BewareMyPower opened a new pull request, #22279:
URL: https://github.com/apache/pulsar/pull/22279
### Motivation
The access on `readOnActiveConsumerTask` is not thread safe.
```java
if (readOnActiveConsumerTask != null) {
return;
}
readOnActiveConsumerTask = topic.getBrokerService().executor().schedule(()
-> {/* ... */});
```
There is a case that:
| Steps | Thread 1 | Thread 2 |
| :- | :- | :- |
| 1 | Read `readOnActiveConsumerTask`: null | |
| 2 | call `schedule` | |
| 3 | | Read `readOnActiveConsumerTask`: null |
| 4 | | call `schedule` |
| 5 | Write `readOnActiveConsumerTask` to the result of `schedule` | | | 6 |
| Write `readOnActiveConsumerTask` to the result of `schedule` |
Then `schedule()` will be called twice and only one result will be assigned
to `readOnActiveConsumerTask`.
### Modifications
Follow the double-checked locking when `readOnActiveConsumerTask` is null to
ensure `readOnActiveConsumerTask` cannot be called concurrently.
### Documentation
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- [ ] `doc` <!-- Your PR contains doc changes. -->
- [ ] `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:
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