David Glasser created KAFKA-6905:
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Summary: Document that Processor objects can be reused
Key: KAFKA-6905
URL: https://issues.apache.org/jira/browse/KAFKA-6905
Project: Kafka
Issue Type: Improvement
Components: documentation, streams
Reporter: David Glasser
We learned the hard way that Kafka Streams will reuse Processor objects by
calling init() on them after they've been close()d. This caused a bug in our
application as we assumed we didn't have to reset all of our Processor's state
to a proper starting state on init().
As far as I can tell, this is completely undocumented. The fact that we provide
Processors to Kafka Streams via a ProcessorSupplier factory rather than just by
passing in a Processor object made it seem likely that in fact Streams was
creating Processors from scratch each time it needed a new one.
The developer guide
([https://docs.confluent.io/current/streams/developer-guide/processor-api.html)]
doesn't even allude to the existence of the close() method, let alone the idea
that init() may be called after close().
The Javadocs for Processor.init says: "The framework ensures this is called
once per processor when the topology that contains it is initialized." I
personally interpreted that as meaning that it only is ever called once! I can
see that you could interpret it otherwise, but it's definitely unclear.
I can send a PR but first want to confirm that this is a doc problem and not a
bug!
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