poorbarcode opened a new pull request, #23123:
URL: https://github.com/apache/pulsar/pull/23123
### Motivation
**Conditions under which problems occur**
- `Failover/Exclusive` subscription
- Sockets of Pulsar IO are not stable
- `ServerCnx` thread is busy.
| time | `registering consumer 1st` | `registering consumer 2nd` |
| --- | --- | --- |
| 1 | Registered |
| 2 | Socket is unstable |
| 3 | Closing `ServerCnx` |
| 4 | | Retry to subscribe |
| 5 | | Check whether the previous consumer is still active<sup>[1]</sup>,
if not override it by the current registering |
| 6 | `ServerCnx` is closed |
| 7 | | Call `serverCnx.checkConnectionLiveness`, the Completable Future
returned will never be completed |
**[1]**: `AbstractDispatcherSingleActiveConsumer.java`
```java
public synchronized CompletableFuture<Void> addConsumer(Consumer consumer) {
if (getActiveConsumer() != null) {
return
actConsumer.cnx().checkConnectionLiveness().thenCompose(actConsumerStillAlive
-> {
if (actConsumerStillAlive.isEmpty() ||
actConsumerStillAlive.get()) {
return FutureUtil.failedFuture(new
ConsumerBusyException("Exclusive consumer is already"
+ " connected"));
} else {
return addConsumer(consumer);
}
});
}
}
```
### Affects
It leads to the following subscribing can never succeed due to the ServerCnx
maintaining a failed future and it can never be removed.
### Error logs
```
2024-07-25T09:28:00,109+0000 [pulsar-io-4-30] WARN
org.apache.pulsar.broker.service.ServerCnx -
[/127.0.0.2:48345][persistent://{tenant}/{namespace}/__change_events-partition-0][multiTopicsReader-381f38cdef]
A failed consumer with id is already present on the connection, consumerId=7425
2024-07-25T09:28:00,109+0000 [pulsar-io-4-30] ERROR
org.apache.pulsar.broker.service.ServerCnx - A failed consumer with id is
already present on the connection. consumerId: 7425, remoteAddress:
/127.0.0.2:48345, subscription: multiTopicsReader-381f38cdef
...
...
...
// loop
```
### Modifications
Fix the bug.
### Verifying this change
- [ ] Make sure that the change passes the CI checks.
*(Please pick either of the following options)*
This change is a trivial rework / code cleanup without any test coverage.
*(or)*
This change is already covered by existing tests, such as *(please describe
tests)*.
*(or)*
This change added tests and can be verified as follows:
*(example:)*
- *Added integration tests for end-to-end deployment with large payloads
(10MB)*
- *Extended integration test for recovery after broker failure*
### Does this pull request potentially affect one of the following parts:
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*If the box was checked, please highlight the changes*
- [ ] Dependencies (add or upgrade a dependency)
- [ ] The public API
- [ ] The schema
- [ ] The default values of configurations
- [ ] The threading model
- [ ] The binary protocol
- [ ] The REST endpoints
- [ ] The admin CLI options
- [ ] The metrics
- [ ] Anything that affects deployment
### Documentation
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- [ ] `doc` <!-- Your PR contains doc changes. -->
- [ ] `doc-required` <!-- Your PR changes impact docs and you will update
later -->
- [ ] `doc-not-needed` <!-- Your PR changes do not impact docs -->
- [ ] `doc-complete` <!-- Docs have been already added -->
### Matching PR in forked repository
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