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  1. Kafka
  2. KAFKA-6905

Document that Processor objects can be reused

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    Details

    • Type: Improvement
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 2.0.0
    • Component/s: documentation, streams
    • Labels:
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      Description

      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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            • Assignee:
              glasser David Glasser
              Reporter:
              glasser David Glasser
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