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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