Dubbo分析之Transport層

Dubbo Netty · 發表 2018-10-23 17:09:24

摘要：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網路傳輸層，此層使用了現有的一些通訊開源框架(ex:netty,mina,grizzly)來做底層通訊，上文...

前言

上一篇文章ofollow,noindex" target="_blank">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網路傳輸層，此層使用了現有的一些通訊開源框架(ex:netty,mina,grizzly)來做底層通訊，上文也做了簡單介紹，本文將做更深入的瞭解；

Transporter類分析

dubbo為通訊框架提供了統一的bind和connet介面，方便進行管理和擴充套件，封裝在介面類：Transporter中：

@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介面，分別對應這伺服器端和客戶端，具體有哪些實現類，如下圖所示：

以預設使用的netty框架為例，程式碼如下：

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);
}

}

具體的伺服器端封裝在NettyServer中，客戶端封裝在NettyClient；url引數是包含了xml配置的資訊(包括：對外的介面，使用的協議，使用的序列化方式，使用的通訊框架等)，listener是一個Handler，在解碼之後將資料交給它做後續的業務處理；對應以上的幾種通訊開源框架，分別提供了對應的Transporter包括：NettyTransporter，NettyTransporter(netty4)，MinaTransporter以及GrizzlyTransporter，具體使用哪種型別的Transporter，在Transporters類中提供了getTransporter方法：

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

這裡並沒有像在獲取具體serialization類一樣，通過在url指定transporter引數，然後載入具體的transporter類，而是生成了一個動態的transporter，由此動態transporter去載入具體的類；

因為Server端和Client可以分別設定成不同的通訊框架，一次獲取唯一的Transporter不能滿足此需求；具體的生成動態程式碼的方法在ExtensionLoader的createAdaptiveExtensionClassCode方法中，此處不在列出原始碼，在此展示一下預設生成的動態程式碼擴充套件類：

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);
}
}

可以發現Server端可以通過transporter和server兩個引數來設定擴充套件類，而且server引數設定的值是可以覆蓋transporter引數的值，同理Client也類似；最後不管是bind()還是connet()都是通過ExtensionLoader的getExtension方法來獲取具體的transporter類；同serialize層，相關的transporter也同樣定義在META-INF/dubbo/internal/com.alibaba.dubbo.remoting.Transporter檔案中：

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

在例項化具體的Server類時，會首先呼叫父類的構造器，進行引數初始化，同時呼叫bind()方法，啟動伺服器；父類AbstractServer構造器如下：

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獲取啟動引數包括：ip，port，accepts(可接受的連線數，0表示不受限制數量，預設為0)，idleTimeout等；然後呼叫doOpen方法通過具體的通訊框架繫結埠啟動服務；已預設使用的Netty為例，檢視doOpen()方法如下：

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());
}

以上是常規的啟動netty程式，需要指定編解碼器，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端在資料經過解碼之後就交給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作：建立連線，斷開連線，接收訊息，傳送訊息，異常處理；看一下部分原始碼：

@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儲存在NettyChannel的內部靜態變數channelMap中；這裡的方法都統一呼叫了getOrAddChannel方法，先新增進去，最後在finally中判定channel是否已經關閉，如果關閉從channelMap中移除；中間部分呼叫了handler對應的方法，此處的handler就是在例項化時傳入的NettyServer，NettyServer本身也是一個ChannelHandler，可以看一下channelHandler介面類：

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類中也可以做一些處理，比如connected時判段是否超過accepts，如果超過拒絕連線；處理完之後交給例項化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))));
}

}

可以發現這裡具體的ChannelHandler是DecodeHandler，注這裡的Decode和Netty本身的decode不一樣，Netty本身的decode在執行NettyHandler之前就執行解碼了；後續的操作在Exchange層進行處理，本文暫時先不做介紹；

2.Client端

同樣檢視父類AbstractClient，構造方法如下：

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()));
}

客戶端需要提供重連機制，所以初始化的幾個引數都和重連有關，send_reconnect表示在傳送訊息時發現連線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表示連線伺服器一直連線不上的超時時間；接下來就是呼叫doOpen()方法，同樣已Netty為例：

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客戶端的常規程式碼，設定了和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();
}
}

首先判定是否已經連線，如果連線直接return；接下來初始化連線狀態檢查器，定期檢查channel是否連線，連線斷開會進行重連操作，具體程式碼如下：

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，用來檢測是否連線，如果連線斷開，呼叫connect方法；定時排程交給ScheduledThreadPoolExecutor來執行；初始化之後就呼叫具體Client的doConnect操作，也是通訊框架的一些常規程式碼，此處不列出了；後續關於NettyChannel的介紹和Server端類似，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資訊交換層；

示例程式碼地址

https://github.com/ksfzhaohui/blog

https://gitee.com/OutOfMemory/blog

Dubbo分析之Transport層

您可能也會喜歡…