Chris Egerton created KAFKA-8304:
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Summary: Connect susceptible to deadlock while registering REST
extensions
Key: KAFKA-8304
URL: https://issues.apache.org/jira/browse/KAFKA-8304
Project: Kafka
Issue Type: Bug
Components: KafkaConnect
Affects Versions: 2.1.1, 2.2.0, 2.0.2, 2.3.0, 2.1.2, 2.2.1
Reporter: Chris Egerton
Assignee: Chris Egerton
As part of KAFKA-7503, the {{ConnectClusterStateImpl}} class was altered to use
a {{HerderProvider}} instance instead of a {{Herder}}. However, the Connect
{{RestServer}} registers REST extensions before a herder is given to that
{{HerderProvider}}, so any extensions that invoke, e.g.,
{{ConnectClusterState.connector()}} in their {{register(...)}} method end up in
a deadlock that eventually causes Connect startup to fail with the error
message "Timed out waiting for herder to be initialized."
If possible, the {{HerderProvider}} used for {{ConnectClusterStateImpl}}
instances given to REST extensions should be supplied with a {{Herder}} before
those extensions are registered. If that isn't feasible, another option could
be to install Connect REST extensions on a separate thread so that they don't
block the Connect startup process and eventual call of
{{HerderProvider.setHerder(...)}}.
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