[jira] [Created] (SLING-13132) ABBA deadlock between JobConsumerManager.topicToConsumerMap and QueueJobCache.cache locks

["Carsten Ziegeler (Jira)" <ji...@apache.org>]

Carsten Ziegeler created SLING-13132:
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             Summary: ABBA deadlock between JobConsumerManager.topicToConsumerMap and QueueJobCache.cache locks
                 Key: SLING-13132
                 URL: https://issues.apache.org/jira/browse/SLING-13132
             Project: Sling
          Issue Type: Bug
          Components: Event
            Reporter: Carsten Ziegeler


A concurrency review identified a lock-order inversion (ABBA deadlock) between two locks:

Thread A (OSGi unbind path): JobConsumerManager.unbindService() holds synchronized(topicToConsumerMap), then calls context.asyncProcessingFinished() which triggers the async handler chain: finishedJob() -> reschedule() -> requeue() -> cache.reschedule() -> synchronized(cache)

Thread B (job processing): JobQueueImpl.startJobs() -> cache.getNextJob() holds synchronized(cache), then calls jobConsumerManager.getExecutor() -> synchronized(topicToConsumerMap)

Lock ordering:
- Thread A: topicToConsumerMap -> cache
- Thread B: cache -> topicToConsumerMap

This is a classic ABBA deadlock. With retry delay <= 0, the requeue path is synchronous and the deadlock is reachable in production. This can cause a complete system freeze.

Proposed fix: In unbindService(), collect the async callback contexts into a local list while holding the topicToConsumerMap lock, then invoke asyncProcessingFinished() outside the lock. This breaks the topicToConsumerMap -> cache path while preserving the cache -> topicToConsumerMap path unchanged.



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