netty源码分析（13）- 创建NioSocketChanne

上一节研究了新连接接入的过程，通过检测IO事件轮询新连接，当前成功检测到连接接入事件之后，会调用NioServerSocketChannel#doReadMessages()方法，进行创建NioSocketChannel

 @Override
    protected int doReadMessages(List<Object> buf) throws Exception {
        //获取jdk底层的channel：客户端channel
        SocketChannel ch = SocketUtils.accept(javaChannel());

        try {
            if (ch != null) {
                //将jdk底层的channel封装到netty的channel，并存储到传入的容器当中
                //this为服务端channel
                buf.add(new NioSocketChannel(this, ch));
                //成功和创建 客户端接入的一条通道，并返回
                return 1;
            }
        } catch (Throwable t) {
            logger.warn("Failed to create a new channel from an accepted socket.", t);

            try {
                ch.close();
            } catch (Throwable t2) {
                logger.warn("Failed to close a socket.", t2);
            }
        }

        return 0;
    }

本节研究创建NioSocketChannel，即客户端channel的过程

查看原代码做了两件事，调用父类构造方法，实例化一个NioSocketChannelConfig。

    public NioSocketChannel(Channel parent, SocketChannel socket) {
        super(parent, socket);
        //实例化一个NioSocketChannelConfig
        config = new NioSocketChannelConfig(this, socket.socket());
    }

• 首先看看NioSocketChannelConfig实例化。主要是保存了javaSocket，并且通过setTcpNoDelay(true);禁止了tcp的Nagle算法，目的是为了尽量让小的数据包整合成大的发送出去,降低延时。

        private NioSocketChannelConfig(NioSocketChannel channel, Socket javaSocket) {
            super(channel, javaSocket);
            calculateMaxBytesPerGatheringWrite();
        }

    public DefaultSocketChannelConfig(SocketChannel channel, Socket javaSocket) {
        super(channel);
        if (javaSocket == null) {
            throw new NullPointerException("javaSocket");
        }
        //保存socket
        this.javaSocket = javaSocket;

        // Enable TCP_NODELAY by default if possible.
        if (PlatformDependent.canEnableTcpNoDelayByDefault()) {
            try {
                //禁止Nagle算法,目的是为了让小的数据包尽量集合成大的数据包发送出去
                setTcpNoDelay(true);
            } catch (Exception e) {
                // Ignore.
            }
        }
    }

• 接着查看NioSocketChannel父类构造方法,主要是保存客户端注册的读事件、channel为成员变量，以及设置柱塞模式为非阻塞

    public NioSocketChannel(Channel parent, SocketChannel socket) {
        super(parent, socket);
        //实例化一个NioSocketChannelConfig
        config = new NioSocketChannelConfig(this, socket.socket());
    }
    protected AbstractNioByteChannel(Channel parent, SelectableChannel ch) {
        //传入感兴趣的读事件：客户端channel的读事件
        super(parent, ch, SelectionKey.OP_READ);
    }

    protected AbstractNioChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
        super(parent);
        //保存客户端channel为成员变量
        this.ch = ch;
        //保存感兴趣的读事件为成员变量
        this.readInterestOp = readInterestOp;
        try {
            //配置阻塞模式为非阻塞
            ch.configureBlocking(false);
        } catch (IOException e) {
            try {
                ch.close();
            } catch (IOException e2) {
                if (logger.isWarnEnabled()) {
                    logger.warn(
                            "Failed to close a partially initialized socket.", e2);
                }
            }

            throw new ChannelException("Failed to enter non-blocking mode.", e);
        }
    }

调用父类的构造方法，是设置该客户端channel对应的服务端channel，以及channel的id和两大组件unsafe和pipeline

    protected AbstractChannel(Channel parent) {
        //parent为创建次客户端channel的服务端channel（服务端启动过程中通过反射创建的）
        this.parent = parent;
        id = newId();
        unsafe = newUnsafe();
        pipeline = newChannelPipeline();
    }