Chris Cranford created KAFKA-8665:
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Summary: WorkerSourceTask race condition when rebalance occurs
before task has started
Key: KAFKA-8665
URL: https://issues.apache.org/jira/browse/KAFKA-8665
Project: Kafka
Issue Type: Bug
Components: KafkaConnect
Affects Versions: 2.2.0
Reporter: Chris Cranford
In our project we have several {{SourceTask}} implementations that perform a
set of sequential steps in the {{SourceTask#start}} call. It's possible that
during these sequential operations, a rebalance occurs which leads to the
situation where the {{WorkerSourceTask}} transitions to the state where
{{startedShutdownBeforeStartCompleted=true}} and then the runtime starts a
brand new task.
This is mostly a problem around specific named resources that are registered
when a call to {{SourceTask#start}} happens and those same resources are
unregistered later when the call to {{SourceTask#stop}} occurs.
For us specifically, this is a problem with JMX resource
registration/unregistration. We register those beans at the end of the call to
{{SourceTask#start}} and unregister in the call to {{stop}}. Due to the order
of start/stop pairs combined with where a rebalance is triggered, this leads to
# Register JMX beans when SourceTask A1 is started.
# Register JMX beans when SourceTask A2 is started with rebalance.
## JMX beans failed to register as they're already registered.
# SourceTask A1 finally stops, triggers unregistering JMX beans
In our use case we're experiencing a problem with the
registration/unregistration of JMX resources with the nature of how a rebalance
is triggered while the task hasn't yet fully started and never gets stopped
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