ASP.NET Core initialize singleton after configuring DI

Question

So let\'s say I have a singleton class instance that I register in the DI like this:

services.AddSingleton();

And let\'s s

Answer 1

Do it yourself during startup.

var foo = new Foo();
services.AddSingleton(foo);

Or "warm it up"

public void Configure(IApplicationBuilder app) 
{
    app.ApplicationServices.GetService();
}

or alternatively

public void Configure(IApplicationBuilder app, IFoo foo) 
{
    ...
}

But this feels just dirty and is more a problem with your design, if you do something that you shouldn't in the constructor. Class instantiation has to be fast and if you do long-running operations within it, you break against a bunch of best practices and need to refactor your code base rather than looking for ways to hack around it