netty服务端辅助类ServerBootstrap如何创建

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ServerBootstrap创建

ServerBootstrap 为 netty 建立服务端的辅助类, 以 NIO为例，创建代码如下：

public static void main(String[] args) throws Exception {        ServerBootstrap bs = new ServerBootstrap();        bs.group(new NioEventLoopGroup(1), new NioEventLoopGroup())                .channel(NiOServerSocketChannel.class)                .childHandler(new ChannelInitializer<Channel>() {                    @Override                    protected void initChannel(Channel ch) throws Exception {                        ch.pipeline()                        .addLast(new httpserverCodec())                        .addLast(new HttpObjectAggregator(65535))                        .addLast(new Controller());                    }                }).bind(8080).sync().channel().closeFuture().sync();    }

核心参数

//配置属性，如 SO_KEEPALIVE 等private final ServerBootstrapConfig config = new ServerBootstrapConfig(this);    //acceot 的 子channel所绑定的 事件循环组"    private volatile EventLoopGroup childGroup;    private volatile ChannelHandler childHandler;

初始化流程

主要为 绑定本地端口 -> 注册自身到 EventLoop ， 并注册 accept 和 read 事件 -> EventLoop的主循环中会不断的select注册的channel的事件，并处理。

首先执行绑定

核心逻辑位于 

io.netty.bootstrap.AbstractBootstrap.doBind(SocketAddress) 和  io.netty.bootstrap.AbstractBootstrap.initAndReGISter()中

private ChannelFuture doBind(final SocketAddress localAddress) {        final ChannelFuture regFuture = initAndRegister();        ..........if (regFuture.isDone()) {            // At this point we know that the registration was complete and successful.            ChannelPromise promise = channel.newPromise();            //绑定逻辑            doBind0(regFuture, channel, localAddress, promise);            return promise;        } else {            // Registration future is almost always fulfilled already, but just in case it's not.            final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel);            regFuture.addListener(new ChannelFutureListener() {                @Override                public void operationComplete(ChannelFuture future) throws Exception {                    Throwable cause = future.cause();                    if (cause != null) {                        // Registration on the EventLoop failed so fail the ChannelPromise directly to not cause an                        // IllegalStateException once we try to access the EventLoop of the Channel.                        promise.setFailure(cause);                    } else {                        // Registration was successful, so set the correct executor to use.                        // See https://GitHub.com/netty/netty/issues/2586                        promise.registered();                        doBind0(regFuture, channel, localAddress, promise);                    }                }            });            return promise;        }    }

注册自身到 EventLoop

先来看 initAndRegister ， 核心逻辑就是利用channelFactory初始化一个NioServerSocketChannel实例，并为其设置上config中的参数，然后将其注册到EventLoop中，实际上是委托的channel的Unsafe来实现注册的，核心逻辑位于 AbstractUnsafe.register0 中 完成注册

final ChannelFuture initAndRegister() {        Channel channel = null;        try {            //本例子中实际调用的是  NioServerSocketChannel的构造参数， 并为其设置感兴趣的事件类型为  OP_ACCEPT            channel = channelFactory.newChannel();            init(channel);        } catch (Throwable t) {            if (channel != null) {                // channel can be null if newChannel crashed (eg SocketException("too many open files"))                channel.unsafe().closeForcibly();            }            // as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor            return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t);        }        ChannelFuture regFuture = config().group().register(channel);        if (regFuture.cause() != null) {            if (channel.isRegistered()) {                channel.close();            } else {                channel.unsafe().closeForcibly();            }        }         return regFuture;    }

 void init(Channel channel) throws Exception {         //设置属性          ..........         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() {                         //为NioServerSocketChannel 设置一个 默认的 channelhandler ： ServerBootstrapAcceptor ， 当发生 accept事件时，将 accept的channel注册到 childEventLoop中                         pipeline.addLast(new ServerBootstrapAcceptor(                                 ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));                     }                 });             }         });     }

private void register0(ChannelPromise promise) {            try {                // check if the channel is still open as it could be closed in the mean time when the register                // call was outside of the eventLoop                if (!promise.setUncancellable() || !ensureOpen(promise)) {                    return;                }                boolean firstRegistration = neverRegistered;                //执行channel到 eventloop的 selector                doRegister();                neverRegistered = false;                registered = true;                // Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the                // user may already fire events through the pipeline in the ChannelFutureListener.                pipeline.invokeHandlerAddedIfNeeded();                safeSetSuccess(promise);

//触发 InboundChannelHnader.channelRegistered 事件                  pipeline.fireChannelRegistered();

// Only fire a channelActive if the channel has never been registered. This prevents firing // multiple channel actives if the channel is deregistered and re-registered. if (isActive()) { if (firstRegistration) {                        //触发channelActive事件，并会为 channel 绑定上 read 事件                         pipeline.fireChannelActive();                    } else if (config().isAutoRead()) {                        // This channel was registered before and autoRead() is set. This means we need to begin read                        // again so that we process inbound data.                        //                        // See https://github.com/netty/netty/issues/4805                        beginRead();                    }                }            } catch (Throwable t) {                // Close the channel directly to avoid FD leak.                closeForcibly();                closeFuture.setClosed();                safeSetFailure(promise, t);            }        }

绑定端口逻辑

initAndRegister注册成功后,开始执行真正的绑定端口逻辑，核心逻辑位于 NioSocketChannel.doBind0(SocketAddress) 中

private void doBind0(SocketAddress localAddress) throws Exception {        if (PlatfORMDependent.javaVersion() >= 7) {            SocketUtils.bind(javaChannel(), localAddress);        } else {            SocketUtils.bind(javaChannel().socket(), localAddress);        }    }

至此 绑定个成功， 当触发 ACCEPT 事件时， 会触发  NioServerSocketChannel.doReadMessages -> ServerBootstrapAcceptor.channelRead , 并将 子channel 注册到 childEventLoop中

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 {                //注册channel                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);            }        }

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