[.net 7] Inject HostedService into another HostedService?

[AachoLoya]

I have two Services: ServiceA and ServiceB. Both derive from BackgroundService and are added as such to the builder in Program.cs

var builder = WebApplication.CreateBuilder(args);
            var config = builder.Configuration;
            builder.Services.AddHostedService<ServiceA>();
            builder.Services.AddHostedService<ServiceB>();

ServiceB needs access to ServiceA instance, so that it can queue tasks that ServiceA needs to perform. I'm trying to inject ServiceA into ServiceB, but keep getting into issues.

1. Tried constructor DI approach but it results in an exception at startup.

System.AggregateException: 'Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: Microsoft.Extensions.Hosting.IHostedService Lifetime: Singleton ImplementationType: MyProject.ServiceB': Unable to resolve service for type 'MyProject.ServiceA' while attempting to activate 'MyProject.ServiceB'.)'

2. Tried using IServiceProvider to GetService() in constructor of ServiceB and also in ExecuteAsync method of ServiceB, but in both cases, GetService returns null.

While researching, I finally came upon this answer (read last line), which seems to suggest AddHostedService instances cannot be used in DI? https://stackoverflow.com/a/74376651/934257

[AachoLoya]

Found this: https://stackoverflow.com/a/69771070/934257

This seems to be working:

builder.Services.AddSingleton<ServiceA>();
builder.Services.AddHostedService<ServiceA>(provider => provider.GetRequiredService<ServiceA>());

Is this the correct approach to ensure that a HostedService can be injected into another HostedService?

[gfoidl]

so that it can queue tasks that ServiceA needs to perform

For a different design you could use Channels, register that as singleton, and inject it in ServiceA and ServiceB. One of them produces things, the other one consumes things.
So ServiceA and ServiceB are decoupled, no need for "hacky" workarounds.

[AachoLoya]

I've used channels in this project, but need somewhat tighter coupling for certain things, so can't use Channels for this specific scenario.

[gfoidl]

Out of interest: can you share more info why this design is needed?
That coupling is IMO a bad choice -- but I don't know your requirements, so aplogize the "bad" (and I don't try to push you in another direction again 😉).
Can something like https://github.com/jbogard/MediatR work for it.

[adityamandaleeka]

Triage: we haven't had many reports of this being a problem for folks.

If we had more demand for it, we could consider making a breaking change that essentially implements that workaround in our code, but for now we don't believe that cost is worth it.

[AachoLoya]

Would be helpful, if this was added in Hosted Service or AddHostedService documentation. I had to spent hours to figure out this solution.

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[adityamandaleeka]

Would be helpful, if this was added in Hosted Service or AddHostedService documentation.

That seems reasonable. Reopening this to track updating the docs.