IOptionsSnapshot is not working with singleton services

[aspnet-hello]

From @ductrantb on Thursday, December 14, 2017 12:42:32 AM

Hi friends,
I have a problem with IOptionsSnapshot. I was tried to use BackgroundServiceManagerConfigsFactory as a transient service to renew configs on change.

services.AddTransient<BackgroundServiceManagerConfigsFactory, BackgroundServiceManagerConfigsFactory>();
services.AddSingleton<BackgroundServiceManager, BackgroundServiceManager>();

The constructor of my configs factory was called on every request (by singleton service), but configs value was not changed.

public BackgroundServiceManagerConfigs Configs { get; protected set; }
public BackgroundServiceManagerConfigsFactory(IOptionsSnapshot<BackgroundServiceManagerConfigs> options)
{
        Configs = options.Value;
}

I tried to call this factory in a controller, it worked.
I used netcore 2.0 and Microsoft.Extensions.Options version 2.0.0.0
Thank you.

Copied from original issue: aspnet/Options#247

[clairernovotny]

IOptionsSnapshot provides access to the Get method to provide access to named options. These should be available from Singleton services.

[ajcvickers]

@HaoK Your thoughts on this?

[HaoK]

IOptionsFactory's registered as transient, so you will get one every time, perhaps there's an issue with scopes in your app, BackgroundService tends to make it sound like something that lives across requests? Can you include more code/details about how you've registered all the various pieces of your app?

[clairernovotny]

@HaoK The core issue is that I have a service that needs named config. It should be a singleton since it has no state.

I can get an IOptions<T> to get config, but not an IOptionsSnapshot<T> since IOptionsSnapshot<T> is registered as scoped.

A singleton cannot get an instance of a scoped service (but it can of a transient one since transient returns a new instance each time).

Right now, both IOptions<T> and IOptionsSnapshot<T> are implemented by the same type OptionsManager<T>. While that could change, it seems like the only real difference is that the Get method required to access a named instance is only exposed on IOptionsSnapshot<T> despite being available in the implementation class for IOptions<T>.

The hole here is that there's no easy way for a singleton object to get to a named configuration object due to this.

[HaoK]

Just use IOptionsMonitor, that's what you are looking for. Closing this issue since IOptionsSnapshot is not intended to be used from singleton services.