[API Proposal]: AutoActivation should support async initialization

[alrz]

Background and motivation

If you are using auto activation you would likely need some logic to run upon activation that could potentially require async code.

API Proposal

namespace Microsoft.Extensions.DependencyInjection;

public interface IAsyncAutoActivation : IAsyncDisposable 
{
    Task OnActivationAsync(); 
}

API Usage

class MySingleton : IAsyncAutoActivation { .. }

services.AddActivatedSingleton<MySingleton>();

Additional considerations

Async activations should not block each other, that is, they would run concurrently.

There's also the question of how to handle failed tasks which I think it should prevent the application from running.

[joperezr]

Thanks for the proposal @alrz.

Can you share more around an example scenario of when you think this would be useful?

Tagging @mobratil who is one of the owners of this area.

[alrz]

An example would be some broker subscription, something like:

class Subscription(IMessageBus bus) : IAsyncAutoActivation
{
  public async Task OnActivationAsync() {
    _subscription = await bus.SubscribeAsync(...);
  }
  public async ValueTask DisposeAsync() {
    await _subscription.UnsubscribeAsync()
  }
}

(there's definitely more use cases out there because I've seen requests for async init/dispose for injected services but I don't have reference at hand right now, perhaps some would also involve scoped registrations but I'm not sure this package is the right place to implement that)