This is somewhat unrelated to the discussion about how to actually do
the triggering when sources shut down, I'll write on that separately. I
just wanted to get this quick thought out.
For letting operators decide whether they actually want to wait for a
final checkpoint, which is relevant at least for Async I/O and
potentially for sinks.
We could introduce an interface, sth like `RequiresFinalization` or
`FinalizationListener` (all bad names). The operator itself knows when
it is ready to completely shut down, Async I/O would wait for all
requests, sink would potentially wait for a given number of checkpoints.
The interface would have a method like `isFinalized()` that the
framework can call after each checkpoint (and potentially at other
points)
This way we would decouple that logic from things that don't actually
need it. What do you think?
Best,
Aljoscha
