Java tutorial
/* * (C) Copyright 2006-2007 Nuxeo SAS (http://nuxeo.com/) and contributors. * * All rights reserved. This program and the accompanying materials * are made available under the terms of the GNU Lesser General Public License * (LGPL) version 2.1 which accompanies this distribution, and is available at * http://www.gnu.org/licenses/lgpl.html * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * Contributors: * bstefanescu * * $Id$ */ package org.nuxeo.runtime.detection; import java.io.IOException; import java.net.DatagramPacket; import java.net.InetAddress; import java.net.MulticastSocket; import java.net.SocketTimeoutException; import java.util.HashMap; import java.util.Map; import java.util.Timer; import java.util.TimerTask; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * @author <a href="mailto:bs@nuxeo.com">Bogdan Stefanescu</a> */ public class MulticastDetector<T> { private static final Log log = LogFactory.getLog(MulticastDetector.class); protected final InetAddress groupAddr; protected final int groupPort; protected final String identity; protected final Map<String, Peer<T>> peers; protected MulticastSocket socket; protected long heartBeatTimeout = 5000; // 10 sec private DetectionHandler handler; private HeartBeatDetection heartBeatDetection; private Timer heartBeatTimer; private Timer processingTimer; public MulticastDetector(String identity, InetAddress groupAddr, int groupPort) throws IOException { this.identity = identity; this.groupAddr = groupAddr; this.groupPort = groupPort; socket = new MulticastSocket(groupPort); peers = new HashMap<String, Peer<T>>(); } public MulticastDetector(String identity) throws IOException { this(identity, "224.1.9.2", 4444); } public MulticastDetector(String identity, String groupAddr, int groupPort) throws IOException { this(identity, InetAddress.getByName(groupAddr), groupPort); } public void setDetectionHandler(DetectionHandler handler) { this.handler = handler; } public DetectionHandler getDetectionHandler() { return handler; } public MulticastSocket getSocket() { return socket; } public void setHeartBeatTimeout(long ms) { heartBeatTimeout = ms; } public long getHeartBeatTimeout() { return heartBeatTimeout; } public synchronized void start() { if (heartBeatDetection != null) { return; } try { socket.setSoTimeout((int) heartBeatTimeout); // give a chance to stop heart beat detector heartBeatDetection = new HeartBeatDetection(); heartBeatDetection.start(); processingTimer = new Timer("Nuxeo.Detection.Cleanup"); processingTimer.schedule(new CleanupTask(), heartBeatTimeout, heartBeatTimeout); socket.joinGroup(groupAddr); heartBeatTimer = new Timer("Nuxeo.Detection.HeartBeat"); heartBeatTimer.schedule(new HeartBeatTask(), 0, heartBeatTimeout); } catch (Throwable t) { stop(); } } public synchronized void stop() { if (heartBeatDetection == null) { return; } heartBeatTimer.cancel(); heartBeatTimer = null; heartBeatDetection.cancel(); heartBeatDetection = null; processingTimer.cancel(); processingTimer = null; } public String getIdentity() { return identity; } @SuppressWarnings("unchecked") public Peer<T>[] getPeers() { synchronized (peers) { return peers.values().toArray(new Peer[peers.size()]); } } private DatagramPacket createHeartBeat() { byte[] bytes = identity.getBytes(); return new DatagramPacket(bytes, bytes.length, groupAddr, groupPort); } private String readHeartBeat(DatagramPacket p) { return new String(p.getData(), p.getOffset(), p.getLength()); } protected void notifyPeerOnline(Peer<T> peer) { // async exec needed in that case otherwise // heartbeat detection may be significantly delayed and some heartbeats lost if (handler != null) { processingTimer.schedule(new NotifyTask(peer, true), 0); } } protected void notifyPeerOffline(Peer<T> peer) { // async exec not needed in that case if (handler != null) { handler.peerOffline(peer); } } class HeartBeatDetection extends Thread { private boolean running = false; private final Object runLock = new Object(); HeartBeatDetection() { super("Nuxeo.HeartBeatDetection"); } public void cancel() { synchronized (runLock) { running = false; } interrupt(); } @Override public synchronized void start() { synchronized (runLock) { running = true; } super.start(); } @Override public void run() { while (true) { //System.out.println(identity+": running heart beat listener"); try { synchronized (runLock) { if (!running) { break; // detector was stopped } } byte[] bytes = new byte[4000]; DatagramPacket p = new DatagramPacket(bytes, bytes.length); socket.receive(p); // block until a new message is received String identity = readHeartBeat(p); if (MulticastDetector.this.identity.equals(identity)) { continue; } Peer<T> peer; synchronized (peers) { peer = peers.get(identity); if (peer == null) { // create new peer peer = new Peer<T>(p.getAddress(), p.getPort(), identity); assert peer.addr.equals(p.getAddress()); assert peer.port == p.getPort(); peers.put(identity, peer); } else { // update peer last heart beat peer.lastHeartBeat = System.currentTimeMillis(); peer = null; } } if (peer != null) { // new peer detected System.out.println("Peer online: " + peer); notifyPeerOnline(peer); } } catch (SocketTimeoutException e) { // socket timeout -> continue } catch (Throwable e) { log.error(e, e); } } } } class HeartBeatTask extends TimerTask { @Override public void run() { //System.out.println(identity+": running heart beat task"); try { socket.send(createHeartBeat()); } catch (IOException e) { log.error(e, e); } } } class CleanupTask extends TimerTask { @SuppressWarnings("unchecked") @Override public void run() { //System.out.println(identity+": running cleanup task"); long tm = System.currentTimeMillis(); // copy existing peers into an array to avoid race conditions Peer[] arPeers = getPeers(); // remove expired peers for (Peer peer : arPeers) { if (tm - peer.lastHeartBeat > heartBeatTimeout * 2) { synchronized (peers) { peers.remove(peer.identity); } System.out.println("Peer Offline: " + peer); notifyPeerOffline(peer); peer.data = null; } } } } class NotifyTask extends TimerTask { private final boolean online; private final Peer peer; NotifyTask(Peer<T> peer, boolean online) { this.peer = peer; this.online = online; } @Override public void run() { if (handler == null) { return; } if (online) { handler.peerOnline(peer); } else { handler.peerOffline(peer); } } } }