If you want a set-once static instance property, and for calling threads to block until it's set...

ServiceLocator.cs

public static class ServiceLocator
{

    static readonly TaskCompletionSource<IContainer> __container = new TaskCompletionSource<IContainer>();

    public static IContainer Instance {
        get => __container.Task.Result;
        set => __container.SetResult(value);
    }

}