[jira] [Created] (KAFKA-9950) MirrorMaker2 sharing of ConfigDef can lead to ConcurrentModificationException

["Chris Egerton (Jira)" <ji...@apache.org>]

Chris Egerton created KAFKA-9950:
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             Summary: 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: 2.4.1, 2.5.0, 2.4.0
            Reporter: Chris Egerton
            Assignee: Chris Egerton


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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