archiva/archiva-modules/archiva-base/archiva-event/src/main/java/org/apache/archiva/event/AsynchronousEventBus.java

package org.apache.archiva.event;

/*
 * 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.
 */

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;

/**
 * Simple Async Event Bus implementation
 * 
 * @author jdumay
 */
public class AsynchronousEventBus implements EventBus
{
    private final Set<EventObserver> observers = Collections.synchronizedSet(new HashSet());

    private final BlockingQueue<Event> events = new LinkedBlockingQueue<Event>();

    private final Thread workerThread;

    private final int threads;

    public AsynchronousEventBus(int threads)
    {
        this.threads = threads;
        workerThread = new Thread(new WorkerRunnable());
        workerThread.start();
    }

    public void emit(EventEmitter emitter, EventMessage message)
    {
        events.offer(new Event(emitter, message));
    }

    public void subscribe(EventObserver observer)
    {
        observers.add(observer);
    }

    public void unsubscribe(EventObserver observer)
    {
        observers.remove(observer);
    }

    public Set<EventObserver> getObservers() {
        return new HashSet<EventObserver>(observers);
    }

    class WorkerRunnable implements Runnable
    {
        private final ExecutorService service;

        public WorkerRunnable()
        {
            service = Executors.newFixedThreadPool(threads);
        }
        
        public void run()
        {
            while (true)
            {
                dequeueAndExecute();
            }
        }

        private void dequeueAndExecute()
        {
            try
            {
                final Event event = events.take();
                for (final EventObserver observer : observers)
                {
                    service.execute(new Runnable()
                    {
                        public void run()
                        {
                            try
                            {
                                observer.observe(event);
                            }
                            finally
                            {
                                //log me
                            }
                        }
                    });
                }
            }
            catch (InterruptedException e)
            {
                //Do nothing
            }
        }
    }
}