using System;

using System.Reactive;

using System.Reactive.Linq;

using System.Threading;

using System.Threading.Tasks;

​

public class Program

{

    public static void Main()

    {

        var cts = new CancellationTokenSource(500);

        cts.Token.Register(() => Console.WriteLine("### Token Canceled! ###"));

        try

        {

            Observable

                .Timer(TimeSpan.Zero, TimeSpan.FromMilliseconds(1000))

                .TakeUntil(Observable.Create<Unit>(observer =>

                    cts.Token.Register(() =>

                    {

                        Console.WriteLine("Before observer.OnNext");

                        observer.OnNext(Unit.Default);

                        Console.WriteLine("After observer.OnNext");

                    })))

                .Select(_ =>

                {

                    return Observable.StartAsync(async () =>

                    {

                        Console.WriteLine("Action starting");

                        await Task.Delay(1000, cts.Token);

                        return 1;

                    });

                })

                .Switch()

                .Wait();

        }

        catch (Exception ex) { Console.WriteLine("Failed: {0}", ex.Message); }

        Thread.Sleep(500);

        Console.WriteLine("Finished");

    }

}

​