Producer启动流程

　　DefaultMQProducer构造方法

    public DefaultMQProducer(final String producerGroup) {
        this(null, producerGroup, null);
    }

    public DefaultMQProducer(final String namespace, final String producerGroup, RPCHook rpcHook) {
        this.namespace = namespace;
        this.producerGroup = producerGroup;
        defaultMQProducerImpl = new DefaultMQProducerImpl(this, rpcHook);
    }

　　DefaultMQProducerImpl的构造方法

    public DefaultMQProducerImpl(final DefaultMQProducer defaultMQProducer, RPCHook rpcHook) {
        this.defaultMQProducer = defaultMQProducer;
        this.rpcHook = rpcHook;

        this.asyncSenderThreadPoolQueue = new LinkedBlockingQueue<Runnable>(50000);
        this.defaultAsyncSenderExecutor = new ThreadPoolExecutor(
            Runtime.getRuntime().availableProcessors(),
            Runtime.getRuntime().availableProcessors(),
            1000 * 60,
            TimeUnit.MILLISECONDS,
            this.asyncSenderThreadPoolQueue,
            new ThreadFactory() {
                private AtomicInteger threadIndex = new AtomicInteger(0);

                @Override
                public Thread newThread(Runnable r) {
                    return new Thread(r, "AsyncSenderExecutor_" + this.threadIndex.incrementAndGet());
                }
            });
    }

　　启动producer：DefaultMQProducer#start方法

    public void start() throws MQClientException {
        this.setProducerGroup(withNamespace(this.producerGroup));
        this.defaultMQProducerImpl.start();
        if (null != traceDispatcher) {
            try {
                traceDispatcher.start(this.getNamesrvAddr(), this.getAccessChannel());
            } catch (MQClientException e) {
                log.warn("trace dispatcher start failed ", e);
            }
        }
    }

　　DefaultMQProducerImpl#start(boolean)方法

public void start(final boolean startFactory) throws MQClientException {
        switch (this.serviceState) {
            case CREATE_JUST:
                this.serviceState = ServiceState.START_FAILED;

                this.checkConfig();

                if (!this.defaultMQProducer.getProducerGroup().equals(MixAll.CLIENT_INNER_PRODUCER_GROUP)) {
                    this.defaultMQProducer.changeInstanceNameToPID();
                }

                this.mQClientFactory = MQClientManager.getInstance().getOrCreateMQClientInstance(this.defaultMQProducer, rpcHook);

                boolean registerOK = mQClientFactory.registerProducer(this.defaultMQProducer.getProducerGroup(), this);
                if (!registerOK) {
                    this.serviceState = ServiceState.CREATE_JUST;
                    throw new MQClientException("The producer group[" + this.defaultMQProducer.getProducerGroup()
                        + "] has been created before, specify another name please." + FAQUrl.suggestTodo(FAQUrl.GROUP_NAME_DUPLICATE_URL),
                        null);
                }

                this.topicPublishInfoTable.put(this.defaultMQProducer.getCreateTopicKey(), new TopicPublishInfo());

                if (startFactory) {
                    mQClientFactory.start();
                }

                log.info("the producer [{}] start OK. sendMessageWithVIPChannel={}", this.defaultMQProducer.getProducerGroup(),
                    this.defaultMQProducer.isSendMessageWithVIPChannel());
                this.serviceState = ServiceState.RUNNING;
                break;
            case RUNNING:
            case START_FAILED:
            case SHUTDOWN_ALREADY:
                throw new MQClientException("The producer service state not OK, maybe started once, "
                    + this.serviceState
                    + FAQUrl.suggestTodo(FAQUrl.CLIENT_SERVICE_NOT_OK),
                    null);
            default:
                break;
        }

        this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();

        RequestFutureHolder.getInstance().startScheduledTask(this);

    }

　　mQClientFactory.sendHeartbeatToAllBrokerWithLock()：发送心跳到所有的broker，最终执行的方法为MQClientAPIImpl#sendHearbeat：

    public int sendHearbeat(
        final String addr,
        final HeartbeatData heartbeatData,
        final long timeoutMillis
    ) throws RemotingException, MQBrokerException, InterruptedException {
        RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.HEART_BEAT, null);
        request.setLanguage(clientConfig.getLanguage());
        request.setBody(heartbeatData.encode());
        RemotingCommand response = this.remotingClient.invokeSync(addr, request, timeoutMillis);
        assert response != null;
        switch (response.getCode()) {
            case ResponseCode.SUCCESS: {
                return response.getVersion();
            }
            default:
                break;
        }

        throw new MQBrokerException(response.getCode(), response.getRemark(), addr);
    }

　　与broker通信，request 的 code 为 HEART_BEAT

　　MQClientInstance的启动，方法为MQClientInstance#start

public void start() throws MQClientException {

    synchronized (this) {
        switch (this.serviceState) {
            case CREATE_JUST:
                this.serviceState = ServiceState.START_FAILED;
                // 获取 nameServer 的地址
                if (null == this.clientConfig.getNamesrvAddr()) {
                    this.mQClientAPIImpl.fetchNameServerAddr();
                }
                // 启动远程服务，这个方法只是装配了netty客户端相关配置
                // 注意：1. 这里是netty客户端，2. 这里并没有创建连接
                this.mQClientAPIImpl.start();
                // 启动定时任务
                this.startScheduledTask();
                // pull服务，仅对consumer启作用
                this.pullMessageService.start();
                // 启动负载均衡服务，仅对consumer启作用
                this.rebalanceService.start();
                // 启用内部的 producer
                this.defaultMQProducer.getDefaultMQProducerImpl().start(false);
                log.info("the client factory [{}] start OK", this.clientId);
                this.serviceState = ServiceState.RUNNING;
                break;
            case START_FAILED:
                throw new MQClientException(...);
            default:
                break;
        }
    }
}

mQClientAPIImpl.start()：配置netty客户端，使用的是Bootstrap而非ServerBootstrap，表示这是netty客户端

    public void start() {
        this.defaultEventExecutorGroup = new DefaultEventExecutorGroup(
            nettyClientConfig.getClientWorkerThreads(),
            new ThreadFactory() {

                private AtomicInteger threadIndex = new AtomicInteger(0);

                @Override
                public Thread newThread(Runnable r) {
                    return new Thread(r, "NettyClientWorkerThread_" + this.threadIndex.incrementAndGet());
                }
            });

        Bootstrap handler = this.bootstrap.group(this.eventLoopGroupWorker).channel(NioSocketChannel.class)
            .option(ChannelOption.TCP_NODELAY, true)
            .option(ChannelOption.SO_KEEPALIVE, false)
            .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, nettyClientConfig.getConnectTimeoutMillis())
            .handler(new ChannelInitializer<SocketChannel>() {
                @Override
                public void initChannel(SocketChannel ch) throws Exception {
                    ChannelPipeline pipeline = ch.pipeline();
                    if (nettyClientConfig.isUseTLS()) {
                        if (null != sslContext) {
                            pipeline.addFirst(defaultEventExecutorGroup, "sslHandler", sslContext.newHandler(ch.alloc()));
                            log.info("Prepend SSL handler");
                        } else {
                            log.warn("Connections are insecure as SSLContext is null!");
                        }
                    }
                    pipeline.addLast(
                        defaultEventExecutorGroup,
                        new NettyEncoder(),
                        new NettyDecoder(),
                        new IdleStateHandler(0, 0, nettyClientConfig.getClientChannelMaxIdleTimeSeconds()),
                        new NettyConnectManageHandler(),
                        new NettyClientHandler());
                }
            });
        if (nettyClientConfig.getClientSocketSndBufSize() > 0) {
            log.info("client set SO_SNDBUF to {}", nettyClientConfig.getClientSocketSndBufSize());
            handler.option(ChannelOption.SO_SNDBUF, nettyClientConfig.getClientSocketSndBufSize());
        }
        if (nettyClientConfig.getClientSocketRcvBufSize() > 0) {
            log.info("client set SO_RCVBUF to {}", nettyClientConfig.getClientSocketRcvBufSize());
            handler.option(ChannelOption.SO_RCVBUF, nettyClientConfig.getClientSocketRcvBufSize());
        }
        if (nettyClientConfig.getWriteBufferLowWaterMark() > 0 && nettyClientConfig.getWriteBufferHighWaterMark() > 0) {
            log.info("client set netty WRITE_BUFFER_WATER_MARK to {},{}",
                    nettyClientConfig.getWriteBufferLowWaterMark(), nettyClientConfig.getWriteBufferHighWaterMark());
            handler.option(ChannelOption.WRITE_BUFFER_WATER_MARK, new WriteBufferWaterMark(
                    nettyClientConfig.getWriteBufferLowWaterMark(), nettyClientConfig.getWriteBufferHighWaterMark()));
        }

        this.timer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                try {
                    NettyRemotingClient.this.scanResponseTable();
                } catch (Throwable e) {
                    log.error("scanResponseTable exception", e);
                }
            }
        }, 1000 * 3, 1000);

        if (this.channelEventListener != null) {
            this.nettyEventExecutor.start();
        }
    }

启动定时任务的方法为MQClientInstance#startScheduledTask，代码如下：

    private void startScheduledTask() {
        if (null == this.clientConfig.getNamesrvAddr()) {
            this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

                @Override
                public void run() {
                    try {
                        MQClientInstance.this.mQClientAPIImpl.fetchNameServerAddr();
                    } catch (Exception e) {
                        log.error("ScheduledTask fetchNameServerAddr exception", e);
                    }
                }
            }, 1000 * 10, 1000 * 60 * 2, TimeUnit.MILLISECONDS);
        }

        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

            @Override
            public void run() {
                try {
                    MQClientInstance.this.updateTopicRouteInfoFromNameServer();
                } catch (Exception e) {
                    log.error("ScheduledTask updateTopicRouteInfoFromNameServer exception", e);
                }
            }
        }, 10, this.clientConfig.getPollNameServerInterval(), TimeUnit.MILLISECONDS);

        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

            @Override
            public void run() {
                try {
                    MQClientInstance.this.cleanOfflineBroker();
                    MQClientInstance.this.sendHeartbeatToAllBrokerWithLock();
                } catch (Exception e) {
                    log.error("ScheduledTask sendHeartbeatToAllBroker exception", e);
                }
            }
        }, 1000, this.clientConfig.getHeartbeatBrokerInterval(), TimeUnit.MILLISECONDS);

        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

            @Override
            public void run() {
                try {
                    MQClientInstance.this.persistAllConsumerOffset();
                } catch (Exception e) {
                    log.error("ScheduledTask persistAllConsumerOffset exception", e);
                }
            }
        }, 1000 * 10, this.clientConfig.getPersistConsumerOffsetInterval(), TimeUnit.MILLISECONDS);

        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

            @Override
            public void run() {
                try {
                    MQClientInstance.this.adjustThreadPool();
                } catch (Exception e) {
                    log.error("ScheduledTask adjustThreadPool exception", e);
                }
            }
        }, 1, 1, TimeUnit.MINUTES);
    }

• 定时获取 nameServer 的地址，MQClientInstance#start开始会调用MQClientAPIImpl#fetchNameServerAddr获取nameServer
• 定时更新topic的路由信息，会去nameServer获取路由信息
• 定时发送心跳信息到nameServer，在DefaultMQProducerImpl#start(boolean)中，我们也提到了向nameServer发送心跳信息，两处调用的是同一个方法
• 持久化消费者的消费偏移量，对消费者consumer有效
• 调整线程池的线程数量