Source code

001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.wake.impl;
020
021import org.apache.reef.wake.EventHandler;
022import org.apache.reef.wake.exception.WakeRuntimeException;
023
024import java.util.HashMap;
025import java.util.LinkedList;
026import java.util.List;
027import java.util.Map;
028import java.util.concurrent.locks.ReadWriteLock;
029import java.util.concurrent.locks.ReentrantReadWriteLock;
030import java.util.logging.Level;
031import java.util.logging.Logger;
032
033/**
034 * Event handler that provides publish/subscribe interfaces.
035 *
036 * @param <T> type
037 */
038public class PubSubEventHandler<T> implements EventHandler<T> {
039
040  private static final Logger LOG = Logger.getLogger(PubSubEventHandler.class.getCanonicalName());
041  private final Map<Class<? extends T>, List<EventHandler<? extends T>>> clazzToListOfHandlersMap;
042  private final ReadWriteLock lock = new ReentrantReadWriteLock();
043
044  /**
045   * Constructs a pub-sub event handler.
046   */
047  public PubSubEventHandler() {
048    this.clazzToListOfHandlersMap = new HashMap<>();
049  }
050
051  /**
052   * Constructs a pub-sub event handler with initial subscribed event handlers.
053   *
054   * @param clazzToListOfHandlersMap a map of event class types to lists of event handlers
055   */
056  public PubSubEventHandler(final Map<Class<? extends T>, List<EventHandler<? extends T>>> clazzToListOfHandlersMap) {
057    this.clazzToListOfHandlersMap = clazzToListOfHandlersMap;
058  }
059
060  /**
061   * Subscribes an event handler for an event class type.
062   *
063   * @param clazz   an event class
064   * @param handler an event handler
065   */
066  public void subscribe(final Class<? extends T> clazz, final EventHandler<? extends T> handler) {
067    lock.writeLock().lock();
068    try {
069      List<EventHandler<? extends T>> list = clazzToListOfHandlersMap.get(clazz);
070      if (list == null) {
071        list = new LinkedList<EventHandler<? extends T>>();
072        clazzToListOfHandlersMap.put(clazz, list);
073      }
074      list.add(handler);
075    } finally {
076      lock.writeLock().unlock();
077    }
078  }
079
080  /**
081   * Invokes subscribed handlers for the event class type.
082   *
083   * @param event an event
084   * @throws WakeRuntimeException
085   */
086  @Override
087  public void onNext(final T event) {
088    LOG.log(Level.FINEST, "Invoked for event: {0}", event);
089    lock.readLock().lock();
090    final List<EventHandler<? extends T>> list;
091    try {
092      list = clazzToListOfHandlersMap.get(event.getClass());
093      if (list == null) {
094        throw new WakeRuntimeException("No event " + event.getClass() + " handler");
095      }
096      for (final EventHandler<? extends T> handler : list) {
097        LOG.log(Level.FINEST, "Invoking {0}", handler);
098        ((EventHandler<T>) handler).onNext(event);
099      }
100    } finally {
101      lock.readLock().unlock();
102    }
103  }
104
105}