[API Proposal]: Startup activation of singletons #86075
Description
Background and motivation
Currently, singleton dependencies are resolved at runtime when they are first requested. This could be an issue for response times and one might want them to be ready when the application starts. Another scenario is when the creation of a singleton should not block multiple requests that could be executed in parallel and be blocked (thundering herd).
The proposal is to create new extension methods that will allow to register auto-activated dependencies. Internally it would use a specifically crafted IHostedService that would resolve them preemptively.
API Proposal
namespace Microsoft.Extensions.DependencyInjection;
public static class AutoActivationExtensions
{
public static IServiceCollection Activate<TService>(this IServiceCollection services)
where TService : class
public static IServiceCollection AddActivatedSingleton<TService, TImplementation>(this IServiceCollection services, Func<IServiceProvider, TImplementation> implementationFactory)
where TService : class
where TImplementation : class, TService
public static IServiceCollection AddActivatedSingleton<TService>(this IServiceCollection services, Func<IServiceProvider, TService> implementationFactory)
where TService : class
public static IServiceCollection AddActivatedSingleton<TService>(this IServiceCollection services)
where TService : class
public static IServiceCollection AddActivatedSingleton(this IServiceCollection services, Type serviceType)
public static IServiceCollection AddActivatedSingleton<TService, TImplementation>(this IServiceCollection services)
where TService : class
where TImplementation : class, TService
public static IServiceCollection AddActivatedSingleton(this IServiceCollection services, Type serviceType, Func<IServiceProvider, object> implementationFactory)
public static IServiceCollection AddActivatedSingleton(this IServiceCollection services, Type serviceType, Type implementationType)
public static void TryAddActivatedSingleton(this IServiceCollection services, Type serviceType)
public static void TryAddActivatedSingleton(this IServiceCollection services, Type serviceType, Type implementationType)
public static void TryAddActivatedSingleton(this IServiceCollection services, Type serviceType, Func<IServiceProvider, object> implementationFactory)
public static void TryAddActivatedSingleton<TService>(this IServiceCollection services)
where TService : class
public static void TryAddActivatedSingleton<TService, TImplementation>(this IServiceCollection services)
where TService : class
where TImplementation : class, TService
public static void TryAddActivatedSingleton<TService>(this IServiceCollection services, Func<IServiceProvider, TService> implementationFactory)
where TService : class
}API Usage
// Registers and auto-activates a class
builder.Services.AddActivatedSingleton<WindowsCounters>();
// Auto-activates a pre-registered singleton. If the service is not registered, System.InvalidOperationException is thrown.
builder.Services.AddSingleton<IFakeService, FakeService>().Activate<IFakeService>());Alternative Designs
User can already get this behavior by using available components: IHostedService.
Risks
No response