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https://issues.apache.org/jira/browse/LUCENE-9791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17287196#comment-17287196
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Uwe Schindler commented on LUCENE-9791:
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Another idea would be to remove the scratch BytesRef: Maybe we can simply
access the byte[] behind the BytesRefHash and use a standard Arrays.equals()
with correct offset and count. As this is a private method, I see no issue in
this.
Nevertheless: You should never ever add new entries while doing lookups at same
time. IMHO, a class like this should allow lookups concurrently, once all
entries were added (like a HashMap: If you have build a HashMap, you can
concurerntly access the getters/contains - but never ever change it again).
Maybe another clean way would be some method in BytesRefHash that returns a
read-only clone.
> 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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