netty (四) serverBootStrap启动

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之前的操作都是在为serverbootstrap进行配置，完成内部属性的初始化。在绑定到端口的时候才开始启动。

先对内部的属性进行校验，然后绑定本机地址。

这个是具体启动流程的代码：分为两步，一个是绑定，一个是注册

private ChannelFuture doBind(final SocketAddress localAddress) {
    这里开始绑定和注册
    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;
    }
}

bind和register

final ChannelFuture initAndRegister() {
    Channel channel = null;
    try {
        1.通过反射创建了serversocketchannel
        channel = channelFactory.newChannel();
        2.进行初始化，为channel设置channeloption和mapattribute等属性。
        init(channel);
    } catch (Throwable t) {
        if (channel != null) {
            // channel can be null if newChannel crashed (eg SocketException("too many open files"))
            channel可能为空，进行一些其他的处理
            channel.unsafe().closeForcibly();  强制关闭
            // as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
            因为channel还没注册，所以要使用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);
    }

    3.将channel注册到eventloopgroup
    ChannelFuture regFuture = config().group().register(channel);
    if (regFuture.cause() != null) {
        if (channel.isRegistered()) {
            channel.close();
        } else {
            如果中间出现了错误就强制关闭
            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;
}

ServerBootstrap 对channel的初始化

void init(Channel channel) throws Exception {
    final Map<ChannelOption<?>, Object> options = options0();
    synchronized (options) {
        为这个serversocketchannel设置channeloption
        setChannelOptions(channel, options, logger);
    }

    final Map<AttributeKey<?>, Object> attrs = attrs0();
    synchronized (attrs) {
        for (Entry<AttributeKey<?>, Object> e: attrs.entrySet()) {
            @SuppressWarnings("unchecked")
            AttributeKey<Object> key = (AttributeKey<Object>) e.getKey();
            为这个serversocketchannel设置channelAttributeKey
            channel.attr(key).set(e.getValue());
        }
    }
 
    获取到channel关联的ChannelPipeline 
    ChannelPipeline p = channel.pipeline();

    这个是 worker EventLoopGroup 
    final EventLoopGroup currentChildGroup = childGroup;
    final ChannelHandler currentChildHandler = childHandler;
    final Entry<ChannelOption<?>, Object>[] currentChildOptions;
    final Entry<AttributeKey<?>, Object>[] currentChildAttrs;
    synchronized (childOptions) {
        currentChildOptions = childOptions.entrySet().toArray(newOptionArray(0));
    }
    synchronized (childAttrs) {
        currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(0));
    }

    给ChannelPipeline 添加一个channelhandler
    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));
                }
            });
        }
    });
}