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From "Kevin Sutter (JIRA)" <>
Subject [jira] [Commented] (OPENJPA-2507) Weird EmptyStackException in CriteriaQueryImpl
Date Tue, 03 Jun 2014 13:40:03 GMT


Kevin Sutter commented on OPENJPA-2507:

Thank you, Thomas.  I like this approach the best thus far.  I agree with where you think
the problem originates.  And, I didn't like the idea of changing the data structure itself
due to the ripple effect to other parts. But, wrapping the Stack in a ThreadLocal seems to
be an easy, safe mechanism to overcome the problem.  I want to experiment and look at the
patch a bit more to ensure that we're removing this ThreadLocal appropriately, otherwise we
could end up with a leak.

Thanks, Kevin

> Weird EmptyStackException in CriteriaQueryImpl
> ----------------------------------------------
>                 Key: OPENJPA-2507
>                 URL:
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: criteria
>    Affects Versions: 2.2.0, 2.3.0
>         Environment: openjpa 2.2.0 & 2.3.0, spring-data-jpa up to 1.4.2
>            Reporter: Ioannis Alexandrakis
>            Priority: Minor
>              Labels: criteria_api, openjpa
>         Attachments: OPENJPA-2507-Wrap-ContextStack-in-ThreadLocal.patch, exceptions.txt,
> Using spring-data-jpa with openjpa, I sometimes encounter a strange error (not all the
times, but under heavy load it makes its appearance, sparsely though):
> ....
> Caused by: java.util.EmptyStackException
>         at java.util.Stack.peek(<arbitrary line>)
>         at org.apache.openjpa.persistence.criteria.CriteriaQueryImpl.ctx(<arbitrary
> ....
> I do not know which behaviour triggers it, however I think it would be an improvement
to change (I did not know where exactly to file it, because it is both an improvement and
a bug in my opinion), in org.apache.openjpa.persistence.criteria.CriteriaQueryImpl, method:
Context ctx(), this:
> return _contexts == null || _contexts.isEmpty() ? null :  _contexts.peek();
> to something like this:
> try {
> 	return _contexts == null || _contexts.isEmpty() ? null :  _contexts.peek();
> } catch (EmptyStackException e) {
>     return null;
> }
> , in order to prevent a case where multiple threads modify the "_contexts" between the
evaluation of the inline "if".
> I am not able to reproduce it all the time, thus I can't create a useful test, neither
have I created a patch due to the simplicity of the 'fix'. However I believe it is a harmless
fix which could be considered a minor improvement.

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