Task加入取消功能

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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. }