在此声明，Netty 是基于java NIO 的，建议知道java NIO 运行机制（Selector,Channel ,ByteBuffer ,zeroCopy） ，再阅读此篇文章，不然会一头雾水
EventLoopGroup :事件循环组：
EventLoopGroup bossGroup =new NioEventLoopGroup();EventLoopGroup workGroup =new NioEventLoopGroup();
主要是完成一些变量的赋值
主要发生了什么：Look，源码就是一层一层的调用构造函数，往里面赋值；
1.extends 多线程事件循环组， 被用于基于channel 的NIO selector 实现
/** * {@link MultithreadEventLoopGroup} implementations which is used for NIO {@link Selector} based {@link Channel}s. */public class NioEventLoopGroup extends MultithreadEventLoopGroup {2.我们一步一步点击下来，发现就是在它的构造函数里面调来调去，我们发现他创建了一个空的 Executor 对象 （java 1. 5 并发库重要内容，执行器，进行线程执行），以及 nThreads 线程数量为 0（这里的0并不是说我们给我们创建 0个线程，后面会有判断）；
?*/ ???public NioEventLoopGroup() { ???????this(0); ???} ???/** ????* Create a new instance using the specified number of threads, {@link ThreadFactory} and the ????* {@link SelectorProvider} which is returned by {@link SelectorProvider#provider()}. ????*/ ???public NioEventLoopGroup(int nThreads) { ???????this(nThreads, (Executor) null); ???}3.我们可以看到在这个构造方法里调用了 SelectorProvider.provider()，这个不陌生吧，在java nio 中创建selector 的Selector.open() 方法中其实调用的就是这个
/** * Create a new instance using the specified number of threads, the given {@link ThreadFactory} and the * {@link SelectorProvider} which is returned by {@link SelectorProvider#provider()}. */ public NioEventLoopGroup(int nThreads, Executor executor) {this(nThreads, executor, SelectorProvider.provider());}4.继续点，可以看到它又添加了一些新的内容 DefaultSelectStrategyFactory 工厂 Factory which uses the default select strategy. 默认的选择策略
public NioEventLoopGroup(int nThreads, Executor executor, final SelectorProvider selectorProvider) {this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);}//在这个构造方法里用添加了一个参数 ?DefaultSelectStrategyFactory.INSTANCE ，提供一个默认选择策略，工厂模式/*** Factory which uses the default select strategy.*/public final class DefaultSelectStrategyFactory implements SelectStrategyFactory {public static final SelectStrategyFactory INSTANCE = new DefaultSelectStrategyFactory();private DefaultSelectStrategyFactory() { }@Overridepublic SelectStrategy newSelectStrategy() {return DefaultSelectStrategy.INSTANCE;}}5. 继续走，这里就开始调用父类super（MultithreadEventLoopGroup）方法了，在这里我们就可以知道默认给我们创建多少线程了；
public NioEventLoopGroup(int nThreads, Executor executor, final SelectorProvider selectorProvider,final SelectStrategyFactory selectStrategyFactory) {super(nThreads, executor, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject());}protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) { super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args); }
//分析线程数量//线程数量判断，如果是0的话，就是 DEFAULT_EVENT_LOOP_THREADS ?，是多少呢？我们点进去看一看，我们会看到一个静态代码块static {DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt("io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));if (logger.isDebugEnabled()) {logger.debug("-Dio.netty.eventLoopThreads: {}", DEFAULT_EVENT_LOOP_THREADS);}}//调用Runtime.availableProcessors将会获取 可用的处理器@SuppressForbidden(reason = "to obtain default number of available processors")synchronized int availableProcessors() {if (this.availableProcessors == 0) {final int availableProcessors =SystemPropertyUtil.getInt("io.netty.availableProcessors",Runtime.getRuntime().availableProcessors());setAvailableProcessors(availableProcessors);}return this.availableProcessors;}由此可以看到 默认创建的线程数不是0 而是根据不同电脑的处理器个数*26，接下来就是Excutor 的赋值了，因为从第二部可以看到，初始的Excutor 的null;
protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object... args) {this(nThreads, executor, DefaultEventExecutorChooserFactory.INSTANCE, args);}protected MultithreadEventExecutorGroup(int nThreads, Executor executor,EventExecutorChooserFactory chooserFactory, Object... args) {if (nThreads <= 0) {throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads));}
//**********源码解释***********//
//我们看红色部分，就是对 executor 进行初始化操作，这里我们需要了解的是Excutor 接口 以及ThreadFactory 接口的作用
//在netty 里实现了ThreadFactory关于自己的DefaultThreadFactoryif (executor == null) {executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());}children = new EventExecutor[nThreads];for (int i = 0; i < nThreads; i ++) {boolean success = false;try {children[i] = newChild(executor, args);success = true;} catch (Exception e) {// TODO: Think about if this is a good exception typethrow new IllegalStateException("failed to create a child event loop", e);} finally {if (!success) {for (int j = 0; j < i; j ++) {children[j].shutdownGracefully();}for (int j = 0; j < i; j ++) {EventExecutor e = children[j];try {while (!e.isTerminated()) {e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);}} catch (InterruptedException interrupted) {// Let the caller handle the interruption.Thread.currentThread().interrupt();break;}}}}}chooser = chooserFactory.newChooser(children);final FutureListener<Object> terminationListener = new FutureListener<Object>() {@Overridepublic void operationComplete(Future<Object> future) throws Exception {if (terminatedChildren.incrementAndGet() == children.length) {terminationFuture.setSuccess(null);}}};for (EventExecutor e: children) {e.terminationFuture().addListener(terminationListener);}Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length);Collections.addAll(childrenSet, children);readonlyChildren = Collections.unmodifiableSet(childrenSet);}Bootstrap: 服务辅助类
Netty ---源码剖析
原文地址：https://www.cnblogs.com/iscys/p/9693796.html