AliMQ(RocketMQ)源码(二)producer.start()

在创建完成Producer后，就进入了Producer的start()方法。start()方法DefaultMQProducerImpl的start()方法。

                this.serviceState = ServiceState.START_FAILED;

                this.checkConfig();

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

                this.mQClientFactory = MQClientManager.getInstance().getAndCreateMQClientInstance(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;

上面现将状态设置为START_FAILED，启动成功后再设置为RUNNING状态。
this.checkConfig(); 检查是否设置group
前面的代码都是做下缓存，没有功能的实际意义，真正的启动是在

mQClientFactory.start();

                    this.serviceState = ServiceState.START_FAILED;
                    // If not specified,looking address from name server
                    if (null == this.clientConfig.getNamesrvAddr()) {
                        this.mQClientAPIImpl.fetchNameServerAddr();
                    }
                    // Start request-response channel
                    this.mQClientAPIImpl.start();
                    // Start various schedule tasks
                    this.startScheduledTask();
                    // Start pull service
                    this.pullMessageService.start();
                    // Start rebalance service
                    this.rebalanceService.start();
                    // Start push service
                    this.defaultMQProducer.getDefaultMQProducerImpl().start(false);
                    log.info("the client factory [{}] start OK", this.clientId);
                    this.serviceState = ServiceState.RUNNING;

1、获取NameServer

                    if (null == this.clientConfig.getNamesrvAddr()) {
                        this.mQClientAPIImpl.fetchNameServerAddr();
                    }

上面这段是获取NameServer

2、启动channel

众所周知，RocketMQ通讯是通过Netty的，Netty的通信需要通过channel

this.mQClientAPIImpl.start();

就是初始化channel。
这个start()方法，进入了NettyRemotingClient的start()方法，这这个start方法的前面一部分是在创建netty通讯的客户端

Bootstrap handler = this.bootstrap.group(this.eventLoopGroupWorker).channel(NioSocketChannel.class)

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

是检查发送的消息是否超时，并做相应处理。

        this.timer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                try {
                    NettyRemotingClient.this.scanChannelTablesOfNameServer();
                } catch (Exception e) {
                    log.error("scanChannelTablesOfNameServer exception", e);
                }
            }
        }, 1000 * 3, 10 * 1000);

上面这段代码是通过心跳检查查看NameServer的连接是佛正常。

3、启动多个定时任务

this.startScheduledTask();

其中的方法拆开分析如下：

        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);
        }

每个2分钟更新一个NameServer。

        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);

更新topic在NameServer中的路由信息。

        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);

上面这段是清除下线的Broker，并与Broker的心跳检测，后面发送消息，真正的通讯是与Broker直接进行的。

        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);

上面是将消费端的offset持久化到你本机上。

        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);

上面这段是调整发送消息的线程池的大小，其实是空方法，不起作用。

4、启动拉取消息的线程

this.pullMessageService.start();

上面这个方法是启动拉取消息的线程。

5、启动重新负载均衡的线程

this.rebalanceService.start();

上面的方法，会根据topic或者服务的变化等重新进行负载均衡。

this.defaultMQProducer.getDefaultMQProducerImpl().start(false);

上面这段，把之前的方法再验证一遍，没有实际意义。

至此，producer的start()方法就结束了。

二、super.start()

在ProducerImpl的super.start()方法中，就是做了一件事，不停将消息的轨迹持久化到控制台。

    public void start() throws MQClientException {
        TraceProducerFactory.registerTraceDispatcher(dispatcherId);
        this.worker = new Thread(new AsyncRunnable(), "MQ-AsyncArrayDispatcher-Thread-" + dispatcherId);
        this.worker.setDaemon(true);
        this.worker.start();
        this.registerShutDownHook();
    }