using System;

using System.Reactive.Linq;

using System.Threading.Tasks;

​

public class Program

{

    public static async Task Main()

    {

        var sequence = Observable

            .Create<int>(async (observer, ct) =>

            {

                observer.OnNext(1);

                observer.OnNext(2);

                await Task.Delay(500, ct);

                observer.OnError(new Exception());

            })

            .Select(x => Observable.FromAsync(async (ct) =>

            {

                Console.WriteLine($"Item {x} started");

                try { await Task.Delay(1000, ct); }

                catch (OperationCanceledException) { Console.WriteLine($"Item {x} aborted"); throw; }

                Console.WriteLine($"Item {x} finished");

                return x;

            }))

            .Concat()

            //.Merge(1)

            .Do(x => Console.WriteLine($"Received: {x}"));

​

        try { await sequence.DefaultIfEmpty(); }

        catch (Exception ex) { Console.WriteLine($"Await failed ({ex.Message})"); }

​

        await Task.Delay(200);

    }

}

​