启动服务端的代码如下： publicstaticvoidmain(String[]args)throwsException{SelfSignedCertificatessc=newSelfSigned
启动服务端的代码如下：
public static void main(String[] args) throws Exception { SelfSignedCertificate ssc = new SelfSignedCertificate(); SslContext sslCtx = SslContext.newServerContext(ssc.certificate(), ssc.privateKey()); EventLoopGroup bossGroup = new NioEventLoopGroup(1); EventLoopGroup workerGroup = new NioEventLoopGroup(); try { ServerBootstrap b = new ServerBootstrap(); b.group(bossGroup, workerGroup) .channel(NioServerSocketChannel.class) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new SecureChatServerInitializer(sslCtx)); b.bind(PORT).sync().channel().closeFuture().sync();//调用bind方法时启动线程 } finally { bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); } }其中ServerBootstrap的bind方法通过调用父类的initAndRegister构造一个Channel，并把Channel注册到EventLoopGroup
final ChannelFuture initAndRegister() { final Channel channel = channelFactory().newChannel(); try { init(channel); } catch (Throwable t) { channel.unsafe().closeForcibly(); return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t); } ChannelFuture regFuture = group().register(channel);//把channel注册到EventLoopGroup(NioEventLoopGroup) if (regFuture.cause() != null) { if (channel.isRegistered()) { channel.close(); } else { channel.unsafe().closeForcibly(); } } return regFuture; }注册代码如下
public ChannelFuture register(Channel channel) { return next().register(channel);//从EventLoopGroup里获取一个NioEventLoop,并注册channel } public ChannelFuture register(final Channel channel, final ChannelPromise promise) { if (channel == null) { throw new NullPointerException("channel"); } if (promise == null) { throw new NullPointerException("promise"); } channel.unsafe().register(this, promise);//注册过程其实是把NioEventLoop（中的selector）注册到channel return promise; }可以看到Channel注册到EventLoopGroup的过程被转换成NioEventLoop（中的selector）注册到channel。
转换后的注册过程如下：
public final void register(EventLoop eventLoop, final ChannelPromise promise) { if (eventLoop == null) { throw new NullPointerException("eventLoop"); } if (isRegistered()) { promise.setFailure(new IllegalStateException("registered to an event loop already")); return; } if (!isCompatible(eventLoop)) { promise.setFailure( new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName())); return; } AbstractChannel.this.eventLoop = eventLoop; if (eventLoop.inEventLoop()) { register0(promise); } else {//启动的时候执行else中的代码 try { eventLoop.execute(new OneTimeTask() {//这个方法调用回启动 @Override public void run() { register0(promise); } }); } catch (Throwable t) { logger.warn( "Force-closing a channel whose registration task was not accepted by an event loop: {}", AbstractChannel.this, t); closeForcibly(); closeFuture.setClosed(); safeSetFailure(promise, t); } } }启动的时候执行else里的代码，调用eventLoop的execute方法，该方法启动eventLoop中的线程，并把register0作为一个任务，提交给eventLoop中的任务队列。
register0的代码如下：
private void register0(ChannelPromise promise) { try { if (!promise.setUncancellable() || !ensureOpen(promise)) { return; } boolean firstRegistration = neverRegistered; doRegister(); neverRegistered = false; registered = true; safeSetSuccess(promise); pipeline.fireChannelRegistered(); if (firstRegistration && isActive()) { pipeline.fireChannelActive(); } } catch (Throwable t) { closeForcibly(); closeFuture.setClosed(); safeSetFailure(promise, t); } } protected void doRegister() throws Exception { boolean selected = false; for (;;) { try { selectionKey = javaChannel().register(eventLoop().selector, 0, this);//SelectableChannel return; } catch (CancelledKeyException e) { if (!selected) { eventLoop().selectNow(); selected = true; } else { throw e; } } } }可以看到最终的注册过程是调用jdk的SelectableChannel的register方法，把NioEventLoop的selector注册到了channel上。
下面再看看eventLoop中的线程执行循环,代码如下：
@Override protected void run() { for (;;) { boolean oldWakenUp = wakenUp.getAndSet(false); try { if (hasTasks()) { selectNow(); } else { select(oldWakenUp); if (wakenUp.get()) { selector.wakeup(); } } cancelledKeys = 0; needsToSelectAgain = false; final int ioRatio = this.ioRatio; if (ioRatio == 100) { processSelectedKeys(); runAllTasks(); //执行任务队列中的任务 } else { final long ioStartTime = System.nanoTime(); processSelectedKeys(); final long ioTime = System.nanoTime() - ioStartTime; runAllTasks(ioTime * (100 - ioRatio) / ioRatio);//执行任务队列中的任务 } if (isShuttingDown()) { closeAll(); if (confirmShutdown()) { break; } } } catch (Throwable t) { try { Thread.sleep(1000); } catch (InterruptedException e) { } } } }总结一下：
调用ServerBootstrap的bind方法启动服务端的时候，先创建一个Channel对象，然后从NioEventLoopGroup里获取一个NioEventLoop，然后启动NioEventLoop中的线程，同时把注册任务提交到NioEventLoop中的任务队列。NioEventLoop中的线程循环执行，在一定条件下会执行任务队列中的注册任务，从而把NioEventLoop的selector注册到Channel对象。
