参考：http://www.cnblogs.com/scy251147/archive/2013/01/04/2843875.html

1. static
   void TaskWithCancellation()
2. {
3.     var cancellationTokenSource = new CancellationTokenSource();
4.     var cancellationToken = cancellationTokenSource.Token; //主要用于任务取消操作的信号量设置
5.  
6.     Task t = new Task(() =>
7.     {
8.         int i = 0;
9.         while (true)
10.         {
11.             i++;
12.             Thread.Sleep(1000);
13.             Console.WriteLine("this is task iteration " + i);
14.  
15.             //注册信号量，如果用户取消，那么将会中断在此处
16.             cancellationToken.ThrowIfCancellationRequested();　
17.  
18.             Console.WriteLine("Test to see if below can be excuted...");
19.             Console.WriteLine("I am not excute");
20.         }
21.     }, cancellationToken);
22.  
23.     t.Start();　　//开始任务
24.  
25.     Thread.Sleep(1000);
26.  
27.     cancellationTokenSource.Cancel();　//取消任务
28.  
29.     try
30.     {
31.         t.Wait();
32.     }
33.     catch (AggregateException e)
34.     {
35.         if (e.InnerException is OperationCanceledException)
36.             Console.WriteLine("the opeartion has been canceled...");
37.         else
38.             Console.WriteLine("encounter some unexpected exceptions...");
39.     }
40. }