ServerBootstrap的构造：
1 public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel> {
2 private static final InternalLogger logger = InternalLoggerFactory.getInstance(ServerBootstrap.class);
3 private final Map<ChannelOption<?>, Object> childOptions = new LinkedHashMap();
4 private final Map<AttributeKey<?>, Object> childAttrs = new LinkedHashMap();
5 private final ServerBootstrapConfig config = new ServerBootstrapConfig(this);
6 private volatile EventLoopGroup childGroup;
7 private volatile ChannelHandler childHandler;
8
9 public ServerBootstrap() {
10 }
11 ......
12 }
隐式地执行了父类的无参构造：
1 public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable {
2 volatile EventLoopGroup group;
3 private volatile ChannelFactory<? extends C> channelFactory;
4 private volatile SocketAddress localAddress;
5 private final Map<ChannelOption<?>, Object> options = new LinkedHashMap();
6 private final Map<AttributeKey<?>, Object> attrs = new LinkedHashMap();
7 private volatile ChannelHandler handler;
8
9 AbstractBootstrap() {
10 }
11 ......
12 }
只是初始化了几个容器成员
在ServerBootstrap创建后，需要调用group方法，绑定EventLoopGroup，有关EventLoopGroup的创建在我之前博客中写过：Netty中NioEventLoopGroup的创建源码分析
ServerBootstrap的group方法：
1 public ServerBootstrap group(EventLoopGroup group) {
2 return this.group(group, group);
3 }
4
5 public ServerBootstrap group(EventLoopGroup parentGroup, EventLoopGroup childGroup) {
6 super.group(parentGroup);
7 if (childGroup == null) {
8 throw new NullPointerException("childGroup");
9 } else if (this.childGroup != null) {
10 throw new IllegalStateException("childGroup set already");
11 } else {
12 this.childGroup = childGroup;
13 return this;
14 }
15 }
首先调用父类的group方法绑定parentGroup：
1 public B group(EventLoopGroup group) {
2 if (group == null) {
3 throw new NullPointerException("group");
4 } else if (this.group != null) {
5 throw new IllegalStateException("group set already");
6 } else {
7 this.group = group;
8 return this.self();
9 }
10 }
11
12 private B self() {
13 return this;
14 }
将传入的parentGroup绑定给AbstractBootstrap的group成员，将childGroup绑定给ServerBootstrap的childGroup成员。
group的绑定仅仅是交给了成员保存。
再来看看ServerBootstrap的channel方法,，是在AbstractBootstrap中实现的：
1 public B channel(Class<? extends C> channelClass) {
2 if (channelClass == null) {
3 throw new NullPointerException("channelClass");
4 } else {
5 return this.channelFactory((io.netty.channel.ChannelFactory)(new ReflectiveChannelFactory(channelClass)));
6 }
7 }
使用channelClass构建了一个ReflectiveChannelFactory对象：
1 public class ReflectiveChannelFactory<T extends Channel> implements ChannelFactory<T> {
2 private final Class<? extends T> clazz;
3
4 public ReflectiveChannelFactory(Class<? extends T> clazz) {
5 if (clazz == null) {
6 throw new NullPointerException("clazz");
7 } else {
8 this.clazz = clazz;
9 }
10 }
11
12 public T newChannel() {
13 try {
14 return (Channel)this.clazz.getConstructor().newInstance();
15 } catch (Throwable var2) {
16 throw new ChannelException("Unable to create Channel from class " + this.clazz, var2);
17 }
18 }
19
20 public String toString() {
21 return StringUtil.simpleClassName(this.clazz) + ".class";
22 }
23 }
可以看到ReflectiveChannelFactory的作用就是通过反射机制，产生clazz的实例（这里以NioServerSocketChannel为例）。
在创建完ReflectiveChannelFactory对象后， 调用channelFactory方法：
1 public B channelFactory(io.netty.channel.ChannelFactory<? extends C> channelFactory) {
2 return this.channelFactory((ChannelFactory)channelFactory);
3 }
4
5 public B channelFactory(ChannelFactory<? extends C> channelFactory) {
6 if (channelFactory == null) {
7 throw new NullPointerException("channelFactory");
8 } else if (this.channelFactory != null) {
9 throw new IllegalStateException("channelFactory set already");
10 } else {
11 this.channelFactory = channelFactory;
12 return this.self();
13 }
14 }
将刚才创建的ReflectiveChannelFactory对象交给channelFactory成员，用于后续服务端NioServerSocketChannel的创建。
再来看ServerBootstrap的childHandler方法：
1 public ServerBootstrap childHandler(ChannelHandler childHandler) {
2 if (childHandler == null) {
3 throw new NullPointerException("childHandler");
4 } else {
5 this.childHandler = childHandler;
6 return this;
7 }
8 }
还是交给了childHandler成员保存，可以看到上述这一系列的操作，都是为了填充ServerBootstrap，而ServerBootstrap真正的启动是在bind时：
ServerBootstrap的bind方法，在AbstractBootstrap中实现：
1 public ChannelFuture bind(int inetPort) {
2 return this.bind(new InetSocketAddress(inetPort));
3 }
4
5 public ChannelFuture bind(String inetHost, int inetPort) {
6 return this.bind(SocketUtils.socketAddress(inetHost, inetPort));
7 }
8
9 public ChannelFuture bind(InetAddress inetHost, int inetPort) {
10 return this.bind(new InetSocketAddress(inetHost, inetPort));
11 }
12
13 public ChannelFuture bind(SocketAddress localAddress) {
14 this.validate();
15 if (localAddress == null) {
16 throw new NullPointerException("localAddress");
17 } else {
18 return this.doBind(localAddress);
19 }
20 }
可以看到首先调用了ServerBootstrap的validate方法，：
1 public ServerBootstrap validate() {
2 super.validate();
3 if (this.childHandler == null) {
4 throw new IllegalStateException("childHandler not set");
5 } else {
6 if (this.childGroup == null) {
7 logger.warn("childGroup is not set. Using parentGroup instead.");
8 this.childGroup = this.config.group();
9 }
10
11 return this;
12 }
13 }
先调用了AbstractBootstrap的validate方法：
1 public B validate() {
2 if (this.group == null) {
3 throw new IllegalStateException("group not set");
4 } else if (this.channelFactory == null) {
5 throw new IllegalStateException("channel or channelFactory not set");
6 } else {
7 return this.self();
8 }
9 }
这个方法就是用来检查是否绑定了group和channel以及childHandler，所以在执行bind方法前，无论如何都要执行group、channel和childHandler方法。
实际的bind交给了doBind来完成：
1 private ChannelFuture doBind(final SocketAddress localAddress) {
2 final ChannelFuture regFuture = this.initAndRegister();
3 final Channel channel = regFuture.channel();
4 if (regFuture.cause() != null) {
5 return regFuture;
6 } else if (regFuture.isDone()) {
7 ChannelPromise promise = channel.newPromise();
8 doBind0(regFuture, channel, localAddress, promise);
9 return promise;
10 } else {
11 final AbstractBootstrap.PendingRegistrationPromise promise = new AbstractBootstrap.PendingRegistrationPromise(channel);
12 regFuture.addListener(new ChannelFutureListener() {
13 public void operationComplete(ChannelFuture future) throws Exception {
14 Throwable cause = future.cause();
15 if (cause != null) {
16 promise.setFailure(cause);
17 } else {
18 promise.registered();
19 AbstractBootstrap.doBind0(regFuture, channel, localAddress, promise);
20 }
21 }
22 });
23 return promise;
24 }
25 }
首先调用initAndRegister，完成ServerSocketChannel的创建以及注册：
1 final ChannelFuture initAndRegister() {
2 Channel channel = null;
3
4 try {
5 channel = this.channelFactory.newChannel();
6 this.init(channel);
7 } catch (Throwable var3) {
8 if (channel != null) {
9 channel.unsafe().closeForcibly();
10 return (new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE)).setFailure(var3);
11 }
12
13 return (new DefaultChannelPromise(new FailedChannel(), GlobalEventExecutor.INSTANCE)).setFailure(var3);
14 }
15
16 ChannelFuture regFuture = this.config().group().register(channel);
17 if (regFuture.cause() != null) {
18 if (channel.isRegistered()) {
19 channel.close();
20 } else {
21 channel.unsafe().closeForcibly();
22 }
23 }
24
25 return regFuture;
26 }
首先调用channelFactory的newChannel通过反射机制构建Channel实例，也就是NioServerSocketChannel，
NioServerSocketChannel的无参构造：
1 public class NioServerSocketChannel extends AbstractNioMessageChannel implements ServerSocketChannel {
2 private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();
3
4 public NioServerSocketChannel() {
5 this(newSocket(DEFAULT_SELECTOR_PROVIDER));
6 }
7 ......
8 }
SelectorProvider 是JDK的，关于SelectorProvider在我之前的博客中有介绍：【Java】NIO中Selector的创建源码分析
在Windows系统下默认产生WindowsSelectorProvider，即DEFAULT_SELECTOR_PROVIDER，再来看看newSocket方法：
1 private static java.nio.channels.ServerSocketChannel newSocket(SelectorProvider provider) {
2 try {
3 return provider.openServerSocketChannel();
4 } catch (IOException var2) {
5 throw new ChannelException("Failed to open a server socket.", var2);
6 }
7 }
使用WindowsSelectorProvider创建了一个ServerSocketChannelImpl，其实看到这里就明白了，NioServerSocketChannel是为了封装JDK的ServerSocketChannel
接着调用另一个重载的构造：
1 public NioServerSocketChannel(java.nio.channels.ServerSocketChannel channel) {
2 super((Channel)null, channel, 16);
3 this.config = new NioServerSocketChannel.NioServerSocketChannelConfig(this, this.javaChannel().socket());
4 }
首先调用父类的三参构造，其中16对应的是JDK中SelectionKey的ACCEPT状态：
1 public static final int OP_ACCEPT = 1 << 4;
其父类的构造处于一条继承链上：
AbstractNioMessageChannel：
1 protected AbstractNioMessageChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
2 super(parent, ch, readInterestOp);
3 }
AbstractNioChannel：
1 protected AbstractNioChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
2 super(parent);
3 this.ch = ch;
4 this.readInterestOp = readInterestOp;
5
6 try {
7 ch.configureBlocking(false);
8 } catch (IOException var7) {
9 try {
10 ch.close();
11 } catch (IOException var6) {
12 if (logger.isWarnEnabled()) {
13 logger.warn("Failed to close a partially initialized socket.", var6);
14 }
15 }
16
17 throw new ChannelException("Failed to enter non-blocking mode.", var7);
18 }
19 }
AbstractChannel：
1 private final ChannelId id;
2 private final Channel parent;
3 private final Unsafe unsafe;
4 private final DefaultChannelPipeline pipeline;
5
6 protected AbstractChannel(Channel parent) {
7 this.parent = parent;
8 this.id = this.newId();
9 this.unsafe = this.newUnsafe();
10 this.pipeline = this.newChannelPipeline();
11 }
在AbstractChannel中使用newUnsafe和newChannelPipeline分别创建了一个Unsafe和一个DefaultChannelPipeline对象，
在前面的博客介绍NioEventLoopGroup时候，在NioEventLoop的run方法中，每次轮询完调用processSelectedKeys方法时，都是通过这个unsafe根据SelectedKey来完成数据的读或写，unsafe是处理基础的数据读写
（unsafe在NioServerSocketChannel创建时，产生NioMessageUnsafe实例，在NioSocketChannel创建时产生NioSocketChannelUnsafe实例）
而pipeline的实现是一条双向责任链，负责处理unsafe提供的数据，进而进行用户的业务逻辑 （Netty中的ChannelPipeline源码分析）
在AbstractNioChannel中调用configureBlocking方法给JDK的ServerSocketChannel设置为非阻塞模式，且让readInterestOp成员赋值为16用于未来注册ACCEPT事件。
在调用完继承链后回到NioServerSocketChannel构造，调用了javaChannel方法：
1 protected java.nio.channels.ServerSocketChannel javaChannel() {
2 return (java.nio.channels.ServerSocketChannel)super.javaChannel();
3 }
其实这个javaChannel就是刚才出传入到AbstractNioChannel中的ch成员：
1 protected SelectableChannel javaChannel() {
2 return this.ch;
3 }
也就是刚才创建的JDK的ServerSocketChannelImpl，用其socket方法，得到一个ServerSocket对象，然后产生了一个NioServerSocketChannelConfig对象，用于封装相关信息。
NioServerSocketChannel构建完毕，回到initAndRegister方法，使用刚创建的NioServerSocketChannel调用init方法，这个方法是在ServerBootstrap中实现的：
1 void init(Channel channel) throws Exception {
2 Map<ChannelOption<?>, Object> options = this.options0();
3 synchronized(options) {
4 setChannelOptions(channel, options, logger);
5 }
6
7 Map<AttributeKey<?>, Object> attrs = this.attrs0();
8 synchronized(attrs) {
9 Iterator var5 = attrs.entrySet().iterator();
10
11 while(true) {
12 if (!var5.hasNext()) {
13 break;
14 }
15
16 Entry<AttributeKey<?>, Object> e = (Entry)var5.next();
17 AttributeKey<Object> key = (AttributeKey)e.getKey();
18 channel.attr(key).set(e.getValue());
19 }
20 }
21
22 ChannelPipeline p = channel.pipeline();
23 final EventLoopGroup currentChildGroup = this.childGroup;
24 final ChannelHandler currentChildHandler = this.childHandler;
25 Map var9 = this.childOptions;
26 final Entry[] currentChildOptions;
27 synchronized(this.childOptions) {
28 currentChildOptions = (Entry[])this.childOptions.entrySet().toArray(newOptionArray(0));
29 }
30
31 var9 = this.childAttrs;
32 final Entry[] currentChildAttrs;
33 synchronized(this.childAttrs) {
34 currentChildAttrs = (Entry[])this.childAttrs.entrySet().toArray(newAttrArray(0));
35 }
36
37 p.addLast(new ChannelHandler[]{new ChannelInitializer<Channel>() {
38 public void initChannel(final Channel ch) throws Exception {
39 final ChannelPipeline pipeline = ch.pipeline();
40 ChannelHandler handler = ServerBootstrap.this.config.handler();
41 if (handler != null) {
42 pipeline.addLast(new ChannelHandler[]{handler});
43 }
44
45 ch.eventLoop().execute(new Runnable() {
46 public void run() {
47 pipeline.addLast(new ChannelHandler[]{new ServerBootstrap.ServerBootstrapAcceptor(ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs)});
48 }
49 });
50 }
51 }});
52 }
首先对attrs和options这两个成员进行了填充属性配置，这不是重点，然后获取刚才创建的NioServerSocketChannel的责任链pipeline，通过addLast将ChannelInitializer加入责任链，在ChannelInitializer中重写了initChannel方法，首先根据handler是否是null（这个handler是ServerBootstrap调用handler方法添加的，和childHandler方法不一样），若是handler不是null，将handler加入责任链，无论如何，都会异步将一个ServerBootstrapAcceptor对象加入责任链（后面会说为什么是异步）
这个ChannelInitializer的initChannel方法的执行需要等到后面注册时才会被调用，在后面pipeline处理channelRegistered请求时，此initChannel方法才会被执行 （Netty中的ChannelPipeline源码分析）
ChannelInitializer的channelRegistered方法：
1 public final void channelRegistered(ChannelHandlerContext ctx) throws Exception {
2 if (initChannel(ctx)) {
3 ctx.pipeline().fireChannelRegistered();
4 } else {
5 ctx.fireChannelRegistered();
6 }
7 }
首先调用initChannel方法（和上面的initChannel不是一个）：
1 private boolean initChannel(ChannelHandlerContext ctx) throws Exception {
2 if (initMap.putIfAbsent(ctx, Boolean.TRUE) == null) {
3 try {
4 initChannel((C) ctx.channel());
5 } catch (Throwable cause) {
6 exceptionCaught(ctx, cause);
7 } finally {
8 remove(ctx);
9 }
10 return true;
11 }
12 return false;
13 }
可以看到，这个ChannelInitializer只会在pipeline中初始化一次，仅用于Channel的注册，在完成注册后，会调用remove方法将其从pipeline中移除：
remove方法：
1 private void remove(ChannelHandlerContext ctx) {
2 try {
3 ChannelPipeline pipeline = ctx.pipeline();
4 if (pipeline.context(this) != null) {
5 pipeline.remove(this);
6 }
7 } finally {
8 initMap.remove(ctx);
9 }
10 }
在移除前，就会回调用刚才覆盖的initChannel方法，异步向pipeline添加了ServerBootstrapAcceptor，用于后续的NioServerSocketChannel侦听到客户端连接后，完成在服务端的NioSocketChannel的注册。
回到initAndRegister，在对NioServerSocketChannel初始化完毕，接下来就是注册逻辑：
1 ChannelFuture regFuture = this.config().group().register(channel);
首先调用config().group()，这个就得到了一开始在ServerBootstrap的group方法传入的parentGroup，调用parentGroup的register方法，parentGroup是NioEventLoopGroup，这个方法是在子类MultithreadEventLoopGroup中实现的：
1 public ChannelFuture register(Channel channel) {
2 return this.next().register(channel);
3 }
首先调用next方法：
1 public EventLoop next() {
2 return (EventLoop)super.next();
3 }
实际上调用父类MultithreadEventExecutorGroup的next方法：
1 public EventExecutor next() {
2 return this.chooser.next();
3 }
关于chooser在我之前博客：Netty中NioEventLoopGroup的创建源码分析 介绍过，在NioEventLoopGroup创建时，默认会根据cpu个数创建二倍个NioEventLoop，而chooser就负责通过取模，每次选择一个NioEventLoop使用
所以在MultithreadEventLoopGroup的register方法实际调用了NioEventLoop的register方法：
NioEventLoop的register方法在子类SingleThreadEventLoop中实现：
1 public ChannelFuture register(Channel channel) {
2 return this.register((ChannelPromise)(new DefaultChannelPromise(channel, this)));
3 }
4
5 public ChannelFuture register(ChannelPromise promise) {
6 ObjectUtil.checkNotNull(promise, "promise");
7 promise.channel().unsafe().register(this, promise);
8 return promise;
9 }
先把channel包装成ChannelPromise，默认是DefaultChannelPromise （Netty中的ChannelFuture和ChannelPromise），用于处理异步操作
调用重载方法，而在重载方法里，可以看到，实际上的register操作交给了channel的unsafe来实现：
unsafe的register方法在AbstractUnsafe中实现：
1 public final void register(EventLoop eventLoop, final ChannelPromise promise) {
2 if (eventLoop == null) {
3 throw new NullPointerException("eventLoop");
4 } else if (AbstractChannel.this.isRegistered()) {
5 promise.setFailure(new IllegalStateException("registered to an event loop already"));
6 } else if (!AbstractChannel.this.isCompatible(eventLoop)) {
7 promise.setFailure(new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
8 } else {
9 AbstractChannel.this.eventLoop = eventLoop;
10 if (eventLoop.inEventLoop()) {
11 this.register0(promise);
12 } else {
13 try {
14 eventLoop.execute(new Runnable() {
15 public void run() {
16 AbstractUnsafe.this.register0(promise);
17 }
18 });
19 } catch (Throwable var4) {
20 AbstractChannel.logger.warn("Force-closing a channel whose registration task was not accepted by an event loop: {}", AbstractChannel.this, var4);
21 this.closeForcibly();
22 AbstractChannel.this.closeFuture.setClosed();
23 this.safeSetFailure(promise, var4);
24 }
25 }
26
27 }
28 }
前面的判断做了一些检查就不细说了，直接看到else块
首先给当前Channel绑定了eventLoop，即通过刚才chooser选择的eventLoop，该Channel也就是NioServerSocketChannel
由于Unsafe的操作是在轮询线程中异步执行的，所里，这里需要判断inEventLoop是否处于轮询中
在之前介绍NioEventLoopGroup的时候说过，NioEventLoop在没有调用doStartThread方法时并没有启动轮询的，所以inEventLoop判断不成立
那么就调用eventLoop的execute方法，实际上的注册方法可以看到调用了AbstractUnsafe的register0方法，而将这个方法封装为Runnable交给eventLoop作为一个task去异步执行
先来看eventLoop的execute方法实现，是在NioEventLoop的子类SingleThreadEventExecutor中实现的：
1 public void execute(Runnable task) {
2 if (task == null) {
3 throw new NullPointerException("task");
4 } else {
5 boolean inEventLoop = this.inEventLoop();
6 this.addTask(task);
7 if (!inEventLoop) {
8 this.startThread();
9 if (this.isShutdown() && this.removeTask(task)) {
10 reject();
11 }
12 }
13
14 if (!this.addTaskWakesUp && this.wakesUpForTask(task)) {
15 this.wakeup(inEventLoop);
16 }
17
18 }
19 }
这里首先将task，即刚才的注册事件放入阻塞任务队列中，然后调用startThread方法：
1 private void startThread() {
2 if (this.state == 1 && STATE_UPDATER.compareAndSet(this, 1, 2)) {
3 try {
4 this.doStartThread();
5 } catch (Throwable var2) {
6 STATE_UPDATER.set(this, 1);
7 PlatformDependent.throwException(var2);
8 }
9 }
10
11 }
NioEventLoop此时还没有轮询，所以状态是1，对应ST_NOT_STARTED，此时利用CAS操作，将状态修改为2，即ST_STARTED ，标志着NioEventLoop要启动轮询了，果然，接下来就调用了doStartThread开启轮询线程：
1 private void doStartThread() {
2 assert this.thread == null;
3
4 this.executor.execute(new Runnable() {
5 public void run() {
6 SingleThreadEventExecutor.this.thread = Thread.currentThread();
7 if (SingleThreadEventExecutor.this.interrupted) {
8 SingleThreadEventExecutor.this.thread.interrupt();
9 }
10
11 boolean success = false;
12 SingleThreadEventExecutor.this.updateLastExecutionTime();
13 boolean var112 = false;
14
15 int oldState;
16 label1907: {
17 try {
18 var112 = true;
19 SingleThreadEventExecutor.this.run();
20 success = true;
21 var112 = false;
22 break label1907;
23 } catch (Throwable var119) {
24 SingleThreadEventExecutor.logger.warn("Unexpected exception from an event executor: ", var119);
25 var112 = false;
26 } finally {
27 if (var112) {
28 int oldStatex;
29 do {
30 oldStatex = SingleThreadEventExecutor.this.state;
31 } while(oldStatex < 3 && !SingleThreadEventExecutor.STATE_UPDATER.compareAndSet(SingleThreadEventExecutor.this, oldStatex, 3));
32
33 if (success && SingleThreadEventExecutor.this.gracefulShutdownStartTime == 0L && SingleThreadEventExecutor.logger.isErrorEnabled()) {
34 SingleThreadEventExecutor.logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " + SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called before run() implementation terminates.");
35 }
36
37 try {
38 while(!SingleThreadEventExecutor.this.confirmShutdown()) {
39 ;
40 }
41 } finally {
42 try {
43 SingleThreadEventExecutor.this.cleanup();
44 } finally {
45 SingleThreadEventExecutor.STATE_UPDATER.set(SingleThreadEventExecutor.this, 5);
46 SingleThreadEventExecutor.this.threadLock.release();
47 if (!SingleThreadEventExecutor.this.taskQueue.isEmpty() && SingleThreadEventExecutor.logger.isWarnEnabled()) {
48 SingleThreadEventExecutor.logger.warn("An event executor terminated with non-empty task queue (" + SingleThreadEventExecutor.this.taskQueue.size() + ')');
49 }
50
51 SingleThreadEventExecutor.this.terminationFuture.setSuccess((Object)null);
52 }
53 }
54
55 }
56 }
57
58 do {
59 oldState = SingleThreadEventExecutor.this.state;
60 } while(oldState < 3 && !SingleThreadEventExecutor.STATE_UPDATER.compareAndSet(SingleThreadEventExecutor.this, oldState, 3));
61
62 if (success && SingleThreadEventExecutor.this.gracefulShutdownStartTime == 0L && SingleThreadEventExecutor.logger.isErrorEnabled()) {
63 SingleThreadEventExecutor.logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " + SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called before run() implementation terminates.");
64 }
65
66 try {
67 while(!SingleThreadEventExecutor.this.confirmShutdown()) {
68 ;
69 }
70
71 return;
72 } finally {
73 try {
74 SingleThreadEventExecutor.this.cleanup();
75 } finally {
76 SingleThreadEventExecutor.STATE_UPDATER.set(SingleThreadEventExecutor.this, 5);
77 SingleThreadEventExecutor.this.threadLock.release();
78 if (!SingleThreadEventExecutor.this.taskQueue.isEmpty() && SingleThreadEventExecutor.logger.isWarnEnabled()) {
79 SingleThreadEventExecutor.logger.warn("An event executor terminated with non-empty task queue (" + SingleThreadEventExecutor.this.taskQueue.size() + ')');
80 }
81
82 SingleThreadEventExecutor.this.terminationFuture.setSuccess((Object)null);
83 }
84 }
85 }
86
87 do {
88 oldState = SingleThreadEventExecutor.this.state;
89 } while(oldState < 3 && !SingleThreadEventExecutor.STATE_UPDATER.compareAndSet(SingleThreadEventExecutor.this, oldState, 3));
90
91 if (success && SingleThreadEventExecutor.this.gracefulShutdownStartTime == 0L && SingleThreadEventExecutor.logger.isErrorEnabled()) {
92 SingleThreadEventExecutor.logger.error("Buggy " + EventExecutor.class.getSimpleName() + " implementation; " + SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called before run() implementation terminates.");
93 }
94
95 try {
96 while(!SingleThreadEventExecutor.this.confirmShutdown()) {
97 ;
98 }
99 } finally {
100 try {
101 SingleThreadEventExecutor.this.cleanup();
102 } finally {
103 SingleThreadEventExecutor.STATE_UPDATER.set(SingleThreadEventExecutor.this, 5);
104 SingleThreadEventExecutor.this.threadLock.release();
105 if (!SingleThreadEventExecutor.this.taskQueue.isEmpty() && SingleThreadEventExecutor.logger.isWarnEnabled()) {
106 SingleThreadEventExecutor.logger.warn("An event executor terminated with non-empty task queue (" + SingleThreadEventExecutor.this.taskQueue.size() + ')');
107 }
108
109 SingleThreadEventExecutor.this.terminationFuture.setSuccess((Object)null);
110 }
111 }
112
113 }
114 });
115 }
关于doStartThread方法，我在 Netty中NioEventLoopGroup的创建源码分析 中已经说的很细了，这里就不再一步一步分析了
因为此时还没真正意义上的启动轮询，所以thread等于null成立的，然后调用executor的execute方法，这里的executor是一个线程池，在之前说过的，所以里面的run方法是处于一个线程里面的，然后给thread成员赋值为当前线程，表明正式进入了轮询。
而SingleThreadEventExecutor.this.run()才是真正的轮询逻辑，这在之前也说过，这个run的实现是在父类NioEventLoop中：
1 protected void run() {
2 while(true) {
3 while(true) {
4 try {
5 switch(this.selectStrategy.calculateStrategy(this.selectNowSupplier, this.hasTasks())) {
6 case -2:
7 continue;
8 case -1:
9 this.select(this.wakenUp.getAndSet(false));
10 if (this.wakenUp.get()) {
11 this.selector.wakeup();
12 }
13 default:
14 this.cancelledKeys = 0;
15 this.needsToSelectAgain = false;
16 int ioRatio = this.ioRatio;
17 if (ioRatio == 100) {
18 try {
19 this.processSelectedKeys();
20 } finally {
21 this.runAllTasks();
22 }
23 } else {
24 long ioStartTime = System.nanoTime();
25 boolean var13 = false;
26
27 try {
28 var13 = true;
29 this.processSelectedKeys();
30 var13 = false;
31 } finally {
32 if (var13) {
33 long ioTime = System.nanoTime() - ioStartTime;
34 this.runAllTasks(ioTime * (long)(100 - ioRatio) / (long)ioRatio);
35 }
36 }
37
38 long ioTime = System.nanoTime() - ioStartTime;
39 this.runAllTasks(ioTime * (long)(100 - ioRatio) / (long)ioRatio);
40 }
41 }
42 } catch (Throwable var21) {
43 handleLoopException(var21);
44 }
45
46 try {
47 if (this.isShuttingDown()) {
48 this.closeAll();
49 if (this.confirmShutdown()) {
50 return;
51 }
52 }
53 } catch (Throwable var18) {
54 handleLoopException(var18);
55 }
56 }
57 }
58 }
首先由于task已经有一个了，就是刚才的注册事件，所以选择策略calculateStrategy最终调用selectNow（也是之前说过的）：
1 private final IntSupplier selectNowSupplier = new IntSupplier() {
2 public int get() throws Exception {
3 return NioEventLoop.this.selectNow();
4 }
5 };
6
7 int selectNow() throws IOException {
8 int var1;
9 try {
10 var1 = this.selector.selectNow();
11 } finally {
12 if (this.wakenUp.get()) {
13 this.selector.wakeup();
14 }
15
16 }
17
18 return var1;
19 }
使用JDK原生Selector进行selectNow，由于此时没有任何Channel的注册，所以selectNow会立刻返回0，此时就进入default逻辑，由于没有任何注册，processSelectedKeys方法也做不了什么，所以在这一次的轮询实质上只进行了runAllTasks方法，此方法会执行阻塞队列中的task的run方法（还是在之前博客中介绍过），由于轮询是在线程池中的一个线程中运行的，所以task的执行是一个异步操作。（在执行完task，将task移除阻塞对立，线程继续轮询）
这时就可以回到AbstractChannel的register方法中了，由上面可以知道task实际上异步执行了：
1 AbstractUnsafe.this.register0(promise);
register0方法：
1 private void register0(ChannelPromise promise) {
2 try {
3 if (!promise.setUncancellable() || !this.ensureOpen(promise)) {
4 return;
5 }
6
7 boolean firstRegistration = this.neverRegistered;
8 AbstractChannel.this.doRegister();
9 this.neverRegistered = false;
10 AbstractChannel.this.registered = true;
11 AbstractChannel.this.pipeline.invokeHandlerAddedIfNeeded();
12 this.safeSetSuccess(promise);
13 AbstractChannel.this.pipeline.fireChannelRegistered();
14 if (AbstractChannel.this.isActive()) {
15 if (firstRegistration) {
16 AbstractChannel.this.pipeline.fireChannelActive();
17 } else if (AbstractChannel.this.config().isAutoRead()) {
18 this.beginRead();
19 }
20 }
21 } catch (Throwable var3) {
22 this.closeForcibly();
23 AbstractChannel.this.closeFuture.setClosed();
24 this.safeSetFailure(promise, var3);
25 }
26
27 }
可以看到实际上的注册逻辑又交给了AbstractChannel的doRegister，而这个方法在AbstractNioChannel中实现：
1 protected void doRegister() throws Exception {
2 boolean selected = false;
3
4 while(true) {
5 try {
6 this.selectionKey = this.javaChannel().register(this.eventLoop().unwrappedSelector(), 0, this);
7 return;
8 } catch (CancelledKeyException var3) {
9 if (selected) {
10 throw var3;
11 }
12
13 this.eventLoop().selectNow();
14 selected = true;
15 }
16 }
17 }
javaChannel就是之前产生的JDK的ServerSocketChannel，unwrappedSelector在之前说过，就是未经修改的JDK原生Selector，这个Selector和eventLoop是一对一绑定的，可以看到调用JDK原生的注册方法，完成了对ServerSocketChannel的注册，但是注册的是一个0状态（缺省值），而传入的this，即AbstractNioChannel对象作为了一个附件，用于以后processSelectedKeys方法从SelectionKey中得到对应的Netty的Channel（还是之前博客说过）
关于缺省值，是由于AbstractNioChannel不仅用于NioServerSocketChannel的注册，还用于NioSocketChannel的注册，只有都使用缺省值注册才不会产生异常 【Java】NIO中Channel的注册源码分析 ，并且，在以后processSelectedKeys方法会对0状态判断，再使用unsafe进行相应的逻辑处理。
在完成JDK的注册后，调用pipeline的invokeHandlerAddedIfNeeded方法（Netty中的ChannelPipeline源码分析），处理ChannelHandler的handlerAdded的回调，即调用用户添加的ChannelHandler的handlerAdded方法。
调用safeSetSuccess，标志异步操作完成：
1 protected final void safeSetSuccess(ChannelPromise promise) {
2 if (!(promise instanceof VoidChannelPromise) && !promise.trySuccess()) {
3 logger.warn("Failed to mark a promise as success because it is done already: {}", promise);
4 }
5 }
关于异步操作我在之前的博客中说的很清楚了：Netty中的ChannelFuture和ChannelPromise
接着调用pipeline的fireChannelRegistered方法，也就是在责任链上调用channelRegistered方法，这时，就会调用之在ServerBootstrap中向pipeline添加的ChannelInitializer的channelRegistered，进而回调initChannel方法，完成对ServerBootstrapAcceptor的添加。
回到register0方法，在处理完pipeline的责任链后，根据当前AbstractChannel即NioServerSocketChannel的isActive：
1 public boolean isActive() {
2 return this.javaChannel().socket().isBound();
3 }
获得NioServerSocketChannel绑定的JDK的ServerSocketChannel，进而获取ServerSocket，判断isBound：
1 public boolean isBound() {
2 // Before 1.3 ServerSockets were always bound during creation
3 return bound || oldImpl;
4 }
这里实际上就是判断ServerSocket是否调用了bind方法，前面说过register0方法是一个异步操作，在多线程环境下不能保证执行顺序，若是此时已经完成了ServerSocket的bind，根据firstRegistration判断是否需要pipeline传递channelActive请求，首先会执行pipeline的head即HeadContext的channelActive方法：
1 @Override
2 public void channelActive(ChannelHandlerContext ctx) throws Exception {
3 ctx.fireChannelActive();
4
5 readIfIsAutoRead();
6 }
在HeadContext通过ChannelHandlerContext 传递完channelActive请求后，会调用readIfIsAutoRead方法：
1 private void readIfIsAutoRead() {
2 if (channel.config().isAutoRead()) {
3 channel.read();
4 }
5 }
此时调用AbstractChannel的read方法：
1 public Channel read() {
2 pipeline.read();
3 return this;
4 }
最终在请求链由HeadContext执行read方法：
1 public void read(ChannelHandlerContext ctx) {
2 unsafe.beginRead();
3 }
终于可以看到此时调用unsafe的beginRead方法：
1 public final void beginRead() {
2 assertEventLoop();
3
4 if (!isActive()) {
5 return;
6 }
7
8 try {
9 doBeginRead();
10 } catch (final Exception e) {
11 invokeLater(new Runnable() {
12 @Override
13 public void run() {
14 pipeline.fireExceptionCaught(e);
15 }
16 });
17 close(voidPromise());
18 }
19 }
最终执行了doBeginRead方法，由AbstractNioChannel实现：
1 protected void doBeginRead() throws Exception {
2 final SelectionKey selectionKey = this.selectionKey;
3 if (!selectionKey.isValid()) {
4 return;
5 }
6
7 readPending = true;
8
9 final int interestOps = selectionKey.interestOps();
10 if ((interestOps & readInterestOp) == 0) {
11 selectionKey.interestOps(interestOps | readInterestOp);
12 }
13 }
这里，就完成了向Selector注册readInterestOp事件，从前面来看就是ACCEPT事件
回到AbstractBootstrap的doBind方法，在initAndRegister逻辑结束后，由上面可以知道，实际上的register注册逻辑是一个异步操作，在register0中完成
根据ChannelFuture来判断异步操作是否完成，如果isDone，则表明异步操作先完成，即完成了safeSetSuccess方法，
然后调用newPromise方法：
1 public ChannelPromise newPromise() {
2 return pipeline.newPromise();
3 }
给channel的pipeline绑定异步操作ChannelPromise
然后调用doBind0方法完成ServerSocket的绑定，若是register0这个异步操作还没完成，就需要给ChannelFuture产生一个异步操作的侦听ChannelFutureListener对象，等到register0方法调用safeSetSuccess时，在promise的trySuccess中会回调ChannelFutureListener的operationComplete方法，进而调用doBind0方法
doBind0方法：
1 private static void doBind0(
2 final ChannelFuture regFuture, final Channel channel,
3 final SocketAddress localAddress, final ChannelPromise promise) {
4 channel.eventLoop().execute(new Runnable() {
5 @Override
6 public void run() {
7 if (regFuture.isSuccess()) {
8 channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
9 } else {
10 promise.setFailure(regFuture.cause());
11 }
12 }
13 });
14 }
向轮询线程提交了一个任务，异步处理bind，可以看到，只有在regFuture异步操作成功结束后，调用channel的bind方法：
1 public ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
2 return pipeline.bind(localAddress, promise);
3 }
实际上的bind又交给pipeline，去完成，pipeline中就会交给责任链去完成，最终会交给HeadContext完成：
1 public void bind(
2 ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise)
3 throws Exception {
4 unsafe.bind(localAddress, promise);
5 }
可以看到，绕了一大圈，交给了unsafe完成：
1 public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
2 assertEventLoop();
3
4 if (!promise.setUncancellable() || !ensureOpen(promise)) {
5 return;
6 }
7
8 if (Boolean.TRUE.equals(config().getOption(ChannelOption.SO_BROADCAST)) &&
9 localAddress instanceof InetSocketAddress &&
10 !((InetSocketAddress) localAddress).getAddress().isAnyLocalAddress() &&
11 !PlatformDependent.isWindows() && !PlatformDependent.maybeSuperUser()) {
12 logger.warn(
13 "A non-root user can't receive a broadcast packet if the socket " +
14 "is not bound to a wildcard address; binding to a non-wildcard " +
15 "address (" + localAddress + ") anyway as requested.");
16 }
17
18 boolean wasActive = isActive();
19 try {
20 doBind(localAddress);
21 } catch (Throwable t) {
22 safeSetFailure(promise, t);
23 closeIfClosed();
24 return;
25 }
26
27 if (!wasActive && isActive()) {
28 invokeLater(new Runnable() {
29 @Override
30 public void run() {
31 pipeline.fireChannelActive();
32 }
33 });
34 }
35
36 safeSetSuccess(promise);
37 }
然而，真正的bind还是回调了doBind方法，最终是由NioServerSocketChannel来实现：
1 @Override
2 protected void doBind(SocketAddress localAddress) throws Exception {
3 if (PlatformDependent.javaVersion() >= 7) {
4 javaChannel().bind(localAddress, config.getBacklog());
5 } else {
6 javaChannel().socket().bind(localAddress, config.getBacklog());
7 }
8 }
在这里终于完成了对JDK的ServerSocketChannel的bind操作
在上面的
1 if (!wasActive && isActive()) {
2 invokeLater(new Runnable() {
3 @Override
4 public void run() {
5 pipeline.fireChannelActive();
6 }
7 });
8 }
这个判断，就是确保在register0中isActive时，还没完成绑定，也就没有beginRead操作来向Selector注册ACCEPT事件，那么就在这里进行注册，进而让ServerSocket去侦听客户端的连接
在服务端ACCEPT到客户端的连接后，在NioEventLoop轮询中，就会调用processSelectedKeys处理ACCEPT的事件就绪，然后交给unsafe的read去处理 Netty中NioEventLoopGroup的创建源码分析
在服务端，由NioMessageUnsafe实现：
1 public void read() {
2 assert eventLoop().inEventLoop();
3 final ChannelConfig config = config();
4 final ChannelPipeline pipeline = pipeline();
5 final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle();
6 allocHandle.reset(config);
7
8 boolean closed = false;
9 Throwable exception = null;
10 try {
11 try {
12 do {
13 int localRead = doReadMessages(readBuf);
14 if (localRead == 0) {
15 break;
16 }
17 if (localRead < 0) {
18 closed = true;
19 break;
20 }
21
22 allocHandle.incMessagesRead(localRead);
23 } while (allocHandle.continueReading());
24 } catch (Throwable t) {
25 exception = t;
26 }
27
28 int size = readBuf.size();
29 for (int i = 0; i < size; i ++) {
30 readPending = false;
31 pipeline.fireChannelRead(readBuf.get(i));
32 }
33 readBuf.clear();
34 allocHandle.readComplete();
35 pipeline.fireChannelReadComplete();
36
37 if (exception != null) {
38 closed = closeOnReadError(exception);
39
40 pipeline.fireExceptionCaught(exception);
41 }
42
43 if (closed) {
44 inputShutdown = true;
45 if (isOpen()) {
46 close(voidPromise());
47 }
48 }
49 } finally {
50 if (!readPending && !config.isAutoRead()) {
51 removeReadOp();
52 }
53 }
54 }
55 }
核心在doReadMessages方法，由NioServerSocketChannel实现：
1 protected int doReadMessages(List<Object> buf) throws Exception {
2 SocketChannel ch = SocketUtils.accept(javaChannel());
3
4 try {
5 if (ch != null) {
6 buf.add(new NioSocketChannel(this, ch));
7 return 1;
8 }
9 } catch (Throwable t) {
10 logger.warn("Failed to create a new channel from an accepted socket.", t);
11
12 try {
13 ch.close();
14 } catch (Throwable t2) {
15 logger.warn("Failed to close a socket.", t2);
16 }
17 }
18
19 return 0;
20 }
SocketUtils的accept方法其实就是用来调用JDK中ServerSocketChannel原生的accept方法，来得到一个JDK的SocketChannel对象，然后通过这个SocketChannel对象，将其包装成NioSocketChannel对象添加在buf这个List中
由此可以看到doReadMessages用来侦听所有就绪的连接，包装成NioSocketChannel将其放在List中
然后遍历这个List，调用 NioServerSocketChannel的pipeline的fireChannelRead方法，传递channelRead请求，、
在前面向pipeline中添加了ServerBootstrapAcceptor这个ChannelHandler，此时，它也会响应这个请求，回调channelRead方法：
1 public void channelRead(ChannelHandlerContext ctx, Object msg) {
2 final Channel child = (Channel) msg;
3
4 child.pipeline().addLast(childHandler);
5
6 setChannelOptions(child, childOptions, logger);
7
8 for (Entry<AttributeKey<?>, Object> e: childAttrs) {
9 child.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
10 }
11
12 try {
13 childGroup.register(child).addListener(new ChannelFutureListener() {
14 @Override
15 public void operationComplete(ChannelFuture future) throws Exception {
16 if (!future.isSuccess()) {
17 forceClose(child, future.cause());
18 }
19 }
20 });
21 } catch (Throwable t) {
22 forceClose(child, t);
23 }
24 }
msg就是侦听到的NioSocketChannel对象，给该对象的pipeline添加childHandler，也就是我们在ServerBootstrap中通过childHandler方法添加的
然后通过register方法完成对NioSocketChannel的注册（和NioServerSocketChannel注册逻辑一样）
至此Netty服务端的启动结束。
来源：https://www.cnblogs.com/a526583280/p/10969275.html