StephanEwen commented on pull request #11856:
URL: https://github.com/apache/flink/pull/11856#issuecomment-619636516
The changes look fine to me, +1 to merge this.
Maybe some comments for separate improvements, as follow-ups:
- The use of `AtomicBoolean` is a bit confusing. It looks like these are
mainly `volatile boolean` to report status with a `happens-before`
ordering/visibility.
- The whole "interrupting"-based flow control is difficult to follow, and
I believe very difficult to get right. One interrupt flag clearing/setting can
make the difference between correctness, a deadlock, or a "hot loop lock". And
the interrupt flags are hellishly hard to reason about, especially because they
can be mutated by any component outside the fetcher.
One way to solve this is by turning the fetch queue into a "wakeup-able
queue". That pulls a good amount of the the wakeup logic out of the fetcher
class, making that one easier to read and to test. The
[Handover](https://github.com/apache/flink/blob/master/flink-connectors/flink-connector-kafka/src/main/java/org/apache/flink/streaming/connectors/kafka/internal/Handover.java)
in the current KafkaConsumer is like a "wakeup-able size-one queue", as an
example. We probably need something slightly different (wake up consumer of the
queue). A simple notify/wait implementation is quite straightforward, and if we
have time we can make this more efficient with Java's `LockSupport` classes.
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