[Bug] Deadlock in DrainingHashesTracker due to synchronized methods

[lhotari]

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• I searched in the issues and found nothing similar.

Read release policy

• I understand that unsupported versions don't get bug fixes. I will attempt to reproduce the issue on a supported version of Pulsar client and Pulsar broker.

Version

Pulsar 4.0.1

Minimal reproduce step

Exact steps to reproduce aren't yet confirmed.

This problem was faced in a test. The problem is that there isn't a jstack -l <PID> thread dump of the deadlocked state. I have a heap dump, but since heap dumps don't contain exactly the same information as a thread dump about threads, it's hard to find out the exact reason why the dead lock happens. There are multiple blocked threads which indicates a dead lock:

What did you expect to see?

No dead locks.

What did you see instead?

There are multiple threads in blocked state which indicates a dead lock.

Anything else?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!

[lhotari]

I'm planning to first reproduce the issue and then addressing that. One improvement in DrainingHashesTracker is to replace synchronized with the use of a read-write lock.