[GROOVY-5121] ClassInfo.modifiedExpandos is not thread safe, it can cause an infinite loop

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.8.4, 2.0-beta-1
• Fix Version/s: 2.4.0
• Component/s: groovy-runtime
• Assignee: Unassigned
• Reporter: Lari Hotari
• Created: 14/Nov/11 00:11
• Updated: 21/Mar/15 07:11
• Resolved: 13/Mar/15 15:11

Description

There is a thread safety problem in ClassInfo class. Concurrent access to ClassInfo.modifiedExpandos (used in ClassInfo.setStrongMetaClass / clearModifiedExpandos) can cause an infinite loop.

Concurrent access to HashSet could cause an infinite loop when the tree data structure gets corrupted because of concurrent changes.
(http://lightbody.net/blog/2005/07/hashmapget_can_cause_an_infini.html , HashSet uses HashMap under the covers)

https://github.com/groovy/groovy-core/blob/GROOVY_1_8_X/src/main/org/codehaus/groovy/reflection/ClassInfo.java#L38

private static final Set<ClassInfo> modifiedExpandos = new HashSet<ClassInfo>();

modifiedExpandos seems to be used to maintain/clear strong references to EMCs? (ExpandoMetaClassCreationHandle.enable / disable calls ClassInfo.clearModifiedExpandos())

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discussion on mailing list about ClassInfo.modifiedExpandos (in another context):

http://groovy.329449.n5.nabble.com/PermGen-leak-when-executing-many-scripts-via-GroovyShell-td3329653.html