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https://issues.apache.org/jira/browse/KAFKA-9950?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Konstantine Karantasis resolved KAFKA-9950.
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Resolution: Fixed
> MirrorMaker2 sharing of ConfigDef can lead to ConcurrentModificationException
> -----------------------------------------------------------------------------
>
> Key: KAFKA-9950
> URL: https://issues.apache.org/jira/browse/KAFKA-9950
> Project: Kafka
> Issue Type: Bug
> Components: mirrormaker
> Affects Versions: 2.4.0, 2.5.0, 2.4.1
> Reporter: Chris Egerton
> Assignee: Chris Egerton
> Priority: Major
> Fix For: 2.6.0, 2.4.2, 2.5.1
>
>
> The
> [MirrorConnectorConfig::CONNECTOR_CONFIG_DEF|https://github.com/apache/kafka/blob/34824b7bff64ba387a04466d74ac6bbbd10bf37c/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorConnectorConfig.java#L397]
> object is reused across multiple MirrorMaker2 classes, which is fine the
> most part since it's a constant. However, the actual {{ConfigDef}} object
> itself is mutable, and is mutated when the {{MirrorTaskConfig}} class
> [statically constructs its own
> ConfigDef|https://github.com/apache/kafka/blob/34824b7bff64ba387a04466d74ac6bbbd10bf37c/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorTaskConfig.java#L62].
> This has two unintended effects:
> # Since the two {{ConfigDef}} objects for the {{MirrorConnectorConfig}} and
> {{MirrorTaskConfig}} classes are actually the same object, the additional
> properties that the {{MirrorTaskConfig}} class defines for its {{ConfigDef}}
> are also added to the {{MirrorConnectorConfig}} class's {{ConfigDef}}. The
> impact of this isn't huge since both additional properties have default
> values, but this does cause those properties to appear in the
> {{/connectors/\{name}/config/validate}} endpoint once the
> {{MirrorTaskConfig}} class is loaded for the first time.
> # It's possible that, if a config for a MirrorMaker2 connector is submitted
> at approximately the same time that the {{MirrorTaskConfig}} class is loaded,
> a {{ConcurrentModificationException}} will be thrown by the
> {{AbstractHerder}} class when it tries to [iterate over all of the keys of
> the connector's
> ConfigDef|https://github.com/apache/kafka/blob/34824b7bff64ba387a04466d74ac6bbbd10bf37c/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/AbstractHerder.java#L357].
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