netty初探ServerBootstrap主要类和起动流程

几个关键类:

1.NioServerSocketChannel

 

2.NioSocketChannel

两个继承和实现的接口都差不多,功能也差不多

3.ServerBootstrap 和 Bootstrap都继承自AbstractBootstrap功能都是作为入口,构建服务端和客户端

4.NioEventLoopGroup

5.NioEventLoop

6.DefaultChannelPipeline

 

二.初始化流程

创建一个服务端代码

EventLoopGroup bossgroup = new NioEventLoopGroup();
EventLoopGroup workgroup = new NioEventLoopGroup();
try{
    ServerBootstrap b = new ServerBootstrap();
    b.group(bossgroup,workgroup)
     .channel(NioServerSocketChannel.class)
     .option(ChannelOption.SO_BACKLOG,100)
     .handler(new LoggingHandler(LogLevel.INFO))
     .childHandler(new ChannelInitializer() {

        @Override
        public void initChannel(SocketChannel socketChannel) throws Exception {
            socketChannel.pipeline().addLast(new ProtobufVarint32FrameDecoder());
            socketChannel.pipeline().addLast(new                                 
                   ProtobufDecoder(SubscribeReqProto.SubscribeReq.getDefaultInstance()));

            socketChannel.pipeline().addLast(new ProtobufVarint32LengthFieldPrepender());
            socketChannel.pipeline().addLast(new ProtobufEncoder());
            socketChannel.pipeline().addLast(new SubReqHandler());

        }
     });

    ChannelFuture f = b.bind(port).sync();
    f.channel().closeFuture().sync();
}finally {
    bossgroup.shutdownGracefully();
    workgroup.shutdownGracefully();
}

group()、channel()、option() 、handler() 、childHandler()都是配置属性信息

整个创建初始化注册是在bind()方法内

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

public ChannelFuture bind(SocketAddress localAddress) {
    validate();
    if (localAddress == null) {
        throw new NullPointerException("localAddress");
    }
    return doBind(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;
    }
}

再看一下initAndRegister() 主要是创建server channel和注册selector

final ChannelFuture initAndRegister() {

    Channel channel = null;

    try {
        //创建channel对象
        channel = channelFactory.newChannel();
        //初始化配置
        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 GlobalEventExecutor
        return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t);
    }

    //注册channel到selector上
    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;
}

 

channelFactory 是在调用channel()方法时初始化的

public B channel(Class channelClass) {

    if (channelClass == null) {
        throw new NullPointerException("channelClass");
    }
    return channelFactory(new ReflectiveChannelFactory(channelClass));
}

public B channelFactory(io.netty.channel.ChannelFactory channelFactory) {
    return channelFactory((ChannelFactory) channelFactory);
}

public B channelFactory(ChannelFactory channelFactory) {

    if (channelFactory == null) {
        throw new NullPointerException("channelFactory");
    }

    if (this.channelFactory != null) {
        throw new IllegalStateException("channelFactory set already");
    }

    this.channelFactory = channelFactory;
    return self();
}

channelFactory.newChannel(); 根据传入的具体类名来实例化channel对象,比较常见的是NioServerSocketChannel,下面具体看一下NioServerSocketChannel对象初始化过程

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 #2308.
        */
        return provider.openServerSocketChannel();
    } catch (IOException e) {
        throw new ChannelException("Failed to open a server socket.", e);
    }
}

public NioServerSocketChannel() {
    this(newSocket(DEFAULT_SELECTOR_PROVIDER));
}

provider对象是通过java SelectorProvider 的provider方法来创建

public static SelectorProvider provider() {

    synchronized (lock) {

        if (provider != null)
            return provider;

        return AccessController.doPrivileged(
                    new PrivilegedAction() {

                          public SelectorProvider run() {

                                if (loadProviderFromProperty())
                                    return provider;

                                if (loadProviderAsService())
                                    return provider;

                                provider = sun.nio.ch.DefaultSelectorProvider.create();
                                return provider;
                          }
                    });
    }
}

pipeline是在NioServerSocketChannel 父类AbstractChannel的构造函数中创建的

protected AbstractChannel(Channel parent) {
    this.parent = parent;
    id = newId();
    unsafe = newUnsafe();
    pipeline = newChannelPipeline();
}

protected DefaultChannelPipeline newChannelPipeline() {
    return new DefaultChannelPipeline(this);
}

创建完channel之后要对channel进行一些配置,init(channel)方法是在子类ServerBootstrap中

void init(Channel channel) throws Exception {

    final Map, Object> options = options0();
    synchronized (options) {
        setChannelOptions(channel, options, logger);
    }

    final Map, Object> attrs = attrs0();
    synchronized (attrs) {
        for (Entry, Object> e: attrs.entrySet()) {
            @SuppressWarnings("unchecked")
            AttributeKey