to field |
| this.listeners = newListeners; |
| } |
| return; |
| } |
| } |
| } |
| |
| private void removing(int mask) { |
| if ((mask & 1) != 0) |
| count1--; |
| if ((mask & 2) != 0) |
| count2--; |
| if ((mask & 4) != 0) |
| count4--; |
| if ((mask & 8) != 0) |
| count8--; |
| if ((mask & 16) != 0) |
| count16--; |
| if ((mask & 32) != 0) |
| count32--; |
| } |
| } |