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https://issues.apache.org/jira/browse/LUCENE-9791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17287130#comment-17287130
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Robert Muir commented on LUCENE-9791:
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I don't know of anything else using BytesRefHash with multiple threads, so
instead of trying to make it thread safe (or partially thread safe), maybe it
is the monitor code that should be fixed here?
> 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
>
>
> _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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