Dubbo源码学习--Multicast 注册中心（四）

Multicast 注册中心不需要启动任何中心节点，只要广播地址一样，就可以互相发现。

提供方启动时广播自己的地址
消费方启动时广播订阅请求
提供方收到订阅请求时，单播自己的地址给订阅者，如果设置了

unicast=false

，则广播给订阅者
消费方收到提供方地址时，连接该地址进行 RPC 调用。

组播受网络结构限制，只适合小规模应用或开发阶段使用。组播地址段: 224.0.0.0 - 239.255.255.255

配置

<dubbo:registry address="multicast://224.5.6.7:1234"

或

<dubbo:registry protocol="multicast" address="224.5.6.7:1234"

为了减少广播量，Dubbo 缺省使用单播发送提供者地址信息给消费者，如果一个机器上同时启了多个消费者进程，消费者需声明

unicast=false

，否则只会有一个消费者能收到消息：

<dubbo:registry address="multicast://224.5.6.7:1234?unicast=false"

或

<dubbo:registry protocol="multicast" address="224.5.6.7:1234">
    <dubbo:parameter key="unicast" value="false"

</dubbo:registry>

MulticastRegistryFactory是一个工厂类，用来创建MulticastRegistry实例。

public class MulticastRegistryFactory extends AbstractRegistryFactory {

    public Registry createRegistry(URL url) {
        return new MulticastRegistry(url);
    }

}

MulticastRegistry中主要实现了如下接口：

（1）doRegister(URL url);//向注册中心注册服务

（2）doUnregister(URL url);//取消服务注册

（3）doSubscribe(URL url, NotifyListener listener);//向注册中心监听服务

（4）doUnsubscribe(URL url, NotifyListener listener);//取消监听注册中心服务

1、在MulticastRegistry构造函数中会根据广播IP建立一个线程用来接收通知数据，在接收到通知数据时会进行广播并通知本地数据

public class MulticastRegistry extends FailbackRegistry {

    // logging output
    private static final Logger logger = LoggerFactory.getLogger(MulticastRegistry.class);

    private static final int DEFAULT_MULTICAST_PORT = 1234;

    private final InetAddress mutilcastAddress;

    private final MulticastSocket mutilcastSocket;

    private final int mutilcastPort;

    private final ConcurrentMap<URL, Set<URL>> received = new ConcurrentHashMap<URL, Set<URL>>();

    private final ScheduledExecutorService cleanExecutor = Executors.newScheduledThreadPool(1, new NamedThreadFactory("DubboMulticastRegistryCleanTimer", true));

    private final ScheduledFuture<?> cleanFuture;

    private final int cleanPeriod;

    private volatile boolean admin = false;

    public MulticastRegistry(URL url) {
        super(url);
        if (url.isAnyHost()) {
            throw new IllegalStateException("registry address == null");
        }
        if (!isMulticastAddress(url.getHost())) {
            throw new IllegalArgumentException("Invalid multicast address " + url.getHost() + ", scope: 224.0.0.0 - 239.255.255.255");
        }
        try {
            mutilcastAddress = InetAddress.getByName(url.getHost());
            mutilcastPort = url.getPort() <= 0 ? DEFAULT_MULTICAST_PORT : url.getPort();
            mutilcastSocket = new MulticastSocket(mutilcastPort);
            mutilcastSocket.setLoopbackMode(false);
            mutilcastSocket.joinGroup(mutilcastAddress);
            Thread thread = new Thread(new Runnable() {
                public void run() {
                    byte[] buf = new byte[2048];
                    DatagramPacket recv = new DatagramPacket(buf, buf.length);
                    while (!mutilcastSocket.isClosed()) {
                        try {
                            mutilcastSocket.receive(recv);
                            String msg = new String(recv.getData()).trim();
                            int i = msg.indexOf('\n');
                            if (i > 0) {
                                msg = msg.substring(0, i).trim();
                            }
                            MulticastRegistry.this.receive(msg, (InetSocketAddress) recv.getSocketAddress());
                            Arrays.fill(buf, (byte) 0);
                        } catch (Throwable e) {
                            if (!mutilcastSocket.isClosed()) {
                                logger.error(e.getMessage(), e);
                            }
                        }
                    }
                }
            }, "DubboMulticastRegistryReceiver");
            thread.setDaemon(true);
            thread.start();
        } catch (IOException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        this.cleanPeriod = url.getParameter(Constants.SESSION_TIMEOUT_KEY, Constants.DEFAULT_SESSION_TIMEOUT);
        if (url.getParameter("clean", true)) {
            this.cleanFuture = cleanExecutor.scheduleWithFixedDelay(new Runnable() {
                public void run() {
                    try {
                        clean(); // Remove the expired
                    } catch (Throwable t) { // Defensive fault tolerance
                        logger.error("Unexpected exception occur at clean expired provider, cause: " + t.getMessage(), t);
                    }
                }
            }, cleanPeriod, cleanPeriod, TimeUnit.MILLISECONDS);
        } else {
            this.cleanFuture = null;
        }
    }

    private static boolean isMulticastAddress(String ip) {
        int i = ip.indexOf('.');
        if (i > 0) {
            String prefix = ip.substring(0, i);
            if (StringUtils.isInteger(prefix)) {
                int p = Integer.parseInt(prefix);
                return p >= 224 && p <= 239;
            }
        }
        return false;
    }

    private void clean() {
        if (admin) {
            for (Set<URL> providers : new HashSet<Set<URL>>(received.values())) {
                for (URL url : new HashSet<URL>(providers)) {
                    if (isExpired(url)) {
                        if (logger.isWarnEnabled()) {
                            logger.warn("Clean expired provider " + url);
                        }
                        doUnregister(url);
                    }
                }
            }
        }
    }

    private boolean isExpired(URL url) {
        if (!url.getParameter(Constants.DYNAMIC_KEY, true)
                || url.getPort() <= 0
                || Constants.CONSUMER_PROTOCOL.equals(url.getProtocol())
                || Constants.ROUTE_PROTOCOL.equals(url.getProtocol())
                || Constants.OVERRIDE_PROTOCOL.equals(url.getProtocol())) {
            return false;
        }
        Socket socket = null;
        try {
            socket = new Socket(url.getHost(), url.getPort());
        } catch (Throwable e) {
            try {
                Thread.sleep(100);
            } catch (Throwable e2) {
            }
            Socket socket2 = null;
            try {
                socket2 = new Socket(url.getHost(), url.getPort());
            } catch (Throwable e2) {
                return true;
            } finally {
                if (socket2 != null) {
                    try {
                        socket2.close();
                    } catch (Throwable e2) {
                    }
                }
            }
        } finally {
            if (socket != null) {
                try {
                    socket.close();
                } catch (Throwable e) {
                }
            }
        }
        return false;
    }
    
    //在接收到数据时会今天广播数据
    private void receive(String msg, InetSocketAddress remoteAddress) {
        if (logger.isInfoEnabled()) {
            logger.info("Receive multicast message: " + msg + " from " + remoteAddress);
        }
        if (msg.startsWith(Constants.REGISTER)) {
            URL url = URL.valueOf(msg.substring(Constants.REGISTER.length()).trim());
            //如果注册时会通知数据
            registered(url);
        } else if (msg.startsWith(Constants.UNREGISTER)) {
            URL url = URL.valueOf(msg.substring(Constants.UNREGISTER.length()).trim());
            //解除注册时会通知数据
            unregistered(url);
        } else if (msg.startsWith(Constants.SUBSCRIBE)) {
            URL url = URL.valueOf(msg.substring(Constants.SUBSCRIBE.length()).trim());
            Set<URL> urls = getRegistered();
            if (urls != null && !urls.isEmpty()) {
                for (URL u : urls) {
                    if (UrlUtils.isMatch(url, u)) {
                        String host = remoteAddress != null && remoteAddress.getAddress() != null
                                ? remoteAddress.getAddress().getHostAddress() : url.getIp();
                        if (url.getParameter("unicast", true) // Whether the consumer's machine has only one process
                                && !NetUtils.getLocalHost().equals(host)) { // Multiple processes in the same machine cannot be unicast with unicast or there will be only one process receiving information
                            //单播数据
                           unicast(Constants.REGISTER + " " + u.toFullString(), host);
                        } else {
                            //广播数据
                            broadcast(Constants.REGISTER + " " + u.toFullString());
                        }
                    }
                }
            }
        }/* else if (msg.startsWith(UNSUBSCRIBE)) {
        }*/
    }
    //广播数据
    private void broadcast(String msg) {
        if (logger.isInfoEnabled()) {
            logger.info("Send broadcast message: " + msg + " to " + mutilcastAddress + ":" + mutilcastPort);
        }
        try {
            byte[] data = (msg + "\n").getBytes();
            DatagramPacket hi = new DatagramPacket(data, data.length, mutilcastAddress, mutilcastPort);
            mutilcastSocket.send(hi);
        } catch (Exception e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
    }
    //单播数据
    private void unicast(String msg, String host) {
        if (logger.isInfoEnabled()) {
            logger.info("Send unicast message: " + msg + " to " + host + ":" + mutilcastPort);
        }
        try {
            byte[] data = (msg + "\n").getBytes();
            DatagramPacket hi = new DatagramPacket(data, data.length, InetAddress.getByName(host), mutilcastPort);
            mutilcastSocket.send(hi);
        } catch (Exception e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
    }
    
    //注册时会广播数据
    protected void doRegister(URL url) {
        broadcast(Constants.REGISTER + " " + url.toFullString());
    }
    //消除注册时会广播数据
    protected void doUnregister(URL url) {
        broadcast(Constants.UNREGISTER + " " + url.toFullString());
    }

    //订阅数据的时候会广播数据
    protected void doSubscribe(URL url, NotifyListener listener) {
        if (Constants.ANY_VALUE.equals(url.getServiceInterface())) {
            admin = true;
        }
        broadcast(Constants.SUBSCRIBE + " " + url.toFullString());
        synchronized (listener) {
            try {
                listener.wait(url.getParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT));
            } catch (InterruptedException e) {
            }
        }
    }

    //取消订阅数据的时候会广播数据
    protected void doUnsubscribe(URL url, NotifyListener listener) {
        if (!Constants.ANY_VALUE.equals(url.getServiceInterface())
                && url.getParameter(Constants.REGISTER_KEY, true)) {
            unregister(url);
        }
        broadcast(Constants.UNSUBSCRIBE + " " + url.toFullString());
    }

    public boolean isAvailable() {
        try {
            return mutilcastSocket != null;
        } catch (Throwable t) {
            return false;
        }
    }

    public void destroy() {
        super.destroy();
        try {
            if (cleanFuture != null) {
                cleanFuture.cancel(true);
            }
        } catch (Throwable t) {
            logger.warn(t.getMessage(), t);
        }
        try {
            mutilcastSocket.leaveGroup(mutilcastAddress);
            mutilcastSocket.close();
        } catch (Throwable t) {
            logger.warn(t.getMessage(), t);
        }
    }
    //注册时通知监听者
    protected void registered(URL url) {
        for (Map.Entry<URL, Set<NotifyListener>> entry : getSubscribed().entrySet()) {
            URL key = entry.getKey();
            if (UrlUtils.isMatch(key, url)) {
                Set<URL> urls = received.get(key);
                if (urls == null) {
                    received.putIfAbsent(key, new ConcurrentHashSet<URL>());
                    urls = received.get(key);
                }
                urls.add(url);
                List<URL> list = toList(urls);
                for (NotifyListener listener : entry.getValue()) {
                    notify(key, listener, list);
                    synchronized (listener) {
                        listener.notify();
                    }
                }
            }
        }
    }
    //消除注册时会通知监听者
    protected void unregistered(URL url) {
        for (Map.Entry<URL, Set<NotifyListener>> entry : getSubscribed().entrySet()) {
            URL key = entry.getKey();
            if (UrlUtils.isMatch(key, url)) {
                Set<URL> urls = received.get(key);
                if (urls != null) {
                    urls.remove(url);
                }
                if (urls == null || urls.isEmpty()){
                    if (urls == null){
                        urls = new ConcurrentHashSet<URL>();
                    }
                    URL empty = url.setProtocol(Constants.EMPTY_PROTOCOL);
                    urls.add(empty);
                }
                List<URL> list = toList(urls);
                for (NotifyListener listener : entry.getValue()) {
                    notify(key, listener, list);
                }
            }
        }
    }
}

Dubbo源码学习--Multicast 注册中心（四）

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