/***********************************************************************************************************************
* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* Licensed 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 eu.stratosphere.nephele.event.task;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* The event notification manager manages the subscription of {@link EventListener} objects to
* particular event types. Moreover, it handles the dispatching of the events.
* This class is thread-safe.
*
*/
public class EventNotificationManager {
/**
* Stores the subscriptions for the individual event types.
*/
private final Map<Class<? extends AbstractTaskEvent>, List<EventListener>> subscriptions = new HashMap<Class<? extends AbstractTaskEvent>, List<EventListener>>();
/**
* Subscribes the given event listener object to the specified event type.
*
* @param eventListener
* the {@link EventListener} object to create the subscription for
* @param eventType
* the event type the given listener object wants to be notified about
*/
public void subscribeToEvent(final EventListener eventListener, final Class<? extends AbstractTaskEvent> eventType) {
synchronized (this.subscriptions) {
List<EventListener> subscribers = this.subscriptions.get(eventType);
if (subscribers == null) {
subscribers = new ArrayList<EventListener>();
this.subscriptions.put(eventType, subscribers);
}
subscribers.add(eventListener);
}
}
/**
* Removes a subscription of an {@link EventListener} object for the given event type.
*
* @param eventListener
* the event listener to remove the subscription for
* @param eventType
* the event type to remove the subscription for
*/
public void unsubscribeFromEvent(final EventListener eventListener, final Class<? extends AbstractEvent> eventType) {
synchronized (this.subscriptions) {
List<EventListener> subscribers = this.subscriptions.get(eventType);
if (subscribers == null) {
return;
}
subscribers.remove(eventListener);
if (subscribers.isEmpty()) {
this.subscriptions.remove(eventType);
}
}
}
/**
* Delivers a event to all of the registered subscribers.
*
* @param event The event to deliver.
*/
public void deliverEvent(AbstractTaskEvent event) {
synchronized (this.subscriptions) {
List<EventListener> subscribers = this.subscriptions.get(event.getClass());
if (subscribers == null) {
return;
}
final Iterator<EventListener> it = subscribers.iterator();
while (it.hasNext()) {
it.next().eventOccurred(event);
}
}
}
}