netty 实现
1. 各组件之间的关系
每个ServerBootstrap与一个事件循环对象（一个线程）都会与一个Channel绑定，如NioServerSocketChannel
2. 如何绑定
在做bind操作时，会执行方法，register进行注册
ChannelFuture regFuture = config().group().register(channel);关键接口及类之间的关系：
EventLoopGroup与EventLoop及其类关系图之间形成组合模式。
@Overridepublic ChannelFuture register(Channel channel) { ???return next().register(channel);//选择一个线程执行器，调用register方法，绑定channel}@Overridepublic ChannelFuture register(Channel channel) { ???return register(new DefaultChannelPromise(channel, this));}3. 代表客户端的channel创建
注意到ServerBootstrap有两个EventLoopGroup,parent 负责代表客户端channel的分发，child负责代码客户端channel的处理。
- Accept事件，创建代表客户端的channel
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) { ???unsafe.read();}try { ???do { ???????int localRead = doReadMessages(readBuf); ???????if (localRead == 0) { ???????????break; ???????} ???????if (localRead < 0) { ???????????closed = true; ???????????break; ???????} ???????allocHandle.incMessagesRead(localRead); ???} while (allocHandle.continueReading());} catch (Throwable t) { ???exception = t;}int size = readBuf.size();for (int i = 0; i < size; i ++) { ???readPending = false; ???pipeline.fireChannelRead(readBuf.get(i));}readBuf.clear();allocHandle.readComplete();pipeline.fireChannelReadComplete();protected int doReadMessages(List<Object> buf) throws Exception { ???SocketChannel ch = SocketUtils.accept(javaChannel()); ???try { ???????if (ch != null) { ???????????buf.add(new NioSocketChannel(this, ch)); ???????????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;}注意到doReadMessages会创建代表客户端的channel,创建完成会触发，fireChannelRead 事件。
4. 代表客户端的channel分发
上一节知道，channel创建完成会触发fireChannelRead 事件。在ServerSocketChannel初始化时，会注册ServerBootstrapAcceptor 用户接收代表客户端channel并分发到child EventLoopGroup中执行。
p.addLast(new ChannelInitializer<Channel>() { ???@Override ???public void initChannel(final Channel ch) throws Exception { ???????final ChannelPipeline pipeline = ch.pipeline(); ???????ChannelHandler handler = config.handler(); ???????if (handler != null) { ???????????pipeline.addLast(handler); ???????} ???????ch.eventLoop().execute(new Runnable() { ???????????@Override ???????????public void run() { ???????????????pipeline.addLast(new ServerBootstrapAcceptor( ???????????????????????ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs)); ???????????} ???????}); ???}});@Override@SuppressWarnings("unchecked")public void channelRead(ChannelHandlerContext ctx, Object msg) { ???final Channel child = (Channel) msg; ???child.pipeline().addLast(childHandler); ???setChannelOptions(child, childOptions, logger); ???for (Entry<AttributeKey<?>, Object> e: childAttrs) { ???????child.attr((AttributeKey<Object>) e.getKey()).set(e.getValue()); ???} ???try { ???????childGroup.register(child).addListener(new ChannelFutureListener() { ???????????@Override ???????????public void operationComplete(ChannelFuture future) throws Exception { ???????????????if (!future.isSuccess()) { ???????????????????forceClose(child, future.cause()); ???????????????} ???????????} ???????}); ???} catch (Throwable t) { ???????forceClose(child, t); ???}}5. netty线程模型
不管是客户端还是服务端可以通过一个Channel同时读或者写，不需要阻塞，读写多路复用。
6. handler链模型
netty 原理
原文地址：https://www.cnblogs.com/dragonfei/p/9074752.html