深入浅出Netty之四 Client请求处理

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netty java nio

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();

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);
    }

二.创建channel时，分配worker

 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

NioClientSocketChannel(
            ChannelFactory factory, ChannelPipeline pipeline,
            ChannelSink sink, NioWorker worker) {
	//创建socketChannel，并配置成异步模式
        super(null, factory, pipeline, sink, newSocket(), worker);
        //触发open事件
        fireChannelOpen(this);
    }

四.创建socketChannel过程

private static SocketChannel newSocket() {
        SocketChannel socket;
	//创建SocketChannel
        try {
            socket = SocketChannel.open();
        } catch (IOException e) {
            throw new ChannelException("Failed to open a socket.", e);
        }

        boolean success = false;
	//使用异步模式
        try {
            socket.configureBlocking(false);
            success = true;
        } catch (IOException e) {
            throw new ChannelException("Failed to enter non-blocking mode.", e);
        } finally {
           ......
        }

        return socket;
    }

五.通过Channel进行connect

 public static ChannelFuture connect(Channel channel, SocketAddress remoteAddress) {
        if (remoteAddress == null) {
            throw new NullPointerException("remoteAddress");
        }
	//是否连接成功的future
        ChannelFuture future = future(channel, true);
	//触发connected的downstream事件，对于echo client来说，由于没有downstream handler，所以直接被PipelineSink处理了
        channel.getPipeline().sendDownstream(new DownstreamChannelStateEvent(
                channel, future, ChannelState.CONNECTED, remoteAddress));
        return future;
    }

六.NioClientSocketPipelineSink拿到CONNECTED的downstream事件，处理connect

case CONNECTED:
                if (value != null) {
                    connect(channel, future, (SocketAddress) value);
                } else {
                    channel.worker.close(channel, future);
                }
                break;

private void connect(
            final NioClientSocketChannel channel, final ChannelFuture cf,
            SocketAddress remoteAddress) {
        try {
	    //尝试连接，如果成功，则直接将channel注册到worker线程中
            if (channel.channel.connect(remoteAddress)) {
                channel.worker.register(channel, cf);
            } 
	    //尝试连接失败，则将channel注册到某个boss线程中处理，该boss线程会接管该channel的connect过程
	    else {
                channel.getCloseFuture().addListener(new ChannelFutureListener() {
                    public void operationComplete(ChannelFuture f)
                            throws Exception {
                        if (!cf.isDone()) {
                            cf.setFailure(new ClosedChannelException());
                        }
                    }
                });
                cf.addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
                channel.connectFuture = cf;
                nextBoss().register(channel);
            }

        } catch (Throwable t) {
            cf.setFailure(t);
            fireExceptionCaught(channel, t);
            channel.worker.close(channel, succeededFuture(channel));
        }
    }

七.具体register过程

void register(NioClientSocketChannel channel) {
	    //client的注册任务，让boss线程监听connect事件
            Runnable registerTask = new RegisterTask(this, channel);
            Selector selector;

            synchronized (startStopLock) {
	        //初始化boss线程，并启动之
                if (!started) {
                    // 
                    try {
			//创建一个Selector
                        this.selector = selector =  Selector.open();
                    } catch (Throwable t) {
                        throw new ChannelException(
                                "Failed to create a selector.", t);
                    }

                    // 启动boss线程
                    boolean success = false;
                    try {
                        DeadLockProofWorker.start(bossExecutor,
                                new ThreadRenamingRunnable(this,
                                        "New I/O client boss #" + id + '-' + subId));

                        success = true;
                    } finally {
		......

                started = true;
		//异步提交注册任务
                boolean offered = registerTaskQueue.offer(registerTask);
                assert offered;
            }
	    //根据超时时间，启动一个超时提醒任务
            int timeout = channel.getConfig().getConnectTimeoutMillis();
            if (timeout > 0) {
                if (!channel.isConnected()) {
                    channel.timoutTimer = timer.newTimeout(wakeupTask,
                            timeout, TimeUnit.MILLISECONDS);
                }
            }

        }

八.register之后，主线程就返回了，Boss线程异步执行

    public void run() {
            boolean shutdown = false;
            int selectReturnsImmediately = 0;

            Selector selector = this.selector;

            // use 80% of the timeout for measure
            final long minSelectTimeout = SelectorUtil.SELECT_TIMEOUT_NANOS * 80 / 100;
            boolean wakenupFromLoop = false;
            for (;;) {
                wakenUp.set(false);

                try {
                    long beforeSelect = System.nanoTime();
		    //select，500ms超时
                    int selected = SelectorUtil.select(selector);
		    .......
		    //处理注册任务，将channel注册到自己的selector范围中
                    processRegisterTaskQueue();
		    //处理IO就绪事件，这里是connect事件
                    processSelectedKeys(selector.selectedKeys());

                    // 处理超时，如果超时，则设置future失败
                    long currentTimeNanos = System.nanoTime();
                    processConnectTimeout(selector.keys(), currentTimeNanos);
                   ......

        }

九.注册任务执行

public void run() {
            try {
		//注册一个connect key到boss的selector上
                channel.channel.register(
                        boss.selector, SelectionKey.OP_CONNECT, channel);
            } catch (ClosedChannelException e) {
                channel.worker.close(channel, succeededFuture(channel));
            }
	    //设置超时点
            int connectTimeout = channel.getConfig().getConnectTimeoutMillis();
            if (connectTimeout > 0) {
                channel.connectDeadlineNanos = System.nanoTime() + connectTimeout * 1000000L;
            }
        }

十.boss处理IO，client是connect就绪

private void processSelectedKeys(Set<SelectionKey> selectedKeys) {
           ......
            for (Iterator<SelectionKey> i = selectedKeys.iterator(); i.hasNext();) {
                SelectionKey k = i.next();
                i.remove();

                if (!k.isValid()) {
                    close(k);
                    continue;
                }

                try {
		    //如果connect就位，判断connect是否确实完成
                    if (k.isConnectable()) {
                        connect(k);
                    }
                } catch (Throwable t) {
                   ......
                }
            }
        }

private void connect(SelectionKey k) throws IOException {
            NioClientSocketChannel ch = (NioClientSocketChannel) k.attachment();
	    //如果连接成功，则将channel注册上worker线程中处理读写
            if (ch.channel.finishConnect()) {
                k.cancel();
                if (ch.timoutTimer != null) {
                    ch.timoutTimer.cancel();
                }
                ch.worker.register(ch, ch.connectFuture);
            }
        }

十一.注册过程

public void run() {
           ......
		//默认监听read事件
                synchronized (channel.interestOpsLock) {
                    channel.channel.register(
                            selector, channel.getRawInterestOps(), channel);
                }
		//通知等待线程成功
                if (future != null) {
                    channel.setConnected();
                    future.setSuccess();
                }
                ......
		//触发ChannelConnected事件
                fireChannelConnected(channel, remoteAddress);
            ......
            }

        }

十二.echo client handler处理channelConnected事件，开始发送数据

 public void channelConnected(
              ChannelHandlerContext ctx, ChannelStateEvent e) {
          // Send the first message.  Server will not send anything here
          // because the firstMessage's capacity is 0.
          e.getChannel().write(firstMessage);
      }

十三.write之后的过程client端和server是一样的，可以参考前一篇server端的读写

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