http://xin9le.blogspot.jp/2011/08/tpl-13.html を外からキャンセルするかどうか指定できるように

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;
using System.Collections.Concurrent;

namespace ConsoleApplication1
{
  class Program
  {
    static void Main()
    {
      var source = new CancellationTokenSource();
      var token = source.Token;
      var task = new Task(() =>
      {
        Console.WriteLine("Task : Begin");
        foreach (var item in Enumerable.Range(0, 20))
        {
          Thread.Sleep(100);
          token.ThrowIfCancellationRequested();
        }
        Console.WriteLine("Task : End");
      });
      task.Start();
      Thread.Sleep(2000);
      if (Console.ReadKey().Key == ConsoleKey.C)
      {
        Console.WriteLine("press cancel key");
        source.Cancel();
      }
      try
      {
        task.Wait();
      }
      catch (AggregateException exception)
      {
        foreach (var inner in exception.InnerExceptions)
        {
          Console.WriteLine(inner.Message);
          Console.WriteLine("Type : {0}", inner.GetType());
        }
      }
    }
  }
}