1. 操作取消

1.1 步骤

• 实例化 CancellationTokenSource 对象，该对象管理取消通知并将其发送给单个取消标记
• 将 CancellationTokenSource.Token 属性返回的标记传递给每个侦听取消的任务或线程
• 为每个任务或线程提供响应取消的机制
  
  if (token.IsCancellationRequested)
• 调用 CancellationTokenSource.Cancel 方法以提供取消通知

1.2 代码示例

using System;

using System.Threading;

public class Example

{

   public static void Main()

   {

      CancellationTokenSource cts = new CancellationTokenSource();

      ThreadPool.QueueUserWorkItem(new WaitCallback(DoSomeWork), cts.Token);

      Thread.Sleep(2500);

      cts.Cancel();

      Console.WriteLine("Cancellation set in token source...");

      Thread.Sleep(2500);

      cts.Dispose();

   }

   static void DoSomeWork(object obj)

   {

      CancellationToken token = (CancellationToken)obj;

      for (int i = 0; i < 100000; i++)

      {

         if (token.IsCancellationRequested)

         {

            Console.WriteLine("在 i 为 {0} 时, 监听到 cancellation", i);

            break;

         }

         Thread.SpinWait(500000);

      }

   }

}

// 上诉例子输出：

//    Cancellation set in token source...

//    In iteration 1935, cancellation has been requested...

2. 对象取消

类似于事件的订阅和触发

using System;

using System.Threading;

class CancelableObject

{

   public string id;

   public CancelableObject(string id)

   {

      this.id = id;

   }

   public void Cancel()

   {

      Console.WriteLine("Object {0} Cancel callback", id);

   }

}

public class Example

{

   public static void Main()

   {

      CancellationTokenSource cts = new CancellationTokenSource();

      CancellationToken token = cts.Token;

      var obj1 = new CancelableObject("1");

      var obj2 = new CancelableObject("2");

      token.Register(() => obj1.Cancel());

      token.Register(() => obj2.Cancel());

      cts.Cancel();

      cts.Dispose();

   }

}

// 上诉将输出:

//    Object 2 Cancel callback

//    Object 1 Cancel callback