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https://issues.apache.org/jira/browse/KAFKA-21103?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lucy Liu reassigned KAFKA-21103:
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Assignee: Lucy Liu
> Kafka Streams might lose a thread unnoticed
> -------------------------------------------
>
> Key: KAFKA-21103
> URL: https://issues.apache.org/jira/browse/KAFKA-21103
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: Matthias J. Sax
> Assignee: Lucy Liu
> Priority: Major
>
> KS allows to register an uncaught-exception-handler, which has a
> REPLACE_THREAD return code.
> However, it's possible that starting up the new thread fails, and such an
> error is swallowed silently, letting the user think the thread was restarted
> even if it was not.
> This is especially bad for single-threaded clients, which would stay in state
> RUNNING and not transitioning into DEAD or ERROR.
> A known workaround is to inspect IQ metadata – when the thread dies, it's
> correctly removed there.
> In `KafkaStreams#replaceStreamThread()` we call `addStreamsThread()` but
> ignore it's returned Optional. We should check if the Optional is empty or
> not, and either retry, or somehow surface the error otherwise (throwing an
> exception might also work, which we would need to catch elsewhere, and
> re-triggering the handler?)
> Depending how we want to fix this, a KIP might be needed?
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