None of the OnXxx hooks are async-friendly

[tanveerbadar]

None of the OnXxx hooks on IRegistrationBuilder are async friendly. Here's the problem I am facing right now.

OnActivated(args =>
            {
                var context = args.Instance;
                var cts = new CancellationTokenSource();
                var token = cts.Token;
                context.Entities.RemoveRange(context.Entities);
                context.SaveAsync(token).ConfigureAwait(false).GetAwaiter().GetResult();

                context.Entities.Add(new BasicEntity { Id = 1, Name = "abc" });
                context.Entities.Add(new BasicEntity { Id = 2, Name = "def" });
                context.Entities.Add(new BasicEntity { Id = 3, Name = "ghi" });
                context.SaveAsync(token).ConfigureAwait(false).GetAwaiter().GetResult();
            }

If the idea sounds good - to add Func<T, Task> based overloads - you can assign this issue to me for implementation.

[alistairjevans]

This does somewhat line up with the async Disposal support we've just added. There is a certain symmetry to supporting async OnActivated as well.

I'm not sure if we'd want any other methods than OnActivated to be made async-friendly, because I don't think OnActivating, OnPreparing or OnReleasing should be implied to be something that can take a while to run.

One thing to bear in mind is that we probably don't want to implement a completely asynchronous chain throughout the Resolve path (that would be a pretty huge set of changes), and would suggest that Resolve generally can take a while to run.

[tillig]

I don't have any personal thoughts on this; I think it'd be a fine feature. I do think OnRelease might also need async treatment (to take advantage of async disposal in a more manual capacity, maybe). I don't know that I'd hold 5.0 up for it.