09 - ServerBootstrap-绑定过程doBind0

Posted 2021-09-16 1160636144

1. 前面说ServerBootstrap的bind()方法内部进行了注册register和绑定bind0，第4节已经分析了register，这里分析bind0过程

   class AbstractBootstrap {
   private ChannelFuture doBind(final SocketAddress localAddress) {
       ChannelFuture regFuture = initAndRegister(); // 初始化Channel并注册
       Channel channel = regFuture.channel();
       if (regFuture.isDone()) {                    // 注册Channel完成，调用doBind0绑定
           ChannelPromise promise = channel.newPromise();
           doBind0(regFuture, channel, localAddress, promise);
           return promise;
       } else {                                     // 注册Channel未完成，添加操作完成监听并调用doBind0绑定
           final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel);
           regFuture.addListener(new ChannelFutureListener() 
               public void operationComplete(ChannelFuture future) throws Exception {
                   Throwable cause = future.cause();
                   if (cause != null) {
                       promise.setFailure(cause);
                   } else {
                       promise.registered();
                       doBind0(regFuture, channel, localAddress, promise);
                   }
               }
           });
           return promise;
       }
   }
   }

2. doBind0内部会获取到该channel绑定的eventLoop并提交任务进行异步Bind。根据内部判断逻辑，只有regFuture.isSuccess()才会进行绑定，即只有注册成功之后才会执行bind操作。

   class AbstractBootstrap {
   private static void doBind0(
           final ChannelFuture regFuture,
           final Channel channel,
           final SocketAddress localAddress,
           final ChannelPromise promise) {
       channel.eventLoop().execute(new Runnable() {
           public void run() {
               if (regFuture.isSuccess()) {
                   channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
               } else {
                   promise.setFailure(regFuture.cause());
               }
           }
       });
   }
   }

3. 当eventLoop轮询线程获取到bind任务时，对于Channel来说可视为发生一次出栈事件。Channel会从其pipeline的tail开始查找首个覆写了bind方法的outBoundHandler（即: 找到headContext）然后调用其bind()方法。。

   class AbstractChannel {
   public ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
       return pipeline.bind(localAddress, promise);
   }
   }
   class DefaultChannelPipeline {
   public final ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
       return tail.bind(localAddress, promise);
   }
   }
   class AbstractChannelHandlerContext {
   public ChannelFuture bind(final SocketAddress localAddress, final ChannelPromise promise) {
       final AbstractChannelHandlerContext next = findContextOutbound(MASK_BIND); // 找到首个覆写了bind方法的handler
       EventExecutor executor = next.executor();
       if (executor.inEventLoop()) {
           next.invokeBind(localAddress, promise) {   // 调用bind方法
               ((ChannelOutboundHandler) handler()).bind(this, localAddress, promise)
           }
       } else {
           safeExecute(executor, new Runnable() {
               public void run() {
                   next.invokeBind(localAddress, promise);
               }
           }, promise, null, false);
       }
       return promise;
   }
   }

4. 在headContext覆写的bind方法中，调用了doBind()方法，内部调用了原生JavaNio的bind方法进行绑定。在doBind()成功之后，会提交个异步任务(invokeLater)，来触发channelActive。在active内部进行注册了channel的interestOps。

   class AbstractChannelHandlerContext {
   public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
       boolean wasActive = isActive();
       doBind(localAddress) {
           javaChannel().bind(localAddress, config.getBacklog());
       }
       // 完成绑定之后还做了其它事情，这里会递归调用pipeline上所有handler的channelActive方法
       if (!wasActive && isActive()) {
           invokeLater(new Runnable() {
               public void run() {
                   pipeline.fireChannelActive() {
                       ((ChannelInboundHandler) handler()).channelActive(this);
                   }
               }
           });
       }
       safeSetSuccess(promise);
   }
   }

   总结:

   serverBootstrap的bind(port)方法:
   sb.bind( port )
   |__ doBind()
   |__ initAndRegister()
       |__ ...
   |__ bind0()
       |__ channel.eventLoop().execute( bind() )
           |__ nioEventLoop.run()
               |__ bind()
                   |__ doBind()
                   |__ eventLoop().execute( fireChannelActive() )
               |__ fireChannelActive()