netty源碼分析之一：server的啟動

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nio server啟動的第一步，都是要建立一個serverSocketChannel，我截取一段啟動代碼，一步步分析：

public void afterPropertiesSet() throws Exception {
    // 建立rpc工廠
    ThreadFactory threadRpcFactory = new NamedThreadFactory("NettyRPC ThreadFactory");
    //執行worker線程池數量
    int parallel = Runtime.getRuntime().availableProcessors() * 2;
    // boss
    EventLoopGroup boss = new NioEventLoopGroup(1);
    // worker
    EventLoopGroup worker = new NioEventLoopGroup(parallel,threadRpcFactory, SelectorProvider.provider());
    try {
        ServerBootstrap bootstrap = new ServerBootstrap();
        bootstrap.group(boss, worker).channel(NioServerSocketChannel.class)
                .childHandler(new MessageRecvChannelInitializer(handlerMap))
                .option(ChannelOption.SO_BACKLOG, 128)
                .childOption(ChannelOption.SO_KEEPALIVE, true);

        ChannelFuture future = bootstrap.bind(serverAddress, Integer.valueOf(port)).sync();
        System.out.printf("[author chenjianye] Netty RPC Server start success ip:%s port:%s\n", serverAddress, port);

        // 註冊zookeeper服務
        serviceRegistry.register(serverAddress + ":" + port);
        // wait
        future.channel().closeFuture().sync();
    } finally {
        worker.shutdownGracefully();
        boss.shutdownGracefully();
    }
}
入口就在

ChannelFuture future = bootstrap.bind(serverAddress, Integer.valueOf(port)).sync();

順序往下執行，直到AbstractBootstrap類的doBind方法：

private ChannelFuture doBind(final SocketAddress localAddress) {
    final ChannelFuture regFuture = this.initAndRegister();
    final Channel channel = regFuture.channel();
    if(regFuture.cause() != null) {
        return regFuture;
    } else if(regFuture.isDone()) {
        ChannelPromise promise1 = channel.newPromise();
        doBind0(regFuture, channel, localAddress, promise1);
        return promise1;
    } else {
        final AbstractBootstrap.PendingRegistrationPromise promise = new AbstractBootstrap.PendingRegistrationPromise(channel, null);
        regFuture.addListener(new ChannelFutureListener() {
            public void operationComplete(ChannelFuture future) throws Exception {
                Throwable cause = future.cause();
                if(cause != null) {
                    promise.setFailure(cause);
                } else {
                    promise.executor = channel.eventLoop();
                }

                AbstractBootstrap.doBind0(regFuture, channel, localAddress, promise);
            }
        });
        return promise;
    }
}
=============================================
這個方法需要重點分析，我做個標記，doBind方法分析如下：

1.final ChannelFuture regFuture = this.initAndRegister();

final ChannelFuture initAndRegister() {
    // 通過channel工廠反射建立ServerSocketChannel，並建立了作用於serverSocketChannel的channelPipeline管道
    // 這個管道維護了ctx為元素的雙向鏈表，到目前為止，pipeline的順序為：head(outBound) ----> tail(inbound)
    Channel channel = this.channelFactory().newChannel();

    try {
　　　　 // 這個init方法第一個主要是設定channel的屬性，我不細說了
        // 第二個作用是增加了inbound處理器，channelInitializer，裡面有一個initChannel（）方法會在特定時刻被觸發，什麼時候被觸發，後面我會說到。
        this.init(channel);
    } catch (Throwable var3) {
        channel.unsafe().closeForcibly();
        return (new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE)).setFailure(var3);
    }

　　 // 到了這裡，就開始執行register邏輯，這個是關鍵，我把register的代碼貼出來，跟著後面的代碼繼續看，跳轉到2。
    ChannelFuture regFuture = this.group().register(channel);
    if(regFuture.cause() != null) {
        if(channel.isRegistered()) {
            channel.close();
        } else {
            channel.unsafe().closeForcibly();
        }
    }

    return regFuture;
}

2.AbstractChannel裡的register方法：

public final void register(EventLoop eventLoop, final ChannelPromise promise) {
    if(eventLoop == null) {
        throw new NullPointerException("eventLoop");
    } else if(AbstractChannel.this.isRegistered()) {
        promise.setFailure(new IllegalStateException("registered to an event loop already"));
    } else if(!AbstractChannel.this.isCompatible(eventLoop)) {
        promise.setFailure(new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
    } else {
        AbstractChannel.this.eventLoop = eventLoop;
        // 到這裡還是主線程啟動，所以會執行else，啟動了boss線程,register0方法跳轉到3
        if(eventLoop.inEventLoop()) {
            this.register0(promise);
        } else {
            try {
                eventLoop.execute(new OneTimeTask() {
                    public void run() {
                        AbstractUnsafe.this.register0(promise);
                    }
                });
            } catch (Throwable var4) {
                AbstractChannel.logger.warn("Force-closing a channel whose registration task was not accepted by an event loop: {}", AbstractChannel.this, var4);
                this.closeForcibly();
                AbstractChannel.this.closeFuture.setClosed();
                this.safeSetFailure(promise, var4);
            }
        }

    }
}

3.register0方法

private void register0(ChannelPromise promise) {
    try {
        if(!promise.setUncancellable() || !this.ensureOpen(promise)) {
            return;
        }

        boolean t = this.neverRegistered;
        // 這個方法主要是 this.selectionKey = this.javaChannel().register(this.eventLoop().selector, 0, this);

        AbstractChannel.this.doRegister();
        this.neverRegistered = false;
        AbstractChannel.this.registered = true;
        
        // 回調之前doBind方法的listener，boss線程添加了新的任務：bind任務
        this.safeSetSuccess(promise);
        
        // 這個方法東西內容很多
        // 第一步：this.head.fireChannelRegistered()沒有什麼實質內容，最終執行到inbound的next.invokeChannelRegistered()方法
        // 第二步：根據上文，目前的pipeline順序為head---->initializer---->tail
        // 第三步：執行initializer
        // 第四步：添加一個新的inbound處理器，ServerBootstrapAcceptor，此時的順序為：head---->initizlizer---->ServerBootstrapAcceptor---->tail
        // 第五步：移除initizlizer，此時pipeline順序為：head---->ServerBootstrapAcceptor---->tail
        // 第六步：麼有什麼實質內容，這個方法就算執行結束了
        AbstractChannel.this.pipeline.fireChannelRegistered();
        
        // 這裡channel還沒有綁定，所以isActive()方法返回false，不會繼續執行，目前boss線程還剩下bind任務
        if(t && AbstractChannel.this.isActive()) {
            AbstractChannel.this.pipeline.fireChannelActive();
        }
    } catch (Throwable var3) {
        this.closeForcibly();
        AbstractChannel.this.closeFuture.setClosed();
        this.safeSetFailure(promise, var3);
    }

}

4.bind任務
bind任務是一個outbound，所以會按照tail---->head的順序執行，目前只有head是outbound。
headHandler最終會執行AbstractUnsafe的bind方法：

AbstractChannel.this.doBind(localAddress);

public final void bind(SocketAddress localAddress, ChannelPromise promise) {
    if(promise.setUncancellable() && this.ensureOpen(promise)) {
        if(Boolean.TRUE.equals(AbstractChannel.this.config().getOption(ChannelOption.SO_BROADCAST)) && localAddress instanceof InetSocketAddress && !((InetSocketAddress)localAddress).getAddress().isAnyLocalAddress() && !PlatformDependent.isWindows() && !PlatformDependent.isRoot()) {
            AbstractChannel.logger.warn("A non-root user can\‘t receive a broadcast packet if the socket is not bound to a wildcard address; binding to a non-wildcard address (" + localAddress + ") anyway as requested.");
        }

        boolean wasActive = AbstractChannel.this.isActive();

        try {
　　　　　　  //由於我們是nioServerSocketChannel，所以：this.javaChannel().socket().bind(localAddress, this.config.getBacklog());

            AbstractChannel.this.doBind(localAddress);

        } catch (Throwable var5) {

 this.safeSetFailure(promise, var5);
 this.closeIfClosed();
 return;
 }

　　　　 // 此時已經綁定了，所以isActive()返回true，執行
 if(!wasActive && AbstractChannel.this.isActive()) {
 // 重新往boss線程加入了任務
 this.invokeLater(new OneTimeTask() {
 public void run() {
 AbstractChannel.this.pipeline.fireChannelActive();
 }
 });
 }

 this.safeSetSuccess(promise);
 }
}

public ChannelPipeline fireChannelActive() {
    // 來回調用，貌似這裡沒有什麼實質內容
    this.head.fireChannelActive();
    if(this.channel.config().isAutoRead()) {
        // 這個是outBound，最終會觸發head
　　　　 // head會執行 this.unsafe.beginRead()，最終會執行abstractNioChannel裡的doBeginRead（）方法，最終會執行到5

        this.channel.read();
    }

    return this;
}

5.

protected void doBeginRead() throws Exception {
    if(!this.inputShutdown) {
        SelectionKey selectionKey = this.selectionKey;
        if(selectionKey.isValid()) {
            this.readPending = true;
            int interestOps = selectionKey.interestOps();
            if((interestOps & this.readInterestOp) == 0) {
                selectionKey.interestOps(interestOps | this.readInterestOp);
            }

        }
    }
}

終於看到我們熟悉的東西了，最終把selectionKey的interestOps設定為SelectionKey.OP_ACCEPT。

netty源碼分析之一：server的啟動