[jira] [Created] (KAFKA-14972) Make KafkaConsumer usable in async runtimes

["Erik van Oosten (Jira)" <ji...@apache.org>]

Erik van Oosten created KAFKA-14972:
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             Summary: Make KafkaConsumer usable in async runtimes
                 Key: KAFKA-14972
                 URL: https://issues.apache.org/jira/browse/KAFKA-14972
             Project: Kafka
          Issue Type: Wish
          Components: consumer
            Reporter: Erik van Oosten


KafkaConsumer contains a check that rejects nested invocations from different threads (method {{{}acquire{}}}). For users that use an async runtime, this is an almost impossible requirement. Examples of async runtimes that are affected are Kotlin co-routines (see KAFKA-7143) and Zio.

We propose to replace the thread-id check with an access-id that is stored on a thread-local variable. Existing programs will not be affected. Developers that work in an async runtime can pick up the access-id and set it on the thread-local variable in a thread of their choosing.

Every time a callback is invoked a new access-id is generated. When the callback completes, the previous access-id is restored.

This proposal does not make it impossible to use the client incorrectly. However, we think it strikes a good balance between making correct usage from an async runtime possible while making incorrect usage difficult.

Alternatives considered:
 # Configuration that switches off the check completely.



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