源码分析Dubbo网络通信篇NettyClient

前言

在源码分析Dubbo通讯篇之网络核心类一文中已给出Dubbo netty client的启动流程，如下图： 

正文

以Dubbo协议为例，DubboProtocol#refer中，在创建Invoker时，通过getClient方法，开始Client（连接的）创建过程，先重点看一下：

private ExchangeClient[] getClients(URL url) {    // @1
        // whether to share connection
        boolean service_share_connect = false;
        int connections = url.getParameter(Constants.CONNECTIONS_KEY, 0);    // @2
        // if not configured, connection is shared, otherwise, one connection for one service      
        if (connections == 0) {
            service_share_connect = true;
            connections = 1;
        }

        ExchangeClient[] clients = new ExchangeClient[connections];   // @3
        for (int i = 0; i  clients.length; i++) {
            if (service_share_connect) {
                clients[i] = getSharedClient(url);       // @4
            } else {
                clients[i] = initClient(url);    // @5
            }
        }
        return clients;
    }

代码@1：参数URL,服务提供者URL。 
代码@2：获取 dubbo:reference connections = “” /，默认0表示客户端对同一个服务提供者的所有服务，使用共享一个连接，如果该值有设置，则使用非共享的客户端，所谓的共享客户端，以Netty为例，也即客户端对同一服务提供者发起的不同服务，使用同一个客户端(NettyClient)进行请求的发送与接收。 
代码@3，根据connections，创建ExchangeClients数组。 
代码@4：如果使用共享连接，则调用getSharedClient获取共享连接，如果客户端未建立，则创建客户端。 
代码@5，如果不使用共享连接，调用initClient创建客户端，其创建时序图如上图所示。

 
接下来，还是以Netty4为例，探究一下Dubbo NettyClient的创建细节。 

首先从全貌上大概看一下NettyClient对象所持有的属性：

AbstractPeer 
   1、private final ChannelHandler handler ： 事件处理Handler。 
   2、private volatile URL url ：该协议的第一个服务提供者的URL，Server只需要用到URL中的参数，与具体某一个服务没什么关系。

AbstractEndpoint 
   1、private Codec2 codec ：编码解码器。 
   2、private int timeout ： 超时时间 
   3、private int connectTimeout ：连接超时时间 
   注，如果通过dubbo:provider改变codec,不同的服务提供者引用的默认服务提供者参数不同，那这个只能是以第一个为主了，应该不科学？

AbstractClient 
   1、protected static final String CLIENT_THREAD_POOL_NAME 
= “DubboClientHandler” Dubbo 客户端线程名称。 
private static final AtomicInteger CLIENT_THREAD_POOL_ID = new AtomicInteger() 客户端线程池ID自增器。 
   2、private static final ScheduledThreadPoolExecutor 
reconnectExecutorService 客户端连接重连线程池。 
   3、private final Lock connectLock = new ReentrantLock() 客户端连接服务端独占锁，保证一个客户端同时只会一个线程在执行连接动作。 
   4、private final boolean send_reconnect 消息发送时，如果当前客户端未连接，是否发起重连操作。 
   5、private final AtomicInteger reconnect_count = new AtomicInteger(0) 记录重连的次数。 
   6、private final AtomicBoolean reconnect_error_log_flag = new AtomicBoolean(false) 连接出错后是否打印过ERROR日志。 
   7、private final int reconnect_warning_period ：对连接异常，以WARN级别日志输出的频率，默认第一次是以Error日志，然后每出现reconnect_warning_period次后，就打印一次warn级别日志。 
   8、private final long shutdown_timeout ：关闭服务的超时时间。 
   9、protected volatile ExecutorService executor 客户端线程池。 
   10、private volatile ScheduledFuture ? reconnectExecutorFuture = null 重连的Future。 
   11、private long lastConnectedTime = System.currentTimeMillis() 上一次重连时间戳。

NettyClient 
   1、private static final NioEventLoopGroup nioEventLoopGroup = new NioEventLoopGroup(Constants.DEFAULT_IO_THREADS, new DefaultThreadFactory(“NettyClientWorker”, true)); IO线程组，同一个JVM中所有的客户端公用一个IO线程组，且线程数固定为(32与CPU核数+1的最小值)。 
   2、private Bootstrap bootstrap ：Netty客户端启动实例。 
   3、private volatile Channel channel：客户端连接，请copy其引用使用。

**1、源码分析NettyClient **

1.1 源码分析构造函数

public NettyClient(final URL url, final ChannelHandler handler) throws RemotingException {    // @1
        super(url, wrapChannelHandler(url, handler));    // @2
}

代码@1：url:服务提供者URL；ChannelHandler handler：事件处理器。 
代码@2：wrapChannelHandler在讲解NettyServer时已重点分析，构造其事件转发模型(Dispatch)。 
接下来重点分析其父类的构造方法：

public AbstractClient(URL url, ChannelHandler handler) throws RemotingException {
        super(url, handler);     // @1

        send_reconnect = url.getParameter(Constants.SEND_RECONNECT_KEY, false);

        shutdown_timeout = url.getParameter(Constants.SHUTDOWN_TIMEOUT_KEY, Constants.DEFAULT_SHUTDOWN_TIMEOUT);

        // The default reconnection interval is 2s, 1800 means warning interval is 1 hour.
        reconnect_warning_period = url.getParameter("reconnect.waring.period", 1800);    // @2

        try {
            doOpen();        // @3
        } catch (Throwable t) {
            close();
            throw new RemotingException(url.toInetSocketAddress(), null,
                    "Failed to start " + getClass().getSimpleName() + " " + NetUtils.getLocalAddress()
                            + " connect to the server " + getRemoteAddress() + ", cause: " + t.getMessage(), t);
        }
        try {
            // connect.
            connect();      // @4
            if (logger.isInfoEnabled()) {
                logger.info("Start " + getClass().getSimpleName() + " " + NetUtils.getLocalAddress() + " connect to the server " + getRemoteAddress());
            }
        } catch (RemotingException t) {
            if (url.getParameter(Constants.CHECK_KEY, true)) {
                close();
                throw t;
            } else {
                logger.warn("Failed to start " + getClass().getSimpleName() + " " + NetUtils.getLocalAddress()
                        + " connect to the server " + getRemoteAddress() + " (check == false, ignore and retry later!), cause: " + t.getMessage(), t);
            }
        } catch (Throwable t) {
            close();
            throw new RemotingException(url.toInetSocketAddress(), null,
                    "Failed to start " + getClass().getSimpleName() + " " + NetUtils.getLocalAddress()
                            + " connect to the server " + getRemoteAddress() + ", cause: " + t.getMessage(), t);
        }

        executor = (ExecutorService) ExtensionLoader.getExtensionLoader(DataStore.class)    // @5
                .getDefaultExtension().get(Constants.CONSUMER_SIDE, Integer.toString(url.getPort()));
        ExtensionLoader.getExtensionLoader(DataStore.class)
                .getDefaultExtension().remove(Constants.CONSUMER_SIDE, Integer.toString(url.getPort()));
    }

代码@1：调用父类的构造其，初始化url、ChannelHandler。 
代码@2：初始化send_reconnect 、shutdown_timeout、reconnect_warning_period（默认1小时打印一次日志） 
代码@3：调用doOpen初始化客户端调用模型，后续重点分析。 
代码@4：调用connect方法，向服务端发起TCP连接。 
代码@5：获取线程池，并从缓存中移除。 

1.2 doOpen

protected void doOpen() throws Throwable {
        NettyHelper.setNettyLoggerFactory();
        final NettyClientHandler nettyClientHandler = new NettyClientHandler(getUrl(), this);    // @1 
        bootstrap = new Bootstrap();                                                                                            // @2
        bootstrap.group(nioEventLoopGroup)                                                                              // @3
                .option(ChannelOption.SO_KEEPALIVE, true)
                .option(ChannelOption.TCP_NODELAY, true)
                .option(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT)
                //.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, getTimeout())
                .channel(NioSocketChannel.class);

        if (getTimeout()  3000) {     // @4
            bootstrap.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 3000);
        } else {
            bootstrap.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, getTimeout());
        }

        bootstrap.handler(new ChannelInitializer() {

            @Override
            protected void initChannel(Channel ch) throws Exception {
                NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec(), getUrl(), NettyClient.this);
                ch.pipeline()//.addLast("logging",new LoggingHandler(LogLevel.INFO))//for debug
                        .addLast("decoder", adapter.getDecoder())
                        .addLast("encoder", adapter.getEncoder())
                        .addLast("handler", nettyClientHandler);      // @5
            }
        });
    }

代码@1：创建NettyClientHandler。 
代码@2：创建Netty客户端启动实例bootstrap. 
代码@3：客户端绑定IO线程组（池），注意，一个JVM中所有的NettyClient共享其IO线程。 
代码@4：设置连接超时时间，最小连接超时时间为3s。 
代码@5：设置编码器、事件连接器，当触发事件后，将调用nettyClientHandler中相关的方法。

 
1.3 doConnect

protected void doConnect() throws Throwable {
        long start = System.currentTimeMillis();
        ChannelFuture future = bootstrap.connect(getConnectAddress());   // @1
        try {
            boolean ret = future.awaitUninterruptibly(3000, TimeUnit.MILLISECONDS);   // @2

            if (ret && future.isSuccess()) {
                Channel newChannel = future.channel();
                try {
                    // Close old channel
                    Channel oldChannel = NettyClient.this.channel; // copy reference
                    if (oldChannel != null) {
                        try {
                            if (logger.isInfoEnabled()) {
                                logger.info("Close old netty channel " + oldChannel + " on create new netty channel " + newChannel);
                            }
                            oldChannel.close();
                        } finally {
                            NettyChannel.removeChannelIfDisconnected(oldChannel);
                        }
                    }
                } finally {
                    if (NettyClient.this.isClosed()) {
                        try {
                            if (logger.isInfoEnabled()) {
                                logger.info("Close new netty channel " + newChannel + ", because the client closed.");
                            }
                            newChannel.close();
                        } finally {
                            NettyClient.this.channel = null;
                            NettyChannel.removeChannelIfDisconnected(newChannel);
                        }
                    } else {
                        NettyClient.this.channel = newChannel;
                    }
                }
            } else if (future.cause() != null) {
                throw new RemotingException(this, "client(url: " + getUrl() + ") failed to connect to server "
                        + getRemoteAddress() + ", error message is:" + future.cause().getMessage(), future.cause());
            } else {
                throw new RemotingException(this, "client(url: " + getUrl() + ") failed to connect to server "
                        + getRemoteAddress() + " client-side timeout "
                        + getConnectTimeout() + "ms (elapsed: " + (System.currentTimeMillis() - start) + "ms) from netty client "
                        + NetUtils.getLocalHost() + " using dubbo version " + Version.getVersion());
            }
        } finally {
            if (!isConnected()) {
                //future.cancel(true);
            }
        }
    }

代码@1：调用bootstrap.connect方法发起TCP连接。 
代码@2：future.awaitUninterruptibly，连接事件只等待3S，这里写成固定了，显然没有与doOpen方法中ChannelOption.CONNECT_TIMEOUT_MILLIS保持一致。

文/编辑  by  Justin

 原创   by  丁威

 

原文始发于微信公众号（Justin的后端书架）：