Is there a Rx.Net Operator that tells the number of subscribed observers? - system.reactive

Question

I am trying to debug if I am correctly disposing the observers to a long running services (services exposing IObservable). And I am wondering if there an operator or something that we can create to log the number of active observers, say something like.
public class NewsService
{
IObservable<Article> GetArticles();
}
NewsService.Instance
.GetArticles()
.DoCount(x=> Trace.Writeline("The current count is {x}"))
.Subscribe();
There is a solution proposed here, which works on the Subject. What if we don't have access to the Subject and a library is exposing IObservable.

Answer 1

Generally speaking, the concept of subscriber count for an arbitrary observable sequence is not defined.
For cold observables such as Observable.Interval, every time you subscribe to the observable, a new pipeline instance is created, which - from its point of view sees only a single observer at a time.
We can, nonetheless, warm up a cold observable, and watch subscriptions come and go.
public static IObservable<T> RefCount<T>(this IObservable<T> source, Action<int> onChange)
{
var subscribers = 0;
var shared = source.Publish().RefCount();
void callback(int count) => onChange(Interlocked.Add(ref subscribers, count));
return Observable.Create<T>(observer =>
{
callback(+1);
var subscription = shared.Subscribe(observer);
var dispose = Disposable.Create(() => callback(-1));
return new CompositeDisposable(subscription, dispose);
});
}
Demo
var values =
Observable
.Interval(TimeSpan.FromSeconds(0.1))
.RefCount(count => Console.WriteLine($"Subscribers: {count}"));
values.Take(5).Subscribe();
values.Take(10).Subscribe();
values.Take(15).Subscribe();
Output
Subscribers: 1
Subscribers: 2
Subscribers: 3
Subscribers: 2
Subscribers: 1
Subscribers: 0
Now, this works because we have a shared view of the parent observable.
So try to make all subscriptions point to the same instance.
_articles = GetArticles().RefCount(count => Console.WriteLine($"Subscribers: {count}")));
...
_articles.Subscribe();