引言

• 拉取消息的核心处理类。
• 一共有两种实现，并发消费和顺序消费。
• 想当然并发消费的实现比顺序消费简单点。那么接下来就看整个拉取信息的过程流转。

手撕鸡

ConsumeMessageOrderlyService

接上篇的启动流程中调用了start方法。
什么？你还不知道start在哪里被调用的。请看手撕RocketMQ源码之DefaultMQPushConsumer,传送门
具体的源码在下面
执行了定时锁住MQ，如果是集群消费的话。

public void start() {
// 集群模式需要用锁保证单个消费者消费if (MessageModel.CLUSTERING.equals(ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.messageModel())) {this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {@Overridepublic void run() {ConsumeMessageOrderlyService.this.lockMQPeriodically();}}, 1000 * 1, ProcessQueue.REBALANCE_LOCK_INTERVAL, TimeUnit.MILLISECONDS);}}

处理消息请求

public void submitConsumeRequest(final List<MessageExt> msgs,final ProcessQueue processQueue,final MessageQueue messageQueue,final boolean dispathToConsume) {if (dispathToConsume) {ConsumeRequest consumeRequest = new ConsumeRequest(processQueue, messageQueue);this.consumeExecutor.submit(consumeRequest);}}

核心的处理消息过程

public void run() {// 校验if (this.processQueue.isDropped()) {log.warn("run, the message queue not be able to consume, because it's dropped. {}", this.messageQueue);return;}// 保证单队列消息消费final Object objLock = messageQueueLock.fetchLockObject(this.messageQueue);synchronized (objLock) {// 广播模式的话只要保证单队列消费即可// 集群模式下需要保证单队列 单消费者消费。if (MessageModel.BROADCASTING.equals(ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.messageModel())|| (this.processQueue.isLocked() && !this.processQueue.isLockExpired())) {final long beginTime = System.currentTimeMillis();for (boolean continueConsume = true; continueConsume; ) {if (this.processQueue.isDropped()) {log.warn("the message queue not be able to consume, because it's dropped. {}", this.messageQueue);break;}if (MessageModel.CLUSTERING.equals(ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.messageModel())&& !this.processQueue.isLocked()) {log.warn("the message queue not locked, so consume later, {}", this.messageQueue);ConsumeMessageOrderlyService.this.tryLockLaterAndReconsume(this.messageQueue, this.processQueue, 10);break;}if (MessageModel.CLUSTERING.equals(ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.messageModel())&& this.processQueue.isLockExpired()) {log.warn("the message queue lock expired, so consume later, {}", this.messageQueue);ConsumeMessageOrderlyService.this.tryLockLaterAndReconsume(this.messageQueue, this.processQueue, 10);break;}long interval = System.currentTimeMillis() - beginTime;if (interval > MAX_TIME_CONSUME_CONTINUOUSLY) {ConsumeMessageOrderlyService.this.submitConsumeRequestLater(processQueue, messageQueue, 10);break;}final int consumeBatchSize =ConsumeMessageOrderlyService.this.defaultMQPushConsumer.getConsumeMessageBatchMaxSize();// 获取消息List<MessageExt> msgs = this.processQueue.takeMessags(consumeBatchSize);defaultMQPushConsumerImpl.resetRetryAndNamespace(msgs, defaultMQPushConsumer.getConsumerGroup());if (!msgs.isEmpty()) {final ConsumeOrderlyContext context = new ConsumeOrderlyContext(this.messageQueue);ConsumeOrderlyStatus status = null;ConsumeMessageContext consumeMessageContext = null;if (ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.hasHook()) {consumeMessageContext = new ConsumeMessageContext();consumeMessageContext.setConsumerGroup(ConsumeMessageOrderlyService.this.defaultMQPushConsumer.getConsumerGroup());consumeMessageContext.setNamespace(defaultMQPushConsumer.getNamespace());consumeMessageContext.setMq(messageQueue);consumeMessageContext.setMsgList(msgs);consumeMessageContext.setSuccess(false);// init the consume context typeconsumeMessageContext.setProps(new HashMap<String, String>());ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.executeHookBefore(consumeMessageContext);}long beginTimestamp = System.currentTimeMillis();ConsumeReturnType returnType = ConsumeReturnType.SUCCESS;boolean hasException = false;try {// 这个是保证rebalance和消费串行this.processQueue.getLockConsume().lock();if (this.processQueue.isDropped()) {log.warn("consumeMessage, the message queue not be able to consume, because it's dropped. {}",this.messageQueue);break;}// 调用用户实现的接口status = messageListener.consumeMessage(Collections.unmodifiableList(msgs), context);} catch (Throwable e) {log.warn("consumeMessage exception: {} Group: {} Msgs: {} MQ: {}",RemotingHelper.exceptionSimpleDesc(e),ConsumeMessageOrderlyService.this.consumerGroup,msgs,messageQueue);hasException = true;} finally {this.processQueue.getLockConsume().unlock();}if (null == status|| ConsumeOrderlyStatus.ROLLBACK == status|| ConsumeOrderlyStatus.SUSPEND_CURRENT_QUEUE_A_MOMENT == status) {log.warn("consumeMessage Orderly return not OK, Group: {} Msgs: {} MQ: {}",ConsumeMessageOrderlyService.this.consumerGroup,msgs,messageQueue);}long consumeRT = System.currentTimeMillis() - beginTimestamp;if (null == status) {if (hasException) {returnType = ConsumeReturnType.EXCEPTION;} else {returnType = ConsumeReturnType.RETURNNULL;}} else if (consumeRT >= defaultMQPushConsumer.getConsumeTimeout() * 60 * 1000) {returnType = ConsumeReturnType.TIME_OUT;} else if (ConsumeOrderlyStatus.SUSPEND_CURRENT_QUEUE_A_MOMENT == status) {returnType = ConsumeReturnType.FAILED;} else if (ConsumeOrderlyStatus.SUCCESS == status) {returnType = ConsumeReturnType.SUCCESS;}if (ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.hasHook()) {consumeMessageContext.getProps().put(MixAll.CONSUME_CONTEXT_TYPE, returnType.name());}if (null == status) {status = ConsumeOrderlyStatus.SUSPEND_CURRENT_QUEUE_A_MOMENT;}if (ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.hasHook()) {consumeMessageContext.setStatus(status.toString());consumeMessageContext.setSuccess(ConsumeOrderlyStatus.SUCCESS == status || ConsumeOrderlyStatus.COMMIT == status);ConsumeMessageOrderlyService.this.defaultMQPushConsumerImpl.executeHookAfter(consumeMessageContext);}ConsumeMessageOrderlyService.this.getConsumerStatsManager().incConsumeRT(ConsumeMessageOrderlyService.this.consumerGroup, messageQueue.getTopic(), consumeRT);// 处理结果continueConsume = ConsumeMessageOrderlyService.this.processConsumeResult(msgs, status, context, this);} else {continueConsume = false;}}} else {if (this.processQueue.isDropped()) {log.warn("the message queue not be able to consume, because it's dropped. {}", this.messageQueue);return;}ConsumeMessageOrderlyService.this.tryLockLaterAndReconsume(this.messageQueue, this.processQueue, 100);}}}

ConsumeMessageConcurrentlyService

public void start() {this.cleanExpireMsgExecutors.scheduleAtFixedRate(new Runnable() {@Overridepublic void run() {cleanExpireMsg();}}, this.defaultMQPushConsumer.getConsumeTimeout(), this.defaultMQPushConsumer.getConsumeTimeout(), TimeUnit.MINUTES);}

提交请求方法

public void submitConsumeRequest(final List<MessageExt> msgs,final ProcessQueue processQueue,final MessageQueue messageQueue,final boolean dispatchToConsume) {final int consumeBatchSize = this.defaultMQPushConsumer.getConsumeMessageBatchMaxSize();if (msgs.size() <= consumeBatchSize) {ConsumeRequest consumeRequest = new ConsumeRequest(msgs, processQueue, messageQueue);try {this.consumeExecutor.submit(consumeRequest);} catch (RejectedExecutionException e) {this.submitConsumeRequestLater(consumeRequest);}} else {// 多条消息一起条件，那么就一批一批消费for (int total = 0; total < msgs.size(); ) {List<MessageExt> msgThis = new ArrayList<MessageExt>(consumeBatchSize);for (int i = 0; i < consumeBatchSize; i++, total++) {if (total < msgs.size()) {msgThis.add(msgs.get(total));} else {break;}}ConsumeRequest consumeRequest = new ConsumeRequest(msgThis, processQueue, messageQueue);try {this.consumeExecutor.submit(consumeRequest);} catch (RejectedExecutionException e) {for (; total < msgs.size(); total++) {msgThis.add(msgs.get(total));}this.submitConsumeRequestLater(consumeRequest);}}}}

处理流程

public void run() {if (this.processQueue.isDropped()) {log.info("the message queue not be able to consume, because it's dropped. group={} {}", ConsumeMessageConcurrentlyService.this.consumerGroup, this.messageQueue);return;}MessageListenerConcurrently listener = ConsumeMessageConcurrentlyService.this.messageListener;ConsumeConcurrentlyContext context = new ConsumeConcurrentlyContext(messageQueue);ConsumeConcurrentlyStatus status = null;defaultMQPushConsumerImpl.resetRetryAndNamespace(msgs, defaultMQPushConsumer.getConsumerGroup());ConsumeMessageContext consumeMessageContext = null;if (ConsumeMessageConcurrentlyService.this.defaultMQPushConsumerImpl.hasHook()) {consumeMessageContext = new ConsumeMessageContext();consumeMessageContext.setNamespace(defaultMQPushConsumer.getNamespace());consumeMessageContext.setConsumerGroup(defaultMQPushConsumer.getConsumerGroup());consumeMessageContext.setProps(new HashMap<String, String>());consumeMessageContext.setMq(messageQueue);consumeMessageContext.setMsgList(msgs);consumeMessageContext.setSuccess(false);ConsumeMessageConcurrentlyService.this.defaultMQPushConsumerImpl.executeHookBefore(consumeMessageContext);}long beginTimestamp = System.currentTimeMillis();boolean hasException = false;ConsumeReturnType returnType = ConsumeReturnType.SUCCESS;try {if (msgs != null && !msgs.isEmpty()) {for (MessageExt msg : msgs) {MessageAccessor.setConsumeStartTimeStamp(msg, String.valueOf(System.currentTimeMillis()));}}// 调用消息消费实现status = listener.consumeMessage(Collections.unmodifiableList(msgs), context);} catch (Throwable e) {log.warn("consumeMessage exception: {} Group: {} Msgs: {} MQ: {}",RemotingHelper.exceptionSimpleDesc(e),ConsumeMessageConcurrentlyService.this.consumerGroup,msgs,messageQueue);hasException = true;}long consumeRT = System.currentTimeMillis() - beginTimestamp;if (null == status) {if (hasException) {returnType = ConsumeReturnType.EXCEPTION;} else {returnType = ConsumeReturnType.RETURNNULL;}} else if (consumeRT >= defaultMQPushConsumer.getConsumeTimeout() * 60 * 1000) {returnType = ConsumeReturnType.TIME_OUT;} else if (ConsumeConcurrentlyStatus.RECONSUME_LATER == status) {returnType = ConsumeReturnType.FAILED;} else if (ConsumeConcurrentlyStatus.CONSUME_SUCCESS == status) {returnType = ConsumeReturnType.SUCCESS;}if (ConsumeMessageConcurrentlyService.this.defaultMQPushConsumerImpl.hasHook()) {consumeMessageContext.getProps().put(MixAll.CONSUME_CONTEXT_TYPE, returnType.name());}if (null == status) {log.warn("consumeMessage return null, Group: {} Msgs: {} MQ: {}",ConsumeMessageConcurrentlyService.this.consumerGroup,msgs,messageQueue);status = ConsumeConcurrentlyStatus.RECONSUME_LATER;}if (ConsumeMessageConcurrentlyService.this.defaultMQPushConsumerImpl.hasHook()) {consumeMessageContext.setStatus(status.toString());consumeMessageContext.setSuccess(ConsumeConcurrentlyStatus.CONSUME_SUCCESS == status);ConsumeMessageConcurrentlyService.this.defaultMQPushConsumerImpl.executeHookAfter(consumeMessageContext);}ConsumeMessageConcurrentlyService.this.getConsumerStatsManager().incConsumeRT(ConsumeMessageConcurrentlyService.this.consumerGroup, messageQueue.getTopic(), consumeRT);if (!processQueue.isDropped()) {// 处理结果// 处理失败的消息会发送回broker，topic改成retry的，失败16次后进入死信队列DLQ// 处理成功则提交offset// 要求延迟处理的就要请求延迟提交ConsumeMessageConcurrentlyService.this.processConsumeResult(status, context, this);} else {log.warn("processQueue is dropped without process consume result. messageQueue={}, msgs={}", messageQueue, msgs);}}