【Alibaba中间件技术系列】「RocketMQ技术专题」让我们一起探索一下DefaultMQPushConsumer的实现原理及源码分析

RocketMQ开源是使用文件作为持久化工具,阿里内部未开源的性能会更高,使用oceanBase作为持久化工具。 在RocketMQ1.x和2.x使用zookeeper管理集群,3.x开始使用nameserver代替zk,更轻量级,此外RocketMQ的客户端拥有两种的操作方式:DefaultMQPushConsumer和DefaultMQPullConsumer。

<dependency><groupId>org.apache.rocketmqgroupId><artifactId>rocketmq-clientartifactId><version>4.3.0version>
dependency>

以上所说的第一次启动是指从来没有消费过的消费者,如果该消费者消费过,那么会在broker端记录该消费者的消费位置,如果该消费者挂了再启动,那么自动从上次消费的进度开始

public class MQPushConsumer {public static void main(String[] args) throws MQClientException {String groupName = "rocketMqGroup1";DefaultMQPushConsumer consumer = new DefaultMQPushConsumer(groupName);consumer.setNamesrvAddr("name-serverl-ip:9876;name-server2-ip:9876"); consumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_FIRST_OFFSET);consumer.setMessageModel(MessageModel.BROADCASTING);consumer.subscribe("order-topic", "*");consumer.registerMessageListener(new MessageListenerConcurrently() {public ConsumeConcurrentlyStatus consumeMessage(List mgs,ConsumeConcurrentlyContext consumeconcurrentlycontext) {System.out.println(Thread.currentThread().getName()+"Receive New Messages:"+mgs);return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;}});consumer.start();}
}
  • CLUSTERING:默认模式,同一个ConsumerGroup(groupName相同)每个consumer只消费所订阅消息的一部分内容,同一个ConsumerGroup里所有的Consumer消息加起来才是所
  • 订阅topic整体,从而达到负载均衡的目的
  • BROADCASTING:同一个ConsumerGroup每个consumer都消费到所订阅topic所有消息,也就是一个消费会被多次分发,被多个consumer消费。

ConsumeConcurrentlyStatus.RECONSUME_LATER boker会根据设置的messageDelayLevel发起重试,默认16次。

DefaultMQPushConsumerImpl中各个对象的主要功能如下:

RebalancePushImpl:主要负责决定,当前的consumer应该从哪些Queue中消费消息;

  • 1)PullAPIWrapper:长连接,负责从broker处拉取消息,然后利用ConsumeMessageService回调用户的Listener执行消息消费逻辑;
  • 2)ConsumeMessageService:实现所谓的"Push-被动"消费机制;从Broker拉取的消息后,封装成ConsumeRequest提交给ConsumeMessageSerivce,此service负责回调用户的Listener消费消息;
  • 3)OffsetStore:维护当前consumer的消费记录(offset);有两种实现,Local和Rmote,Local存储在本地磁盘上,适用于BROADCASTING广播消费模式;而Remote则将消费进度存储在Broker上,适用于CLUSTERING集群消费模式;
  • 4)MQClientFactory:负责管理client(consumer、producer),并提供多中功能接口供各个Service(Rebalance、PullMessage等)调用;大部分逻辑均在这个类中完成;

consumer.registerMessageListener执行过程:

public void registerMessageListener(MessageListenerConcurrently messageListener) {this.messageListener = messageListener; this.defaultMQPushConsumerImpl.registerMessageListener(messageListener);}

通过源码可以看出主要实现过程在DefaultMQPushConsumerImpl类中consumer.start后调用DefaultMQPushConsumerImpl的同步start方法

public synchronized void start() throws MQClientException {switch (this.serviceState) {case CREATE_JUST:log.info("the consumer [{}] start beginning. messageModel={}, isUnitMode={}", this.defaultMQPushConsumer.getConsumerGroup(),this.defaultMQPushConsumer.getMessageModel(), this.defaultMQPushConsumer.isUnitMode());this.serviceState = ServiceState.START_FAILED;this.checkConfig();this.copySubscription();if (this.defaultMQPushConsumer.getMessageModel() == MessageModel.CLUSTERING) {this.defaultMQPushConsumer.changeInstanceNameToPID();}this.mQClientFactory = MQClientManager.getInstance().getAndCreateMQClientInstance(this.defaultMQPushConsumer, this.rpcHook);this.rebalanceImpl.setConsumerGroup(this.defaultMQPushConsumer.getConsumerGroup());this.rebalanceImpl.setMessageModel(this.defaultMQPushConsumer.getMessageModel());this.rebalanceImpl.setAllocateMessageQueueStrategy(this.defaultMQPushConsumer.getAllocateMessageQueueStrategy());this.rebalanceImpl.setmQClientFactory(this.mQClientFactory);this.pullAPIWrapper = new PullAPIWrapper(mQClientFactory,this.defaultMQPushConsumer.getConsumerGroup(), isUnitMode());this.pullAPIWrapper.registerFilterMessageHook(filterMessageHookList);if (this.defaultMQPushConsumer.getOffsetStore() != null) {this.offsetStore = this.defaultMQPushConsumer.getOffsetStore();} else {switch (this.defaultMQPushConsumer.getMessageModel()) {case BROADCASTING:this.offsetStore = new LocalFileOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());break;case CLUSTERING:this.offsetStore = new RemoteBrokerOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());break;default:break;}this.defaultMQPushConsumer.setOffsetStore(this.offsetStore);}this.offsetStore.load();if (this.getMessageListenerInner() instanceof MessageListenerOrderly) {this.consumeOrderly = true;this.consumeMessageService =new ConsumeMessageOrderlyService(this, (MessageListenerOrderly) this.getMessageListenerInner());} else if (this.getMessageListenerInner() instanceof MessageListenerConcurrently) {this.consumeOrderly = false;this.consumeMessageService =new ConsumeMessageConcurrentlyService(this, (MessageListenerConcurrently) this.getMessageListenerInner());}this.consumeMessageService.start();boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);if (!registerOK) {this.serviceState = ServiceState.CREATE_JUST;this.consumeMessageService.shutdown();throw new MQClientException("The consumer group[" + this.defaultMQPushConsumer.getConsumerGroup()+ "] has been created before, specify another name please." + FAQUrl.suggestTodo(FAQUrl.GROUP_NAME_DUPLICATE_URL),null);}mQClientFactory.start();log.info("the consumer [{}] start OK.", this.defaultMQPushConsumer.getConsumerGroup());this.serviceState = ServiceState.RUNNING;break;case RUNNING:case START_FAILED:case SHUTDOWN_ALREADY:throw new MQClientException("The PushConsumer service state not OK, maybe started once, "+ this.serviceState+ FAQUrl.suggestTodo(FAQUrl.CLIENT_SERVICE_NOT_OK),null);default:break;}this.updateTopicSubscribeInfoWhenSubscriptionChanged();this.mQClientFactory.checkClientInBroker();this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();this.mQClientFactory.rebalanceImmediately();}

通过mQClientFactory.start();发我们发现他调用

public void start() throws MQClientException {synchronized (this) {switch (this.serviceState) {case CREATE_JUST:this.serviceState = ServiceState.START_FAILED;if (null == this.clientConfig.getNamesrvAddr()) {this.mQClientAPIImpl.fetchNameServerAddr();}this.mQClientAPIImpl.start();this.startScheduledTask();this.pullMessageService.start();this.rebalanceService.start();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;}}}

在这个方法中有多个start,我们主要看pullMessageService.start();通过这里我们发现RocketMQ的Push模式底层其实也是通过pull实现的,下面我们来看下pullMessageService处理了哪些逻辑:

private void pullMessage(final PullRequest pullRequest) {final MQConsumerInner consumer = this.mQClientFactory.selectConsumer(pullRequest.getConsumerGroup());if (consumer != null) {DefaultMQPushConsumerImpl impl = (DefaultMQPushConsumerImpl) consumer;impl.pullMessage(pullRequest);} else {log.warn("No matched consumer for the PullRequest {}, drop it", pullRequest);}}

我们发现其实他还是通过DefaultMQPushConsumerImpl类的pullMessage方法来进行消息的逻辑处理.

PullRequest这里说明一下,上面我们已经提了一下rocketmq的push模式其实是通过pull模式封装实现的,pullrequest这里是通过长轮询的方式达到push效果。

长轮询方式既有pull的优点又有push模式的实时性有点。

  • push方式是server端接收到消息后,主动把消息推送给client端,实时性高。弊端是server端工作量大,影响性能,其次是client端处理能力不同且client端的状态不受server端的控制,如果client端不能及时处理消息容易导致消息堆积已经影响正常业务等。
  • pull方式是client循环从server端拉取消息,主动权在client端,自己处理完一个消息再去拉取下一个,缺点是循环的时间不好设定,时间太短容易忙等,浪费CPU资源,时间间隔太长client的处理能力会下降,有时候有些消息会处理不及时。

PullAPIWrapper.pullKernelImpl(MessageQueue mq, String subExpression, long subVersion,long offset, int maxNums, int sysFlag,long commitOffset,long brokerSuspendMaxTimeMillis, long timeoutMillis, CommunicationMode communicationMode, PullCallback pullCallback)方法进行消息拉取操作。

将回调类PullCallback传入该方法中,当采用异步方式拉取消息时,在收到响应之后会回调该回调类的方法。

public void pullMessage(final PullRequest pullRequest) {final ProcessQueue processQueue = pullRequest.getProcessQueue();if (processQueue.isDropped()) {log.info("the pull request[{}] is dropped.", pullRequest.toString());return;}pullRequest.getProcessQueue().setLastPullTimestamp(System.currentTimeMillis());try {this.makeSureStateOK();} catch (MQClientException e) {log.warn("pullMessage exception, consumer state not ok", e);this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);return;}if (this.isPause()) {log.warn("consumer was paused, execute pull request later. instanceName={}, group={}", this.defaultMQPushConsumer.getInstanceName(), this.defaultMQPushConsumer.getConsumerGroup());this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_SUSPEND);return;}long cachedMessageCount = processQueue.getMsgCount().get();long cachedMessageSizeInMiB = processQueue.getMsgSize().get() / (1024 * 1024);if (cachedMessageCount > this.defaultMQPushConsumer.getPullThresholdForQueue()) {this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);if ((queueFlowControlTimes++ % 1000) == 0) {log.warn("the cached message count exceeds the threshold {}, so do flow control, minOffset={}, maxOffset={}, count={}, size={} MiB, pullRequest={}, flowControlTimes={}",this.defaultMQPushConsumer.getPullThresholdForQueue(), processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), cachedMessageCount, cachedMessageSizeInMiB, pullRequest, queueFlowControlTimes);}return;}if (cachedMessageSizeInMiB > this.defaultMQPushConsumer.getPullThresholdSizeForQueue()) {this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);if ((queueFlowControlTimes++ % 1000) == 0) {log.warn("the cached message size exceeds the threshold {} MiB, so do flow control, minOffset={}, maxOffset={}, count={}, size={} MiB, pullRequest={}, flowControlTimes={}",this.defaultMQPushConsumer.getPullThresholdSizeForQueue(), processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), cachedMessageCount, cachedMessageSizeInMiB, pullRequest, queueFlowControlTimes);}return;}if (!this.consumeOrderly) {if (processQueue.getMaxSpan() > this.defaultMQPushConsumer.getConsumeConcurrentlyMaxSpan()) {this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_FLOW_CONTROL);if ((queueMaxSpanFlowControlTimes++ % 1000) == 0) {log.warn("the queue's messages, span too long, so do flow control, minOffset={}, maxOffset={}, maxSpan={}, pullRequest={}, flowControlTimes={}",processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), processQueue.getMaxSpan(),pullRequest, queueMaxSpanFlowControlTimes);}return;}} else {if (processQueue.isLocked()) {if (!pullRequest.isLockedFirst()) {final long offset = this.rebalanceImpl.computePullFromWhere(pullRequest.getMessageQueue());boolean brokerBusy = offset < pullRequest.getNextOffset();log.info("the first time to pull message, so fix offset from broker. pullRequest: {} NewOffset: {} brokerBusy: {}",pullRequest, offset, brokerBusy);if (brokerBusy) {log.info("[NOTIFYME]the first time to pull message, but pull request offset larger than broker consume offset. pullRequest: {} NewOffset: {}",pullRequest, offset);}pullRequest.setLockedFirst(true);pullRequest.setNextOffset(offset);}} else {this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);log.info("pull message later because not locked in broker, {}", pullRequest);return;}}final SubscriptionData subscriptionData = this.rebalanceImpl.getSubscriptionInner().get(pullRequest.getMessageQueue().getTopic());if (null == subscriptionData) {this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);log.warn("find the consumer's subscription failed, {}", pullRequest);return;}final long beginTimestamp = System.currentTimeMillis();PullCallback pullCallback = new PullCallback() {public void onSuccess(PullResult pullResult) {if (pullResult != null) {pullResult = DefaultMQPushConsumerImpl.this.pullAPIWrapper.processPullResult(pullRequest.getMessageQueue(), pullResult,subscriptionData);switch (pullResult.getPullStatus()) {case FOUND:long prevRequestOffset = pullRequest.getNextOffset();pullRequest.setNextOffset(pullResult.getNextBeginOffset());long pullRT = System.currentTimeMillis() - beginTimestamp;DefaultMQPushConsumerImpl.this.getConsumerStatsManager().incPullRT(pullRequest.getConsumerGroup(),pullRequest.getMessageQueue().getTopic(), pullRT);long firstMsgOffset = Long.MAX_VALUE;if (pullResult.getMsgFoundList() == null || pullResult.getMsgFoundList().isEmpty()) {DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);} else {firstMsgOffset = pullResult.getMsgFoundList().get(0).getQueueOffset();DefaultMQPushConsumerImpl.this.getConsumerStatsManager().incPullTPS(pullRequest.getConsumerGroup(),pullRequest.getMessageQueue().getTopic(), pullResult.getMsgFoundList().size());boolean dispatchToConsume = processQueue.putMessage(pullResult.getMsgFoundList());DefaultMQPushConsumerImpl.this.consumeMessageService.submitConsumeRequest(pullResult.getMsgFoundList(),processQueue,pullRequest.getMessageQueue(),dispatchToConsume);if (DefaultMQPushConsumerImpl.this.defaultMQPushConsumer.getPullInterval() > 0) {DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest,DefaultMQPushConsumerImpl.this.defaultMQPushConsumer.getPullInterval());} else {DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);}}if (pullResult.getNextBeginOffset() < prevRequestOffset|| firstMsgOffset < prevRequestOffset) {log.warn("[BUG] pull message result maybe data wrong, nextBeginOffset: {} firstMsgOffset: {} prevRequestOffset: {}",pullResult.getNextBeginOffset(),firstMsgOffset,prevRequestOffset);}break;case NO_NEW_MSG:pullRequest.setNextOffset(pullResult.getNextBeginOffset());DefaultMQPushConsumerImpl.this.correctTagsOffset(pullRequest);DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);break;case NO_MATCHED_MSG:pullRequest.setNextOffset(pullResult.getNextBeginOffset());DefaultMQPushConsumerImpl.this.correctTagsOffset(pullRequest);DefaultMQPushConsumerImpl.this.executePullRequestImmediately(pullRequest);break;case OFFSET_ILLEGAL:log.warn("the pull request offset illegal, {} {}",pullRequest.toString(), pullResult.toString());pullRequest.setNextOffset(pullResult.getNextBeginOffset());pullRequest.getProcessQueue().setDropped(true);DefaultMQPushConsumerImpl.this.executeTaskLater(new Runnable() {public void run() {try {DefaultMQPushConsumerImpl.this.offsetStore.updateOffset(pullRequest.getMessageQueue(),pullRequest.getNextOffset(), false);DefaultMQPushConsumerImpl.this.offsetStore.persist(pullRequest.getMessageQueue());DefaultMQPushConsumerImpl.this.rebalanceImpl.removeProcessQueue(pullRequest.getMessageQueue());log.warn("fix the pull request offset, {}", pullRequest);} catch (Throwable e) {log.error("executeTaskLater Exception", e);}}}, 10000);break;default:break;}}}public void onException(Throwable e) {if (!pullRequest.getMessageQueue().getTopic().startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {log.warn("execute the pull request exception", e);}DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);}};boolean commitOffsetEnable = false;long commitOffsetValue = 0L;if (MessageModel.CLUSTERING == this.defaultMQPushConsumer.getMessageModel()) {commitOffsetValue = this.offsetStore.readOffset(pullRequest.getMessageQueue(), ReadOffsetType.READ_FROM_MEMORY);if (commitOffsetValue > 0) {commitOffsetEnable = true;}}String subExpression = null;boolean classFilter = false;SubscriptionData sd = this.rebalanceImpl.getSubscriptionInner().get(pullRequest.getMessageQueue().getTopic());if (sd != null) {if (this.defaultMQPushConsumer.isPostSubscriptionWhenPull() && !sd.isClassFilterMode()) {subExpression = sd.getSubString();}classFilter = sd.isClassFilterMode();}int sysFlag = PullSysFlag.buildSysFlag(commitOffsetEnable,true,subExpression != null,classFilter);try {this.pullAPIWrapper.pullKernelImpl(pullRequest.getMessageQueue(),subExpression,subscriptionData.getExpressionType(),subscriptionData.getSubVersion(),pullRequest.getNextOffset(),this.defaultMQPushConsumer.getPullBatchSize(),sysFlag,commitOffsetValue,BROKER_SUSPEND_MAX_TIME_MILLIS,CONSUMER_TIMEOUT_MILLIS_WHEN_SUSPEND,CommunicationMode.ASYNC,pullCallback);} catch (Exception e) {log.error("pullKernelImpl exception", e);this.executePullRequestLater(pullRequest, PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);}}

在MQClientAPIImpl.pullMessage方法中,根据入参communicationMode的值分为异步拉取和同步拉取方式两种。

无论是异步方式拉取还是同步方式拉取,在发送拉取请求之前都会构造一个ResponseFuture对象,以请求消息的序列号为key值,存入NettyRemotingAbstract.responseTable:ConcurrentHashMap, ResponseFuture>变量中,对该变量有几种情况会处理:

public PullResult pullMessage(final String addr,final PullMessageRequestHeader requestHeader,final long timeoutMillis,final CommunicationMode communicationMode,final PullCallback pullCallback) throws RemotingException, MQBrokerException, InterruptedException {RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.PULL_MESSAGE, requestHeader);switch (communicationMode) {case ONEWAY:assert false;return null;case ASYNC:this.pullMessageAsync(addr, request, timeoutMillis, pullCallback);return null;case SYNC:return this.pullMessageSync(addr, request, timeoutMillis);default:assert false;break;}return null;}

对于同步发送方式,调用MQClientAPIImpl.pullMessageSync(String addr, RemotingCommand request, long timeoutMillis)方法,大致步骤如下:

  • 以上一步的返回值RemotingCommand对象为参数调用MQClientAPIImpl. processPullResponse (RemotingCommand response)方法将返回对象解析并封装成PullResultExt对象然后返回给调用者,响应消息的结果状态转换如下:
    • 若RemotingCommand对象的Code等于SUCCESS,则PullResultExt.pullStatus=FOUND;
    • 若RemotingCommand对象的Code等于PULL_NOT_FOUND,则PullResultExt.pullStatus= NO_NEW_MSG;
    • 若RemotingCommand对象的Code等于PULL_RETRY_IMMEDIATELY,则PullResultExt.pullStatus= NO_MATCHED_MSG;
    • 若RemotingCommand对象的Code等于PULL_OFFSET_MOVED,则PullResultExt.pullStatus= OFFSET_ILLEGAL;
public RemotingCommand invokeSync(String addr, final RemotingCommand request, long timeoutMillis)throws InterruptedException, RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException {long beginStartTime = System.currentTimeMillis();final Channel channel = this.getAndCreateChannel(addr);if (channel != null && channel.isActive()) {try {if (this.rpcHook != null) {this.rpcHook.doBeforeRequest(addr, request);}long costTime = System.currentTimeMillis() - beginStartTime;if (timeoutMillis < costTime) {throw new RemotingTimeoutException("invokeSync call timeout");}RemotingCommand response = this.invokeSyncImpl(channel, request, timeoutMillis - costTime);if (this.rpcHook != null) {this.rpcHook.doAfterResponse(RemotingHelper.parseChannelRemoteAddr(channel), request, response);}return response;} catch (RemotingSendRequestException e) {log.warn("invokeSync: send request exception, so close the channel[{}]", addr);this.closeChannel(addr, channel);throw e;} catch (RemotingTimeoutException e) {if (nettyClientConfig.isClientCloseSocketIfTimeout()) {this.closeChannel(addr, channel);log.warn("invokeSync: close socket because of timeout, {}ms, {}", timeoutMillis, addr);}log.warn("invokeSync: wait response timeout exception, the channel[{}]", addr);throw e;}} else {this.closeChannel(addr, channel);throw new RemotingConnectException(addr);}}

getMQClientAPIImpl().pullMessage最终通过channel写入并刷新队列中。然后在消息服务端大体的处理逻辑是服务端收到新消息请求后,如果队列中没有消息不急于返回,通过一个循环状态,每次waitForRunning一段时间默认5秒,然后再check,如果broker一直没有新新消息,第三次check的时间等到时间超过SuspendMaxTimeMills就返回空,如果在等待过程中收到了新消息直接调用notifyMessageArriving函数返回请求结果。"长轮询"的核心是,Broker端HOLD住客户端过来的请求一小段时间,在这个时间内有新消息到达,就利用现有的连接立刻返回消息给 Consumer 。长轮询的主动权掌握在consumer中,即使broker有大量的消息堆积也不会主动推送给consumer。

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