Only the first of multiple hosted services is being started

Question

I am trying to figure out how to make ASP.NET Core 3.1 start more than a single hosted service so I can run some stuff periodically in the background. I've read a ton of similar questions (e.g., this one) and as far as I understand it's important to return the task from StartAsync() immediately. That's also how StartAsync() from the BackgroundService class is implemented.

However, even if I reduce my own code to the bare minimum, only the first service that gets registered is being executed (read: correctly started and stopped when shutting down the server):

type Foo() =
    interface IHostedService with
        member this.StartAsync ct =
            printfn "Start Foo"
            Task.CompletedTask
            
        member this.StopAsync ct =
            printfn "Stop Foo"
            Task.CompletedTask
            
type Bar() =
    interface IHostedService with
        member this.StartAsync ct =
            printfn "Start Bar"
            Task.CompletedTask
            
        member this.StopAsync ct =
            printfn "Stop Bar"
            Task.CompletedTask

let configureServices (services : IServiceCollection) =
    services
        .AddHostedService<Foo>()
        .AddHostedService<Bar> |> ignore

When the application is started, this results in:

watch : Started
Start Foo
info: Microsoft.Hosting.Lifetime[0]
      Now listening on: http://[::]:5000
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Production
info: Microsoft.Hosting.Lifetime[0]
^Cwatch : info: Microsoft.Hosting.Lifetime[0]
      Application is shutting down...
Shutdown requested. Press Ctrl+C again to force exit.
Stop Foo
watch : Exited

So my question is: Did I hit a bug, or do I miss something?

Sven-Michael Stübe · Accepted Answer · 2020-10-26T23:11:50.657

I think you need to call the function

AddHostedService<Bar>() instead of AddHostedService<Bar>

let configureServices (services : IServiceCollection) =
     services
         .AddHostedService<Foo>()
         .AddHostedService<Bar>() |> ignore

Output:

Start Foo
Start Bar
info: Microsoft.Hosting.Lifetime[0]
      Now listening on: http://localhost:5000
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Development
info: Microsoft.Hosting.Lifetime[0]

Only the first of multiple hosted services is being started

1 Answers1