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From "Jukka Zitting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-798) ConcurrentModificationException during logout
Date Fri, 23 Mar 2007 15:01:33 GMT

    [ https://issues.apache.org/jira/browse/JCR-798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12483625
] 

Jukka Zitting commented on JCR-798:
-----------------------------------

Reading Martijn's description it seems that the problem is simply that the event listener
is not automatically unregistered when the session is closed. Session.logout() should always
unregister all listeners associated with that session, after which the described problem shouldn't
occur.

> ConcurrentModificationException during logout
> ---------------------------------------------
>
>                 Key: JCR-798
>                 URL: https://issues.apache.org/jira/browse/JCR-798
>             Project: Jackrabbit
>          Issue Type: Bug
>          Components: core
>         Environment: Jackrabbit 1.2.1
>            Reporter: Martijn Hendriks
>         Assigned To: Stefan Guggisberg
>             Fix For: 1.3
>
>
> We regularly get the following exception:
> java.util.ConcurrentModificationException
>         at org.apache.commons.collections.map.AbstractReferenceMap$ReferenceEntrySetIterator.checkMod(AbstractReferenceMap.java:761)
>         at org.apache.commons.collections.map.AbstractReferenceMap$ReferenceEntrySetIterator.hasNext(AbstractReferenceMap.java:735)
>         at java.util.Collections$UnmodifiableCollection$1.hasNext(Collections.java:1009)
>         at java.util.Collections$UnmodifiableCollection$1.hasNext(Collections.java:1009)
>         at org.apache.jackrabbit.core.state.LocalItemStateManager.dispose(LocalItemStateManager.java:341)
>         at org.apache.jackrabbit.core.WorkspaceImpl.dispose(WorkspaceImpl.java:170)
>         at org.apache.jackrabbit.core.SessionImpl.logout(SessionImpl.java:1225)
>         at org.apache.jackrabbit.core.XASessionImpl.logout(XASessionImpl.java:379)
> Two causes for this exception have been identified:
>  (Taken from an email to the dev-list from Marcel Reutegger):
> > - session A reads some items I
> > - session B transiently removes items in I
> > - session A logs out and starts to iterate over I in  LocalItemStateManager (LISM)
> > - session B saves changes and removed items are evicted from A's LISM
> > - session A gets concurrent modification exception
> Another scenario is the following:
> - Session A gets the iterator of the values of (the primary cache of) an ItemStateReferenceCache
in LocalItemStateManager.dispose.
> - Session B then does something that triggers the CacheManager.
> - The CacheManager then calls resizeAll, and evicts some items from the secondary cache
of the ItemStateReferenceCache of which the LocalItemStateManager has a values iterator.
> - The garbage collector then runs and evicts the removed items also from the primary
cache, which effectively modifies the set over which is iterated.
> Regards,
> Martijn Hendriks

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