[.net 7] Inject HostedService into another HostedService?

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’.)’

1. Tried using IServiceProvider to GetService<ServiceA>() 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]

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

[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.