CurrentThreadScheduler allows cancellation of recursive or iterative observables without concurrency.

CurrentThreadScheduler

using System;
using System.Reactive.Concurrency;
using System.Reactive.Linq;

namespace ConsoleApplication1
{
  class Program
  {
    static void Main()
    {
      using (Observable.Range(0, 100, CurrentThreadScheduler.Instance)
                       .Do(x => Console.WriteLine("Generated: {0}", x))
                       .Take(10)
                       .Subscribe(x => Console.WriteLine("Observed: {0}", x)))
      {
        Console.ReadKey();
      }
    }
  }
}

Output:

Generated: 0
Observed: 0
Generated: 1
Observed: 1
Generated: 2
Observed: 2
Generated: 3
Observed: 3
Generated: 4
Observed: 4
Generated: 5
Observed: 5
Generated: 6
Observed: 6
Generated: 7
Observed: 7
Generated: 8
Observed: 8
Generated: 9
Observed: 9

Try this:

Observable.Range(0, 100, CurrentThreadScheduler.Instance)
.Do(x => Console.WriteLine("Generated: {0}", x))
.Take(10)
.Subscribe(x => Console.WriteLine("Observed: {0}", x))
.Dispose();

it still output 10 values, so there wasn't a chance to dispose it.
I found it works due internal Sink usage. I couldn't implement my own Take without it.
Can you implement Take() without Rx's internals?

Sorry, my bad. I understand the reason. Forget my question =)