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https://issues.apache.org/jira/browse/SLING-13132?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Carsten Ziegeler updated SLING-13132:
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Labels: Concurrency (was: )
> 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
> Priority: Critical
> Labels: Concurrency
>
> 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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