[Bug]: Triggers with session window not working

[boolangery]

What happened?

Unable to trigger early firings with a session window.

Tried triggers:

windowedUpdates := beam.WindowInto(s,
	window.NewSessions(30*time.Second), propUpdates,
	beam.Trigger(trigger.Repeat(trigger.AfterCount(500))),
	beam.Trigger(trigger.Repeat(trigger.AfterProcessingTime().PlusDelay(60*time.Second))),
	beam.PanesDiscard(),
)

windowedUpdates := beam.WindowInto(s,
	window.NewSessions(30*time.Second), propUpdates,
	beam.Trigger(trigger.AfterEndOfWindow().EarlyFiring(trigger.AfterProcessingTime().PlusDelay(60*time.Second))),
	beam.PanesDiscard(),
)

Context:

• Streaming pipeline
• PubSub input
• Printing output after a groupBy
• Sending one message every second

Result: The window extend indefinitely and no panes are fired

Issue Priority

Priority: 3 (minor)

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[lostluck]

The first one is incorrect, and should be a failure at construction time since two triggers are being specified.

The second one, I would expect it to work though, but triggers with merging Windows are pretty complicated... I agree that it doesn't match with my intuition which would be the merge is supposed to take the earlier of the two "first element times", rather than the later of them...

Which does appear to be the implementation, but it's possible the timer that is being set isn't mapping back to the newly merged window... (which doesn't seem right). Hard to say offhand unless we validate the equivalent outside of Go. There could be some other issue.

Possibly related to #31153, but this feels like a runner side issue.