DiscardServer
1 package io.netty.example.discard; 2 ?????3 import io.netty.bootstrap.ServerBootstrap; 4 ?5 import io.netty.channel.ChannelFuture; 6 import io.netty.channel.ChannelInitializer; 7 import io.netty.channel.ChannelOption; 8 import io.netty.channel.EventLoopGroup; 9 import io.netty.channel.nio.NioEventLoopGroup;10 import io.netty.channel.socket.SocketChannel;11 import io.netty.channel.socket.nio.NioServerSocketChannel;12 ????13 /**14 ?* Discards any incoming data.15 ?*/16 public class DiscardServer {17 ????18 ????private int port;19 ????20 ????public DiscardServer(int port) {21 ????????this.port = port;22 ????}23 ????24 ????public void run() throws Exception {25 ????????EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)26 ????????EventLoopGroup workerGroup = new NioEventLoopGroup();27 ????????try {28 ????????????ServerBootstrap b = new ServerBootstrap(); // (2)29 ????????????b.group(bossGroup, workerGroup)30 ?????????????.channel(NioServerSocketChannel.class) // (3)31 ?????????????.childHandler(new ChannelInitializer<SocketChannel>() { // (4)32 ?????????????????@Override33 ?????????????????public void initChannel(SocketChannel ch) throws Exception {34 ?????????????????????ch.pipeline().addLast(new DiscardServerHandler());35 ?????????????????}36 ?????????????})37 ?????????????.option(ChannelOption.SO_BACKLOG, 128) ?????????// (5)38 ?????????????.childOption(ChannelOption.SO_KEEPALIVE, true); // (6)39 ????40 ????????????// Bind and start to accept incoming connections.41 ????????????ChannelFuture f = b.bind(port).sync(); // (7)42 ????43 ????????????// Wait until the server socket is closed.44 ????????????// In this example, this does not happen, but you can do that to gracefully45 ????????????// shut down your server.46 ????????????f.channel().closeFuture().sync();47 ????????} finally {48 ????????????workerGroup.shutdownGracefully();49 ????????????bossGroup.shutdownGracefully();50 ????????}51 ????}52 ????53 ????public static void main(String[] args) throws Exception {54 ????????int port;55 ????????if (args.length > 0) {56 ????????????port = Integer.parseInt(args[0]);57 ????????} else {58 ????????????port = 8080;59 ????????}60 ????????new DiscardServer(port).run();61 ????}62 }构造Bootstrap时，有一个很重要的元素就是eventLoopGroup，eventLoopGroup继承了eventExecutorGroup，eventExecutorGroup可以认为是eventExecutor的容器，可以通过next()获取到eventExecutor。由下面的类图可知eventExecutorGroup继承了executorService，其具有executorService的特性，比如执行提交的任务（通过next()委托给具体的eventExecutor）并获得代表任务执行进度的Future、关闭执行器（shutdown）等。
eventLoopGroup在eventExecutorGroup的基础上提供了register方法，即可以将channel注册在eventLoop上（eventLoopGroup的register内部仍然会调用next()，将channel注册到具体的eventLoop上）。所谓注册就是将eventLoop与channel绑定，对于nio来说，一个eventLoop（NioEventLoop）会绑定多个channel（还会将channel注册在与eventLoop绑定的selector上），对于oio来说，一个eventLoop（ThreadPerChannelEventLoop）只能绑定一个channel。
下面是EventLoop的类图，EventLoop继承了EventLoopGroup，EventLoop额外提供了inEventLoop()方法来判断当前线程是否在EventLoop中。
我们知道ExecutorService屏蔽了任务如何执行的具体机制，但通常Executor都会持有一个线程池来执行任务，并通过一个阻塞队列来缓存待执行的任务，那EventLoopGroup是怎样的呢？
这里以Nio为例，serverSocketChannel在accept后会将socketChannel注册在EventLoop上，并在EventLoop上execute完成注册操作
//childGroup即在ServerBootstrap中配置的childGroup(EventLoopGroup)childGroup.register(child)
NioEventLoop的execute方法
1 ????public void execute(Runnable task) { 2 ????????if (task == null) { 3 ????????????throw new NullPointerException("task"); 4 ????????} 5 ?6 ????????boolean inEventLoop = inEventLoop(); 7 ????????if (inEventLoop) { 8 ????????????addTask(task); 9 ????????} else {10 ????????????//startThread()会调用executor的execute方法，这个executor就是一个java.util.concurrent.Executor11 ????????????startThread();12 ????????????addTask(task);13 ????????????if (isShutdown() && removeTask(task)) {14 ????????????????reject();15 ????????????}16 ????????}17 18 ????????if (!addTaskWakesUp && wakesUpForTask(task)) {19 ????????????wakeup(inEventLoop);20 ????????}21 ????}EventLoop的execute最终会调用EventLoop中executor的execute，这个executor是哪儿来的呢？
1 public class NioEventLoopGroup extends MultithreadEventLoopGroup { 2 ????//...... 3 ?????4 ????//threadFactory会被包装为一个executor， 5 ????//该executor的execute方法就是threadFactory.newThread(command).start(); 6 ????//threadFactory的newThread一般都会新建thread，因为thread实例只能start一次。 7 ????public NioEventLoopGroup(int nThreads, ThreadFactory threadFactory) { 8 ??????this(nThreads, threadFactory, SelectorProvider.provider()); 9 ????}10 ????11 ????//这里传入的executor就是EventLoop中的executor，12 ????//nThreads表示EventExecutor（EventLoop）的个数，这些eventExecutor会持有同一个executor，13 ????//Group会持有这些eventExecutor，即children，但children还未启动。14 ????//children = new EventExecutor[nThreads];15 ????//迭代children[i] = newChild(executor, args);16 ????public NioEventLoopGroup(int nThreads, Executor executor) {17 ??????this(nThreads, executor, SelectorProvider.provider());18 ????}19 ????20 ????//......21 }由上分析可知，netty中EventLoop的核心在于executor，executor提供了真正的执行能力（即线程），下面就是NioEventLoop在executor中的执行的任务（这里的run并不是Runnable的run），可以看出，所谓EventLoop就是一个循环器，该循环器不停的在处理channel的IO事件。
1 protected void run() { 2 ??for (;;) { 3 ????try { 4 ??????switch (selectStrategy.calculateStrategy(selectNowSupplier, hasTasks())) { 5 ????????case SelectStrategy.CONTINUE: 6 ??????????continue; 7 ????????case SelectStrategy.SELECT: 8 ??????????select(wakenUp.getAndSet(false)); 9 ??????????if (wakenUp.get()) {10 ??????????????selector.wakeup();11 ??????????}12 ????????default:13 ??????????// fallthrough14 ??????}15 16 ??????cancelledKeys = 0;17 ??????needsToSelectAgain = false;18 ??????final int ioRatio = this.ioRatio;19 ??????if (ioRatio == 100) {20 ????????try {21 ??????????processSelectedKeys();22 ????????} finally {23 ??????????// Ensure we always run tasks.24 ??????????runAllTasks();25 ????????}26 ??????} else {27 ????????final long ioStartTime = System.nanoTime();28 ????????try {29 ????????????processSelectedKeys();30 ????????} finally {31 ????????????// Ensure we always run tasks.32 ????????????final long ioTime = System.nanoTime() - ioStartTime;33 ????????????runAllTasks(ioTime * (100 - ioRatio) / ioRatio);34 ????????}35 ??????}36 ????} catch (Throwable t) {37 ??????handleLoopException(t);38 ????}39 ????// Always handle shutdown even if the loop processing threw an exception.40 ????try {41 ??????if (isShuttingDown()) {42 ????????closeAll();43 ????????if (confirmShutdown()) {44 ??????????return;45 ????????}46 ??????}47 ????} catch (Throwable t) {48 ??????handleLoopException(t);49 ????}50 ??}51 }netty-eventloop
原文地址：http://www.cnblogs.com/holoyong/p/7434879.html