gaoyunhaii edited a comment on pull request #16432:
URL: https://github.com/apache/flink/pull/16432#issuecomment-877487310
Very thanks @tillrohrmann for the review and very thanks @StephanEwen for
the detail investigation and analysis!
I also agree with chaining the futures as @tillrohrmann suggested would be
correct and simpler . I'll update the PR according to this method very soon.
And for clarification, for the original method that used
```
sendingExecutor.execute(
() -> {
nonSuccessFuturesTrack.trackFuture(result);
sender.sendEvent(sendAction, result);
});
```
my understanding is that the order is ensured since it all happen inside the
main thread. For detail:
Based on the current implementation, actual event sending (namely
`sendingExecutor`) and
`OperatorCoordinatorHolder#checkpointCoordinatorInternal` are all happens in
the main thread. Then for all the events during checkpointing
1. `OperatorCoordinator#checkpointCoordinator`, happen in main thread, the
implementation may proxy it to the user thread.
2. submit `completeCheckpointOnceEventsAreDone` to the main thread, happen
in user thread.
3. actually execute `completeCheckpointOnceEventsAreDone`, happen in main
thread.
First with my understand now we should request the implementation of
`OperatorCoordinator` to ensure there is not event sending request between 1
and 2, otherwise both methods would have problem. Then for an event sending
request, it either happen before 1 and submit a Runnable to the main thread
before 3, or happen after 2 and submit a Runnable to the main thread after 3:
1. For the first case, `trackFuture` would happen before
`completeCheckpointOnceEventsAreDone` and considered.
2. For the second case, `trackFuture` must happen after
`completeCheckpointOnceEventsAreDone` and would not be considered.
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