系列文章

RocketMQ入门篇
RocketMQ生产者流程篇
RocketMQ生产者消息篇

前言

生产者向消息队列里面写入消息，不同的业务场景会采用不同的写入策略，比如：同步发送，异步发送，延迟发送，事务消息等；本文首先从分析生产者发送消息的流程开始，然后再来介绍各种发送消息的策略。

生产者流程

1.流程概述

生产者首先需要设置namesrv，或者指定其他方式更新namesrv；然后从namesrv获取topic的路由信息，路由信息包括broker以及Message Queue等信息，同时将路由信息保存在本地内存中，方便下次使用；最后从Message Queue列表中选择合适的Queue发送消息，实现负载均衡；

2.启动过程

DefaultMQProducer实例化提供了两个参数分别是：生产者组名称以及RPCHook，RPCHook是一个接口，具体实现交由业务端实现，两个方法分别是：doBeforeRequest和doAfterResponse，表示在执行请求之前和接收返回之后分别执行相关逻辑；
接下来就是调用DefaultMQProducer的start方法，相关的初始化操作都在里面进行，内部其实调用的是DefaultMQProducerImpl的start方法，具体代码如下：

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().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;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();}

默认serviceState的状态为CREATE_JUST，刚进入设置为START_FAILED，初始化完成之后设置为RUNNING，再次初始化时会直接报错，下面看一下具体初始化了哪些信息；

2.1检查配置

这里的检查其实就是对producerGroup进行合法性校验；

2.2设置instanceName

如果producerGroup不等于默认的"CLIENT_INNER_PRODUCER",则设置DefaultMQProducer的instanceName为进程的pid；

2.3创建MQClientInstance对象

首先检查 ConcurrentMap<String/ clientId /, MQClientInstance> factoryTable中是否已经存在已clientId为key的MQClientInstance，如果存在则取出，不存在则实例化；clientId是已ip地址，instanceName以及unitName组成的，例如：10.13.83.7@12500

2.4注册producer

将DefaultMQProducerImpl注册到MQClientInstance中，已producerGroup作为key，注册到ConcurrentMap<String/ group /, MQProducerInner> producerTable中，如果已经存在此Group，则抛出异常；

2.5初始化TopicPublishInfo

已topic名称为"TBW102"为key，实例化TopicPublishInfo作为value，存放在ConcurrentMap<String/ topic /, TopicPublishInfo> topicPublishInfoTable中,TopicPublishInfo用来存放topic的路由信息；

2.6启动MQClientInstance

MQClientInstance启动会启动很多相关服务，具体可以看如下代码：

 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 serverif (null == this.clientConfig.getNamesrvAddr()) {this.mQClientAPIImpl.fetchNameServerAddr();}// Start request-response channelthis.mQClientAPIImpl.start();// Start various schedule tasksthis.startScheduledTask();// Start pull servicethis.pullMessageService.start();// Start rebalance servicethis.rebalanceService.start();// Start push servicethis.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;}}}

默认serviceState的状态为CREATE_JUST，刚进入设置为START_FAILED，初始化完成之后设置为RUNNING，防止重复初始化；

2.6.1初始化NameServerAddr

首先判断DefaultMQProducer是否配置了NameServerAddr，如果没有配置会到一个地址下获取，地址默认为：http://jmenv.tbsite.net:8080/rocketmq/nsaddr，相关的逻辑在MixAll类中，代码如下：

    public static String getWSAddr() {String wsDomainName = System.getProperty("rocketmq.namesrv.domain", DEFAULT_NAMESRV_ADDR_LOOKUP);String wsDomainSubgroup = System.getProperty("rocketmq.namesrv.domain.subgroup", "nsaddr");String wsAddr = "http://" + wsDomainName + ":8080/rocketmq/" + wsDomainSubgroup;if (wsDomainName.indexOf(":") > 0) {wsAddr = "http://" + wsDomainName + "/rocketmq/" + wsDomainSubgroup;}return wsAddr;}

正常情况下我们需要设置自己的地址，可以通过如下方式设置：

System.setProperty("rocketmq.namesrv.domain", "localhost");

这种情况下就可以不用手动设置NameServerAddr；

2.6.2初始化RemotingClient

RemotingClient是一个接口类，底层使用的通讯框架是Netty，提供了实现类NettyRemotingClient，RemotingClient在初始化的时候实例化Bootstrap，方便后续用来创建Channel；

2.6.3启动定时器任务

总共启动了5个定时器任务，分别是：定时更新NameServerAddr信息，定时更新topic的路由信息，定时清理下线的broker，定时持久化Consumer的Offset信息，定时调整线程池；

2.6.3启动服务

pullMessageService和rebalanceService被用在消费端的两个服务类，分别是：从broker拉取消息的服务和均衡消息队列服务，负责分配消费者可消费的消息队列；

3.发送消息

相关发送消息的代码在DefaultMQProducerImpl的sendDefaultImpl方法中，部分代码如下所示：

private SendResult sendDefaultImpl(Message msg,final CommunicationMode communicationMode,final SendCallback sendCallback,final long timeout) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {this.makeSureStateOK();Validators.checkMessage(msg, this.defaultMQProducer);final long invokeID = random.nextLong();long beginTimestampFirst = System.currentTimeMillis();long beginTimestampPrev = beginTimestampFirst;long endTimestamp = beginTimestampFirst;TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic());if (topicPublishInfo != null && topicPublishInfo.ok()) {boolean callTimeout = false;MessageQueue mq = null;Exception exception = null;SendResult sendResult = null;int timesTotal = communicationMode == CommunicationMode.SYNC ? 1 + this.defaultMQProducer.getRetryTimesWhenSendFailed() : 1;int times = 0;String[] brokersSent = new String[timesTotal];for (; times < timesTotal; times++) {String lastBrokerName = null == mq ? null : mq.getBrokerName();MessageQueue mqSelected = this.selectOneMessageQueue(topicPublishInfo, lastBrokerName);if (mqSelected != null) {mq = mqSelected;brokersSent[times] = mq.getBrokerName();try {beginTimestampPrev = System.currentTimeMillis();long costTime = beginTimestampPrev - beginTimestampFirst;if (timeout < costTime) {callTimeout = true;break;}sendResult = this.sendKernelImpl(msg, mq, communicationMode, sendCallback, topicPublishInfo, timeout - costTime);endTimestamp = System.currentTimeMillis();this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, false);switch (communicationMode) {case ASYNC:return null;case ONEWAY:return null;case SYNC:if (sendResult.getSendStatus() != SendStatus.SEND_OK) {if (this.defaultMQProducer.isRetryAnotherBrokerWhenNotStoreOK()) {continue;}}return sendResult;default:break;}...以下代码省略...

此方法的四个参数分别是：msg为要发送的消息，communicationMode要使用的发送方式包括同步、异步、单向，sendCallback在异步情况下的回调函数，timeout发送消息的超时时间；

3.1获取topic的路由信息

通过msg中设置的topic获取路由信息，具体代码如下：

private TopicPublishInfo tryToFindTopicPublishInfo(final String topic) {TopicPublishInfo topicPublishInfo = this.topicPublishInfoTable.get(topic);if (null == topicPublishInfo || !topicPublishInfo.ok()) {this.topicPublishInfoTable.putIfAbsent(topic, new TopicPublishInfo());this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic);topicPublishInfo = this.topicPublishInfoTable.get(topic);}if (topicPublishInfo.isHaveTopicRouterInfo() || topicPublishInfo.ok()) {return topicPublishInfo;} else {this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic, true, this.defaultMQProducer);topicPublishInfo = this.topicPublishInfoTable.get(topic);return topicPublishInfo;}}

首先从变量ConcurrentMap<String/ topic /, TopicPublishInfo> topicPublishInfoTable中获取是否存在指定topic的路由信息，如果获取不到则使用topic去nameServer获取路由信息，如果还是获取不到则使用默认的topic名称为"TBW102"去获取路由信息，需要使用默认名称去获取的情况是没有创建topic，需要broker自动创建topic的情况；获取路由信息使用的是MQClientInstance中的updateTopicRouteInfoFromNameServer方法，此方法根据topic获取路由信息，具体连接哪台nameServer，会从列表中顺序的选择nameServer，实现负载均衡；
注：名称为"TBW102"的topic是系统自动创建的；

3.2选择MessageQueue

成功获取到路由信息之后，需要从MessageQueue列表中选择一个，在这之前获取了默认发送消息失败的重试次数，默认为3次(只有发送模式是同步的情况下)，代码如下：

public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) {if (this.sendLatencyFaultEnable) {try {int index = tpInfo.getSendWhichQueue().getAndIncrement();for (int i = 0; i < tpInfo.getMessageQueueList().size(); i++) {int pos = Math.abs(index++) % tpInfo.getMessageQueueList().size();if (pos < 0)pos = 0;MessageQueue mq = tpInfo.getMessageQueueList().get(pos);if (latencyFaultTolerance.isAvailable(mq.getBrokerName())) {if (null == lastBrokerName || mq.getBrokerName().equals(lastBrokerName))return mq;}}final String notBestBroker = latencyFaultTolerance.pickOneAtLeast();int writeQueueNums = tpInfo.getQueueIdByBroker(notBestBroker);if (writeQueueNums > 0) {final MessageQueue mq = tpInfo.selectOneMessageQueue();if (notBestBroker != null) {mq.setBrokerName(notBestBroker);mq.setQueueId(tpInfo.getSendWhichQueue().getAndIncrement() % writeQueueNums);}return mq;} else {latencyFaultTolerance.remove(notBestBroker);}} catch (Exception e) {log.error("Error occurred when selecting message queue", e);}return tpInfo.selectOneMessageQueue();}return tpInfo.selectOneMessageQueue(lastBrokerName);}

以上代码在MQFaultStrategy，此类提供了选择MessageQueue的策略，相关策略可以看类变量：

private final LatencyFaultTolerance<String> latencyFaultTolerance = new LatencyFaultToleranceImpl();private boolean sendLatencyFaultEnable = false;private long[] latencyMax = {50L, 100L, 550L, 1000L, 2000L, 3000L, 15000L};private long[] notAvailableDuration = {0L, 0L, 30000L, 60000L, 120000L, 180000L, 600000L};

latencyFaultTolerance：延迟容错对象，维护brokers的延迟信息；
sendLatencyFaultEnable：延迟容错开关，默认不开启；
latencyMax：延迟级别数组；
notAvailableDuration ：根据延迟级别，对应broker不可用的时长；

这样上面的这段代码就好理解了，首先判定是否开启开关，如果开启首先获取index，index初始为一个随机值，后面每次+1，这样在后面与MessageQueue长度取模的时候每个MessageQueue可以按顺序获取；获取
MessageQueue之后需要判定其对应的Broker是否可用，同时也需要和当前指定的brokerName进行匹配；如果没有获取到就选择一个延迟相对小的，pickOneAtLeast会做排序处理；如果都不行就直接获取一个MessageQueue，不管其他条件了；

3.3发送消息

在发送之前会做超时检测，如果前面两步已经超时了，则直接报超时，默认超时时间是3秒；部分代码如下：

    private SendResult sendKernelImpl(final Message msg,final MessageQueue mq,final CommunicationMode communicationMode,final SendCallback sendCallback,final TopicPublishInfo topicPublishInfo,final long timeout) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {long beginStartTime = System.currentTimeMillis();String brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(mq.getBrokerName());if (null == brokerAddr) {tryToFindTopicPublishInfo(mq.getTopic());brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(mq.getBrokerName());}SendMessageContext context = null;if (brokerAddr != null) {brokerAddr = MixAll.brokerVIPChannel(this.defaultMQProducer.isSendMessageWithVIPChannel(), brokerAddr);byte[] prevBody = msg.getBody();try {//for MessageBatch,ID has been set in the generating processif (!(msg instanceof MessageBatch)) {MessageClientIDSetter.setUniqID(msg);}int sysFlag = 0;boolean msgBodyCompressed = false;if (this.tryToCompressMessage(msg)) {sysFlag |= MessageSysFlag.COMPRESSED_FLAG;msgBodyCompressed = true;}final String tranMsg = msg.getProperty(MessageConst.PROPERTY_TRANSACTION_PREPARED);if (tranMsg != null && Boolean.parseBoolean(tranMsg)) {sysFlag |= MessageSysFlag.TRANSACTION_PREPARED_TYPE;}if (hasCheckForbiddenHook()) {CheckForbiddenContext checkForbiddenContext = new CheckForbiddenContext();checkForbiddenContext.setNameSrvAddr(this.defaultMQProducer.getNamesrvAddr());checkForbiddenContext.setGroup(this.defaultMQProducer.getProducerGroup());checkForbiddenContext.setCommunicationMode(communicationMode);checkForbiddenContext.setBrokerAddr(brokerAddr);checkForbiddenContext.setMessage(msg);checkForbiddenContext.setMq(mq);checkForbiddenContext.setUnitMode(this.isUnitMode());this.executeCheckForbiddenHook(checkForbiddenContext);}if (this.hasSendMessageHook()) {context = new SendMessageContext();context.setProducer(this);context.setProducerGroup(this.defaultMQProducer.getProducerGroup());context.setCommunicationMode(communicationMode);context.setBornHost(this.defaultMQProducer.getClientIP());context.setBrokerAddr(brokerAddr);context.setMessage(msg);context.setMq(mq);String isTrans = msg.getProperty(MessageConst.PROPERTY_TRANSACTION_PREPARED);if (isTrans != null && isTrans.equals("true")) {context.setMsgType(MessageType.Trans_Msg_Half);}if (msg.getProperty("__STARTDELIVERTIME") != null || msg.getProperty(MessageConst.PROPERTY_DELAY_TIME_LEVEL) != null) {context.setMsgType(MessageType.Delay_Msg);}this.executeSendMessageHookBefore(context);}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);if (requestHeader.getTopic().startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {String reconsumeTimes = MessageAccessor.getReconsumeTime(msg);if (reconsumeTimes != null) {requestHeader.setReconsumeTimes(Integer.valueOf(reconsumeTimes));MessageAccessor.clearProperty(msg, MessageConst.PROPERTY_RECONSUME_TIME);}String maxReconsumeTimes = MessageAccessor.getMaxReconsumeTimes(msg);if (maxReconsumeTimes != null) {requestHeader.setMaxReconsumeTimes(Integer.valueOf(maxReconsumeTimes));MessageAccessor.clearProperty(msg, MessageConst.PROPERTY_MAX_RECONSUME_TIMES);}}SendResult sendResult = null;switch (communicationMode) {case ASYNC:Message tmpMessage = msg;if (msgBodyCompressed) {//If msg body was compressed, msgbody should be reset using prevBody.//Clone new message using commpressed message body and recover origin massage.//Fix bug:https://github.com/apache/rocketmq-externals/issues/66tmpMessage = MessageAccessor.cloneMessage(msg);msg.setBody(prevBody);}long costTimeAsync = System.currentTimeMillis() - beginStartTime;if (timeout < costTimeAsync) {throw new RemotingTooMuchRequestException("sendKernelImpl call timeout");}sendResult = this.mQClientFactory.getMQClientAPIImpl().sendMessage(brokerAddr,mq.getBrokerName(),tmpMessage,requestHeader,timeout - costTimeAsync,communicationMode,sendCallback,topicPublishInfo,this.mQClientFactory,this.defaultMQProducer.getRetryTimesWhenSendAsyncFailed(),context,this);break;case ONEWAY:case SYNC:long costTimeSync = System.currentTimeMillis() - beginStartTime;if (timeout < costTimeSync) {throw new RemotingTooMuchRequestException("sendKernelImpl call timeout");}sendResult = this.mQClientFactory.getMQClientAPIImpl().sendMessage(brokerAddr,mq.getBrokerName(),msg,requestHeader,timeout - costTimeSync,communicationMode,context,this);break;default:assert false;break;}if (this.hasSendMessageHook()) {context.setSendResult(sendResult);this.executeSendMessageHookAfter(context);}return sendResult;

此处的6个参数分别是：msg消息本身，mq要发送到的队列，communicationMode发送策略，sendCallback异步回调函数，topicPublishInfo路由信息，timeout发送超时时间(3秒-前2步消耗的时间)；
首先需要获取指定broker的地址，这要才能创建channel与broker连接；然后就是一些hock处理；接下来就是准备发送的消息头SendMessageRequestHeader，最后根据不同的发送策略执行发送消息，此处就不在进入更加深入的分析；

总结

本文重点介绍了发送者的启动，以及发送消息的大概流程；关于消息的发送策略，以及消息的类型包括：顺序消息，事务消息等，将在后面的文章介绍。