netty源码分析(五)Netty服务器地址绑定底层源码分析

AbstractBootstrapd的initAndRegister方法，完成 初始化和注册：

 final ChannelFuture initAndRegister() {        Channel channel = null;        try {            channel = channelFactory.newChannel();//channelFactory是ReflectiveChannelFactory，ReflectiveChannelFactory             //内部的成员变量是NioServerSocketChannel.class，调用newChannel()即通过反射得到一个NioServerSocketChannel实体对象            //调用无参构造器。在接下来的NioServerSocketChannel介绍你会知道这句代码做了哪些事情，透剧一下：            //设置ServerSocketChannel的兴趣事件（初始状态都是SelectionKey.OP_ACCEPT）、ChannelId（唯一的一个编码）、            //设置ServerSocketChannel为非阻塞、初始化了ServerSocketChannel的pipline。            init(channel);//进入init方法。        } 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);        }        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;    }

紧接着我们进入init方法，init方法是父类AbstractBootstrap的方法，我们到子类ServerBootstrap里边查看：

 void init(Channel channel) throws Exception {        final Map<ChannelOption<?>, Object> options = options0();//ServerBootstrap设置的option集合，是一个LinkedHashMap        synchronized (options) {            setChannelOptions(channel, options, logger);//将options 集合放到channel（NioServerSocketChannel）里边        }        final Map<AttributeKey<?>, Object> attrs = attrs0();//ServerBootstrap设置的属性，也是一个LinkedHashMap        synchronized (attrs) {            for (Entry<AttributeKey<?>, Object> e: attrs.entrySet()) {                @SuppressWarnings("unchecked")                AttributeKey<Object> key = (AttributeKey<Object>) e.getKey();                channel.attr(key).set(e.getValue());//设置到channel里边。            }        }        ChannelPipeline p = channel.pipeline();//获取channel的对应的管道。        final EventLoopGroup currentChildGroup = childGroup;//MyServer实例程序中的workerGroup        final ChannelHandler currentChildHandler = childHandler;//MyServer实例程序中的MyServerInitializer        final Entry<ChannelOption<?>, Object>[] currentChildOptions;        final Entry<AttributeKey<?>, Object>[] currentChildAttrs;        synchronized (childOptions) {            currentChildOptions = childOptions.entrySet().toArray(newOptionArray(childOptions.size()));        }        synchronized (childAttrs) {            currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(childAttrs.size()));        }        p.addLast(new ChannelInitializer<Channel>() {        //ChannelInitializer            /**            This method will be called once the {@link Channel} was registered. After the method returns this instance            will be removed from the {@link ChannelPipeline} of the {@link Channel}.            当Channel被注册的时候当前方法会被调用，当方法返回的时候当前Channel的实例会被删除从ChannelPipeline当中。            */            public void initChannel(final Channel ch) throws Exception {                final ChannelPipeline pipeline = ch.pipeline();                ChannelHandler handler = config.handler();//MyServer实例程序中的LoggingHandler                //LoggingHandler详见MyServer实例程序 http://blog.csdn.net/wzq6578702/article/details/77923602                if (handler != null) {                    pipeline.addLast(handler);//如果ServerBootstrap的handler被设置过，把设置的Handler放到管道当中。                    //详见MyServer实例程序 http://blog.csdn.net/wzq6578702/article/details/77923602                }                ch.eventLoop().execute(new Runnable() {//ch.eventLoop()得到是一个类似于线程池的东西                    @Override                    public void run() {                        pipeline.addLast(new ServerBootstrapAcceptor(                                ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));                    }                });            }        });    }

另外还有一个重要的点，initAndRegister的channel 实例化：channel = channelFactory.newChannel();是对NioServerSocketChannel
调用无参数的构造器通过反射实例化出来的，我们进入到NioServerSocketChannel无参构造器：

public class NioServerSocketChannel extends AbstractNioMessageChannel                             implements io.netty.channel.socket.ServerSocketChannel {      private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();          private static ServerSocketChannel newSocket(SelectorProvider provider) {        try {            /**             *  Use the {@link SelectorProvider} to open {@link SocketChannel} and so remove condition in             *  {@link SelectorProvider#provider()} which is called by each ServerSocketChannel.open() otherwise.             *             *  See <a href="https://github.com/netty/netty/issues/2308">#2308</a>.             */            return provider.openServerSocketChannel();        } catch (IOException e) {            throw new ChannelException(                    "Failed to open a server socket.", e);        }    }             //SelectorProvider是jdk提供的一个提供Channel的提供者,java.nio.channels.DatagramChannel、java.nio.channels.Pipe// java.nio.channels.Selector、java.nio.channels.ServerSocketChannel等Channel都是通过SelectorProvider.provider()//打开一个通道，但是SelectorProvider.provider()是同步的（有synchronized）,netty为了适应在高并发的其工况下，这样的同步会造成性能//的损失，因此将SelectorProvider.provider()获得的SelectorProvider做成一个名字是DEFAULT_SELECTOR_PROVIDER 的常量，获得通道的时候//直接使用[ return provider.openServerSocketChannel();]类似这样的用法返回Channel，不会有同步加锁操作，提高了并发，有兴趣的可以看下//https://github.com/netty/netty/issues/2308 说明，为什么netty这样写。    /**     * Create a new instance     * 无参构造器，主要获取ServerSocketChannel      */    public NioServerSocketChannel() {        this(newSocket(DEFAULT_SELECTOR_PROVIDER));    }                  /**     * Create a new instance using the given {@link ServerSocketChannel}.     * 设置ServerSocketChannel的兴趣事件（初始状态都是SelectionKey.OP_ACCEPT）、ChannelId（唯一的一个编码）、     * 设置ServerSocketChannel为非阻塞、初始化了ServerSocketChannel的pipline。     *      * config 对ServerSocketChannelConfig进行了赋值。     */    public NioServerSocketChannel(ServerSocketChannel channel) {        super(null, channel, SelectionKey.OP_ACCEPT);        config = new NioServerSocketChannelConfig(this, javaChannel().socket());    }}