CoroutineProgram.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;

namespace AsyncKonsole
{
  class Program
	{
		static string htmlBlogspot;
		static string htmlGoogle;
		
		public static void Main(string[] args)
		{
			Coroutine.BeginExecute(MultipleRoutines());			
			Console.ReadLine();
		}
		
		static IEnumerable<Routine> MultipleRoutines() {			
			yield return FirstRoutine;			
			
			if (htmlBlogspot.Length < 1000) {
				Console.WriteLine(htmlBlogspot);
				yield break;
			}
			
			//executa e aguarda a segunda operação
			yield return SecondRoutine;
			
			//imprime quando estiver pronto
			Console.WriteLine(htmlGoogle);
		}
		
		static void FirstRoutine(Action completed) {
			var webClient1 = new WebClient();
			
			webClient1.DownloadStringCompleted += (s1,e1) => {
				htmlBlogspot = e1.Result;
				completed();
			};
			webClient1.DownloadStringAsync(new
				Uri("http://silverlightrush.blogspot.com"));			
		}
		
		static void SecondRoutine(Action completed) {
			var webClient2 = new WebClient();
			webClient2.DownloadStringCompleted += (s2, e2) => {
				htmlGoogle = e2.Result;
				completed();
			};
			webClient2.DownloadStringAsync(new Uri("http://google.com"));
		}
	}

	public delegate void Routine(Action callback);

	public static class Coroutine {
		public static void BeginExecute(this IEnumerable<Routine> enumerable) {
			Continue(enumerable.GetEnumerator());
		}

		static void Continue(IEnumerator<Routine> enumerator) {
			if (!enumerator.MoveNext()) {
				enumerator.Dispose();
			} else {
				var routine = enumerator.Current;
				routine.Invoke(() => Continue(enumerator));
			}
		}
	}
}