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前言
與消息發(fā)送緊密相關(guān)的幾行代碼:
1. DefaultMQProducer producer = new DefaultMQProducer("ProducerGroupName");
2. producer.start();
3. Message msg = new Message(...)
4. SendResult sendResult = producer.send(msg);
5. producer.shutdown();
那這幾行代碼執(zhí)行時(shí),背后都做了什么?
一. 首先是DefaultMQProducer.start
@Override public void start() throws MQClientException { this.defaultMQProducerImpl.start(); }
調(diào)用了默認(rèn)生成消息的實(shí)現(xiàn)類 -- DefaultMQProducerImpl
調(diào)用defaultMQProducerImpl.start()方法,DefaultMQProducerImpl.start()會(huì)初始化得到MQClientInstance實(shí)例對(duì)象,MQClientInstance實(shí)例對(duì)象調(diào)用它自己的start方法會(huì) ,啟動(dòng)一些服務(wù),如拉去消息服務(wù)PullMessageService.Start()、啟動(dòng)負(fù)載平衡服務(wù)RebalanceService.Start(),比如網(wǎng)絡(luò)通信服務(wù)MQClientAPIImpl.Start()
另外,還會(huì)執(zhí)行與生產(chǎn)消息相關(guān)的信息,如注冊(cè)produceGroup、new一個(gè)TopicPublishInfo對(duì)象并以默認(rèn)TopicKey為鍵值,構(gòu)成鍵值對(duì)存入DefaultMQProducerImpl的topicPublishInfoTable中。
efaultMQProducerImpl.start()后,獲取的MQClientInstance實(shí)例對(duì)象會(huì)調(diào)用sendHeartbeatToAllBroker()方法,不斷向broker發(fā)送心跳包,yin'b可以使用下面一幅圖大致描述DefaultMQProducerImpl.start()過程:
上圖中的三個(gè)部分中涉及的內(nèi)容:
1.1 初始化MQClientInstance
一個(gè)客戶端只能產(chǎn)生一個(gè)MQClientInstance實(shí)例對(duì)象,產(chǎn)生方式使用了工廠模式與單例模式。MQClientInstance.start()方法啟動(dòng)一些服務(wù),源碼如下:
public void start() throws MQClientException { synchronized (this) { switch (this.serviceState) { case CREATE_JUST: 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; break; case RUNNING: break; case SHUTDOWN_ALREADY: break; case START_FAILED: throw new MQClientException("The Factory object[" + this.getClientId() + "] has been created before, and failed.", null); default: break; } } }
1.2 注冊(cè)producer
該過程會(huì)將這個(gè)當(dāng)前producer對(duì)象注冊(cè)到MQClientInstance實(shí)例對(duì)象的的producerTable中。一個(gè)jvm(一個(gè)客戶端)中一個(gè)producerGroup只能有一個(gè)實(shí)例,MQClientInstance操作producerTable大概有如下幾個(gè)方法:
注:
根據(jù)不同的clientId,MQClientManager將給出不同的MQClientInstance;
根據(jù)不同的group,MQClientInstance將給出不同的MQProducer和MQConsumer
1.3 向路由信息表中添加路由
topicPublishInfoTable定義:
public class DefaultMQProducerImpl implements MQProducerInner { private final Logger log = ClientLogger.getLog(); private final Random random = new Random(); private final DefaultMQProducer defaultMQProducer; private final ConcurrentMap<String/* topic */, TopicPublishInfo> topicPublishInfoTable = new ConcurrentHashMap<String, TopicPublishInfo>();
它是一個(gè)以topic為key的Map型數(shù)據(jù)結(jié)構(gòu),DefaultMQProducerImpl.start()時(shí)會(huì)默認(rèn)創(chuàng)建一個(gè)key=MixAll.DEFAULT_TOPIC的TopicPublishInfo存放到topicPublishInfoTable中。
1.4 發(fā)送心跳包
MQClientInstance向broker發(fā)送心跳包時(shí),調(diào)用sendHeartbeatToAllBroker( ),以及從MQClientInstance實(shí)例對(duì)象的brokerAddrTable中拿到所有broker地址,向這些broker發(fā)送心跳包。
sendHeartbeatToAllBroker會(huì)涉及到prepareHeartbeatData()方法,該方法會(huì)生成heartbeatData數(shù)據(jù),發(fā)送心跳包時(shí),heartbeatData作為心跳包的body。與producer相關(guān)的部分代碼如下:
// Producer for (Map.Entry<String/* group */, MQProducerInner> entry : this.producerTable.entrySet()) { MQProducerInner impl = entry.getValue(); if (impl != null) { ProducerData producerData = new ProducerData(); producerData.setGroupName(entry.getKey()); heartbeatData.getProducerDataSet().add(producerData); }
二、. SendResult sendResult = producer.send(msg)
首先會(huì)調(diào)用DefaultMQProducer.send(msg) ,繼而調(diào)用sendDefaultImpl:
public SendResult send(Message msg, long timeout) throws MQClientException, RemotingException, MQBrokerException, InterruptedException { return this.sendDefaultImpl(msg, CommunicationMode.SYNC, null, timeout); }
sendDefaultImpl做了啥?
2.1. 獲取topicPublishInfo
根據(jù)msg的topic從topicPublishInfoTable獲取對(duì)應(yīng)的topicPublishInfo,如果沒有則更新路由信息,從nameserver端拉取最新路由信息。從nameserver端拉取最新路由信息大致為:
首先getTopicRouteInfoFromNameServer,然后topicRouteData2TopicPublishInfo。
2.2 選擇消息發(fā)送的隊(duì)列
普通消息:默認(rèn)方式下,selectOneMessageQueue從topicPublishInfo中的messageQueueList中選擇一個(gè)隊(duì)列(MessageQueue)進(jìn)行發(fā)送消息,默認(rèn)采用長輪詢的方式選擇隊(duì)列 。
它的機(jī)制如下:正常情況下,順序選擇queue進(jìn)行發(fā)送;如果某一個(gè)節(jié)點(diǎn)發(fā)生了超時(shí),則下次選擇queue時(shí),跳過相同的broker。不同的隊(duì)列選擇策略形成了生產(chǎn)消息的幾種模式,如順序消息,事務(wù)消息。
順序消息:將一組需要有序消費(fèi)的消息發(fā)往同一個(gè)broker的同一個(gè)隊(duì)列上即可實(shí)現(xiàn)順序消息,假設(shè)相同訂單號(hào)的支付,退款需要放到同一個(gè)隊(duì)列,那么就可以在send的時(shí)候,自己實(shí)現(xiàn)MessageQueueSelector,根據(jù)參數(shù)arg字段來選擇queue。
private SendResult sendSelectImpl( Message msg, MessageQueueSelector selector, Object arg, final CommunicationMode communicationMode, final SendCallback sendCallback, final long timeout ) throws MQClientException, RemotingException, MQBrokerException, InterruptedException { 。。。}
事務(wù)消息:只有在消息發(fā)送成功,并且本地操作執(zhí)行成功時(shí),才發(fā)送提交事務(wù)消息,做事務(wù)提交,消息發(fā)送失敗,直接發(fā)送回滾消息,進(jìn)行回滾,具體如何實(shí)現(xiàn)后面會(huì)單獨(dú)成文分析。
2.3 封裝消息體通信包,發(fā)送數(shù)據(jù)包
首先,根據(jù)獲取的MessageQueue中的getBrokerName,調(diào)用findBrokerAddressInPublish得到該消息存放對(duì)應(yīng)的broker地址,如果沒有找到則跟新路由信息,重新獲取地址 :
brokerAddrTable.get(brokerName).get(MixAll.MASTER_ID)
可知獲取的broker均為master(id=0)
然后, 將與該消息相關(guān)信息打包成RemotingCommand數(shù)據(jù)包,其RequestCode.SEND_MESSAGE
根據(jù)獲取的broke地址,將數(shù)據(jù)包到對(duì)應(yīng)的broker,默認(rèn)是發(fā)送超時(shí)時(shí)間為3s。
封裝消息請(qǐng)求包的包頭:
SendMessageRequestHeader requestHeader = new SendMessageRequestHeader(); requestHeader.setProducerGroup(this.defaultMQProducer.getProducerGroup()); requestHeader.setTopic(msg.getTopic()); requestHeader.setDefaultTopic(this.defaultMQProducer.getCreateTopicKey()); requestHeader.setDefaultTopicQueueNums(this.defaultMQProducer.getDefaultTopicQueueNums()); requestHeader.setQueueId(mq.getQueueId()); requestHeader.setSysFlag(sysFlag); requestHeader.setBornTimestamp(System.currentTimeMillis()); requestHeader.setFlag(msg.getFlag()); requestHeader.setProperties(MessageDecoder.messageProperties2String(msg.getProperties())); requestHeader.setReconsumeTimes(0); requestHeader.setUnitMode(this.isUnitMode()); requestHeader.setBatch(msg instanceof MessageBatch);
發(fā)送消息包(普通消息默認(rèn)為同步方式):
SendResult sendResult = null; switch (communicationMode) { case SYNC: sendResult = this.mQClientFactory.getMQClientAPIImpl().sendMessage( brokerAddr, mq.getBrokerName(), msg, requestHeader, timeout, communicationMode, context, this); break;
處理來自broker端的響應(yīng)數(shù)據(jù)包:
private SendResult sendMessageSync( final String addr, final String brokerName, final Message msg, final long timeoutMillis, final RemotingCommand request ) throws RemotingException, MQBrokerException, InterruptedException { RemotingCommand response = this.remotingClient.invokeSync(addr, request, timeoutMillis); assert response != null; return this.processSendResponse(brokerName, msg, response); }
broker端處理request數(shù)據(jù)包后會(huì)將消息存儲(chǔ)到commitLog,具體過程后續(xù)分析。
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