Dubbo分析之Transport層

時間  2019-11-10
標籤 dubbo 分析 transport 欄目 Dubbo 简体版
原文   原文鏈接

系列文章

Dubbo分析Serialize層
Dubbo分析之Transport層
Dubbo分析之Exchange 層
Dubbo分析之Protocol層git

前言

上一篇文章Dubbo分析之Serialize層，介紹了最底層的序列化/反序列化層，本文繼續分析Serialize層的上一層transport網絡傳輸層，此層使用了現有的一些通信開源框架(ex:netty,mina,grizzly)來作底層通信，上文也作了簡單介紹，本文將作更深刻的瞭解；github

Transporter類分析

dubbo爲通信框架提供了統一的bind和connet接口，方便進行管理和擴展，封裝在接口類：Transporter中：bootstrap

@SPI("netty")
public interface Transporter {
 
    @Adaptive({Constants.SERVER_KEY, Constants.TRANSPORTER_KEY})
    Server bind(URL url, ChannelHandler handler) throws RemotingException;
 
    @Adaptive({Constants.CLIENT_KEY, Constants.TRANSPORTER_KEY})
    Client connect(URL url, ChannelHandler handler) throws RemotingException;
}

提供了bind和connect接口，分別對應這服務器端和客戶端，具體有哪些實現類，以下圖所示：服務器

以默認使用的netty框架爲例，代碼以下：網絡

public class NettyTransporter implements Transporter {
 
    public static final String NAME = "netty";
 
    @Override
    public Server bind(URL url, ChannelHandler listener) throws RemotingException {
        return new NettyServer(url, listener);
    }
 
    @Override
    public Client connect(URL url, ChannelHandler listener) throws RemotingException {
        return new NettyClient(url, listener);
    }
 
}

具體的服務器端封裝在NettyServer中，客戶端封裝在NettyClient；url參數是包含了xml配置的信息(包括：對外的接口，使用的協議，使用的序列化方式，使用的通信框架等)，listener是一個Handler，在解碼以後將數據交給它作後續的業務處理；對應以上的幾種通信開源框架，分別提供了對應的Transporter包括：NettyTransporter，NettyTransporter(netty4)，MinaTransporter以及GrizzlyTransporter，具體使用哪一種類型的Transporter，在Transporters類中提供了getTransporter方法：架構

public static Transporter getTransporter() {
    return ExtensionLoader.getExtensionLoader(Transporter.class).getAdaptiveExtension();
}

這裏並無像在獲取具體serialization類同樣，經過在url指定transporter參數，而後加載具體的transporter類，而是生成了一個動態的transporter，由此動態transporter去加載具體的類；
由於Server端和Client能夠分別設置成不一樣的通信框架，一次獲取惟一的Transporter不能知足此需求；具體的生成動態代碼的方法在ExtensionLoader的createAdaptiveExtensionClassCode方法中，此處不在列出源碼，在此展現一下默認生成的動態代碼擴展類：框架

package com.alibaba.dubbo.remoting;
 
import com.alibaba.dubbo.common.extension.ExtensionLoader;
 
public class Transporter$Adaptive implements com.alibaba.dubbo.remoting.Transporter {
    public com.alibaba.dubbo.remoting.Server bind(
        com.alibaba.dubbo.common.URL arg0,
        com.alibaba.dubbo.remoting.ChannelHandler arg1)
        throws com.alibaba.dubbo.remoting.RemotingException {
        if (arg0 == null) {
            throw new IllegalArgumentException("url == null");
        }
 
        com.alibaba.dubbo.common.URL url = arg0;
        String extName = url.getParameter("server",
                url.getParameter("transporter", "netty"));
 
        if (extName == null) {
            throw new IllegalStateException(
                "Fail to get extension(com.alibaba.dubbo.remoting.Transporter) name from url(" +
                url.toString() + ") use keys([server, transporter])");
        }
 
        com.alibaba.dubbo.remoting.Transporter extension = (com.alibaba.dubbo.remoting.Transporter) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.remoting.Transporter.class)
                                                                                                                   .getExtension(extName);
 
        return extension.bind(arg0, arg1);
    }
 
    public com.alibaba.dubbo.remoting.Client connect(
        com.alibaba.dubbo.common.URL arg0,
        com.alibaba.dubbo.remoting.ChannelHandler arg1)
        throws com.alibaba.dubbo.remoting.RemotingException {
        if (arg0 == null) {
            throw new IllegalArgumentException("url == null");
        }
 
        com.alibaba.dubbo.common.URL url = arg0;
        String extName = url.getParameter("client",
                url.getParameter("transporter", "netty"));
 
        if (extName == null) {
            throw new IllegalStateException(
                "Fail to get extension(com.alibaba.dubbo.remoting.Transporter) name from url(" +
                url.toString() + ") use keys([client, transporter])");
        }
 
        com.alibaba.dubbo.remoting.Transporter extension = (com.alibaba.dubbo.remoting.Transporter) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.remoting.Transporter.class)
                                                                                                                   .getExtension(extName);
 
        return extension.connect(arg0, arg1);
    }
}

能夠發現Server端能夠經過transporter和server兩個參數來設置擴展類，並且server參數設置的值是能夠覆蓋transporter參數的值，同理Client也相似；最後不論是bind()仍是connet()都是經過ExtensionLoader的getExtension方法來獲取具體的transporter類；同serialize層，相關的transporter也一樣定義在META-INF/dubbo/internal/com.alibaba.dubbo.remoting.Transporter文件中：socket

netty=com.alibaba.dubbo.remoting.transport.netty.NettyTransporter
netty4=com.alibaba.dubbo.remoting.transport.netty4.NettyTransporter
mina=com.alibaba.dubbo.remoting.transport.mina.MinaTransporter
grizzly=com.alibaba.dubbo.remoting.transport.grizzly.GrizzlyTransporter

Server端和Client分析

1.Server端

在實例化具體的Server類時，會首先調用父類的構造器，進行參數初始化，同時調用bind()方法，啓動服務器；父類AbstractServer構造器以下：tcp

public AbstractServer(URL url, ChannelHandler handler) throws RemotingException {
        super(url, handler);
        localAddress = getUrl().toInetSocketAddress();
 
        String bindIp = getUrl().getParameter(Constants.BIND_IP_KEY, getUrl().getHost());
        int bindPort = getUrl().getParameter(Constants.BIND_PORT_KEY, getUrl().getPort());
        if (url.getParameter(Constants.ANYHOST_KEY, false) || NetUtils.isInvalidLocalHost(bindIp)) {
            bindIp = NetUtils.ANYHOST;
        }
        bindAddress = new InetSocketAddress(bindIp, bindPort);
        this.accepts = url.getParameter(Constants.ACCEPTS_KEY, Constants.DEFAULT_ACCEPTS);
        this.idleTimeout = url.getParameter(Constants.IDLE_TIMEOUT_KEY, Constants.DEFAULT_IDLE_TIMEOUT);
        try {
            doOpen();
            if (logger.isInfoEnabled()) {
                logger.info("Start " + getClass().getSimpleName() + " bind " + getBindAddress() + ", export " + getLocalAddress());
            }
        } catch (Throwable t) {
            throw new RemotingException(url.toInetSocketAddress(), null, "Failed to bind " + getClass().getSimpleName()
                    + " on " + getLocalAddress() + ", cause: " + t.getMessage(), t);
        }
        //fixme replace this with better method
        DataStore dataStore = ExtensionLoader.getExtensionLoader(DataStore.class).getDefaultExtension();
        executor = (ExecutorService) dataStore.get(Constants.EXECUTOR_SERVICE_COMPONENT_KEY, Integer.toString(url.getPort()));
    }

主要從url獲取啓動參數包括：ip，port，accepts(可接受的鏈接數，0表示不受限制數量，默認爲0)，idleTimeout等；而後調用doOpen方法經過具體的通信框架綁定端口啓動服務；已默認使用的Netty爲例，查看doOpen()方法以下：ide

protected void doOpen() throws Throwable {
       NettyHelper.setNettyLoggerFactory();
       ExecutorService boss = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerBoss", true));
       ExecutorService worker = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerWorker", true));
       ChannelFactory channelFactory = new NioServerSocketChannelFactory(boss, worker, getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS));
       bootstrap = new ServerBootstrap(channelFactory);
 
       final NettyHandler nettyHandler = new NettyHandler(getUrl(), this);
       channels = nettyHandler.getChannels();
       // https://issues.jboss.org/browse/NETTY-365
       // https://issues.jboss.org/browse/NETTY-379
       // final Timer timer = new HashedWheelTimer(new NamedThreadFactory("NettyIdleTimer", true));
       bootstrap.setOption("child.tcpNoDelay", true);
       bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
           @Override
           public ChannelPipeline getPipeline() {
               NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec(), getUrl(), NettyServer.this);
               ChannelPipeline pipeline = Channels.pipeline();
               /*int idleTimeout = getIdleTimeout();
               if (idleTimeout > 10000) {
                   pipeline.addLast("timer", new IdleStateHandler(timer, idleTimeout / 1000, 0, 0));
               }*/
               pipeline.addLast("decoder", adapter.getDecoder());
               pipeline.addLast("encoder", adapter.getEncoder());
               pipeline.addLast("handler", nettyHandler);
               return pipeline;
           }
       });
       // bind
       channel = bootstrap.bind(getBindAddress());
   }

以上是常規的啓動netty程序，須要指定編解碼器，nettyHandler；編解碼已經在上文中介紹過了，此處不在詳細介紹，重點介紹nettyHandler；server端在數據通過解碼以後就交給NettyHandler來處理，NettyHandler繼承於Netty的SimpleChannelHandler類，重寫了channelConnected，channelDisconnected，messageReceived，writeRequested以及exceptionCaught方法，基本上就是常規的幾種操做：創建鏈接，斷開鏈接，接收消息，發送消息，異常處理；看一下部分源碼：

@Override
   public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
       NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
       try {
           if (channel != null) {
               channels.put(NetUtils.toAddressString((InetSocketAddress) ctx.getChannel().getRemoteAddress()), channel);
           }
           handler.connected(channel);
       } finally {
           NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
       }
   }
 
   @Override
   public void channelDisconnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
       NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
       try {
           channels.remove(NetUtils.toAddressString((InetSocketAddress) ctx.getChannel().getRemoteAddress()));
           handler.disconnected(channel);
       } finally {
           NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
       }
   }
    @Override
   public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
       NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
       try {
           handler.received(channel, e.getMessage());
       } finally {
           NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
       }
   }
 
   @Override
   public void writeRequested(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
       super.writeRequested(ctx, e);
       NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
       try {
           handler.sent(channel, e.getMessage());
       } finally {
           NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
       }
   }
 
   @Override
   public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) throws Exception {
       NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
       try {
           handler.caught(channel, e.getCause());
       } finally {
           NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
       }
   }

將netty原生的channel包裝成dubbo的NettyChannel，同時將NettyChannel保存在NettyChannel的內部靜態變量channelMap中；這裏的方法都統一調用了getOrAddChannel方法，先添加進去，最後在finally中斷定channel是否已經關閉，若是關閉從channelMap中移除；中間部分調用了handler對應的方法，此處的handler就是在實例化時傳入的NettyServer，NettyServer自己也是一個ChannelHandler，能夠看一下channelHandler接口類：

public interface ChannelHandler {
 
    void connected(Channel channel) throws RemotingException;
 
    void disconnected(Channel channel) throws RemotingException;
 
    void sent(Channel channel, Object message) throws RemotingException;
 
    void received(Channel channel, Object message) throws RemotingException;
 
    void caught(Channel channel, Throwable exception) throws RemotingException;
}

具體的server類中也能夠作一些處理，好比connected時判段是否超過accepts，若是超過拒絕鏈接；處理完以後交給實例化Server時傳入的ChannelHandler處理，此類具體是在HeaderExchanger中被初始化的：

public class HeaderExchanger implements Exchanger {
 
    public static final String NAME = "header";
 
    @Override
    public ExchangeClient connect(URL url, ExchangeHandler handler) throws RemotingException {
        return new HeaderExchangeClient(Transporters.connect(url, new DecodeHandler(new HeaderExchangeHandler(handler))), true);
    }
 
    @Override
    public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
        return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));
    }
 
}

能夠發現這裏具體的ChannelHandler是DecodeHandler，注這裏的Decode和Netty自己的decode不同，Netty自己的decode在執行NettyHandler以前就執行解碼了；後續的操做在Exchange層進行處理，本文暫時先不作介紹；

2.Client端

一樣查看父類AbstractClient，構造方法以下：

public AbstractClient(URL url, ChannelHandler handler) throws RemotingException {
        super(url, handler);
 
        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);
 
        try {
            doOpen();
        } 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();
            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)
                .getDefaultExtension().get(Constants.CONSUMER_SIDE, Integer.toString(url.getPort()));
        ExtensionLoader.getExtensionLoader(DataStore.class)
                .getDefaultExtension().remove(Constants.CONSUMER_SIDE, Integer.toString(url.getPort()));
    }

客戶端須要提供重連機制，因此初始化的幾個參數都和重連有關，send_reconnect表示在發送消息時發現鏈接已經斷開是否發起重連，reconnect_warning_period表示多久報一次重連警告，shutdown_timeout表示鏈接服務器一直鏈接不上的超時時間；接下來就是調用doOpen()方法，一樣已Netty爲例：

protected void doOpen() throws Throwable {
       NettyHelper.setNettyLoggerFactory();
       bootstrap = new ClientBootstrap(channelFactory);
       // config
       // @see org.jboss.netty.channel.socket.SocketChannelConfig
       bootstrap.setOption("keepAlive", true);
       bootstrap.setOption("tcpNoDelay", true);
       bootstrap.setOption("connectTimeoutMillis", getTimeout());
       final NettyHandler nettyHandler = new NettyHandler(getUrl(), this);
       bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
           @Override
           public ChannelPipeline getPipeline() {
               NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec(), getUrl(), NettyClient.this);
               ChannelPipeline pipeline = Channels.pipeline();
               pipeline.addLast("decoder", adapter.getDecoder());
               pipeline.addLast("encoder", adapter.getEncoder());
               pipeline.addLast("handler", nettyHandler);
               return pipeline;
           }
       });
   }

Netty客戶端的常規代碼，設置了和Server端相同的NettyHandler，decoder和encoder；下面重點看看connect方法：

protected void connect() throws RemotingException {
        connectLock.lock();
        try {
            if (isConnected()) {
                return;
            }
            initConnectStatusCheckCommand();
            doConnect();
            if (!isConnected()) {
                throw new RemotingException(this, "Failed connect to server " + getRemoteAddress() + " from " + getClass().getSimpleName() + " "
                        + NetUtils.getLocalHost() + " using dubbo version " + Version.getVersion()
                        + ", cause: Connect wait timeout: " + getTimeout() + "ms.");
            } else {
                if (logger.isInfoEnabled()) {
                    logger.info("Successed connect to server " + getRemoteAddress() + " from " + getClass().getSimpleName() + " "
                            + NetUtils.getLocalHost() + " using dubbo version " + Version.getVersion()
                            + ", channel is " + this.getChannel());
                }
            }
            reconnect_count.set(0);
            reconnect_error_log_flag.set(false);
        } catch (RemotingException e) {
            throw e;
        } catch (Throwable e) {
            throw new RemotingException(this, "Failed connect to server " + getRemoteAddress() + " from " + getClass().getSimpleName() + " "
                    + NetUtils.getLocalHost() + " using dubbo version " + Version.getVersion()
                    + ", cause: " + e.getMessage(), e);
        } finally {
            connectLock.unlock();
        }
    }

首先斷定是否已經鏈接，若是鏈接直接return；接下來初始化鏈接狀態檢查器，按期檢查channel是否鏈接，鏈接斷開會進行重連操做，具體代碼以下：

private synchronized void initConnectStatusCheckCommand() {
        //reconnect=false to close reconnect
        int reconnect = getReconnectParam(getUrl());
        if (reconnect > 0 && (reconnectExecutorFuture == null || reconnectExecutorFuture.isCancelled())) {
            Runnable connectStatusCheckCommand = new Runnable() {
                @Override
                public void run() {
                    try {
                        if (!isConnected()) {
                            connect();
                        } else {
                            lastConnectedTime = System.currentTimeMillis();
                        }
                    } catch (Throwable t) {
                        String errorMsg = "client reconnect to " + getUrl().getAddress() + " find error . url: " + getUrl();
                        // wait registry sync provider list
                        if (System.currentTimeMillis() - lastConnectedTime > shutdown_timeout) {
                            if (!reconnect_error_log_flag.get()) {
                                reconnect_error_log_flag.set(true);
                                logger.error(errorMsg, t);
                                return;
                            }
                        }
                        if (reconnect_count.getAndIncrement() % reconnect_warning_period == 0) {
                            logger.warn(errorMsg, t);
                        }
                    }
                }
            };
            reconnectExecutorFuture = reconnectExecutorService.scheduleWithFixedDelay(connectStatusCheckCommand, reconnect, reconnect, TimeUnit.MILLISECONDS);
        }
    }

建立了一個Runnable，用來檢測是否鏈接，若是鏈接斷開，調用connect方法；定時調度交給ScheduledThreadPoolExecutor來執行；初始化以後就調用具體Client的doConnect操做，也是通信框架的一些常規代碼，此處不列出了；後續關於NettyChannel的介紹和Server端相似，不過多進行介紹；

總結

本文重點分析了dubbo架構中的transport層，具體圍繞Transporter, Client, Server，ChannelHandler幾個類展開，關於後續的處理將在exchange信息交換層；

示例代碼地址

https://github.com/ksfzhaohui...
https://gitee.com/OutOfMemory...

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