[jira] [Created] (KAFKA-8217) MockConsumer.poll executes pollTasks before checking wakeup flag

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

Kevin created KAFKA-8217:
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             Summary: MockConsumer.poll executes pollTasks before checking wakeup flag
                 Key: KAFKA-8217
                 URL: https://issues.apache.org/jira/browse/KAFKA-8217
             Project: Kafka
          Issue Type: Bug
          Components: unit tests
    Affects Versions: 2.0.1
            Reporter: Kevin


The tasks scheduled in MockConsumer.schedulePollTask seem to be for simulating interactions between the Consumer and the brokers, but MockConsumer.poll runs scheduledPollTasks before it checks the wakeup flag. Given that the KafkaConsumer.poll method checks the wakeup flag before doing any other logic, it seems like the MockConsumer should rather check wakeup before running scheduledPollTasks.

This makes it difficult to control exactly how many Consumer.poll invocations occur in a unit test when using the wakeup() pattern described in "Multithreaded Processing" in the KafkaConsumer docs, as gating each poll so that it returns only when instructed in the test requires submitting a scheduledPollTask that blocks until the test unblocks it. The trouble occurs when trying to shut down the consumer, as the poll() task needs to be unblocked in order to receive the WakeupException but https://issues.apache.org/jira/browse/KAFKA-8216 means that Consumer.poll() can be called many times in the race condition interval after poll has been unblocked but before the test has called Consumer.wakeup().



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