AddHostedService() registers service as Transient in the 2.1.1 apart from the 2.0

Hello.

According to the documentation for the 2.0 https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-2.0#timed-background-tasks We have to register services as Singleton

According to the documentation for the 2.1 https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-2.1#timed-background-tasks We should use the AddHostedService extension which is Transient under the hood now: https://github.com/aspnet/Hosting/blob/master/src/Microsoft.Extensions.Hosting.Abstractions/ServiceCollectionHostedServiceExtensions.cs#L18

So my questions are:

1. Can it be a problem and why have you changed the lifetime?
2. What should I do If I have one more interface to reach the the service from the DI? Right now I’m doing the following: Register custom interface as singleton: services.AddSingleton<ICandleSubscriptionHostedService, CandleSubscriptionHostedService>(); Use the custom resolver for the IHostedService registration: services.AddSingleton<IHostedService, CandleSubscriptionHostedService>(provider => (CandleSubscriptionHostedService) provider.GetRequiredService<ICandleSubscriptionHostedService>()); Both are Singletons so the second lifetime doesn’t matter a lot actually.

Thank you!

[Drawaes]

Agreed but the naming is not great. I suspect when most people hear service they equate it to Singleton… I sure did and it caught me out.

[davidfowl]

I’m saying don’t implement the interface on the IHostedService itself. Here’s an example of a queue:

public interface IQueue<T>
{
    T Dequeue();
    void Enqueue(T item);
}

public class QueueHostedService : IHostedService
{
     public QueueHostedService(IQueue<WorkItem> queue)
     {
     }

     // Write code to Dequeue from the queue and perform some work
}


public class HomeController : Controller
{
     private readonly IQueue<WorkItem> _queue;
     public HomeController(IQueue<WorkItem> queue)
     { 
          _queue = queue;
     }
     
     [Route("/item")]
     public IActionResult Post(WorkItem item)
     {
           _queue.Enqueue(item);
     }
}

In this example, you could implement the IQueue<WorkItem> on the QueueHostedService, or you can implement it on another type that the QueueHostedService uses.