前言
rocketMQ 支持的延迟消息，简单理解就是对于生产者发送的消息，支持设置固定时间的延迟级别，在到达指定的延迟时间时，才会投递到消费者队列，消费者才能消费到消息。
延迟队列和普通消息的发送流程，主要流程都是一致的，区别在于：
可以参考源码架构图来看，在 DledgerCommitLog 组件写入消息之前，会针对设置了setDelayTimeLevel 延迟级别的消息，改写 topic 为 RMQ_SYS_SCHEDULE_TOPIC，那么 ReputMessageService 消息重分发现场就会将消息投递到 RMQ_SYS_SCHEDULE_TOPIC 下。
再由 ScheduleMessageService 调度线程，定时将 RMQ_SYS_SCHEDULE_TOPIC 下的消息取出，判断是否到达延迟时间，如果到达延迟时间，就将消息重新投递到真实的Topic中，这样消费者就能消费到真是的消息。
源码版本：4.9.3
源码架构图
源码分析
1. 源码入口
本地源码入口从一个代码example工程中的一个示例，开始org.apache.rocketmq.example.schedule.ScheduledMessageProducer#main
public class ScheduledMessageProducer {
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();
}
}... 发送流程和普通消息一致，对通用流程感兴趣可以看下另一篇文章，RocketMQ源码 发送消息源码分析-CSDN博客...
2. DledgerCommitLog 存储消息
broker接受的消息后，会调用 DLedgerCommitLog 存储组件，进行消息存储写入 CommitLog组件。在写的过程中有一个 setMessageInfo 信息的函数，会改写 topic 为 RMQ_SYS_SCHEDULE_TOPIC。
org.apache.rocketmq.store.dledger.DLedgerCommitLog#asyncPutMessage
// 异步写入消息
@Override
public CompletableFuture<PutMessageResult> asyncPutMessage(MessageExtBrokerInner msg) {
// 存储统计服务
StoreStatsService storeStatsService = this.defaultMessageStore.getStoreStatsService();
// 事务类型
final int tranType = MessageSysFlag.getTransactionValue(msg.getSysFlag());
// 设置消息信息：包含延迟消息的处理，改写延迟消息topic和queueId
setMessageInfo(msg, tranType);
final String finalTopic = msg.getTopic();
}
private void setMessageInfo(MessageExtBrokerInner msg, int tranType) {
// Set the storage time
msg.setStoreTimestamp(System.currentTimeMillis());
// Set the message body BODY CRC (consider the most appropriate setting
// on the client)
msg.setBodyCRC(UtilAll.crc32(msg.getBody()));
//should be consistent with the old version
if (tranType == MessageSysFlag.TRANSACTION_NOT_TYPE
|| tranType == MessageSysFlag.TRANSACTION_COMMIT_TYPE) {
// 延时消息，延迟投递
// Delay Delivery
// 如果延时级别大于0
if (msg.getDelayTimeLevel() > 0) {
if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) {
msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel());
}
// 系统级延时调度topic，用于延时调度投递
String topic = TopicValidator.RMQ_SYS_SCHEDULE_TOPIC;
// 根据延时级别获取对应的队列,队列的id为delayLevel-1
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()));
// 设置topic和queueId
msg.setTopic(topic);
msg.setQueueId(queueId);
}
}
InetSocketAddress bornSocketAddress = (InetSocketAddress) msg.getBornHost();
if (bornSocketAddress.getAddress() instanceof Inet6Address) {
msg.setBornHostV6Flag();
}
InetSocketAddress storeSocketAddress = (InetSocketAddress) msg.getStoreHost();
if (storeSocketAddress.getAddress() instanceof Inet6Address) {
msg.setStoreHostAddressV6Flag();
}
}... ReputMessageService 重分发服务会定时将延迟消息投递到 RMQ_SYS_SCHEDULE_TOPIC ...
3. ScheduleMessageService 定时调度消息服务
投递延迟消息定时任务，会定时 100ms 扫描 RMQ_SYS_SCHEDULE_TOPIC 主题下的队列中的消息，计算消息的延迟时间，是不是已经到期，如果到期，就将消息投递倒真实的 Topic中。
org.apache.rocketmq.store.schedule.ScheduleMessageService.DeliverDelayedMessageTimerTask
// 投递延时消息定时任务
class DeliverDelayedMessageTimerTask implements Runnable {
// 延时级别
private final int delayLevel;
// 偏移量
private final long offset;
public DeliverDelayedMessageTimerTask(int delayLevel, long offset) {
this.delayLevel = delayLevel;
this.offset = offset;
}
@Override
public void run() {
try {
if (isStarted()) {
// 执行延时消息投递
this.executeOnTimeup();
}
} catch (Exception e) {
// XXX: warn and notify me
log.error("ScheduleMessageService, executeOnTimeup exception", e);
this.scheduleNextTimerTask(this.offset, DELAY_FOR_A_PERIOD);
}
}
/**
* 计算正确的延时投递时间，如果延时消息已经过期，返回当前时间
* @return
*/
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;
}
// 执行延时消息投递
public void executeOnTimeup() {
// 根据topic、queueId获取对应的CQ
ConsumeQueue cq =
ScheduleMessageService.this.defaultMessageStore.findConsumeQueue(TopicValidator.RMQ_SYS_SCHEDULE_TOPIC,
delayLevel2QueueId(delayLevel));
if (cq == null) {
// 延时指定时间后，再次执行
this.scheduleNextTimerTask(this.offset, DELAY_FOR_A_WHILE);
return;
}
// 根据偏移量读取到CQ内存映射数据
SelectMappedBufferResult bufferCQ = cq.getIndexBuffer(this.offset);
if (bufferCQ == null) {
long resetOffset;
if ((resetOffset = cq.getMinOffsetInQueue()) > this.offset) {
log.error("schedule CQ offset invalid. offset={}, cqMinOffset={}, queueId={}",
this.offset, resetOffset, cq.getQueueId());
} else if ((resetOffset = cq.getMaxOffsetInQueue()) < this.offset) {
log.error("schedule CQ offset invalid. offset={}, cqMaxOffset={}, queueId={}",
this.offset, resetOffset, cq.getQueueId());
} else {
resetOffset = this.offset;
}
this.scheduleNextTimerTask(resetOffset, DELAY_FOR_A_WHILE);
return;
}
long nextOffset = this.offset;
try {
int i = 0;
ConsumeQueueExt.CqExtUnit cqExtUnit = new ConsumeQueueExt.CqExtUnit();
// 遍历CQ内存映射队列
for (; i < bufferCQ.getSize() && isStarted(); i += ConsumeQueue.CQ_STORE_UNIT_SIZE) {
long offsetPy = bufferCQ.getByteBuffer().getLong(); // 物理偏移量
int sizePy = bufferCQ.getByteBuffer().getInt(); // 物理大小
long tagsCode = bufferCQ.getByteBuffer().getLong(); // deliverTimestamp
if (cq.isExtAddr(tagsCode)) {
if (cq.getExt(tagsCode, cqExtUnit)) {
tagsCode = cqExtUnit.getTagsCode();
} else {
//can't find ext content.So re compute tags code.
log.error("[BUG] can't find consume queue extend file content!addr={}, offsetPy={}, sizePy={}",
tagsCode, offsetPy, sizePy);
long msgStoreTime = defaultMessageStore.getCommitLog().pickupStoreTimestamp(offsetPy, sizePy);
tagsCode = computeDeliverTimestamp(delayLevel, msgStoreTime);
}
}
long now = System.currentTimeMillis();
// 计算正确的延时投递时间
long deliverTimestamp = this.correctDeliverTimestamp(now, tagsCode);
// 下一个消息的偏移量 = 起始偏移量 + 遍历的步长
nextOffset = offset + (i / ConsumeQueue.CQ_STORE_UNIT_SIZE);
long countdown = deliverTimestamp - now;
// 如果延时时间还未到，则继续等待，100毫秒后再次执行
if (countdown > 0) {
this.scheduleNextTimerTask(nextOffset, DELAY_FOR_A_WHILE);
return;
}
// 读取消息
MessageExt msgExt = ScheduleMessageService.this.defaultMessageStore.lookMessageByOffset(offsetPy, sizePy);
if (msgExt == null) {
continue;
}
// 转换消息，还原消息真实的topic
MessageExtBrokerInner msgInner = ScheduleMessageService.this.messageTimeup(msgExt);
if (TopicValidator.RMQ_SYS_TRANS_HALF_TOPIC.equals(msgInner.getTopic())) {
log.error("[BUG] the real topic of schedule msg is {}, discard the msg. msg={}",
msgInner.getTopic(), msgInner);
continue;
}
boolean deliverSuc;
if (ScheduleMessageService.this.enableAsyncDeliver) {
deliverSuc = this.asyncDeliver(msgInner, msgExt.getMsgId(), offset, offsetPy, sizePy);
} else {
// 将消息同步投递到，真实的topic中
deliverSuc = this.syncDeliver(msgInner, msgExt.getMsgId(), offset, offsetPy, sizePy);
}
if (!deliverSuc) {
// 如果投递失败，则继续等待，100毫秒后再次执行
this.scheduleNextTimerTask(nextOffset, DELAY_FOR_A_WHILE);
return;
}
}
// 计算下一个消息的偏移量，下一个偏移量 = 起始偏移量 + 遍历的步长
nextOffset = this.offset + (i / ConsumeQueue.CQ_STORE_UNIT_SIZE);
} catch (Exception e) {
log.error("ScheduleMessageService, messageTimeup execute error, offset = {}", nextOffset, e);
} finally {
bufferCQ.release();
}
// 进行下一次调度
this.scheduleNextTimerTask(nextOffset, DELAY_FOR_A_WHILE);
}
// 调度下一个延时投递消息
public void scheduleNextTimerTask(long offset, long delay) {
// 延时投递消息
ScheduleMessageService.this.deliverExecutorService.schedule(new DeliverDelayedMessageTimerTask(
this.delayLevel, offset), delay, TimeUnit.MILLISECONDS);
}
// 同步投递消息
private boolean syncDeliver(MessageExtBrokerInner msgInner, String msgId, long offset, long offsetPy,
int sizePy) {
PutResultProcess resultProcess = deliverMessage(msgInner, msgId, offset, offsetPy, sizePy, false);
PutMessageResult result = resultProcess.get();
boolean sendStatus = result != null && result.getPutMessageStatus() == PutMessageStatus.PUT_OK;
if (sendStatus) {
ScheduleMessageService.this.updateOffset(this.delayLevel, resultProcess.getNextOffset());
}
return sendStatus;
}
private boolean asyncDeliver(MessageExtBrokerInner msgInner, String msgId, long offset, long offsetPy,
int sizePy) {
Queue<PutResultProcess> processesQueue = ScheduleMessageService.this.deliverPendingTable.get(this.delayLevel);
//Flow Control
int currentPendingNum = processesQueue.size();
int maxPendingLimit = ScheduleMessageService.this.defaultMessageStore.getMessageStoreConfig()
.getScheduleAsyncDeliverMaxPendingLimit();
if (currentPendingNum > maxPendingLimit) {
log.warn("Asynchronous deliver triggers flow control, " +
"currentPendingNum={}, maxPendingLimit={}", currentPendingNum, maxPendingLimit);
return false;
}
//Blocked
PutResultProcess firstProcess = processesQueue.peek();
if (firstProcess != null && firstProcess.need2Blocked()) {
log.warn("Asynchronous deliver block. info={}", firstProcess.toString());
return false;
}
PutResultProcess resultProcess = deliverMessage(msgInner, msgId, offset, offsetPy, sizePy, true);
processesQueue.add(resultProcess);
return true;
}
// 异步投递消息
private PutResultProcess deliverMessage(MessageExtBrokerInner msgInner, String msgId, long offset,
long offsetPy, int sizePy, boolean autoResend) {
CompletableFuture<PutMessageResult> future =
ScheduleMessageService.this.writeMessageStore.asyncPutMessage(msgInner);
return new PutResultProcess()
.setTopic(msgInner.getTopic())
.setDelayLevel(this.delayLevel)
.setOffset(offset)
.setPhysicOffset(offsetPy)
.setPhysicSize(sizePy)
.setMsgId(msgId)
.setAutoResend(autoResend)
.setFuture(future)
.thenProcess();
}
}
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