Shh! Is this really good for asynchronous events?

The story background

At the beginning of this year, I wrote an article 《 gather and watch ： The process of internal decoupling based on event mechanism 》. This article is mainly about using ES Heterogeneous data scenarios . Program subscription Mysql Binlog Changes , Then the program uses Spring Event To distribute specific events , Because the data change of a table may need to update more than one ES Indexes .

In order to make it easier for you to understand, I copied the pictures of the previous scheme , as follows ：

There is a problem with the scheme in the figure above , That's what we're going to talk about today .

The problem is when MQ Consumer After receiving the message , Just post it directly Event 了 , If it's synchronous , No problem . If a EventListener Failed to process in , So this message will not ACK.

If it's an asynchronous release Event Scene , As soon as the news is released ACK 了 . Even if someone EventListener Failed to process in ,MQ I can't feel it , There will be no redelivery of messages , That's the problem .

Solution

Scheme 1

Now that the news has ACK 了 , Then don't use MQ The retrying function of , Can users try again by themselves ？

It's certainly possible , Whether the internal processing is successful or not is certain to be known , If the processing fails, you can try again by default , Or try again with a certain strategy . I can't, but I can drop it in the library , Keep records .

The problem is that it's too boring , Every place you use it has to do it , And for the program brother who will take over your code in the future , This is likely to make the little brother's hair fall off slowly ....

It doesn't matter if you fall off , The point is that he doesn't know what to do with it , Maybe one day I'll be carrying the pot , Pathetic ....

Option two

To ensure the consistency of messages and business processing , You can't do it right away ACK operation . It's about waiting for the business to complete before deciding whether to ACK.

If there is a failure to handle, it should not ACK, So you can reuse MQ The retrial mechanism of .

Analyze it , This is a typical asynchronous to synchronous scenario . image Dubbo There's also this scene in , So we can learn from Dubbo In the realization of ideas .

Create a DefaultFuture It is used to synchronously wait to get the result of task execution . And then in MQ Where to consume DefaultFuture.

  
   @Service
   @RocketMQMessageListener(topic = "${rocketmq.topic.data_change}", consumerGroup = "${rocketmq.group.data_change_consumer}")
   public class DataChangeConsume implements RocketMQListener<DataChangeRequest> {
       @Autowired
       private ApplicationContext applicationContext;
       @Autowired
       private CustomApplicationContextAware customApplicationContextAware;
       @Override
       public void onMessage(DataChangeRequest dataChangeRequest) {
           log.info("received message {} , Thread {}", dataChangeRequest, Thread.currentThread().getName());
           DataChangeEvent event = new DataChangeEvent(this);
           event.setChangeType(dataChangeRequest.getChangeType());
           event.setTable(dataChangeRequest.getTable());
           event.setMessageId(dataChangeRequest.getMessageId());
           DefaultFuture defaultFuture = DefaultFuture.newFuture(dataChangeRequest, customApplicationContextAware.getTaskCount(), 6000 * 10);
           applicationContext.publishEvent(event);
           Boolean result = defaultFuture.get();
           log.info("MessageId {}  Processing results  {}", dataChangeRequest.getMessageId(), result);
           if (!result) {
               throw new RuntimeException(" Processing failed , No news ACK, Wait for the next time to try again ");
           }
       }
   }

newFuture() Event parameters are passed in , Timeout time , Number of tasks several parameters . The number of tasks is used to judge all EventListener Is it all done .

defaultFuture.get(); It doesn't block , Wait for all tasks to complete before returning the result , If all the business is successful , So it will return true, End of the process , Message automatically ACK.

If you return false Prove that there are processing failures or timeouts , There is no need to ACK 了 , Throw an exception and wait to try again .

  
   public Boolean get() {
       if (isDone()) {
           return true;
       }
       long start = System.currentTimeMillis();
       lock.lock();
       try {
           while (!isDone()) {
               done.await(timeout, TimeUnit.MILLISECONDS);
               //  There is feedback from failed tasks 
               if (!isSuccessDone()) {
                   return false;
               }
               //  All executed successfully 
               if (isDone()) {
                   return true;
               }
               //  Overtime 
               if (System.currentTimeMillis() - start > timeout) {
                   return false;
               }
           }
       } catch (InterruptedException e) {
           throw new RuntimeException(e);
       } finally {
           lock.unlock();
       }
       return true;
   }

isDone() Can judge whether the number of tasks with feedback results is consistent with the total number , If it is consistent, it means that the whole execution is completed .

  
   public boolean isDone() {
       return feedbackResultCount.get() == taskCount;
   }

How to give feedback after the task is completed ? It's impossible for every method used to care about , So we define a facet to do this .

  
   @Aspect
   @Component
   public class EventListenerAspect {
       @Around(value = "@annotation(eventListener)")
       public Object aroundAdvice(ProceedingJoinPoint joinpoint, EventListener eventListener) throws Throwable {
         DataChangeEvent event = null;
         boolean executeResult = true;
          try {
            event = (DataChangeEvent)joinpoint.getArgs()[0];
            Object result = joinpoint.proceed();
            return result;
         } catch (Exception e) {
            executeResult = false;
             throw e;
         } finally {
            DefaultFuture.received(event.getMessageId(), executeResult);
         }
       }
   }

adopt DefaultFuture.received() Feedback on execution results .

  
   public static void received(String id, boolean result) {
       DefaultFuture future = FUTURES.get(id);
       if (future != null) {
           //  Add up the number of failed tasks 
           if (!result) {
               future.feedbackFailResultCount.incrementAndGet();
           }
           //  Add up the number of completed tasks 
           future.feedbackResultCount.incrementAndGet();
           if (future.isDone()) {
               FUTURES.remove(id);
               future.doReceived();
           }
       }
   }
   private void doReceived() {
       lock.lock();
       try {
           if (done != null) {
               //  Wake up blocked threads 
               done.signal();
           }
       } finally {
           lock.unlock();
       }
   }

Let's summarize the whole process ：

received MQ news , Assemble into DefaultFuture, adopt get Method to get the execution result , This method blocks when the execution is not finished .
Cut through the section and add EventListener Methods , Judge whether there is an exception to judge the execution result of the task .
adopt DefaultFuture.received() Feedback results .
Whether the calculation is complete in feedback , When all is done, the blocked thread is awakened .DefaultFuture.get() You can get the results .
Is it necessary to ACK operation .

It's important to note that each EventListener The logic of internal consumption should be idempotent control .

Source code address ：https://github.com/yinjihuan/kitty-cloud/tree/master/kitty-cloud-mqconsume

About author ： Yin Jihuan , Simple technology enthusiasts ,《Spring Cloud Microservices - Full stack technology and case analysis 》, 《Spring Cloud Microservices introduction Actual combat and advanced 》 author , official account Ape world Originator . Personal wechat jihuan900, Welcome to hook up with .

I have compiled a complete set of learning materials , Those who are interested can search through wechat 「 Ape world 」, Reply key 「 Learning materials 」 Get what I've sorted out Spring Cloud,Spring Cloud Alibaba,Sharding-JDBC Sub database and sub table , Task scheduling framework XXL-JOB,MongoDB, Reptiles and other related information .

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Shh! Is this really good for asynchronous events?

The story background

Solution

Scheme 1

Option two

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