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Posted to issues@lucene.apache.org by "Michael McCandless (Jira)" <ji...@apache.org> on 2021/03/11 14:03:00 UTC
[jira] [Commented] (LUCENE-9791) Monitor (aka Luwak) has
concurrency issues related to BytesRefHash#find
[ https://issues.apache.org/jira/browse/LUCENE-9791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17299578#comment-17299578 ]
Michael McCandless commented on LUCENE-9791:
--------------------------------------------
I am trying to port this back to 8.x, but the {{Arrays.equals}} we used in the PR is JDK 9+. Any clever alternatives? Else I will just break out my own {{for}} loop and start dancing!
> 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: main (9.0), 8.7, 8.8
> Reporter: Paweł Bugalski
> Priority: Major
> Attachments: LUCENE-9791.patch, LUCENE-9791_example.patch
>
> Time Spent: 4h 20m
> 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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