[State Processor API] unable to load the state of a trigger attached to a session window

[Dongwon Kim]

Hi,

I'm using Flink-1.14.4 and failed to load in WindowReaderFunction the state
of a stateful trigger attached to a session window.
I found that the following data become available in WindowReaderFunction:
- the state defined in the ProcessWindowFunction
- the registered timers of the stateful trigger attached to the session
window
- all the elements of the window
, but the state of the stateful trigger attached to the session window is
not available when using State Processor API.
In other words, the following code always returns null when used with
session windows:

>             ReducingState<Long> state =
> context.triggerState(triggerCountDesc);
>             Long val = state.get();
>
On the other hand, the above code snippet returns expected data when used
with sliding and tumbling windows.

To explain the problem, I made up an example in a similar spirit to
o.a.f.state.api.SavepointWindowReaderITCase.
Here you can find three test cases each with different types of event-time
windows: Session, Sliding, and Tumbling.
With sliding and tumbling windows, I can read the state of the trigger
attached to the windows in WindowReaderFunction.
However, with a session window, I cannot read the state of the trigger in
WindowReaderFunction.

Is it a bug, or did I miss something?

Best,

Dongwon

SavepointWindowReaderTestForDifferentWindows.java
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