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https://issues.apache.org/jira/browse/LUCENE-9791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17290018#comment-17290018
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Paweł Bugalski commented on LUCENE-9791:
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I've open pull request on github so that it should be easier to discuss this
issue.
> Monitor (aka Luwak) has concurrency issues related to BytesRefHash#find
> -----------------------------------------------------------------------
>
> Key: LUCENE-9791
> URL: https://issues.apache.org/jira/browse/LUCENE-9791
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/other
> Affects Versions: master (9.0), 8.7, 8.8
> Reporter: Paweł Bugalski
> Priority: Major
> Attachments: LUCENE-9791.patch
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> _org.apache.lucene.monitor.Monitor_ can sometimes *NOT* match a document that
> should be matched by one of registered queries if match operations are run
> concurrently from multiple threads.
> This is because sometimes in a concurrent environment
> _TermFilteredPresearcher_ might not select a query that could later on match
> one of documents being matched.
> Internally _TermFilteredPresearcher_ is using a term acceptor: an instance of
> _org.apache.lucene.monitor.QueryIndex.QueryTermFilter_. _QueryTermFilter_ is
> correctly initialized under lock and its internal state (a map of
> _org.apache.lucene.util.BytesRefHash_ instances) is correctly published.
> Later one when those instances are used concurrently a problem with
> _org.apache.lucene.util.BytesRefHash#find_ is triggered since it is not
> thread safe.
> _org.apache.lucene.util.BytesRefHash#find_ internally is using a private
> _org.apache.lucene.util.BytesRefHash#equals_ method, which is using an
> instance field _scratch1_ as a temporary buffer to compare its _ByteRef_
> parameter with contents of _ByteBlockPool_. This is not thread safe and can
> cause incorrect answers as well as _ArrayOutOfBoundException_.
> __
>
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