客户端connect过程分析

BootStrap.connect()解析

最新推荐文章于 2024-05-06 00:06:21 发布

转载最新推荐文章于 2024-05-06 00:06:21 发布 · 1k 阅读

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本文详细剖析了BootStrap.connect()方法的工作流程，从初始化和注册到连接远程地址的具体实现，包括参数验证、事件循环调用及最终的连接操作。

转载自：https://blog.youkuaiyun.com/pzw_0612/article/details/78068194

　　BootStrap.connect() 分析：

public ChannelFuture connect(String inetHost, int inetPort) {
    return connect(InetSocketAddress.createUnresolved(inetHost, inetPort));
}

public ChannelFuture connect(SocketAddress remoteAddress) {
    if (remoteAddress == null) {
        throw new NullPointerException("remoteAddress");
    }

    validate();
    return doResolveAndConnect(remoteAddress, config.localAddress());
}

/**
 * @see #connect()
 */
private ChannelFuture doResolveAndConnect(final SocketAddress remoteAddress, final SocketAddress localAddress) {
    final ChannelFuture regFuture = initAndRegister();
    final Channel channel = regFuture.channel();

    if (regFuture.isDone()) {
        if (!regFuture.isSuccess()) {
            return regFuture;
        }
        return doResolveAndConnect0(channel, remoteAddress, localAddress, channel.newPromise());
    } else {
        //...略
    }
}

　　initAndRegister不再赘述，之后会调用doResolveAndConnect0， doResolveAndConnect0中会进行一些参数检查, 最终调用doConnect 方法, 其实现如下:

private static void doConnect(
        final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise connectPromise) {

    // This method is invoked before channelRegistered() is triggered.  Give user handlers a chance to set up
    // the pipeline in its channelRegistered() implementation.
    final Channel channel = connectPromise.channel();
    channel.eventLoop().execute(new Runnable() {
        @Override
        public void run() {
            if (localAddress == null) {
                channel.connect(remoteAddress, connectPromise);
            } else {
                channel.connect(remoteAddress, localAddress, connectPromise);
            }
            connectPromise.addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
        }
    });
}

　　在doConnect 中, 会在 event loop 线程中调用 Channel 的 connect 方法, 而这个channel就是 NioSocketChannel。跟进channel.connect ,它调用的实际是AbstractChannel#connect：

@Override
public ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise) {
    return pipeline.connect(remoteAddress, promise);
}

@Override
public final ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise) {
    return tail.connect(remoteAddress, promise);
}

　　tail是TailContext实例, 而TailContext是 AbstractChannelHandlerContext的子类, 因此这里调用的其实是 AbstractChannelHandlerContext#connect, 看一下这个方法的实现:

@Override
public ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise) {
    return connect(remoteAddress, null, promise);
}

@Override
public ChannelFuture connect(
        final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise promise) {

    if (remoteAddress == null) {
        throw new NullPointerException("remoteAddress");
    }
    if (isNotValidPromise(promise, false)) {
        // cancelled
        return promise;
    }

    final AbstractChannelHandlerContext next = findContextOutbound();
    EventExecutor executor = next.executor();
    if (executor.inEventLoop()) {
        next.invokeConnect(remoteAddress, localAddress, promise);
    } else {
        safeExecute(executor, new Runnable() {
            @Override
            public void run() {
                next.invokeConnect(remoteAddress, localAddress, promise);
            }
        }, promise, null);
    }
    return promise;
}

　　findContextOutbound返回的是head，然后会调用到HeadContext#connect:

@Override
public void connect(
        ChannelHandlerContext ctx,
        SocketAddress remoteAddress, SocketAddress localAddress,
        ChannelPromise promise) throws Exception {
    unsafe.connect(remoteAddress, localAddress, promise);
}

　　这个unsafe 其实就是 NioSocketChannelUnsafe，而NioSocketChannelUnsafe.connnect方法的实现是 AbstractNioUnsafe.connect，其代码实现：

@Override
public final void connect(
        final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise promise) {
    boolean wasActive = isActive();
    if (doConnect(remoteAddress, localAddress)) {
        fulfillConnectPromise(promise, wasActive);
    } else {
        ...
    }
}

　　AbstractNioUnsafe.connect 的实现如上代码所示, 在这个 connect 方法中, 调用了 doConnect 方法, 注意, 这个方法并不是 AbstractNioUnsafe 的方法, 而是 AbstractNioChannel 的抽象方法. doConnect 方法是在 NioSocketChannel 中实现的, 因此进入到 NioSocketChannel.doConnect 中:

@Override
protected boolean doConnect(SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
    if (localAddress != null) {
        javaChannel().socket().bind(localAddress);
    }

    boolean success = false;
    try {
        boolean connected = javaChannel().connect(remoteAddress);
        if (!connected) {
            selectionKey().interestOps(SelectionKey.OP_CONNECT);
        }
        success = true;
        return connected;
    } finally {
        if (!success) {
            doClose();
        }
    }
}