[jira] Commented: (JCR-2746) Deadlock caused by ObservationDispatcher

["Thomas Mueller (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JCR-2746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12912473#action_12912473 ] 

Thomas Mueller commented on JCR-2746:
-------------------------------------

Thread.sleep can't be the root cause of a new deadlock. (Thread.sleep was added in JCR-2402, but no additional synchronization or locking was introduced). But Thread.sleep can *trigger* a deadlock that normally doesn't show up. So it it's really a deadlock, it could also occur even without JCR-2402 (but less likely).

JCR-2402 calls Thread.sleep in a loop. If I replace the loop with an "if" then I can reproduce some kind of deadlock. Currently it looks more like a bug in DefaultISMLocking however... I'm analyzing it.

> Deadlock caused by ObservationDispatcher 
> -----------------------------------------
>
>                 Key: JCR-2746
>                 URL: https://issues.apache.org/jira/browse/JCR-2746
>             Project: Jackrabbit Content Repository
>          Issue Type: Bug
>          Components: jackrabbit-core, observation
>    Affects Versions: 2.0.0, 2.1.0, 2.1.1
>            Reporter: Jukka Zitting
>            Assignee: Thomas Mueller
>             Fix For: 2.2.0
>
>
> The rate-limitation code we added in JCR-2402 to prevent the observation queue from growing too large was a good idea, but the current implementation is a bit troublesome since it blocks the thread while it still holds the journal lock, the SISM reader lock, and the SessionState lock. This can cause a deadlock under heavy workloads if any of the observation listeners attempts to reuse the session (not recommended/supported, but can still happen) or write to the repository (quite likely).
> To solve this problem we should move the rate-limiter code to outside the scope of any internal locks.

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