Netty4.x 源码实战系列(一): 深入理解ServerBootstrap 与 Bootstrap (1)

  从Java1.4开始, Java引入了non-blocking IO,简称NIO。NIO与传统socket最大的不同就是引入了Channel和多路复用selector的概念。传统的socket是基于stream的,它是单向的,有InputStream表示read和OutputStream表示写。而Channel是双工的,既支持读也支持写,channel的读/写都是面向Buffer。 NIO中引入的多路复用Selector机制(如果是linux系统,则应用的epoll事件通知机制)可使一个线程同时监听多个Channel上发生的事件。 虽然Java NIO相比于以往确实是一个大的突破,但是如果要真正上手进行开发,且想要开发出好的一个服务端网络程序,那么你得要花费一点功夫了,毕竟Java NIO只是提供了一大堆的API而已,对于一般的软件开发人员来说只能呵呵了。因此,社区中就涌现了很多基于Java NIO的网络应用框架,其中以Apache的Mina,以及Netty最为出名,从本篇开始我们将深入的分析一下Netty的内部实现细节

  本系列是基于Netty4.1.18这个版本。

  在分析源码之前,我们还是先看看Netty官方的样例代码,了解一下Netty一般是如何进行服务端及客户端开发的。

  Netty服务端示例:

 

EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)
EventLoopGroup workerGroup = new NioEventLoopGroup();
try
{ ServerBootstrap b = new ServerBootstrap(); // (2) b.group(bossGroup, workerGroup)  // (3) .channel(NioServerSocketChannel.class) // (4)
.handler(new LoggingHandler()) // (5)
.childHandler(new ChannelInitializer<SocketChannel>() { // (6) @Override public void initChannel(SocketChannel ch) throws Exception { ch.pipeline().addLast(new DiscardServerHandler()); } }) .option(ChannelOption.SO_BACKLOG, 128) // (7) .childOption(ChannelOption.SO_KEEPALIVE, true); // (8) // Bind and start to accept incoming connections. ChannelFuture f = b.bind(port).sync(); // (9) // Wait until the server socket is closed. // In this example, this does not happen, but you can do that to gracefully // shut down your server. f.channel().closeFuture().sync(); } finally { workerGroup.shutdownGracefully(); bossGroup.shutdownGracefully(); }

上面这段代码展示了服务端的一个基本步骤:

(1)、 初始化用于Acceptor的主"线程池"以及用于I/O工作的从"线程池";
(2)、 初始化ServerBootstrap实例, 此实例是netty服务端应用开发的入口,也是本篇介绍的重点, 下面我们会深入分析;
(3)、 通过ServerBootstrap的group方法,设置(1)中初始化的主从"线程池";
(4)、 指定通道channel的类型,由于是服务端,故而是NioServerSocketChannel;
(5)、 设置ServerSocketChannel的处理器(此处不详述,后面的系列会进行深入分析)
(6)、 设置子通道也就是SocketChannel的处理器, 其内部是实际业务开发的"主战场"(此处不详述,后面的系列会进行深入分析)
(7)、 配置ServerSocketChannel的选项
(8)、 配置子通道也就是SocketChannel的选项
(9)、 绑定并侦听某个端口

接着,我们再看看客户端是如何开发的:

Netty客户端示例:

public class TimeClient {
    public static void main(String[] args) throws Exception {
        String host = args[0];
        int port = Integer.parseInt(args[1]);
        EventLoopGroup workerGroup = new NioEventLoopGroup(); // (1)
        
        try {
            Bootstrap b = new Bootstrap(); // (2)
            b.group(workerGroup); // (3)
            b.channel(NioSocketChannel.class); // (4)
            b.option(ChannelOption.SO_KEEPALIVE, true); // (5)
            b.handler(new ChannelInitializer<SocketChannel>() { // (6)
                @Override
                public void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new TimeClientHandler());
                }
            });
            
            // Start the client.
            ChannelFuture f = b.connect(host, port).sync(); // (7)

            // Wait until the connection is closed.
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }
}

 客户端的开发步骤和服务端都差不多:

(1)、 初始化用于连接及I/O工作的"线程池";
(2)、 初始化Bootstrap实例, 此实例是netty客户端应用开发的入口,也是本篇介绍的重点, 下面我们会深入分析;
(3)、 通过Bootstrap的group方法,设置(1)中初始化的"线程池";
(4)、 指定通道channel的类型,由于是客户端,故而是NioSocketChannel;
(5)、 设置SocketChannel的选项(此处不详述,后面的系列会进行深入分析);
(6)、 设置SocketChannel的处理器, 其内部是实际业务开发的"主战场"(此处不详述,后面的系列会进行深入分析);
(7)、 连接指定的服务地址;

通过对上面服务端及客户端代码分析,Bootstrap是Netty应用开发的入口,如果想要理解Netty内部的实现细节,那么有必要先了解一下Bootstrap内部的实现机制。

首先我们先看一下ServerBootstrap及Bootstrap的类继承结构图:

通过类图我们知道AbstractBootstrap类是ServerBootstrap及Bootstrap的基类,我们先看一下AbstractBootstrap类的主要代码:

public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> implements Cloneable {

    volatile EventLoopGroup group;
    private volatile ChannelFactory<? extends C> channelFactory;
    private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();
    private final Map<AttributeKey<?>, Object> attrs = new LinkedHashMap<AttributeKey<?>, Object>();
    private volatile ChannelHandler handler;

    
    public B group(EventLoopGroup group) {
        if (group == null) {
            throw new NullPointerException("group");
        }
        if (this.group != null) {
            throw new IllegalStateException("group set already");
        }
        this.group = group;
        return self();
    }

    private B self() {
        return (B) this;
    }

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

    @Deprecated
    public B channelFactory(ChannelFactory<? extends C> channelFactory) {
        if (channelFactory == null) {
            throw new NullPointerException("channelFactory");
        }
        if (this.channelFactory != null) {
            throw new IllegalStateException("channelFactory set already");
        }

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

    public B channelFactory(io.netty.channel.ChannelFactory<? extends C> channelFactory) {
        return channelFactory((ChannelFactory<C>) channelFactory);
    }

    public <T> B option(ChannelOption<T> option, T value) {
        if (option == null) {
            throw new NullPointerException("option");
        }
        if (value == null) {
            synchronized (options) {
                options.remove(option);
            }
        } else {
            synchronized (options) {
                options.put(option, value);
            }
        }
        return self();
    }

    public <T> B attr(AttributeKey<T> key, T value) {
        if (key == null) {
            throw new NullPointerException("key");
        }
        if (value == null) {
            synchronized (attrs) {
                attrs.remove(key);
            }
        } else {
            synchronized (attrs) {
                attrs.put(key, value);
            }
        }
        return self();
    }

    public B validate() {
        if (group == null) {
            throw new IllegalStateException("group not set");
        }
        if (channelFactory == null) {
            throw new IllegalStateException("channel or channelFactory not set");
        }
        return self();
    }

    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;
        }
    }

    final 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);
        }

        ChannelFuture regFuture = config().group().register(channel);
        if (regFuture.cause() != null) {
            if (channel.isRegistered()) {
                channel.close();
            } else {
                channel.unsafe().closeForcibly();
            }
        }

        return regFuture;
    }

    abstract void init(Channel channel) throws Exception;

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

    public B handler(ChannelHandler handler) {
        if (handler == null) {
            throw new NullPointerException("handler");
        }
        this.handler = handler;
        return self();
    }public abstract AbstractBootstrapConfig<B, C> config();

}

 

现在我们以示例代码为出发点,来详细分析一下引导类内部实现细节:

1、 首先看看服务端的b.group(bossGroup, workerGroup):

    调用ServerBootstrap的group方法,设置react模式的主线程池 以及 IO 操作线程池,ServerBootstrap中的group代码如下:

public ServerBootstrap group(EventLoopGroup parentGroup, EventLoopGroup childGroup) {
        super.group(parentGroup);
        if (childGroup == null) {
            throw new NullPointerException("childGroup");
        }
        if (this.childGroup != null) {
            throw new IllegalStateException("childGroup set already");
        }
        this.childGroup = childGroup;
        return this;
    }

在group方法中,会继续调用父类的group方法,而通过类继承图我们知道,super.group(parentGroup)其实调用的就是AbstractBootstrap的group方法。AbstractBootstrap中group代码如下:

public B group(EventLoopGroup group) {
        if (group == null) {
            throw new NullPointerException("group");
        }
        if (this.group != null) {
            throw new IllegalStateException("group set already");
        }
        this.group = group;
        return self();
    }

通过以上分析,我们知道了AbstractBootstrap中定义了主线程池group的引用,而子线程池childGroup的引用是定义在ServerBootstrap中。

当我们查看客户端Bootstrap的group方法时,我们发现,其是直接调用的父类AbstractBoostrap的group方法。

2、示例代码中的 channel()方法

无论是服务端还是客户端,channel调用的都是基类的channel方法,其实现细节如下:

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

 

public B channelFactory(ChannelFactory<? extends C> channelFactory) {
        if (channelFactory == null) {
            throw new NullPointerException("channelFactory");
        }
        if (this.channelFactory != null) {
            throw new IllegalStateException("channelFactory set already");
        }

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

我们发现,其实channel方法内部,只是初始化了一个用于生产指定channel类型的工厂实例。

3、option / handler / attr 方法

     option: 设置通道的选项参数, 对于服务端而言就是ServerSocketChannel, 客户端而言就是SocketChannel;

  handler: 设置主通道的处理器, 对于服务端而言就是ServerSocketChannel,也就是用来处理Acceptor的操作;

      对于客户端的SocketChannel,主要是用来处理 业务操作;

    attr: 设置通道的属性;

 option / handler / attr方法都定义在AbstractBootstrap中, 所以服务端和客户端的引导类方法调用都是调用的父类的对应方法。

4、childHandler / childOption / childAttr 方法(只有服务端ServerBootstrap才有child类型的方法)

   对于服务端而言,有两种通道需要处理, 一种是ServerSocketChannel:用于处理用户连接的accept操作, 另一种是SocketChannel,表示对应客户端连接。而对于客户端,一般都只有一种channel,也就是SocketChannel。

   因此以child开头的方法,都定义在ServerBootstrap中,表示处理或配置服务端接收到的对应客户端连接的SocketChannel通道。

  childHandler / childOption / childAttr 在ServerBootstrap中的对应代码如下:

public ServerBootstrap childHandler(ChannelHandler childHandler) {
        if (childHandler == null) {
            throw new NullPointerException("childHandler");
        }
        this.childHandler = childHandler;
        return this;
    }
public <T> ServerBootstrap childOption(ChannelOption<T> childOption, T value) {
        if (childOption == null) {
            throw new NullPointerException("childOption");
        }
        if (value == null) {
            synchronized (childOptions) {
                childOptions.remove(childOption);
            }
        } else {
            synchronized (childOptions) {
                childOptions.put(childOption, value);
            }
        }
        return this;
    }
public <T> ServerBootstrap childAttr(AttributeKey<T> childKey, T value) {
        if (childKey == null) {
            throw new NullPointerException("childKey");
        }
        if (value == null) {
            childAttrs.remove(childKey);
        } else {
            childAttrs.put(childKey, value);
        }
        return this;
    }

至此,引导类的属性配置都设置完毕了。

本篇总结:

1、服务端由两种线程池,用于Acceptor的React主线程和用于I/O操作的React从线程池; 客户端只有用于连接及IO操作的React的主线程池;

2、ServerBootstrap中定义了服务端React的"从线程池"对应的相关配置,都是以child开头的属性。 而用于"主线程池"channel的属性都定义在AbstractBootstrap中;

 

本篇只是简单介绍了一下引导类的配置属性, 下一篇我将详细介绍服务端引导类的Bind过程分析。

 

 



posted @ 2017-12-30 17:30  随风飘扬123  阅读(26945)  评论(4编辑  收藏  举报