bootstrap-boss-worker关系

对于启动类，有以下这种简单的方式：

ServerBootstrap serverBootstrap = new ServerBootstrap();
        NioEventLoopGroup boss = new NioEventLoopGroup();
        NioEventLoopGroup worker = new NioEventLoopGroup();
        serverBootstrap
                .group(boss, worker)
                .channel(NioServerSocketChannel.class)
                .childHandler(new TestServerChannelInitializer())
                .bind(1234); 

比较诡异的有以下(伪代码)：

//第一种
serverBootstrap.group(boss,worker).bind(1234);
serverBootstrap.bind(1235);
serverBootstrap.bind(1236);
//第二种
serverBootstrap.group(boss,boss);
//第三种
serverBootstrap1.group(boss,worker);
serverBootstrap2.group(boss,worker);
//这样的组合剩下的脑补

对于这样的代码，可以有很多种。其实NioEventLoopGroup对应于一个线程池，这个线程池里的NioEventLoop是单线程的，NioEventLoop中可以对应多个Channel，每个Channel对应于1个端口。而ServerBootstrap其实仅仅是把boss，worker，NioServerSocketChannel组装起来。组装起来后获取的是ServerBootstrap的引用，然后bind后才会获取到一个ChannelFuture。而对于boss和worker来说，这样的复用，也只是线程池这个概念被2个地方使用了而已。

//代码来自AbstractBootstrap
  final ChannelFuture initAndRegister() {
        Channel channel = null;
        try {
            channel = channelFactory.newChannel();
            init(channel);//这一步会把新建的channel放入worker中。
        } catch (Throwable t) {
            if (channel != null) {
                // channel can be null if newChannel crashed (eg SocketException("too many open files"))
                channel.unsafe().closeForcibly();
                // as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
                return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t);
            }
            // as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
            return new DefaultChannelPromise(new FailedChannel(), GlobalEventExecutor.INSTANCE).setFailure(t);
        }
      //这一步会把channel放入boss中。
        ChannelFuture regFuture = config().group().register(channel);
        if (regFuture.cause() != null) {
            if (channel.isRegistered()) {
                channel.close();
            } else {
                channel.unsafe().closeForcibly();
            }
        }

        // If we are here and the promise is not failed, it's one of the following cases:
        // 1) If we attempted registration from the event loop, the registration has been completed at this point.
        //    i.e. It's safe to attempt bind() or connect() now because the channel has been registered.
        // 2) If we attempted registration from the other thread, the registration request has been successfully
        //    added to the event loop's task queue for later execution.
        //    i.e. It's safe to attempt bind() or connect() now:
        //         because bind() or connect() will be executed *after* the scheduled registration task is executed
        //         because register(), bind(), and connect() are all bound to the same thread.

        return regFuture;
    }