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https://issues.apache.org/jira/browse/GEODE-8671?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17294066#comment-17294066
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ASF GitHub Bot commented on GEODE-8671:
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kirklund edited a comment on pull request #5925:
URL: https://github.com/apache/geode/pull/5925#issuecomment-789321362


   > Looks like you have a few small changes to make but I'll give my approval 
now. Please consider adding unit test coverage for the changes in LocalRegion. 
There is an existing `LocalRegionTest` that uses Mockito. I also suggest you 
remove the `tearDown` since it's doing the same thing that the 
`DistributedBlackboard` Rule does after every test method.
   
   By the way, I verified that you don't need to invoke 
`DUnitBlackboard.initBlackboard()` in the `tearDown`. The Rule completely 
dereferences the instance of `DUnitBlackboard` and so it becomes available to 
GC. The Rule effectively handles the initialization and cleanup of 
`DUnitBlackboard` so that a test doesn't need to do this.


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> Two threads calling get and retrieve the same PdxInstance, resulting in 
> corruption
> ----------------------------------------------------------------------------------
>
>                 Key: GEODE-8671
>                 URL: https://issues.apache.org/jira/browse/GEODE-8671
>             Project: Geode
>          Issue Type: Improvement
>          Components: regions
>            Reporter: Dan Smith
>            Assignee: Jianxia Chen
>            Priority: Major
>              Labels: blocks-1.14.0​, pull-request-available
>
> Even if copy-on-read is set to true, two threads calling get on a partitioned 
> region can end up with the same PdxInstance object.
> This is problematic because some PdxInstances methods are not thread safe. 
> Although the underlying bytes are immutatable, the PDXInstance has a 
> ByteSource with a position field that changes. That means two threads doing 
> serialization or calling toString on the PdxInstance could result in one or 
> more threads getting a corrupt read.
> It looks like they are ending up with the same instance because of the 
> behavior in LocalRegion.optimizedGetObject. We use futures to make sure there 
> is only 1 get that goes through, and both threads receive the same value.
>     
> Ending up in optimizedGetObject requires a race with the put, because if the 
> value was in the cache at the beginning of the get it would be returned 
> earlier in the get process.
> I put a test that reproduces this issue here -   
> https://github.com/upthewaterspout/geode/pull/new/feature/pdx-instances-shared



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