[jira] [Created] (LUCENE-9791) Monitor (aka Luwak) has concurrency issues related to BytesRefHash#find

["Paweł Bugalski (Jira)" <ji...@apache.org>]

Paweł Bugalski created LUCENE-9791:
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             Summary: 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: 8.8, 8.7, master (9.0)
            Reporter: Paweł Bugalski


_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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