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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