/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.openjpa.lib.util.concurrent;
import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import org.apache.openjpa.lib.util.EventManager;
/**
* Base event manager that handles adding/removing listeners
* and firing events. Meant for high concurrency. This class is
* reentrant-safe; listeners can be added and removed by other listeners when
* they receive events. The changes will not be visible until the event fire
* that initiated the recursive sequence of calls completes, however.
*
* @author Abe White
*/
public abstract class AbstractConcurrentEventManager
implements EventManager, Serializable {
private static final Exception[] EMPTY_EXCEPTIONS = new Exception[0];
protected final Collection _listeners;
private boolean _failFast = false;
/**
* Default constructor.
*/
public AbstractConcurrentEventManager() {
_listeners = newListenerCollection();
}
/**
* Whether to fail after the first exception thrown by any listener.
*/
public boolean isFailFast() {
return _failFast;
}
/**
* Whether to fail after the first exception thrown by any listener.
*/
public void setFailFast(boolean failFast) {
_failFast = failFast;
}
/**
* Register an event listener.
*/
public void addListener(Object listener) {
if (listener != null)
_listeners.add(listener);
}
/**
* Remove an event listener.
*/
public boolean removeListener(Object listener) {
return _listeners.remove(listener);
}
/**
* Return whether the given instance is in the list of listeners.
*/
public boolean hasListener(Object listener) {
return _listeners.contains(listener);
}
/**
* Return true if there are any registered listeners.
*/
public boolean hasListeners() {
return !_listeners.isEmpty();
}
/**
* Return a read-only list of listeners.
*/
public Collection getListeners() {
return Collections.unmodifiableCollection(_listeners);
}
/**
* Fire the given event to all listeners.
*/
public Exception[] fireEvent(Object event) {
if (_listeners.isEmpty())
return EMPTY_EXCEPTIONS;
List exceptions = null;
for (Iterator itr = _listeners.iterator(); itr.hasNext();) {
try {
fireEvent(event, itr.next());
} catch (Exception e) {
if (_failFast)
return new Exception[] { e };
if (exceptions == null)
exceptions = new LinkedList();
exceptions.add(e);
}
}
if (exceptions == null)
return EMPTY_EXCEPTIONS;
return (Exception[]) exceptions.toArray
(new Exception[exceptions.size()]);
}
/**
* Implement this method to fire the given event to the given listener.
*/
protected abstract void fireEvent(Object event, Object listener)
throws Exception;
/**
* Return a new concurrent container for listeners. Uses a
* {@link CopyOnWriteArrayList} by default.
*/
protected Collection newListenerCollection() {
return new CopyOnWriteArrayList();
}
}