RocketMq源码解析四：生产者Producer启动

一、主要接口和类

生产者服务核心接口和类的关系如下图所示：

MQProducer是生产者解耦，这里找几个有代表性的方法

// 同步发送消息

SendResult send(final Message msg) throws MQClientException, RemotingException, MQBrokerException,InterruptedException;

// 同步超时发送消息如果超过了timeout的时间就抛出异常

SendResult send(final Message msg, final long timeout) throws MQClientException,
RemotingException, MQBrokerException, InterruptedException;

// 异步发送消息

void send(final Message msg, final SendCallback sendCallback) throws MQClientException,RemotingException, InterruptedException;
// 异步超时发送消息如果超过了timeout的时间就抛出异常
void send(final Message msg, final SendCallback sendCallback, final long timeout)
throws MQClientException, RemotingException, InterruptedException;

// 指定消息队列同步发送消息

SendResult send(final Message msg, final MessageQueue mq) throws MQClientException,
RemotingException, MQBrokerException, InterruptedException;

DefaultMQProducer除了实现MQProducer的方法外，还继承了ClientConfig类，ClientConfig中主要记录了客户端的一些连接配置信息，我们重点看下DefaultMQProducer中有哪些核心属性

producerGroup:生产者所属组
createTopickey:默认Topic

defaultTopicQueueNums:默认主题在每一个Broker队列数量

sendMsgTimeout:发送消息默认超时时间，默认3s

compressMsgBodyOverHowmuch:消息体超过该值则启用压缩，默认4k

retryTimeswhensendFailed:同步方式发送消息重试次数，默认为2，总共执行3次retryTimeswhensendAsyncFailed:异步方法发送消息重试次数，默认为2

retryAnotherBrokerwhenNotstoreOK:消息重试时选择另外一个Broker时，是否不等待存储结果就返回，默认为false

maxMessagesize:允许发送的最大消息长度，默认为4M

我们看到 DefaultMQProducer中持有了一个transient 修饰的DefaultMQProducerImpl类的成员属性defaultMQProducerImpl，实际上核心的功能都封装在了这个DefaultMQProducerImpl类中，下面我们逐一来为读者展开说明。

二、生产者启动流程

我们先来看生产者启动的方法 DefaultMQProducer::start

    @Override
    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);
            }
        }
    }

第一步是获取并设置生产者组的信息；

第二步调用defaultMQProducerImpl的start方法，我们上文讲过DefaultMQProducer的大部分核心功能都是封装在DefaultMQProducerImpl类中。我们来看下defaultMQProducerImpl中的start方法：

流程图如下：

源码如下：

public void start(final boolean startFactory) throws MQClientException {
        switch (this.serviceState) {
            // 如果是启动
            case CREATE_JUST:
                this.serviceState = ServiceState.START_FAILED;
                // 1、先检查一下配置
                this.checkConfig();
                // 2、设置自身的客户端名称为进程ID
                if (!this.defaultMQProducer.getProducerGroup().equals(MixAll.CLIENT_INNER_PRODUCER_GROUP)) {
                    this.defaultMQProducer.changeInstanceNameToPID();
                }
                // 3、获取MQClientManager并获得MQClientInstance实例
                this.mQClientFactory = MQClientManager.getInstance().getOrCreateMQClientInstance(this.defaultMQProducer, rpcHook);

                // 4、把当前的生产者注入MQClientFactory中
                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());
                
                // 5、调用start方法启动
                if (startFactory) {
                    mQClientFactory.start();
                }

                log.info("the producer [{}] start OK. sendMessageWithVIPChannel={}", this.defaultMQProducer.getProducerGroup(),
                    this.defaultMQProducer.isSendMessageWithVIPChannel());
                this.serviceState = ServiceState.RUNNING;
                break;
            ...
        }
        this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
        RequestFutureHolder.getInstance().startScheduledTask(this);
    }

重点讲一下第3步：获取MQClientManager并获得MQClientInstance实例。整个JVM中只存在一个MQClienManager实例，维护一个MQClientInstance缓存表

ConcurrentMap<String/* clientld */, MQClientinstance> factoryTable = newConcurrentHashMap<String,MQClientlnstance>():

同一个clientld只会创建一个MQClientInstance。MQClientinstance封装了RocketMQ网络处理API，是消息生产者和消息消费者与NameServer、Broker打交道的网络通道
代码:MQClientManager::getAndCreateMQClientInstance

    public MQClientInstance getOrCreateMQClientInstance(final ClientConfig clientConfig, RPCHook rpcHook) {
        String clientId = clientConfig.buildMQClientId();
        MQClientInstance instance = this.factoryTable.get(clientId);
        if (null == instance) {
            instance =
                new MQClientInstance(clientConfig.cloneClientConfig(),
                    this.factoryIndexGenerator.getAndIncrement(), clientId, rpcHook);
            MQClientInstance prev = this.factoryTable.putIfAbsent(clientId, instance);
            if (prev != null) {
                instance = prev;
                log.warn("Returned Previous MQClientInstance for clientId:[{}]", clientId);
            } else {
                log.info("Created new MQClientInstance for clientId:[{}]", clientId);
            }
        }

        return instance;
    }

a：构建客户端的id；

b：从缓存表factoryTable中获取对应clientId的实例；

c：如果没有就生成一个并放入到缓存表中；

d：返回

最后我们来看下mQClientFactory.start()当中的源码。

// 先把服务状态改为失败

this.serviceState = ServiceState.START_FAILED;
// 如果配置中的namesrv地址为空，重新获取
if (null == this.clientConfig.getNamesrvAddr()) {
this.mQClientAPIImpl.fetchNameServerAddr();
}
// Start request-response channel 启动一个netty服务用于处理请求
this.mQClientAPIImpl.start();
// Start various schedule tasks 启动一系列定时任务用于更新namesrv地址，topic消费情况等
this.startScheduledTask();
// Start pull service 启动拉取消息服务
this.pullMessageService.start();
// Start rebalance service 启动relalance服务
this.rebalanceService.start();
// Start push service 启动推送服务
this.defaultMQProducer.getDefaultMQProducerImpl().start(false);
log.info("the client factory [{}] start OK", this.clientId);

// 把服务状态改为运行中
this.serviceState = ServiceState.RUNNING;