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Date: Mon, 7 Nov 2016 14:57:58 +0000 (UTC)
From: "Keith Turner (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (ACCUMULO-4502) Called next when there is no top
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archived-at: Mon, 07 Nov 2016 14:58:00 -0000


    [ https://issues.apache.org/jira/browse/ACCUMULO-4502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15644401#comment-15644401 ] 

Keith Turner commented on ACCUMULO-4502:
----------------------------------------

bq. The switch and subsequent pointer assignment is done on one thread, and the pointer is read on another. This is the only explanation I can come up with unless the dumped file is somehow not identical to the original memory file.

I think synchronized should cover that case, if both threads sync on the same thing. Volatile would cover reads outside of sync block.  Could just be some other bug, like the one you found with the Value being changed.  


> Called next when there is no top
> --------------------------------
>
>                 Key: ACCUMULO-4502
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-4502
>             Project: Accumulo
>          Issue Type: Bug
>          Components: core, tserver
>    Affects Versions: 1.6.6
>            Reporter: Ivan Bella
>            Assignee: Ivan Bella
>             Fix For: 1.7.3, 1.8.1, 2.0.0
>
>          Time Spent: 20m
>  Remaining Estimate: 0h
>
> This happens very rarely but we have seen the following exception (pulled from a server running 1.6.4).  Looking at the code I believe this condition can still happen in 1.8.0:
> java.util.concurrent.ExecutionException: java.lang.IllegalStateException: Called next() when there is no top
> ...
> Caused by: java.lang.IllegalStateException: Called next() when there is no top
> HeapIterator.next(HeapIterator.java: 77)
> WrappingIterator.next(WrappingIterator.java: 96)
> MemKeyConversionIterator.next(InMemoryMap.java:162)
> SourceSwitchingIterator.readNext(SourceSwitchingIterator.java: 139)
> SourceSwitchingIterator.next(SourceSwitchingIterator.java: 123)
> PartialMutationSkippingIterator.consume(InMemoryMap.java:108)
> SkippingIterator.seek(SkippingIterator.java:43)


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