[JCR-798] ConcurrentModificationException during logout

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.3
• Component/s: jackrabbit-core
• Environment: Jackrabbit 1.2.1
• Assignee: Stefan Guggisberg
• Reporter: Martijn Hendriks
• Created: 19/Mar/07 09:15
• Updated: 25/Apr/07 08:45
• Resolved: 18/Apr/07 09:10

Description

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