Netty4源碼分析—ServerSocketChannel注冊到Selector

一、生成serversocketchannel

     ServerBootstrap設定channel類型 bootstrap.channel(NioServerSocketChannel.class)時，ServerBootstrap的父類AbstractBootstrap的初始ChannelFactory的對象，ChannelFactory的作用是生成ServerSocketChannel對象，channel方法代碼：

public B channel(Class<? extends C> channelClass) {
        if (channelClass == null) {
            throw new NullPointerException("channelClass");
        }
        return channelFactory(new BootstrapChannelFactory<C>(channelClass));
}

           

    BootstrapChannelFactory為AbstractBootstrap的内部類。

二、将serverchannel注冊到selector

  ServerBootstrap在綁定端口（bootstrap.bind(8080)）時，調用AbstractBootstrap的initAndRegister方法：

final ChannelFuture initAndRegister() {
        final Channel channel = channelFactory().newChannel();//(1)
        try {
            init(channel);//(2)
        } catch (Throwable t) {
            channel.unsafe().closeForcibly();
            return channel.newFailedFuture(t);
        }

        ChannelPromise regPromise = channel.newPromise();//(3)
        group().register(channel, regPromise);//(4)
        if (regPromise.cause() != null) {
            if (channel.isRegistered()) {
                channel.close();
            } else {
                channel.unsafe().closeForcibly();
            }
        }

        return regPromise;
    }
           

      1、調用ChannelFactory對象生成ServerBootstrap 的channel(Class<? extends C> channelClass)方法中設定的channelClass對象即NioServerSocketChannel對象，也就是Netty重新封裝過的ServerSocketChannel對象，至于Netty為什麼要封裝ServerSocketChannel後面章節再寫。

      2、 初化NioServerSocketChannel對象，将我們在建立ServerBootstrap對象中設定的option 和attr值設定到NioServerSocketChannel對象中的config和arrs屬性中。

      3、生成ChannelPromise對象，這個對象主要是對channel的注冊狀态進行監聽

      4、 取eventLoop設定到channel中，并調用AbstractChannel$AbstractUnsafe的register0方法獎channel注冊到eventLoop中的selector，并将ChannelPromise狀态設定為成功：

private void register0(ChannelPromise promise) {
            try {
                // check if the channel is still open as it could be closed in the mean time when the register
                // call was outside of the eventLoop
                if (!ensureOpen(promise)) {
                    return;
                }
                doRegister();     //将serverchannel注冊到selector中
                registered = true;
                promise.setSuccess();
                pipeline.fireChannelRegistered();
                if (isActive()) {
                    pipeline.fireChannelActive();
                }
            } catch (Throwable t) {
                // Close the channel directly to avoid FD leak.
                closeForcibly();
                closeFuture.setClosed();
                if (!promise.tryFailure(t)) {
                    logger.warn(
                            "Tried to fail the registration promise, but it is complete already. " +
                                    "Swallowing the cause of the registration failure:", t);
                }
            }
       }
           

三、綁定端口

  通過initAndRegister方法将serverchannel注冊到selector後調用doBind0方法注冊端口

private static void doBind0(
            final ChannelFuture regFuture, final Channel channel,
            final SocketAddress localAddress, final ChannelPromise promise) {

        // This method is invoked before channelRegistered() is triggered.  Give user handlers a chance to set up
        // the pipeline in its channelRegistered() implementation.

        channel.eventLoop().execute(new Runnable() { //(1)
            @Override
            public void run() {
                if (regFuture.isSuccess()) {
                    channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
                } else {
                    promise.setFailure(regFuture.cause());
                }
            }
        });
}