public final class EchoServer {
    static final int PORT = Integer.parseInt(System.getProperty("port", "8007"));
    public static void main(String[] args) throws Exception {
        // Configure the server.
        //创建主从Reactor线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        final EchoServerHandler serverHandler = new EchoServerHandler();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)//配置主从Reactor
             .channel(NioServerSocketChannel.class)//配置主Reactor中的channel类型
             .option(ChannelOption.SO_BACKLOG, 100)//设置主Reactor中channel的option选项
             .handler(new LoggingHandler(LogLevel.INFO))//设置主Reactor中Channel->pipline->handler
             .childHandler(new ChannelInitializer<SocketChannel>() {//设置从Reactor中注册channel的pipeline
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ChannelPipeline p = ch.pipeline();
                     //p.addLast(new LoggingHandler(LogLevel.INFO));
                     p.addLast(serverHandler);
                 }
             });
            // Start the server. 绑定端口启动服务，开始监听accept事件
            ChannelFuture f = b.bind(PORT).sync();
            // Wait until the server socket is closed.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down all event loops to terminate all threads.
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}
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ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)//配置主从Reactor
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public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel> {
     //Main Reactor线程组
    volatile EventLoopGroup group;
    //Sub Reactor线程组
    private volatile EventLoopGroup childGroup;
    public ServerBootstrap group(EventLoopGroup parentGroup, EventLoopGroup childGroup) {
        //父类管理主Reactor线程组
        super.group(parentGroup);
        if (this.childGroup != null) {
            throw new IllegalStateException("childGroup set already");
        }
        this.childGroup = ObjectUtil.checkNotNull(childGroup, "childGroup");
        return this;
    }
}
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ServerBootstrap b = new ServerBootstrap();
b.channel(NioServerSocketChannel.class);
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public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel> {
    //用于创建ServerSocketChannel  ReflectiveChannelFactory
    private volatile ChannelFactory<? extends C> channelFactory;
    public B channel(Class<? extends C> channelClass) {
        return channelFactory(new ReflectiveChannelFactory<C>(
                ObjectUtil.checkNotNull(channelClass, "channelClass")
        ));
    }
    @Deprecated
    public B channelFactory(ChannelFactory<? extends C> channelFactory) {
        ObjectUtil.checkNotNull(channelFactory, "channelFactory");
        if (this.channelFactory != null) {
            throw new IllegalStateException("channelFactory set already");
        }
        this.channelFactory = channelFactory;
        return self();
    }
}
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public class ReflectiveChannelFactory<T extends Channel> implements ChannelFactory<T> {
    //NioServerSocketChannelde 构造器
    private final Constructor<? extends T> constructor;
    public ReflectiveChannelFactory(Class<? extends T> clazz) {
        ObjectUtil.checkNotNull(clazz, "clazz");
        try {
            //反射获取NioServerSocketChannel的构造器
            this.constructor = clazz.getConstructor();
        } catch (NoSuchMethodException e) {
            throw new IllegalArgumentException("Class " + StringUtil.simpleClassName(clazz) +
                    " does not have a public non-arg constructor", e);
        }
    }
    @Override
    public T newChannel() {
        try {
            //创建NioServerSocketChannel实例
            return constructor.newInstance();
        } catch (Throwable t) {
            throw new ChannelException("Unable to create Channel from class " + constructor.getDeclaringClass(), t);
        }
    }
}
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ServerBootstrap b = new ServerBootstrap();
//设置被MainReactor管理的NioServerSocketChannel的Socket选项
b.option(ChannelOption.SO_BACKLOG, 100)
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public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable {
    //serverSocketChannel中的ChannelOption配置
    private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();
    public <T> B option(ChannelOption<T> option, T value) {
        ObjectUtil.checkNotNull(option, "option");
        synchronized (options) {
            if (value == null) {
                options.remove(option);
            } else {
                options.put(option, value);
            }
        }
        return self();
    }
}
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ServerBootstrap b = new ServerBootstrap();
.childOption(ChannelOption.TCP_NODELAY, Boolean.TRUE)
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public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel> {
   //客户端SocketChannel对应的ChannelOption配置
    private final Map<ChannelOption<?>, Object> childOptions = new LinkedHashMap<ChannelOption<?>, Object>();
    public <T> ServerBootstrap childOption(ChannelOption<T> childOption, T value) {
        ObjectUtil.checkNotNull(childOption, "childOption");
        synchronized (childOptions) {
            if (value == null) {
                childOptions.remove(childOption);
            } else {
                childOptions.put(childOption, value);
            }
        }
        return this;
    }
}
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public class ChannelOption<T> extends AbstractConstant<ChannelOption<T>> {
    ..................省略..............
    public static final ChannelOption<Boolean> SO_BROADCAST = valueOf("SO_BROADCAST");
    public static final ChannelOption<Boolean> SO_KEEPALIVE = valueOf("SO_KEEPALIVE");
    public static final ChannelOption<Integer> SO_SNDBUF = valueOf("SO_SNDBUF");
    public static final ChannelOption<Integer> SO_RCVBUF = valueOf("SO_RCVBUF");
    public static final ChannelOption<Boolean> SO_REUSEADDR = valueOf("SO_REUSEADDR");
    public static final ChannelOption<Integer> SO_LINGER = valueOf("SO_LINGER");
    public static final ChannelOption<Integer> SO_BACKLOG = valueOf("SO_BACKLOG");
    public static final ChannelOption<Integer> SO_TIMEOUT = valueOf("SO_TIMEOUT");
    ..................省略..............
}
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   //serverSocketChannel中pipeline里的handler(主要是acceptor)
    private volatile ChannelHandler handler;
    public B handler(ChannelHandler handler) {
        this.handler = ObjectUtil.checkNotNull(handler, "handler");
        return self();
    }
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  ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)//配置主从Reactor
             .channel(NioServerSocketChannel.class)//配置主Reactor中的channel类型
             .handler(new ChannelInitializer<NioServerSocketChannel>() {
                 @Override
                 protected void initChannel(NioServerSocketChannel ch) throws Exception {
                     ChannelPipeline p = ch.pipeline();
                     p.addLast(channelhandler1)
                      .addLast(channelHandler2)                    
                      ......                     
                      .addLast(channelHandler3);
                 }
             })
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  final EchoServerHandler serverHandler = new EchoServerHandler();
            serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {//设置从Reactor中注册channel的pipeline
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ChannelPipeline p = ch.pipeline();            
                     p.addLast(new LoggingHandler(LogLevel.INFO));
                     p.addLast(serverHandler);
                 }
             });
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    //socketChannel中pipeline中的处理handler
    private volatile ChannelHandler childHandler;
    public ServerBootstrap childHandler(ChannelHandler childHandler) {
        this.childHandler = ObjectUtil.checkNotNull(childHandler, "childHandler");
        return this;
    }
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public abstract class ChannelInitializer<C extends Channel> extends ChannelInboundHandlerAdapter {
    @Override
    @SuppressWarnings("unchecked")
    public final void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        //当channelRegister事件发生时，调用initChannel初始化pipeline
        if (initChannel(ctx)) {
                 .................省略...............
        } else {
                 .................省略...............
        }
    }
    private boolean initChannel(ChannelHandlerContext ctx) throws Exception {
        if (initMap.add(ctx)) { // Guard against re-entrance.
            try {
                //此时客户单NioSocketChannel已经创建并初始化好了
                initChannel((C) ctx.channel());
            } catch (Throwable cause) {
                 .................省略...............
            } finally {
                  .................省略...............
            }
            return true;
        }
        return false;
    }
    protected abstract void initChannel(C ch) throws Exception;    
    .................省略...............
}
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   final EchoServerHandler serverHandler = new EchoServerHandler();
            serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {//设置从Reactor中注册channel的pipeline
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ChannelPipeline p = ch.pipeline();           
                     p.addLast(new LoggingHandler(LogLevel.INFO));
                     p.addLast(serverHandler);
                 }
             });
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// Start the server. 绑定端口启动服务，开始监听accept事件
ChannelFuture f = serverBootStrap.bind(PORT).sync();
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    public ChannelFuture bind(int inetPort) {
        return bind(new InetSocketAddress(inetPort));
    }
    public ChannelFuture bind(SocketAddress localAddress) {
        //校验Netty核心组件是否配置齐全
        validate();
        //服务端开始启动，绑定端口地址，接收客户端连接
        return doBind(ObjectUtil.checkNotNull(localAddress, "localAddress"));
    }
   private ChannelFuture doBind(final SocketAddress localAddress) {
        //异步创建，初始化，注册ServerSocketChannel到main reactor上
        final ChannelFuture regFuture = initAndRegister();
        final Channel channel = regFuture.channel();
        if (regFuture.cause() != null) {
            return regFuture;
        }
        if (regFuture.isDone()) {   
           ........serverSocketChannel向Main Reactor注册成功后开始绑定端口....,                            
        } else {
            //如果此时注册操作没有完成，则向regFuture添加operationComplete回调函数，注册成功后回调。
            regFuture.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {

                   ........serverSocketChannel向Main Reactor注册成功后开始绑定端口...., 
            });
            return promise;
        }
    }
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  final ChannelFuture initAndRegister() {
        Channel channel = null;
        try {
            //创建NioServerSocketChannel
            //ReflectiveChannelFactory通过泛型，反射，工厂的方式灵活创建不同类型的channel
            channel = channelFactory.newChannel();
            //初始化NioServerSocketChannel
            init(channel);
        } catch (Throwable t) {
            ..............省略.................
        }
        //向MainReactor注册ServerSocketChannel
        ChannelFuture regFuture = config().group().register(channel);
           ..............省略.................
        return regFuture;
    }
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public class ReflectiveChannelFactory<T extends Channel> implements ChannelFactory<T> {
    private final Constructor<? extends T> constructor;
    @Override
    public T newChannel() {
        try {
            return constructor.newInstance();
        } catch (Throwable t) {
            throw new ChannelException("Unable to create Channel from class " + constructor.getDeclaringClass(), t);
        }
    }
}
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public class NioServerSocketChannel extends AbstractNioMessageChannel
                             implements io.netty.channel.socket.ServerSocketChannel {
    //SelectorProvider(用于创建Selector和Selectable Channels)
    private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();
    public NioServerSocketChannel() {
        this(newSocket(DEFAULT_SELECTOR_PROVIDER));
    }
    //创建JDK NIO ServerSocketChannel
    private static ServerSocketChannel newSocket(SelectorProvider provider) {
        try {
            return provider.openServerSocketChannel();
        } catch (IOException e) {
            throw new ChannelException(
                    "Failed to open a server socket.", e);
        }
    }
     //ServerSocketChannel相关的配置
    private final ServerSocketChannelConfig config;
    public NioServerSocketChannel(ServerSocketChannel channel) {
        //父类AbstractNioChannel中保存JDK NIO原生ServerSocketChannel以及要监听的事件OP_ACCEPT
        super(null, channel, SelectionKey.OP_ACCEPT);
        //DefaultChannelConfig中设置用于Channel接收数据用的buffer->AdaptiveRecvByteBufAllocator
        config = new NioServerSocketChannelConfig(this, javaChannel().socket());
    }

}
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public abstract class AbstractNioChannel extends AbstractChannel {
   //JDK NIO原生Selectable Channel
    private final SelectableChannel ch;
    // Channel监听事件集合 这里是SelectionKey.OP_ACCEPT事件
    protected final int readInterestOp;
    protected AbstractNioChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
        super(parent);
        this.ch = ch;
        this.readInterestOp = readInterestOp;
        try {
            //设置Channel为非阻塞 配合IO多路复用模型
            ch.configureBlocking(false);
        } catch (IOException e) {
            .............省略................
        }
    }
}
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public abstract class AbstractChannel extends DefaultAttributeMap implements Channel {
    //channel是由创建层次的，比如ServerSocketChannel 是 SocketChannel的 parent
    private final Channel parent;
    //channel全局唯一ID machineId+processId+sequence+timestamp+random
    private final ChannelId id;
    //unsafe用于封装对底层socket的相关操作
    private final Unsafe unsafe;
    //为channel分配独立的pipeline用于IO事件编排
    private final DefaultChannelPipeline pipeline;
    protected AbstractChannel(Channel parent) {
        this.parent = parent;
        //channel全局唯一ID machineId+processId+sequence+timestamp+random
        id = newId();
        //unsafe用于定义实现对Channel的底层操作
        unsafe = newUnsafe();
        //为channel分配独立的pipeline用于IO事件编排
        pipeline = newChannelPipeline();
    }
}
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   private DefaultChannelId() {
        data = new byte[MACHINE_ID.length + PROCESS_ID_LEN + SEQUENCE_LEN + TIMESTAMP_LEN + RANDOM_LEN];
        int i = 0;
        // machineId
        System.arraycopy(MACHINE_ID, 0, data, i, MACHINE_ID.length);
        i += MACHINE_ID.length;
        // processId
        i = writeInt(i, PROCESS_ID);
        // sequence
        i = writeInt(i, nextSequence.getAndIncrement());
        // timestamp (kind of)
        i = writeLong(i, Long.reverse(System.nanoTime()) ^ System.currentTimeMillis());
        // random
        int random = PlatformDependent.threadLocalRandom().nextInt();
        i = writeInt(i, random);
        assert i == data.length;
        hashCode = Arrays.hashCode(data);
    }
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interface Unsafe {       
        //分配接收数据用的Buffer
        RecvByteBufAllocator.Handle recvBufAllocHandle();
        //服务端绑定的端口地址
        SocketAddress localAddress();
        //远端地址
        SocketAddress remoteAddress();
        //channel向Reactor注册
        void register(EventLoop eventLoop, ChannelPromise promise);
        //服务端绑定端口地址
        void bind(SocketAddress localAddress, ChannelPromise promise);
        //客户端连接服务端
        void connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise);
        //关闭channle
        void close(ChannelPromise promise);
        //读数据
        void beginRead();
        //写数据
        void write(Object msg, ChannelPromise promise);
    }
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  protected DefaultChannelPipeline(Channel channel) {
        this.channel = ObjectUtil.checkNotNull(channel, "channel");
        succeededFuture = new SucceededChannelFuture(channel, null);
        voidPromise =  new VoidChannelPromise(channel, true);
        tail = new TailContext(this);
        head = new HeadContext(this);
        head.next = tail;
        tail.prev = head;
    }
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  void init(Channel channel) {
        //向NioServerSocketChannelConfig设置ServerSocketChannelOption
        setChannelOptions(channel, newOptionsArray(), logger);
        //向netty自定义的NioServerSocketChannel设置attributes
        setAttributes(channel, attrs0().entrySet().toArray(EMPTY_ATTRIBUTE_ARRAY));
        ChannelPipeline p = channel.pipeline();        
        //获取从Reactor线程组
        final EventLoopGroup currentChildGroup = childGroup;
        //获取用于初始化客户端NioSocketChannel的ChannelInitializer
        final ChannelHandler currentChildHandler = childHandler;
        //获取用户配置的客户端SocketChannel的channelOption以及attributes
        final Entry<ChannelOption<?>, Object>[] currentChildOptions;
        synchronized (childOptions) {
            currentChildOptions = childOptions.entrySet().toArray(EMPTY_OPTION_ARRAY);
        }
        final Entry<AttributeKey<?>, Object>[] currentChildAttrs = childAttrs.entrySet().toArray(EMPTY_ATTRIBUTE_ARRAY);
        //向NioServerSocketChannel中的pipeline添加初始化ChannelHandler的逻辑
        p.addLast(new ChannelInitializer<Channel>() {
            @Override
            public void initChannel(final Channel ch) {
                final ChannelPipeline pipeline = ch.pipeline();
                //ServerBootstrap中用户指定的channelHandler
                ChannelHandler handler = config.handler();
                if (handler != null) {
                    //LoggingHandler
                    pipeline.addLast(handler);
                }
                //添加用于接收客户端连接的acceptor
                ch.eventLoop().execute(new Runnable() {
                    @Override
                    public void run() {
                        pipeline.addLast(new ServerBootstrapAcceptor(
                                ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
                    }
                });
            }
        });
    }
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ChannelFuture regFuture = config().group().register(channel);
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    @Override
    public ChannelFuture register(Channel channel) {
        return next().register(channel);
    }
    @Override
    public EventExecutor next() {
        return chooser.next();
    }
    //获取绑定策略
    @Override
    public EventExecutorChooser newChooser(EventExecutor[] executors) {
        if (isPowerOfTwo(executors.length)) {
            return new PowerOfTwoEventExecutorChooser(executors);
        } else {
            return new GenericEventExecutorChooser(executors);
        }
    }   
    //采用轮询round-robin的方式选择Reactor
    @Override
    public EventExecutor next() {
            return executors[(int) Math.abs(idx.getAndIncrement() % executors.length)];
    }
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public abstract class SingleThreadEventLoop extends SingleThreadEventExecutor implements EventLoop {
    @Override
    public ChannelFuture register(Channel channel) {
        //注册channel到绑定的Reactor上
        return register(new DefaultChannelPromise(channel, this));
    }
    @Override
    public ChannelFuture register(final ChannelPromise promise) {
        ObjectUtil.checkNotNull(promise, "promise");
        //unsafe负责channel底层的各种操作
        promise.channel().unsafe().register(this, promise);
        return promise;
    }
}
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protected abstract class AbstractUnsafe implements Unsafe {
        /**
         * 注册Channel到绑定的Reactor上
         * */
        @Override
        public final void register(EventLoop eventLoop, final ChannelPromise promise) {
            ObjectUtil.checkNotNull(eventLoop, "eventLoop");
            if (isRegistered()) {
                promise.setFailure(new IllegalStateException("registered to an event loop already"));
                return;
            }
            //EventLoop的类型要与Channel的类型一样  Nio Oio Aio
            if (!isCompatible(eventLoop)) {
                promise.setFailure(
                        new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
                return;
            }
            //在channel上设置绑定的Reactor
            AbstractChannel.this.eventLoop = eventLoop;
            /**
             * 执行channel注册的操作必须是Reactor线程来完成
             *
             * 1: 如果当前执行线程是Reactor线程，则直接执行register0进行注册
             * 2：如果当前执行线程是外部线程，则需要将register0注册操作 封装程异步Task 由Reactor线程执行
             * */
            if (eventLoop.inEventLoop()) {
                register0(promise);
            } else {
                try {
                    eventLoop.execute(new Runnable() {
                        @Override
                        public void run() {
                            register0(promise);
                        }
                    });
                } catch (Throwable t) {
                   ...............省略...............
                }
            }
        }
}
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  eventLoop.execute(new Runnable() {
                        @Override
                        public void run() {
                            register0(promise);
                        }
                    });
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public abstract class SingleThreadEventExecutor extends AbstractScheduledEventExecutor implements OrderedEventExecutor {
    @Override
    public void execute(Runnable task) {
        ObjectUtil.checkNotNull(task, "task");
        execute(task, !(task instanceof LazyRunnable) && wakesUpForTask(task));
    }
    private void execute(Runnable task, boolean immediate) {
        //当前线程是否为Reactor线程
        boolean inEventLoop = inEventLoop();
        //addTaskWakesUp = true  addTask唤醒Reactor线程执行任务
        addTask(task);
        if (!inEventLoop) {
            //如果当前线程不是Reactor线程，则启动Reactor线程
            //这里可以看出Reactor线程的启动是通过 向NioEventLoop添加异步任务时启动的
            startThread();
            .....................省略.....................
        }
        .....................省略.....................
    }
}
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public abstract class SingleThreadEventExecutor extends AbstractScheduledEventExecutor implements OrderedEventExecutor {
    //定义Reactor线程状态
    private static final int ST_NOT_STARTED = 1;
    private static final int ST_STARTED = 2;
    private static final int ST_SHUTTING_DOWN = 3;
    private static final int ST_SHUTDOWN = 4;
    private static final int ST_TERMINATED = 5;
     //Reactor线程状态  初始为 未启动状态
    private volatile int state = ST_NOT_STARTED;
    //Reactor线程状态字段state 原子更新器
    private static final AtomicIntegerFieldUpdater<SingleThreadEventExecutor> STATE_UPDATER =
    AtomicIntegerFieldUpdater.newUpdater(SingleThreadEventExecutor.class, "state");
    private void startThread() {
        if (state == ST_NOT_STARTED) {
            if (STATE_UPDATER.compareAndSet(this, ST_NOT_STARTED, ST_STARTED)) {
                boolean success = false;
                try {
                    doStartThread();
                    success = true;
                } finally {
                    if (!success) {
                        STATE_UPDATER.compareAndSet(this, ST_STARTED, ST_NOT_STARTED);
                    }
                }
            }
        }
    }
}
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  //ThreadPerTaskExecutor 用于启动Reactor线程
    private final Executor executor;
    private void doStartThread() {
        assert thread == null;
        executor.execute(new Runnable() {
            @Override
            public void run() {
                thread = Thread.currentThread();
                if (interrupted) {
                    thread.interrupt();
                }
                boolean success = false;
                updateLastExecutionTime();
                try {
                    //Reactor线程开始启动
                    SingleThreadEventExecutor.this.run();
                    success = true;
                }
              
                ................省略..............
        }
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public final class ThreadPerTaskExecutor implements Executor {
    private final ThreadFactory threadFactory;
    @Override
    public void execute(Runnable command) {
        //启动Reactor线程
        threadFactory.newThread(command).start();
    }
}
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    //true if the channel has never been registered, false otherwise 
        private boolean neverRegistered = true;
        private void register0(ChannelPromise promise) {
            try {
                //查看注册操作是否已经取消，或者对应channel已经关闭
                if (!promise.setUncancellable() || !ensureOpen(promise)) {
                    return;
                }
                boolean firstRegistration = neverRegistered;
                //执行真正的注册操作
                doRegister();
                //修改注册状态
                neverRegistered = false;
                registered = true;
                //回调pipeline中添加的ChannelInitializer的handlerAdded方法，在这里初始化channelPipeline
                pipeline.invokeHandlerAddedIfNeeded();
                //设置regFuture为success，触发operationComplete回调,将bind操作放入Reactor的任务队列中，等待Reactor线程执行。
                safeSetSuccess(promise);
                //触发channelRegister事件
                pipeline.fireChannelRegistered();
                //对于服务端ServerSocketChannel来说 只有绑定端口地址成功后 channel的状态才是active的。
                //此时绑定操作作为异步任务在Reactor的任务队列中，绑定操作还没开始，所以这里的isActive()是false
                if (isActive()) {
                    if (firstRegistration) {
                        //触发channelActive事件
                        pipeline.fireChannelActive();
                    } else if (config().isAutoRead()) {
                        beginRead();
                    }
                }
            } catch (Throwable t) {
                 ............省略.............
            }
        }
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public abstract class AbstractChannel extends DefaultAttributeMap implements Channel {
   /**
     * Is called after the {@link Channel} is registered with its {@link EventLoop} as part of the register process.
     *
     * Sub-classes may override this method
     */
    protected void doRegister() throws Exception {
        // NOOP
    }
}
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public abstract class AbstractNioChannel extends AbstractChannel {
    //channel注册到Selector后获得的SelectKey
    volatile SelectionKey selectionKey;
    @Override
    protected void doRegister() throws Exception {
        boolean selected = false;
        for (;;) {
            try {
                selectionKey = javaChannel().register(eventLoop().unwrappedSelector(), 0, this);
                return;
            } catch (CancelledKeyException e) {
                ...............省略....................
            }
        }
    }

}
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public abstract class ChannelInitializer<C extends Channel> extends ChannelInboundHandlerAdapter {
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        if (ctx.channel().isRegistered()) {
            if (initChannel(ctx)) {
                //初始化工作完成后，需要将自身从pipeline中移除
                removeState(ctx);
            }
        }
    }
    //ChannelInitializer实例是被所有的Channel共享的，用于初始化ChannelPipeline
    //通过Set集合保存已经初始化的ChannelPipeline，避免重复初始化同一ChannelPipeline
    private final Set<ChannelHandlerContext> initMap = Collections.newSetFromMap(
            new ConcurrentHashMap<ChannelHandlerContext, Boolean>());

    private boolean initChannel(ChannelHandlerContext ctx) throws Exception {
        if (initMap.add(ctx)) { // Guard against re-entrance.
            try {
                initChannel((C) ctx.channel());
            } catch (Throwable cause) {
                exceptionCaught(ctx, cause);
            } finally {
                ChannelPipeline pipeline = ctx.pipeline();
                if (pipeline.context(this) != null) {
                     //初始化完毕后，从pipeline中移除自身
                    pipeline.remove(this);
                }
            }
            return true;
        }
        return false;
    }
    //匿名类实现，这里指定具体的初始化逻辑
    protected abstract void initChannel(C ch) throws Exception;

    private void removeState(final ChannelHandlerContext ctx) {
        //从initMap防重Set集合中删除ChannelInitializer
        if (ctx.isRemoved()) {
            initMap.remove(ctx);
        } else {
            ctx.executor().execute(new Runnable() {
                @Override
                public void run() {
                    initMap.remove(ctx);
                }
            });
        }
    }
}
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   p.addLast(new ChannelInitializer<Channel>() {
            @Override
            public void initChannel(final Channel ch) {
                final ChannelPipeline pipeline = ch.pipeline();
                //ServerBootstrap中用户指定的channelHandler
                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));
                    }
                });
            }
        });
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public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable {
    private ChannelFuture doBind(final SocketAddress localAddress) {
        //异步创建，初始化，注册ServerSocketChannel
        final ChannelFuture regFuture = initAndRegister();
        final Channel channel = regFuture.channel();
        if (regFuture.cause() != null) {
            return regFuture;
        }
        if (regFuture.isDone()) {
            //如果注册完成，则进行绑定操作
            ChannelPromise promise = channel.newPromise();
            doBind0(regFuture, channel, localAddress, promise);
            return promise;
        } else {
            final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel);
            //添加注册完成 回调函数
            regFuture.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                         ...............省略...............
                          // 注册完成后，Reactor线程回调这里
                        doBind0(regFuture, channel, localAddress, promise);
                    }
                }
            });
            return promise;
        }
    }
}
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   protected final void safeSetSuccess(ChannelPromise promise) {
        if (!(promise instanceof VoidChannelPromise) && !promise.trySuccess()) {
           logger.warn("Failed to mark a promise as success because it is done already: {}", promise);
        }
   }
   @Override
    public boolean trySuccess() {
        return trySuccess(null);
    }
    @Override
    public boolean trySuccess(V result) {
        return setSuccess0(result);
    }
   private boolean setSuccess0(V result) {
        return setValue0(result == null ? SUCCESS : result);
    }
    private boolean setValue0(Object objResult) {
        if (RESULT_UPDATER.compareAndSet(this, null, objResult) ||
            RESULT_UPDATER.compareAndSet(this, UNCANCELLABLE, objResult)) {
            if (checkNotifyWaiters()) {
                //回调注册在promise上的listeners
                notifyListeners();
            }
            return true;
        }
        return false;
    }
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public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable {
    private static void doBind0(
            final ChannelFuture regFuture, final Channel channel,
            final SocketAddress localAddress, final ChannelPromise promise) {
        channel.eventLoop().execute(new Runnable() {
            @Override
            public void run() {
                if (regFuture.isSuccess()) {
                    channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
                } else {
                    promise.setFailure(regFuture.cause());
                }
            }
        });
    }

}
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 private void register0(ChannelPromise promise) {
            try {
                ................省略............
                doRegister();
                pipeline.invokeHandlerAddedIfNeeded();
                safeSetSuccess(promise);
                //触发channelRegister事件
                pipeline.fireChannelRegistered();
                if (isActive()) {
                     ................省略............
                }
            } catch (Throwable t) {
                  ................省略............
            }
        }
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public interface ChannelOutboundInvoker {
    /**
     * Request to bind to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation
     * completes, either because the operation was successful or because of an error.
     *
     */
    ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise);
}
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public abstract class AbstractChannel extends DefaultAttributeMap implements Channel {
   @Override
    public ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
        return pipeline.bind(localAddress, promise);
    }
}
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  final class HeadContext extends AbstractChannelHandlerContext
            implements ChannelOutboundHandler, ChannelInboundHandler {
     @Override
        public void bind(
                ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise) {
            //触发AbstractChannel->bind方法 执行JDK NIO SelectableChannel 执行底层绑定操作
            unsafe.bind(localAddress, promise);
        }
}
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protected abstract class AbstractUnsafe implements Unsafe {
      @Override
        public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
            .................省略................
            //这时channel还未激活  wasActive = false
            boolean wasActive = isActive();
            try {
                //io.netty.channel.socket.nio.NioServerSocketChannel.doBind
                //调用具体channel实现类
                doBind(localAddress);
            } catch (Throwable t) {
                .................省略................
                return;
            }
            //绑定成功后 channel激活 触发channelActive事件传播
            if (!wasActive && isActive()) {
                invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        //pipeline中触发channelActive事件
                        pipeline.fireChannelActive();
                    }
                });
            }
            //回调注册在promise上的ChannelFutureListener
            safeSetSuccess(promise);
        }
        protected abstract void doBind(SocketAddress localAddress) throws Exception;
}
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  @Override
    protected void doBind(SocketAddress localAddress) throws Exception {
        //调用JDK NIO 底层SelectableChannel 执行绑定操作
        if (PlatformDependent.javaVersion() >= 7) {
            javaChannel().bind(localAddress, config.getBacklog());
        } else {
            javaChannel().socket().bind(localAddress, config.getBacklog());
        }
    }
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    final class HeadContext extends AbstractChannelHandlerContext
            implements ChannelOutboundHandler, ChannelInboundHandler {
        @Override
        public void channelActive(ChannelHandlerContext ctx) {
            //pipeline中继续向后传播channelActive事件
            ctx.fireChannelActive();
            //如果是autoRead 则自动触发read事件传播
            //在read回调函数中 触发OP_ACCEPT注册
            readIfIsAutoRead();
        }
        private void readIfIsAutoRead() {
            if (channel.config().isAutoRead()) {
                //如果是autoRead 则触发read事件传播
                channel.read();
            }
        }
        //AbstractChannel
        public Channel read() {
                //触发read事件
                pipeline.read();
                return this;
        }
       @Override
        public void read(ChannelHandlerContext ctx) {
            //触发注册OP_ACCEPT或者OP_READ事件
            unsafe.beginRead();
        }
   }
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protected abstract class AbstractUnsafe implements Unsafe {
     @Override
        public final void beginRead() {
            assertEventLoop();
            //channel必须是Active
            if (!isActive()) {
                return;
            }
            try {
                // 触发在selector上注册channel感兴趣的监听事件
                doBeginRead();
            } catch (final Exception e) {
               .............省略..............
            }
        }
}
public abstract class AbstractChannel extends DefaultAttributeMap implements Channel {
    //子类负责继承实现
    protected abstract void doBeginRead() throws Exception;
}
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public abstract class AbstractNioChannel extends AbstractChannel {
    //channel注册到Selector后获得的SelectKey
    volatile SelectionKey selectionKey;
    // Channel监听事件集合
    protected final int readInterestOp;
    @Override
    protected void doBeginRead() throws Exception {     
        final SelectionKey selectionKey = this.selectionKey;
        if (!selectionKey.isValid()) {
            return;
        }
        readPending = true;

        final int interestOps = selectionKey.interestOps();
        /**
         * 1：ServerSocketChannel 初始化时 readInterestOp设置的是OP_ACCEPT事件
         * */
        if ((interestOps & readInterestOp) == 0) {
            //添加OP_ACCEPT事件到interestOps集合中
            selectionKey.interestOps(interestOps | readInterestOp);
        }
    }
}
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