[jira] [Resolved] (FLINK-40362) DynamicKafkaSource idle reader never finishes when no-more-splits precedes the metadata update

["Martijn Visser (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-40362?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Martijn Visser resolved FLINK-40362.
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    Resolution: Fixed

> DynamicKafkaSource idle reader never finishes when no-more-splits precedes the metadata update
> ----------------------------------------------------------------------------------------------
>
>                 Key: FLINK-40362
>                 URL: https://issues.apache.org/jira/browse/FLINK-40362
>             Project: Flink
>          Issue Type: Bug
>          Components: Connectors / Kafka
>    Affects Versions: kafka-3.4.0, kafka-4.0.1, kafka-5.0.0
>            Reporter: Sylwester Lachiewicz
>            Assignee: Sylwester Lachiewicz
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: kafka-5.1.0, kafka-4.0.2, kafka-5.0.1, kafka-3.4.1
>
>
> An idle reader (a subtask with no assigned splits) that receives the no-more-splits signal before the {{MetadataUpdateEvent}} never forwards that signal to the sub-readers created by the update.
> {{DynamicKafkaSourceReader.handleSourceEvents}} guards the re-notification with {{!pendingSplits.isEmpty()}}, which is false in exactly this case, so {{notifyNoMoreSplits()}} is never re-delivered. The reader then returns {{NOTHING_AVAILABLE}} indefinitely and a bounded job never finishes.
> Reproduced deterministically at unit level: {{DynamicKafkaSourceReaderTest#testIdleReaderFinishesWhenNoMoreSplitsArrivesBeforeMetadata}} calls {{notifyNoMoreSplits()}} before {{handleSourceEvents(metadata)}} and then polls for {{END_OF_INPUT}}. On main it fails with "expected: END_OF_INPUT but was: NOTHING_AVAILABLE"; with the fix it passes.
> Fix: re-deliver the no-more-splits signal after processing a metadata update regardless of whether pending splits exist. {{notifyNoMoreSplits()}} is idempotent and only fires when the signal has already arrived, so this adds no new cross-component traffic.
> This was originally suspected of causing {{DynamicKafkaSourceITTest}} {{testIdleReader}} hangs in CI, but that has not been reproduced locally (11/11 passes on unfixed main), so the ITCase link is unconfirmed.
> Related: FLINK-40094 and FLINK-39979 touch the same reader idleness area.



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