Akka.Actor: IStash improvements - programmatic bounded stash configuration and stash capacity APIs

[Aaronontheweb]

• Add IStash APIs to track whether there's any content inside the IStash at all
• Make it possible to configure bounded stash size programmatically via Props

Is your feature request related to a problem? Please describe.

I'm working on a prototype of reliable delivery for Akka.NET #4720 over at https://github.com/Aaronontheweb/Aaron.Akka.ReliableDelivery, and stashing is pretty integral to how the ConsumerController manages confirmations for both push and pull-based deliveries.

Unfortunately, we're missing some important APIs I need to complete the job over there:

• IStash,IsEmpty - is there anything inside the stash I need to process first?
• IStash.Count - how many messages are left inside the stash?
• And finally, a programmatic way of setting a bounded stash size - this is currently not feasible to do.

Describe the solution you'd like

Expand the IStash interface to some new properties:

    public interface IStash
    {
        // existing methods

       bool IsEmpty { get; }
       
      // are we at capacity?
      bool IsFull { get; }
    
      // is Count > 0
      bool NonEmpty { get; }

       int Count { get; }
       
    }

That will help give me the ability to reason about working with bounded stashes internally inside these actors.

In addition to that, I would like to add StashSize as a property that can be set via Props on actors. That way, this can be configured programmatically or via HOCON.

cc @ismaelhamed

[Aaronontheweb]

In addition to that, I think the way Stash.Unstash works is wrong and has been wrong for nearly 10 years - it's currently a LIFO mechanism, when it should probably work as FIFO. I'm going to file a separate issue for that - but that problem will also need to be resolved before I can complete #4720.

This turned out to be wrong. I checked. Stash.Unstash is FIFO.

[Aaronontheweb]

Reopening because this issue is only half-complete.

[Aaronontheweb]

Completed