5 张图带你理解 RocketMQ 延时消息机制

public static void main(String[] args) throws Exception {
 // Instantiate a producer to send scheduled messages
 DefaultMQProducer producer = new DefaultMQProducer("ExampleProducerGroup");
 // Launch producer
 producer.start();
 int totalMessagesToSend = 100;
 for (int i = 0; i < totalMessagesToSend; i++) {
  Message message = new Message("TestTopic", ("Hello scheduled message " + i).getBytes());
  // This message will be delivered to consumer 10 seconds later.
  message.setDelayTimeLevel(3);
  // Send the message
  producer.send(message);
 }
 
 // Shutdown producer after use.
 producer.shutdown();
}

//MessageStoreConfig类
private String messageDelayLevel = "1s 5s 10s 30s 1m 2m 3m 4m 5m 6m 7m 8m 9m 10m 20m 30m 1h 2h";

//CommitLog 类
if (msg.getDelayTimeLevel() > 0) {
 if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) {
  msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel());
 }

 topic = TopicValidator.RMQ_SYS_SCHEDULE_TOPIC;
 int queueId = ScheduleMessageService.delayLevel2QueueId(msg.getDelayTimeLevel());

 // Backup real topic, queueId
 MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_TOPIC, msg.getTopic());
 MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_QUEUE_ID, String.valueOf(msg.getQueueId()));
 msg.setPropertiesString(MessageDecoder.messageProperties2String(msg.getProperties()));

 msg.setTopic(topic);
 msg.setQueueId(queueId);
}

public void start() {
 if (started.compareAndSet(false, true)) {
  this.load();
  this.deliverExecutorService = new ScheduledThreadPoolExecutor(this.maxDelayLevel, new ThreadFactoryImpl("ScheduleMessageTimerThread_"));
  //省略部分逻辑
  for (Map.Entry<Integer, Long> entry : this.delayLevelTable.entrySet()) {
   Integer level = entry.getKey();
   Long timeDelay = entry.getValue();
   Long offset = this.offsetTable.get(level);
   if (null == offset) {
    offset = 0L;
   }

   if (timeDelay != null) {
    //省略部分逻辑
    this.deliverExecutorService.schedule(new DeliverDelayedMessageTimerTask(level, offset), FIRST_DELAY_TIME, TimeUnit.MILLISECONDS);
   }
  }
        //省略持久化的逻辑
 }
}

public void executeOnTimeup() {
 ConsumeQueue cq =
  ScheduleMessageService.this.defaultMessageStore.findConsumeQueue(TopicValidator.RMQ_SYS_SCHEDULE_TOPIC,
   delayLevel2QueueId(delayLevel));

 if (cq == null) {
  this.scheduleNextTimerTask(this.offset, DELAY_FOR_A_WHILE);
  return;
 }

 SelectMappedBufferResult bufferCQ = cq.getIndexBuffer(this.offset);
 if (bufferCQ == null) {
  //省略部分逻辑
  this.scheduleNextTimerTask(resetOffset, DELAY_FOR_A_WHILE);
  return;
 }

 long nextOffset = this.offset;
 try {
  int i = 0;
  ConsumeQueueExt.CqExtUnit cqExtUnit = new ConsumeQueueExt.CqExtUnit();
  for (; i < bufferCQ.getSize() && isStarted(); i += ConsumeQueue.CQ_STORE_UNIT_SIZE) {
   long offsetPy = bufferCQ.getByteBuffer().getLong();
   int sizePy = bufferCQ.getByteBuffer().getInt();
   long tagsCode = bufferCQ.getByteBuffer().getLong();
            //省略部分逻辑
   long now = System.currentTimeMillis();
   long deliverTimestamp = this.correctDeliverTimestamp(now, tagsCode);
   nextOffset = offset + (i / ConsumeQueue.CQ_STORE_UNIT_SIZE);

   long countdown = deliverTimestamp - now;
   if (countdown > 0) {
    this.scheduleNextTimerTask(nextOffset, DELAY_FOR_A_WHILE);
    return;
   }

   MessageExt msgExt = ScheduleMessageService.this.defaultMessageStore.lookMessageByOffset(offsetPy, sizePy);
   if (msgExt == null) {
    continue;
   }

   MessageExtBrokerInner msgInner = ScheduleMessageService.this.messageTimeup(msgExt);
   //事务消息判断省略
   boolean deliverSuc;
   //只保留同步
   deliverSuc = this.syncDeliver(msgInner, msgExt.getMsgId(), nextOffset, offsetPy, sizePy);

   if (!deliverSuc) {
    this.scheduleNextTimerTask(nextOffset, DELAY_FOR_A_WHILE);
    return;
   }
  }

  nextOffset = this.offset + (i / ConsumeQueue.CQ_STORE_UNIT_SIZE);
 } catch (Exception e) {
  log.error("ScheduleMessageService, messageTimeup execute error, offset = {}", nextOffset, e);
 } finally {
  bufferCQ.release();
 }
 this.scheduleNextTimerTask(nextOffset, DELAY_FOR_A_WHILE);
}

private long correctDeliverTimestamp(final long now, final long deliverTimestamp) {
 long result = deliverTimestamp;

 long maxTimestamp = now + ScheduleMessageService.this.delayLevelTable.get(this.delayLevel);
 if (deliverTimestamp > maxTimestamp) {
  result = now;
 }
 return result;
}

//CommitLog类checkMessageAndReturnSize方法
if (delayLevel > 0) {
 tagsCode = this.defaultMessageStore.getScheduleMessageService().computeDeliverTimestamp(delayLevel,
  storeTimestamp);
}

//类MessageExtBrokerInner，这个方法被 messageTimeup 方法调用。
public static long tagsString2tagsCode(final TopicFilterType filter, final String tags) {
 if (null == tags || tags.length() == 0) { return 0; }

 return tags.hashCode();
}