[jira] [Created] (KAFKA-6905) Document that Processor objects can be reused

["David Glasser (JIRA)" <ji...@apache.org>]

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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