[jira] [Updated] (JENA-100) QueryIteratorBase concurrency issues

["Stephen Allen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/JENA-100?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Stephen Allen updated JENA-100:
-------------------------------

    Attachment: JENA-100-r1157891.patch

> QueryIteratorBase concurrency issues
> ------------------------------------
>
>                 Key: JENA-100
>                 URL: https://issues.apache.org/jira/browse/JENA-100
>             Project: Jena
>          Issue Type: Bug
>          Components: ARQ
>            Reporter: Stephen Allen
>         Attachments: JENA-100-r1157891.patch
>
>
> QueryIteratorBase appears to have some concurrency bugs relating to cancelling a query:
> 1) The cancel() and cancelAllowContinue() methods did not have large enough synchronized blocks (they also used "this" as the lock, which is not recommended)
> 2) The order of setting the cancellation flags and the notifying subclasses via the requestCancel() method was incorrect
> 3) The visibility and happens-before relationships were incorrect for the requestingCancel and abortIterator variables
> The cancelAllowContinue() feature adds a lot of complexity in terms of visibility and ordering.  Unfortunately it is hard to write test cases for these types of concurrency issues, so the existing tests did not uncover the issues.

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