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https://issues.apache.org/jira/browse/LUCENE-6808?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14877340#comment-14877340
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Yonik Seeley commented on LUCENE-6808:
--------------------------------------
{code}
public BytesRef value(int slot) {
// null out the corrisponding Builder to prevent future changes to
returned BytesRef instance
// in cases where the user makes additional slot changes after calling
value
tempBRs[slot] = null;
return values[slot];
}
{code}
+1 to this... seems to have no downsides when used as lucene currenly uses it
(i.e. only called at the end of search)
> Term(Ord)ValComparator.value return BytesRefs that are re-used internally
> -------------------------------------------------------------------------
>
> Key: LUCENE-6808
> URL: https://issues.apache.org/jira/browse/LUCENE-6808
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Hoss Man
> Attachments: LUCENE-6808.patch, LUCENE-6808.patch
>
>
> While working on SOLR-6168, which involves some non-trivial usage of
> {{FieldComparator}}, I discovered some weird bugs anytime I was using
> TermOrdValComparator. I ultimately tracked this down to the fact that the
> {{BytesRef}} instances returned by {{TermOrdValComparator.value(int slot)}}
> are backed by {{BytesRefBuilder}} instances that the Comparator hangs on to
> and re-uses -- so the values a caller gets back from
> {{FieldComparator.value(slot)}} might be changed out from under it before it
> has a chance to use that value in something like
> {{FieldComparator.compareValues(first,second)}}.
> The general approach when dealing with BytesRef instances (as i understand
> it) is that the caller is responsible for making a copy if it wants to hang
> on to it -- but in this case that would violate the generic API of
> FieldComparator -- callers would have to pay attention to when a
> {{FieldComparator}} is a
> {{FieldComparator<BytesRef>}} and do casting to copy the BytesRef.
> It seems like the right solution is for {{TermOrdValComparator.value(slot)}}
> (and {{TermValComparator.value(slot)}} which has a similar BytesRef usage) to
> return {{BytesRef.deepCopyOf(values\[slot\])}}
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