Correct way to start a BackgroundService in ASP.NET Core

Question

I have implemented a BackgroundService in an ASP.NET Core 2.1 application:

public class MyBackgroundService : BackgroundService
{
    protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (true)
        {
            await DoSomethingAsync();
            await Task.Delay(10 * 1000);
        }
        return Task.CompletedTask;
    }
}

I have registered it in my ConfigureServices() method:

services.AddSingleton<MyBackgroundService>();

I am currently (reluctantly) starting it by calling (and not awaiting) the StartAsync() method from within the Configure() method:

app.ApplicationServices.GetService<SummaryCache>().StartAsync(new CancellationToken());

What is the best practice method for starting the long running service?

@junnas This unfortunately appears out of date (ASP.NET 2.0 preview before BackgroundService was made available) and it doesn't explain how to make a service start without explicitly invoking StartAsync() — Creyke
– Creyke, Commented Oct 19, 2018 at 12:06
I implemented a background service using Steve Gordon's approach that runs on 2.2 preview 2 though? — juunas
– juunas, Commented Oct 19, 2018 at 12:28
By default, after registering services.AddSingleton<MyBackgroundService>();, it will start when application start, there is no need to call StartAsync() expecitly from your own code. — Edward
– Edward, Commented Oct 22, 2018 at 7:22
Is there any way to stop the background service starting automatically and instead start on demand? — Simon Gymer
– Simon Gymer, Commented Feb 27, 2020 at 9:38

Cosmin Sontu · Accepted Answer · 2019-02-07 17:12:51Z

29

Explicitly calling StartAsync is not needed.

Calling

services.AddSingleton<MyBackgroundService>();

won't work since all service implementations are resolved via DI through IHostedService interface. edit: e.g. svcProvider.GetServices<IHostedService>() -> IEnumerable<IHostedService>

You need to call either:

services.AddSingleton<IHostedService, MyBackgroundService>();

or

services.AddHostedService<MyBackgroundService>();

edit: AddHostedService also registers an IHostedService: https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.dependencyinjection.servicecollectionhostedserviceextensions.addhostedservice?view=aspnetcore-2.2

edited Feb 7, 2019 at 17:12

answered Feb 4, 2019 at 5:46

Cosmin Sontu

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2 Comments

Cosmin Sontu Over a year ago

* to discover all background services to be run, the framework relies on DI and would call servcies.GetServcies<IHostedService>() which yields IEnumerable<IHostedServcie>. This resolves your service if you register via the Interface. .AddHostedService<T>() does exactly that (learn.microsoft.com/en-us/dotnet/api/…)

Saher Ahwal Over a year ago

what if for test purposes I want to create multiple instances of background services dynamically based on web API call? then can I call StartAsync?

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