[OAK-4824] Deadlock in TarWriter

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Fix Version/s: Segment Tar 0.0.14
• Component/s: segment-tar
• Labels: deadlock resilience threading
• Assignee: Alex Deparvu
• Reporter: Michael Dürig
• Created: 19/Sep/16 16:12
• Updated: 10/Oct/16 11:32
• Resolved: 20/Sep/16 07:34

Description

There is the potential for a deadlock between concurrent calls to TarWriter#createNextGeneration() and TarWriter#flush(): both methods try to acquire a lock on this and another lock on TarWriter.file but in different order. I observed the deadlock when running CompactionAndCleanupIT.randomAccessFileConcurrentReadAndLength().

This is a regression introduced with OAK-4746: the method TarWriter.createNextGeneration() seems over eagerly synchronized. I would argue that we could drop synchronization for that method entirely as the part after the call to close() will in any case only ever be executed once by a single thread. All other threads will fail with an IllegalStateException).

alexparvulescu, WDYT?

Issue Links

• supercedes: OAK-4746 Move writeFile into the TarWriter