Getting Dependency Injection of a hosted service

Question

I have the following code:

builder.Services.AddSingleton<IAvailabilityWorker, AvailabilityWorker>();
builder.Services.AddHostedService<AvailabilityWorker>();

There is a timer in the service with a public function void set_last_time(DateTime time)

But I can't seem to get the dependency injection working. If I inject IAvailabilityWorker into the constructor it works but the time is set for another instance besides the singleton one. Even though there shouldn't be. If I try injecting AvailabilityWorker itself, it only works if I use it without Interface

builder.Services.AddSingleton<AvailabilityWorker>();

But I need the interface registration for testing.

How can I get it working while keeping the interface tied to the implementation?

Steven · Accepted Answer · 2023-09-11 17:11:30Z

3

What you are dealing with is a problem commonly known as Torn Lifestyle. The lifestyle of AvailabilityWorker is said to be torn, because it is registered twice; once as singleton and a second time as transient. This is because AddHostedService under the covers calls AddTransient.

To ensure a single AvailabilityWorker instance to exist for the lifetime of your application, you should change the registrations to the following:

Services.AddSingleton<AvailabilityWorker>();
Services.AddSingleton<IAvailabilityWorker>(
    c => c.GetRequiredService<AvailabilityWorker>());
Services.AddSingleton<IHostedService>(
    c => c.GetRequiredService<AvailabilityWorker>());

answered Sep 11, 2023 at 17:11

Steven

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1 Comment

Foxxy Over a year ago

Thanks a lot. I had the

Services.AddSingleton<AvailabilityWorker>(); Services.AddSingleton<IHostedService>(     c => c.GetRequiredService<AvailabilityWorker>());

Pattern already but didn't know you could do it with the interface too.

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