poorbarcode opened a new pull request, #21498:
URL: https://github.com/apache/pulsar/pull/21498
### Motivation & Modifications
Add a new test used to verify that the Broker will not leave an orphan
consumer in the scenario below:
- Register "consumer-1"
- "consumer-1" will be maintained by the Subscription.
- "consumer-1" will be maintained by the Dispatcher.
- The connection of "consumer-1" has something wrong. We call this
connection "connection-1"
- Try to register "consumer-2"
- "consumer-2" will be maintained by the Subscription. At this time, there
are two consumers under this
subscription.
- This will trigger a connection check task for connection-1, we call this
task "CheckConnectionLiveness".
This task will be executed in another thread, which means it will
release the lock `Synchronized(dispatcher)`
- "consumer-2" was not maintained by the Dispatcher yet.
- "CheckConnectionLiveness" will kick out "consumer-1" after 5 seconds, then
"consumer-2" will be maintained
by the Dispatcher.
---
(Highlight) Race condition: if the connection of "consumer-2" went to a
wrong state before step 4,
"consumer-2" is maintained by the Subscription and not maintained by the
Dispatcher. Would the scenario below
will happen?
- "connection-2" closed.
- Remove "consumer-2" from the Subscription.
- Try to remove "consumer-2" from the Dispatcher, but there are no consumers
under this Dispatcher. To remove
nothing.
- "CheckConnectionLiveness" is finished; put "consumer-2" into the
Dispatcher.
- At this moment, the consumer's state of Subscription and Dispatcher are
not consistent. There is an orphan
consumer under the Dispatcher.
---
### Why there is no orphan consumer?
There are two mechanisms to avoid orphan consumers:
- After the consumer future is complete, it rechecks the connection is still
active. Removed consumers again if the connection is inactive. see
https://github.com/apache/pulsar/blob/master/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java#L919-L921
**PersistentTopic.java**
```java
if (!cnx.isActive()) {
try {
consumer.close();
}
...
}
```
- If the method `consumerFuture.complet(v)` returned `false`, broker will
remove the consumer again. see
https://github.com/apache/pulsar/blob/master/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java#L1271-L1285
```java
if (consumerFuture.complete(consumer)) {
...
} else {
consumer.close();
}
```
### Documentation
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- [ ] `doc-required` <!-- Your PR changes impact docs and you will update
later -->
- [x] `doc-not-needed` <!-- Your PR changes do not impact docs -->
- [ ] `doc-complete` <!-- Docs have been already added -->
### Matching PR in forked repository
PR in forked repository: x
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