reactor-netty的TcpClient如何往eventLoop提交task

序

本文主要研究一下reactor-netty的TcpClient如何往eventLoop提交task

实例

        TcpClient client = TcpClient.create("localhost", 8888);
        LOGGER.info("client:{}",client.getClass());
        Mono handler = client.newHandler((inbound,outbound) -> {
            return outbound.sendString(Mono.just("Hello World!")).then(inbound.receive()
                    .asString().next().log().then());
        });
        LOGGER.info("handler:{}",handler.getClass()); //NOTE reactor.core.publisher.MonoCreate
        handler.subscribe();

TcpClient.newHandler

reactor-netty-0.7.3.RELEASE-sources.jar!/reactor/ipc/netty/tcp/TcpClient.java

    protected Mono newHandler(BiFunction> handler,
            InetSocketAddress address,
            boolean secure,
            Consumer onSetup) {

        final BiFunction>
                targetHandler =
                null == handler ? ChannelOperations.noopHandler() : handler;

        return Mono.create(sink -> {
            SocketAddress remote = address != null ? address : options.getAddress();

            ChannelPool pool = null;

            PoolResources poolResources = options.getPoolResources();
            if (poolResources != null) {
                pool = poolResources.selectOrCreate(remote, options,
                        doHandler(null, sink, secure, remote, null, null),
                        options.getLoopResources().onClient(options.preferNative()));
            }

            ContextHandler contextHandler =
                    doHandler(targetHandler, sink, secure, remote, pool, onSetup);
            sink.onCancel(contextHandler);

            if (pool == null) {
                Bootstrap b = options.get();
                b.remoteAddress(remote);
                b.handler(contextHandler);
                contextHandler.setFuture(b.connect());
            }
            else {
                contextHandler.setFuture(pool.acquire());
            }
        });
    }

注意这里的pool.acquire()或者b.connect()

SimpleChannelPool.acquireHealthyFromPoolOrNew

netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/pool/SimpleChannelPool.java

    /**
     * Tries to retrieve healthy channel from the pool if any or creates a new channel otherwise.
     * @param promise the promise to provide acquire result.
     * @return future for acquiring a channel.
     */
    private Future acquireHealthyFromPoolOrNew(final Promise promise) {
        try {
            final Channel ch = pollChannel();
            if (ch == null) {
                // No Channel left in the pool bootstrap a new Channel
                Bootstrap bs = bootstrap.clone();
                bs.attr(POOL_KEY, this);
                ChannelFuture f = connectChannel(bs);
                if (f.isDone()) {
                    notifyConnect(f, promise);
                } else {
                    f.addListener(new ChannelFutureListener() {
                        @Override
                        public void operationComplete(ChannelFuture future) throws Exception {
                            notifyConnect(future, promise);
                        }
                    });
                }
                return promise;
            }
            EventLoop loop = ch.eventLoop();
            if (loop.inEventLoop()) {
                doHealthCheck(ch, promise);
            } else {
                loop.execute(new Runnable() {
                    @Override
                    public void run() {
                        doHealthCheck(ch, promise);
                    }
                });
            }
        } catch (Throwable cause) {
            promise.tryFailure(cause);
        }
        return promise;
    }

    /**
     * Bootstrap a new {@link Channel}. The default implementation uses {@link Bootstrap#connect()}, sub-classes may
     * override this.
     * 

     * The {@link Bootstrap} that is passed in here is cloned via {@link Bootstrap#clone()}, so it is safe to modify.
     */
    protected ChannelFuture connectChannel(Bootstrap bs) {
        return bs.connect();
    }

pool.acquire()最后调用的是SimpleChannelPool.acquireHealthyFromPoolOrNew，它最后调用connectChannel也是调用Bootstrap.connect

Bootstrap.connect

netty-transport-4.1.20.Final-sources.jar!/io/netty/bootstrap/Bootstrap.java

    /**
     * Connect a {@link Channel} to the remote peer.
     */
    public ChannelFuture connect() {
        validate();
        SocketAddress remoteAddress = this.remoteAddress;
        if (remoteAddress == null) {
            throw new IllegalStateException("remoteAddress not set");
        }

        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 {
            // 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 {
                    // Directly obtain the cause and do a null check so we only need one volatile read in case of a
                    // failure.
                    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();
                        doResolveAndConnect0(channel, remoteAddress, localAddress, promise);
                    }
                }
            });
            return promise;
        }
    }    

注意这里调用了initAndRegister
然后调用doResolveAndConnect0

initAndRegister

netty-transport-4.1.20.Final-sources.jar!/io/netty/bootstrap/AbstractBootstrap.java

    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);
            }
            // 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);
        }

        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;
    }

这里先调用channelFactory.newChannel()来创建一个channel，之后进行初始化，这里可能抛出SocketException("too many open files")，异常的话直接设置fail并返回DefaultChannelPromise
注意这里调用了config().group().register(channel)，在reactor-netty中这个group是MultithreadEventLoopGroup.java

io.netty.channel.ReflectiveChannelFactory.newChannel()

netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/ReflectiveChannelFactory.java

    public T newChannel() {
        try {
            return clazz.getConstructor().newInstance();
        } catch (Throwable t) {
            throw new ChannelException("Unable to create Channel from class " + clazz, t);
        }
    }

这里new的是NioSocketChannel.class
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/socket/nio/NioSocketChannel.java

    private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();

    private static SocketChannel 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 SocketChannel.open() otherwise.
             *
             *  See #2308.
             */
            return provider.openSocketChannel();
        } catch (IOException e) {
            throw new ChannelException("Failed to open a socket.", e);
        }
    }
    /**
     * Create a new instance using the given {@link SelectorProvider}.
     */
    public NioSocketChannel(SelectorProvider provider) {
        this(newSocket(provider));
    }

mac操作系统这里的provider是sun.nio.ch.KQueueSelectorProvider，openSocketChannel调用的是SelectorProviderImpl的方法

jre/lib/rt.jar!/sun/nio/ch/SelectorProviderImpl.class

    public SocketChannel openSocketChannel() throws IOException {
        return new SocketChannelImpl(this);
    }

jre/lib/rt.jar!/sun/nio/ch/SocketChannelImpl.class

    SocketChannelImpl(SelectorProvider var1) throws IOException {
        super(var1);
        this.fd = Net.socket(true);
        this.fdVal = IOUtil.fdVal(this.fd);
        this.state = 0;
    }

注意这里调用了Net.socket(true)，创建FileDescriptor，可能抛出SocketException("too many open files")

Bootstrap.init(channel)

netty-transport-4.1.20.Final-sources.jar!/io/netty/bootstrap/Bootstrap.java

    void init(Channel channel) throws Exception {
        ChannelPipeline p = channel.pipeline();
        p.addLast(config.handler());

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

        final Map, Object> attrs = attrs0();
        synchronized (attrs) {
            for (Entry, Object> e: attrs.entrySet()) {
                channel.attr((AttributeKey