Add support for actor reminders

[sebastianburckhardt]

When writing samples it became clear that there are situations where an actor wants to send itself a message with a time delay.

I believe we should support this, perhaps by adding a method along the lines of

ctx.ScheduleOperation(TimeSpan delay, string operationName, object operationContent);

[cgillum]

Agreed, this would be good to have.

[olitomlinson]

This is a very desirable feature of an Actor!

While your in the design phase, it might be worth checking out Service Fabric Actor Timers & Reminders for some inspiration!

https://docs.microsoft.com/en-us/azure/service-fabric/service-fabric-reliable-actors-timers-reminders

[sebastianburckhardt]

(BTW, based on feedback we renamed actor to entity - just a new name, same thing.)

After going through a few designs my plan is to support as a more general feature which allows an optional scheduleAtUtc argument to all the SignalEntity functions:

ctx.SignalEntity(entityId, operationName, operationInput, scheduleAtUtc);

Then a "reminder" requirement can be implemented by having an entity send a signal to itself, scheduled for some time in the future, e.g.:

ctx.SignalEntity(ctx.Self, operationName, operationInput, DateTime.UtcNow + TimeSpan.FromSeconds(30));

I ran into a gating issue Azure/durabletask#285 so I'll probably delay work on this for a while.

[cgillum]

@sebastianburckhardt The underlying blockers have been resolved for this work item. Do you think you can resume working on it and have it in for beta3? I have a use case for it that I'd like to try out. :)

[sebastianburckhardt]

Yes, I have already resumed work on this. Currently in the debugging stage... some things are still not quite working as expected inside DTFx, when combining timers and ContinueAsNew.