BewareMyPower commented on code in PR #24920:
URL: https://github.com/apache/pulsar/pull/24920#discussion_r2486182394
##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/service/AbstractDispatcherSingleActiveConsumer.java:
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@@ -176,6 +176,11 @@ public synchronized CompletableFuture<Void>
addConsumer(Consumer consumer) {
return FutureUtil.failedFuture(new
ConsumerBusyException("Exclusive consumer is already"
+ " connected"));
} else {
+ try {
+ removeConsumer(actConsumer);
+ } catch (BrokerServiceException e) {
+ log.warn("[{}] Remove inactive exclusive consumer
{}", this.topicName, consumer);
+ }
Review Comment:
@lhotari I think the previous change here is correct:
https://github.com/apache/pulsar/pull/24920/commits/bcb763baa670544ea90bda67243870d5ef085551
`channelInactive` is not synchronized with `addConsumer`, so there is a race
condition.
1. `isActive = false` is called:
https://github.com/apache/pulsar/blob/402ed5bc0a50b07fc7baff6c9c6a0ed0eb07a6b5/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java#L411
2. `addConsumer` is called on a new consumer
3. `consumer.close()` is called:
https://github.com/apache/pulsar/blob/402ed5bc0a50b07fc7baff6c9c6a0ed0eb07a6b5/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java#L447
Then step 2 will always fail with `StackOverflowError`.
```
2025-10-28T22:54:08,431+0000 [configuration-metadata-store-14-1] ERROR
org.apache.pulsar.broker.service.persistent.PersistentTopic -
[persistent://public/default/test-partition-0] Failed to create subscription:
test-subscription
java.util.concurrent.CompletionException: java.lang.StackOverflowError
```
From the thread name, we can see the `StackOverflowError` error happens in
the metadata store thread. However, if the consumer's connection (`ServerCnx`)
is active, the future will always complete in a Netty event loop thread, whose
name starts with `pulsar-io`.
https://github.com/apache/pulsar/blob/402ed5bc0a50b07fc7baff6c9c6a0ed0eb07a6b5/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java#L3697
https://github.com/apache/pulsar/blob/402ed5bc0a50b07fc7baff6c9c6a0ed0eb07a6b5/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java#L3707
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