[fix][broker] Fix deadlock in Key_Shared PIP-379 implementation#23854
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heesung-sohn
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(cherry picked from commit 8f04945)
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…y to DEBUG The `log.warn()` call in `DrainingHashesTracker.ConsumerDrainingHashesStats #updateConsumerStats` fires whenever the hash-iterator observes an entry that was already removed by a concurrent write path. In the original PIP-379 design the draining-hash stats were strongly consistent with the tracker state, so a missing entry on the read path was genuinely unexpected. That strong-consistency guarantee was intentionally dropped in apache#23854 to resolve a deadlock: the stats path is now allowed to race with entry removal. A missing entry is therefore a benign, expected outcome during normal operation, not a signal worth alerting on. Logging this at `WARN` floods broker logs without a corresponding actionable condition. Drop it to `DEBUG` and add an inline comment explaining the race so future readers understand why this is deliberately quiet. Fixes apache#25277
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Fixes #23848
Motivation
The Pulsar 4.0 Key_Shared PIP-379 implementation could deadlock and this problem was first captured in test environment heapdump where the thread stack information included in the heapdump showed multiple threads in blocked state, hinting a deadlock.
With the help of @pdolif, the problem was reproduced in isolation by simply adding this type of test code in a KeySharedSubscriptionTest test case.
In the test case, this triggered a similar pattern of blocked threads and therefore could be considered a reproduction of the previously faced dead lock issue in a test environment.
threaddump with deadlock:
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Documentation
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