Netty 启动源码阅读

文章目录

• 1. 入门
• 2. Netty 代码实例
• 3. Netty bind

• 3.1 initAndRegister

• 3.1.1 newChannel, 创建 NioServerSocketChannel
• 3.1.2 init(channel); 初始化 NioServerSocketChannel
• 3.1.3 register 注册channel

• 3.2 doBind0 绑定端口
• 3.3 ServerBootstrapAcceptor

1. 入门

主从Reactor模型 ：Acceptor 接收到客户端TCP连接请求并处理完成后， 将新创建的SocketChannel 注册到 I/O线程池 （sub Reactor）传送门

主要步骤：

• Acceptor 创建 ServerSocketChannel
• Acceptor ServerSocketChannel 绑定端口
• Acceptor ServerSocketChannel 设置非阻塞
• Acceptor 创建 Selector，将 ServerSocketChannel 注册到 Selector 上，监听 SelectionKey.OP_ACCEPT 事件
• Acceptor ServerSocketChannel 设置分发处理器，处理监听到的SelectionKey.OP_ACCEPT 事件，新创建的 SocketChannel 分发到到 I/O线程池 (sub Reactor）
• I/O线程池 (sub Reactor）不断轮训处理 SocketChannel 上的读写请求

2. Netty 代码实例

 传送门

ServerBootstrap:

• 配置 EventLoopGroup 线程组:
  需要注意的是, 只绑定一个端口, bossEventLoopGroup 1个就够了, 2个会有一个闲置

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NioEventLoopGroup bossEventLoopGroup = new NioEventLoopGroup(2);
   NioEventLoopGroup workerEventLoopGroup = new NioEventLoopGroup(8);

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• 设置 Channel 类型: NioServerSocketChannel
• 设置 childHandler 的 ChannelPipeline
• 绑定端口: 创建 NioServerSocketChannel, 注册, 绑定端口, ServerSocketChannel 添加分发到子线程组的 handler

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import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

import java.nio.charset.CharacterCodingException;
import java.nio.charset.StandardCharsets;

public class NettyServer01 {
    public static void main(String[] args) {
        // 创建BossGroup和WorkerGroup，分别处理连接接受和数据读写
        NioEventLoopGroup bossEventLoopGroup = new NioEventLoopGroup(2);
        NioEventLoopGroup workerEventLoopGroup = new NioEventLoopGroup(8);

        new ServerBootstrap() // 初始化ServerBootstrap
                .group(bossEventLoopGroup, workerEventLoopGroup) // 设置EventLoopGroup
                .channel(NioServerSocketChannel.class) // 指定服务器通道类
                .childHandler(new ChannelInitializer<NioSocketChannel>() { // 设置通道初始化器
                    /**
                     * 初始化通道，添加处理器到通道的管道中
                     * @param ch 当前初始化的通道
                     */
                    protected void initChannel(NioSocketChannel ch) {
                        // 添加多个处理器，分别处理入站和出站事件
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                            /**
                             * 处理入站数据
                             * @param ctx 通道上下文
                             * @param msg 接收到的消息对象
                             */
                            @Override
                            public void channelRead(ChannelHandlerContext ctx, Object msg) {
                                ByteBuf byteBuf = inbound((ByteBuf) msg, "1");
                                ctx.fireChannelRead(byteBuf);
                            }
                        });
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                            @Override
                            public void channelRead(ChannelHandlerContext ctx, Object msg) throws CharacterCodingException {
                                ByteBuf byteBuf = inbound((ByteBuf) msg, "2");
                                ctx.fireChannelRead(byteBuf);
                            }
                        });
                        ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
                            /**
                             * 处理入站数据，将处理后的数据写回通道
                             * @param ctx 通道上下文
                             * @param msg 接收到的消息对象
                             */
                            @Override
                            public void channelRead(ChannelHandlerContext ctx, Object msg) {
                                ByteBuf byteBuf = inbound((ByteBuf) msg, "3");
                                ctx.channel().write(byteBuf);
                            }
                        });
                        ch.pipeline().addLast(new ChannelOutboundHandlerAdapter() {
                            /**
                             * 处理出站数据，在数据写出前进行加工
                             * @param ctx 通道上下文
                             * @param msg 要写出的消息对象
                             * @param promise 写操作的承诺
                             */
                            @Override
                            public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) {
                                ByteBuf byteBuf = outbound((ByteBuf) msg, "4");
                                ctx.writeAndFlush(msg);
                                ctx.write(byteBuf, promise);
                            }
                        });
                        ch.pipeline().addLast(new ChannelOutboundHandlerAdapter() {
                            @Override
                            public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) {
                                ByteBuf byteBuf = outbound((ByteBuf) msg, "5");
                                ctx.write(byteBuf, promise);
                            }
                        });
                        ch.pipeline().addLast(new ChannelOutboundHandlerAdapter() {
                            @Override
                            public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) {
                                ByteBuf byteBuf = outbound((ByteBuf) msg, "6");
                                ctx.write(byteBuf, promise);
                            }
                        });
                    }
                })
                .bind(8080); // 绑定端口并启动服务器
    }

        /**
     * 对出站数据进行处理
     * @param msg 待处理的ByteBuf对象
     * @param no 数据标识号
     * @return 处理后的ByteBuf对象
     */
    private static ByteBuf outbound(ByteBuf msg, String no) {
        ByteBuf byteBuf = msg;
        String output = byteBufToString(byteBuf);
        System.out.printf("\n\noutbound%s output: %s", no, output);
        stringWriteToByteBuf(byteBuf, String.format("\noutbound%s 已处理", no));
        return byteBuf;
    }

    /**
     * 对入站数据进行处理
     * @param msg 待处理的ByteBuf对象
     * @param no 数据标识号
     * @return 处理后的ByteBuf对象
     */
    private static ByteBuf inbound(ByteBuf msg, String no) {
        String input = byteBufToString(msg);
        System.out.printf("\n\ninbound%s input: %s\n", no, input);
        stringWriteToByteBuf(msg, String.format("\ninbound%s 已处理", no));
        return msg;
    }

    /**
     * 将ByteBuf对象转换为字符串
     * @param msg 待转换的ByteBuf对象
     * @return 字符串表示的数据
     */
    private static String byteBufToString(ByteBuf msg) {
        return msg.toString(StandardCharsets.UTF_8);
    }

    /**
     * 将字符串写入ByteBuf对象
     * @param byteBuf 待写入的ByteBuf对象
     * @param msg 要写入的字符串数据
     */
    private static void stringWriteToByteBuf(ByteBuf byteBuf, String msg) {
        byteBuf.writeBytes(msg.getBytes(StandardCharsets.UTF_8));
    }
}

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3. Netty bind

主要下面两个方法：

• final ChannelFuture regFuture = initAndRegister(); 初始化channel，并且注册ServerSocketChannel到 bossEventLoopGroup 的 一个 EventLoop 的 Selector 上
• doBind0(regFuture, channel, localAddress, promise); 绑定端口号

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public ChannelFuture bind(InetAddress inetHost, int inetPort) {
        return bind(new InetSocketAddress(inetHost, inetPort));
    }

    public ChannelFuture bind(SocketAddress localAddress) {
        validate();
        return doBind(ObjectUtil.checkNotNull(localAddress, "localAddress"));
    }

     private ChannelFuture doBind(final SocketAddress localAddress) {
        final ChannelFuture regFuture = initAndRegister();
        final Channel channel = regFuture.channel();
        if (regFuture.cause() != null) {
            return regFuture;
        }

        if (regFuture.isDone()) {
            // At this point we know that the registration was complete and successful.
            ChannelPromise promise = channel.newPromise();
            doBind0(regFuture, channel, localAddress, promise);
            return promise;
        } else {
            // Registration future is almost always fulfilled already, but just in case it's not.
            final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel);
            regFuture.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                    Throwable cause = future.cause();
                    if (cause != null) {
                        // Registration on the EventLoop failed so fail the ChannelPromise directly to not cause an
                        // IllegalStateException once we try to access the EventLoop of the Channel.
                        promise.setFailure(cause);
                    } else {
                        // Registration was successful, so set the correct executor to use.
                        // See https://github.com/netty/netty/issues/2586
                        promise.registered();

                        doBind0(regFuture, channel, localAddress, promise);
                    }
                }
            });
            return promise;
        }
    }

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3.1 initAndRegister

io.netty.bootstrap.AbstractBootstrap#initAndRegister

初始化channel，并且注册ServerSocketChannel到 bossEventLoopGroup 的 一个 EventLoop 的 Selector 上

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inal ChannelFuture initAndRegister() {
        Channel channel = null;
        try {
            channel = channelFactory.newChannel();
            init(channel);
        } 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);
        }

        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;
    }

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3.1.1 newChannel, 创建 NioServerSocketChannel

• 创建 channel = channelFactory.newChannel();
• io.netty.channel.ReflectiveChannelFactory#newChannel
• io.netty.channel.socket.nio.NioServerSocketChannel#NioServerSocketChannel，

• NioServerSocketChannel处理连接事件: super(null, channel, SelectionKey.OP_ACCEPT);
• AbstractNioChannel: 设置非阻塞 ch.configureBlocking(false);
• AbstractChannel 初始化unsafe、pipeline: unsafe = newUnsafe(); pipeline = newChannelPipeline();
• DefaultChannelPipeline: tail = new TailContext(this); head = new HeadContext(this);

3.1.2 init(channel); 初始化 NioServerSocketChannel

初始化 Channel：io.netty.bootstrap.ServerBootstrap#init, pipeline 添加 ServerBootstrapAcceptor 是一个异步过程，需要 EventLoop 线程负责执行。而当前 EventLoop 线程该去执行 register0() 的注册流程，所以等到 register0() 执行完之后才能被添加到 Pipeline 当中

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p.addLast(new ChannelInitializer<Channel>() {
            @Override
            public void initChannel(final Channel ch) throws Exception {
                final ChannelPipeline pipeline = ch.pipeline();
                ChannelHandler handler = config.handler();
                if (handler != null) {
                    pipeline.addLast(handler);
                }

                ch.eventLoop().execute(new Runnable() {
                    @Override
                    public void run() {
                        pipeline.addLast(new ServerBootstrapAcceptor(
                                ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
                    }
                });
            }
        });

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• 注册 Channel : ChannelFuture regFuture = config().group().register(channel);

• config().group() 就是 bossEventLoopGroup

• execute： io.netty.util.concurrent.SingleThreadEventExecutor#execute

• addTask(task);
• if (!inEventLoop) startThread();

3.1.3 register 注册channel

• 注册 ServerSocketChannel 到 bossEventLoopGroup 的一个 EventLoop 的 Selector 上，监听 SelectionKey.OP_ACCEPT 事件

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ChannelFuture regFuture = config().group().register(channel);

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• io.netty.channel.SingleThreadEventLoop#register(io.netty.channel.ChannelPromise)

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@Override
public ChannelFuture register(final ChannelPromise promise) {
    ObjectUtil.checkNotNull(promise, "promise");
    promise.channel().unsafe().register(this, promise);
    return promise;
}

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• io.netty.channel.AbstractChannel.AbstractUnsafe#register

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if (eventLoop.inEventLoop()) {
    register0(promise);
} else {
    try {
        eventLoop.execute(new Runnable() {
        @Override
        public void run() {
            register0(promise);
        }
);

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• io.netty.channel.AbstractChannel.AbstractUnsafe#register0
• io.netty.channel.nio.AbstractNioChannel#doRegister

• 调用java 的 nio：selectionKey = javaChannel().register(eventLoop().unwrappedSelector(), 0, this);

3.2 doBind0 绑定端口

io.netty.bootstrap.AbstractBootstrap#doBind0

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private static void doBind0(
            final ChannelFuture regFuture, final Channel channel,
            final SocketAddress localAddress, final ChannelPromise promise) {
        channel.eventLoop().execute(new Runnable() {
            @Override
            public void run() {
                if (regFuture.isSuccess()) {
                    channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
                } else {
                    promise.setFailure(regFuture.cause());
                }
            }
        });
    }

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• io.netty.channel.AbstractChannel#bind(java.net.SocketAddress, io.netty.channel.ChannelPromise)
• io.netty.channel.DefaultChannelPipeline#bind(java.net.SocketAddress, io.netty.channel.ChannelPromise)
• io.netty.channel.AbstractChannelHandlerContext#bind(java.net.SocketAddress, io.netty.channel.ChannelPromise)
• io.netty.channel.AbstractChannelHandlerContext#invokeBind
• io.netty.channel.DefaultChannelPipeline.HeadContext#bind
• io.netty.channel.AbstractChannel.AbstractUnsafe#bind
• io.netty.channel.socket.nio.NioServerSocketChannel#doBind 调用java 的 bind

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protected void doBind(SocketAddress localAddress) throws Exception {
    if (PlatformDependent.javaVersion() >= 7) {
        javaChannel().bind(localAddress, config.getBacklog());
    } else {
        javaChannel().socket().bind(localAddress, config.getBacklog());
    }
}

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3.3 ServerBootstrapAcceptor

child 就是 workerEventLoopGroup，socketChannel 注册到 workerEventLoopGroup 进行处理

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public void channelRead(ChannelHandlerContext ctx, Object msg) {
    final Channel child = (Channel) msg;

    child.pipeline().addLast(childHandler);

    setChannelOptions(child, childOptions, logger);

    for (Entry<AttributeKey<?>, Object> e: childAttrs) {
        child.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
    }

    try {
        childGroup.register(child).addListener(new ChannelFutureListener() {
        @Override
        public void operationComplete(ChannelFuture future) throws Exception {
            if (!future.isSuccess()) {
                forceClose(child, future.cause());
                    }
                }
            });
        } catch (Throwable t) {
          forceClose(child, t);
        }
    }
}

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原创作者: xuxiangyang 转载于: https://blog.51cto.com/xuxiangyang/11480861