rocketMQ broker 分发并处理请求

// org.apache.rocketmq.remoting.netty.NettyRemotingServer#start
ServerBootstrap childHandler =
    this.serverBootstrap.group(this.eventLoopGroupBoss, this.eventLoopGroupSelector)
    .channel(useEpoll() ? EpollServerSocketChannel.class : NioServerSocketChannel.class)
    .option(ChannelOption.SO_BACKLOG, 1024)
    .option(ChannelOption.SO_REUSEADDR, true)
    .option(ChannelOption.SO_KEEPALIVE, false)
    .childOption(ChannelOption.TCP_NODELAY, true)
    .childOption(ChannelOption.SO_SNDBUF, nettyServerConfig.getServerSocketSndBufSize())
    .childOption(ChannelOption.SO_RCVBUF, nettyServerConfig.getServerSocketRcvBufSize())
    // 绑定端口
    .localAddress(new InetSocketAddress(this.nettyServerConfig.getListenPort()))
    .childHandler(new ChannelInitializer<SocketChannel>() {
        @Override
        public void initChannel(SocketChannel ch) throws Exception {
            ch.pipeline()
                .addLast(defaultEventExecutorGroup, HANDSHAKE_HANDLER_NAME,
                    new HandshakeHandler(TlsSystemConfig.tlsMode))
                .addLast(defaultEventExecutorGroup,
                    new NettyEncoder(),
                    new NettyDecoder(),
                    new IdleStateHandler(0, 0, nettyServerConfig.getServerChannelMaxIdleTimeSeconds()),
                    new NettyConnectManageHandler(),
                    // 分发请求
                    new NettyServerHandler()
                );
        }
    });
// 启动
ChannelFuture sync = this.serverBootstrap.bind().sync();

// org.apache.rocketmq.remoting.netty.NettyRemotingServer.NettyServerHandler
class NettyServerHandler extends SimpleChannelInboundHandler<RemotingCommand> {

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, RemotingCommand msg) throws Exception {
        processMessageReceived(ctx, msg);
    }
}

public void processRequestCommand(final ChannelHandlerContext ctx, final RemotingCommand cmd) {
    // NettyRequestProcessor 是处理具体请求的处理器，ExecutorService 是对应的线程池
    final Pair<NettyRequestProcessor, ExecutorService> matched = this.processorTable.get(cmd.getCode());
    final Pair<NettyRequestProcessor, ExecutorService> pair = null == matched ? this.defaultRequestProcessor : matched;
    final int opaque = cmd.getOpaque();

    if (pair != null) {
        // 创建任务
        Runnable run = new Runnable() {
            @Override
            public void run() {
                try {
                    RPCHook rpcHook = NettyRemotingAbstract.this.getRPCHook();
                    if (rpcHook != null) {
                        rpcHook.doBeforeRequest(RemotingHelper.parseChannelRemoteAddr(ctx.channel()), cmd);
                    }
                    // 调用处理器处理收到的请求
                    final RemotingCommand response = pair.getObject1().processRequest(ctx, cmd);
                    if (rpcHook != null) {
                        rpcHook.doAfterResponse(RemotingHelper.parseChannelRemoteAddr(ctx.channel()), cmd, response);
                    }

                    if (!cmd.isOnewayRPC()) {
                        if (response != null) {
                            response.setOpaque(opaque);
                            response.markResponseType();
                            try {
                                ctx.writeAndFlush(response);
                            } catch (Throwable e) {
                                log.error("process request over, but response failed", e);
                                log.error(cmd.toString());
                                log.error(response.toString());
                            }
                        } else {

                        }
                    }
                } catch (Throwable e) {
                    log.error("process request exception", e);
                    log.error(cmd.toString());

                    if (!cmd.isOnewayRPC()) {
                        final RemotingCommand response = RemotingCommand.createResponseCommand(RemotingSysResponseCode.SYSTEM_ERROR,
                            RemotingHelper.exceptionSimpleDesc(e));
                        response.setOpaque(opaque);
                        ctx.writeAndFlush(response);
                    }
                }
            }
        };

        if (pair.getObject1().rejectRequest()) {
            final RemotingCommand response = RemotingCommand.createResponseCommand(RemotingSysResponseCode.SYSTEM_BUSY,
                "[REJECTREQUEST]system busy, start flow control for a while");
            response.setOpaque(opaque);
            ctx.writeAndFlush(response);
            return;
        }

        try {
            final RequestTask requestTask = new RequestTask(run, ctx.channel(), cmd);
            // 把任务提交到对应的线程池
            pair.getObject2().submit(requestTask);
        } catch (RejectedExecutionException e) {
            if ((System.currentTimeMillis() % 10000) == 0) {
                log.warn(RemotingHelper.parseChannelRemoteAddr(ctx.channel())
                    + ", too many requests and system thread pool busy, RejectedExecutionException "
                    + pair.getObject2().toString()
                    + " request code: " + cmd.getCode());
            }

            if (!cmd.isOnewayRPC()) {
                final RemotingCommand response = RemotingCommand.createResponseCommand(RemotingSysResponseCode.SYSTEM_BUSY,
                    "[OVERLOAD]system busy, start flow control for a while");
                response.setOpaque(opaque);
                ctx.writeAndFlush(response);
            }
        }
    } else {
        String error = " request type " + cmd.getCode() + " not supported";
        final RemotingCommand response =
            RemotingCommand.createResponseCommand(RemotingSysResponseCode.REQUEST_CODE_NOT_SUPPORTED, error);
        response.setOpaque(opaque);
        ctx.writeAndFlush(response);
        log.error(RemotingHelper.parseChannelRemoteAddr(ctx.channel()) + error);
    }
}

// org.apache.rocketmq.broker.BrokerController#BrokerController
// 创建队列
this.sendThreadPoolQueue = new LinkedBlockingQueue<Runnable>(this.brokerConfig.getSendThreadPoolQueueCapacity());

// org.apache.rocketmq.broker.BrokerController#initialize
// 创建线程池
this.sendMessageExecutor = new BrokerFixedThreadPoolExecutor(
    this.brokerConfig.getSendMessageThreadPoolNums(),
    this.brokerConfig.getSendMessageThreadPoolNums(),
    1000 * 60,
    TimeUnit.MILLISECONDS,
    this.sendThreadPoolQueue,
    new ThreadFactoryImpl("SendMessageThread_"));

// org.apache.rocketmq.broker.BrokerController#registerProcessor
// 把不同的请求，请求处理器，线程池对应起来
public void registerProcessor() {
    /**
     * SendMessageProcessor
     */
    SendMessageProcessor sendProcessor = new SendMessageProcessor(this);
    sendProcessor.registerSendMessageHook(sendMessageHookList);
    sendProcessor.registerConsumeMessageHook(consumeMessageHookList);

    this.remotingServer.registerProcessor(RequestCode.SEND_MESSAGE, sendProcessor, this.sendMessageExecutor);
    this.remotingServer.registerProcessor(RequestCode.SEND_MESSAGE_V2, sendProcessor, this.sendMessageExecutor);
    this.remotingServer.registerProcessor(RequestCode.SEND_BATCH_MESSAGE, sendProcessor, this.sendMessageExecutor);
    this.remotingServer.registerProcessor(RequestCode.CONSUMER_SEND_MSG_BACK, sendProcessor, this.sendMessageExecutor);
    this.fastRemotingServer.registerProcessor(RequestCode.SEND_MESSAGE, sendProcessor, this.sendMessageExecutor);
    this.fastRemotingServer.registerProcessor(RequestCode.SEND_MESSAGE_V2, sendProcessor, this.sendMessageExecutor);
    this.fastRemotingServer.registerProcessor(RequestCode.SEND_BATCH_MESSAGE, sendProcessor, this.sendMessageExecutor);
    this.fastRemotingServer.registerProcessor(RequestCode.CONSUMER_SEND_MSG_BACK, sendProcessor, this.sendMessageExecutor);
}