深入浅出Netty之四 Client请求处理

前2篇分析了echo server端的运行机制，本篇同样以echo client为例，分析netty的nio客户端的运行机制。

总体来说client端和server端的处理是类似的，NioWorker是重用的，也就意味着client和server的读写机制是一样的，都是通过worker线程来管理的。所不同的是Boss线程，server端的boss线程一个bind端口起一个，主要负责接收新请求，而client端的boss线程是一个可配置的数组，一个connect端口分配一个，主要负责connect过程，如果connect成功则将channle注册到worker线程中处理。在Client同样有PipelineSink，叫做NioClientSocketPipelineSink，也是负责底层IO和pipeline之间的交互。

EchoClient代码:

// 初始化Bootstrap和NioClientSocketChannelFactory，这一步将启动nioWorker线程，并初始化NioClientSocketPipelineSink，并将Boss线程创建
 ClientBootstrap bootstrap = new ClientBootstrap(
 new NioClientSocketChannelFactory(
 Executors.newCachedThreadPool(),
 Executors.newCachedThreadPool()));

 // 用户自定义的pipeline工厂
 bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
 public ChannelPipeline getPipeline() throws Exception {
 return Channels.pipeline(
 new EchoClientHandler(firstMessageSize));
 }
 });

 // 异步创建连接
 ChannelFuture future = bootstrap.connect(new InetSocketAddress(host, port));

 //等待连接关闭
 future.getChannel().getCloseFuture().awaitUninterruptibly();

 // 关闭资源，线程池等
 bootstrap.releaseExternalResources();

        // 初始化Bootstrap和NioClientSocketChannelFactory，这一步将启动nioWorker线程，并初始化NioClientSocketPipelineSink，并将Boss线程创建
          ClientBootstrap bootstrap = new ClientBootstrap(
                  new NioClientSocketChannelFactory(
                          Executors.newCachedThreadPool(),
                          Executors.newCachedThreadPool()));
  
          // 用户自定义的pipeline工厂
          bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
              public ChannelPipeline getPipeline() throws Exception {
                  return Channels.pipeline(
                          new EchoClientHandler(firstMessageSize));
              }
          });
  
          // 异步创建连接
          ChannelFuture future = bootstrap.connect(new InetSocketAddress(host, port));
  
          //等待连接关闭
          future.getChannel().getCloseFuture().awaitUninterruptibly();
  
          // 关闭资源，线程池等
          bootstrap.releaseExternalResources();

具体connect过程：

一.创建client的channel

public ChannelFuture connect(final SocketAddress remoteAddress, final SocketAddress localAddress) {
 ......
 //拿用户自定义的pipeline
 ChannelPipeline pipeline;
 try {
 pipeline = getPipelineFactory().getPipeline();
 } catch (Exception e) {
 throw new ChannelPipelineException("Failed to initialize a pipeline.", e);
 }

 // 从ChannelFactory中，创建Channel，对于client来说factory是NioClientSocketChannelFactory，Channel是NioClientSocketChannel
 Channel ch = getFactory().newChannel(pipeline);

 // 通过channel连接
 return ch.connect(remoteAddress);
 }

public ChannelFuture connect(final SocketAddress remoteAddress, final SocketAddress localAddress) {
	......
	//拿用户自定义的pipeline
        ChannelPipeline pipeline;
        try {
            pipeline = getPipelineFactory().getPipeline();
        } catch (Exception e) {
            throw new ChannelPipelineException("Failed to initialize a pipeline.", e);
        }
        // 从ChannelFactory中，创建Channel，对于client来说factory是NioClientSocketChannelFactory，Channel是NioClientSocketChannel
        Channel ch = getFactory().newChannel(pipeline);
        // 通过channel连接
        return ch.connect(remoteAddress);
    }

二.创建channel时，分配worker

public SocketChannel newChannel(ChannelPipeline pipeline) {
 return new NioClientSocketChannel(this, pipeline, sink, sink.nextWorker());
 }

 public SocketChannel newChannel(ChannelPipeline pipeline) {
        return new NioClientSocketChannel(this, pipeline, sink, sink.nextWorker());
    }

三.创建内部的SocketChannel，触发ChannelOpen事件，不过echo client的handler没有对channelOpen事件做处理