Pass `duration` in `DispatchInfo`

[shsms]

What's needed?

There are dispatches that need to use the duration to decide what actions to take. For such cases, the duration of the dispatch needs to be shared in the DispatchInfo.

[llucax]

Copying my comment to the PR:

This is tricky and can be misleading. If you use the high-level interface and you are listening to the start/stop events, or your actor is managed, this duration might not match the time your actor is really running if some dispatches were merged.

I think a better approach would be to include a list of active dispatches, and just pass the full Dispatch object there. Another approach would be to pass here a "merged duration" instead of the raw duration of the current dispatch. Depending on the use case one could be more useful than the other.

[llucax]

It seems this is needed for cases where the actor needs to distribute the work evenly throughout the whole duration, but this is not trivial because the duration of one dispatch could not be the entire duration the actor will be active if dispatches are being merged.

Thinking about it, maybe it would make sense to always consider merged dispatches as one logical dispatch that gets updated. In this case we can say there is only one active dispatch (as in dispatch object, with a specific dispatch ID). This approach fits naturally, as this is a use case that actors already need to support (a dispatch that gets updated while it is running).

If we take this approach consistently across all merge strategies (open question: can we even enforce this with the current merge strategies design?), then we can always have one single active dispatch. And then I guess the DispatchInfo object can be just gone and we can send the full Dispatch object, or if we want more info it could be:

class DispatchInfo:
    active_dispatch: Dispatch
    merged_dispatches: set[Dispatch]
    total_duration: timedelta

But if we really treat merged dispatches always as if it was just one dispatch that gets updates when there is overlap, I'm not sure if knowing which dispatches were merged provide any useful information, but maybe providing the total merged duration is something that could be of use.

[llucax]

So we decided to leave the DispatchInfo as it is for now, and just add an extra attribute merged_dispatches. We'll see when we gather more experience if it makes sense to do more changes.

[Marenz]

We could additionally provide a method active_dispatch() which woudl just return the latest/highest id dispatch

[llucax]

But this would imply that we will never merge other things from the dispatch than the duration (i.e. the data in DispatchInfo won't match 1-1 any dispatch object). For now I would leave that door open, for the case we need to address right now the complete list of merged dispatches is enough (as it will only be one in that case) and it is generic enough to be useful in the future whatever decision we make with respect and we want to do/limit merging.

[Marenz]

The thing is, getting that set[] of actors is actually not that easy because it's abstracted away right at the source, so the ActorDispatcher doesn't know ,only the DispatchScheduler does.

After discussing a bit with sahas, we came to the conclusion the best short-term solution is to simply offer the original dispatch as ._src attribute for any extended scenario...