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https://issues.apache.org/jira/browse/LUCENE-9661?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17262219#comment-17262219
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Michael McCandless commented on LUCENE-9661:
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Whoa, thank you for digging to the root cause so quickly [~danmuzi]!
Do you know if this corresponds to a recent change? It looks like
{{BaseTermsEnum}} was factored out in Feb 2019.
{quote}However, it is difficult how to write a test for this issue.
Is there a good way?
{quote}
Hmm, I'm confused – it looks like your attached patch already has a
{{testDeadlock}} test case? Is it difficult to make that real test (move it to
a separate {{TestFooBar}} source)? Or, would that break the test, since it
relies specifically on when classloader inits {{TermsEnum}} and
{{BaseTermsEnum}}?
Did we create tests for the past couple classloader deadlocks?
> Another classloader deadlock?
> -----------------------------
>
> Key: LUCENE-9661
> URL: https://issues.apache.org/jira/browse/LUCENE-9661
> Project: Lucene - Core
> Issue Type: Bug
> Affects Versions: master (9.0)
> Reporter: Michael McCandless
> Priority: Major
> Attachments: deadlock_test.patch
>
>
> The {{java}} processes spawned by our Lucene nightly benchmarks sometimes
> randomly hang, apparently while loading classes across threads, under
> contention.
> I've opened [this {{luceneutil}} issue with some
> details|https://github.com/mikemccand/luceneutil/issues/89], but
> [~uschindler] suggested I open an issue here too since he has been seeing
> this in CI builds too.
> It is rare, maybe once a week in the nightly benchmarks (which spawn many
> {{java}} processes with many threads across 128 CPU cores). It is clearly a
> deadlock – when it strikes, the process hangs forever until I notice and
> {{kill -9}} it. I posted a coupled {{jstacks}} in the issue above.
> [~rcmuir] suggested using {{classcycle}} to maybe statically dig into
> possible deadlocks ... I have not tried that yet.
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