zjncs opened a new pull request, #11107:
URL: https://github.com/apache/rocketmq/pull/11107
## Motivation
`RebalanceImpl.doRebalance` iterates the `subscriptionInner` entry set and,
once the allocation result changes, hands the topic over to
`messageQueueChanged`. The push implementation re-reads the entry:
```java
SubscriptionData subscriptionData = this.subscriptionInner.get(topic);
long newVersion = System.currentTimeMillis();
log.info("... {} ...", ..., subscriptionData.getSubVersion(), newVersion);
subscriptionData.setSubVersion(newVersion);
```
`DefaultMQPushConsumer.unsubscribe(topic)` is a public API that runs on a
user thread and removes the entry from the same `ConcurrentHashMap`. When it
interleaves between the rebalance loop's iteration and this call,
`subscriptionInner.get(topic)` returns null and the rebalance thread dies with:
```
java.lang.NullPointerException: Cannot invoke
"SubscriptionData.getSubVersion()" because "subscriptionData" is null
```
That aborts `doRebalance` for the remaining topics of this consumer until
the next scheduled round.
## Modification
`RebalancePushImpl.messageQueueChanged`: if the subscription is already
gone, log and return — there is nothing to update or notify for a topic this
consumer no longer subscribes to.
## Test Evidence
Fail-before (unpatched develop, new regression test):
```
docker exec rmq-build mvn -q -pl client test
-Dtest='RebalancePushImplTest#testMessageQueueChanged_SubscriptionRemovedConcurrently'
Tests run: 1, Failures: 0, Errors: 1
java.lang.NullPointerException: Cannot invoke
"SubscriptionData.getSubVersion()" because "subscriptionData" is null
```
Pass-after (full class):
```
docker exec rmq-build mvn -q -pl client test -Dtest='RebalancePushImplTest'
Tests run: 8, Failures: 0, Errors: 0, Skipped: 0
```
No associated issue (self-discovered during a client-module self-audit).
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