1     /// 
 2     /// 任务扩展，传入取消操作 3     /// 
 4     public static class TaskExtensionDemo 5     { 6         //因为没有非泛型的TaskCompleteSource类 7         private struct Void { } 8  9         public static async Task
     
       WithCancellation
      
       (this Task
       
         originalTask, CancellationToken cancellationToken)10         {11             var cancelTask = new TaskCompletionSource
        
         ();12 13             // 注册一个将在取消此 System.Threading.CancellationToken 时调用的委托。14             using (cancellationToken.Register(t => ((TaskCompletionSource
         
          )t).TrySetResult(new Void()), cancelTask))15             {16                 Task any = await Task.WhenAny(originalTask, cancelTask.Task);17 18                 if (any == cancelTask.Task)19                 {20                     cancellationToken.ThrowIfCancellationRequested();21                 }22             }23 24             return await originalTask;25         }26 27         public static async Task Go()28         {29             //在指定的延迟（以毫秒为单位）后将被取消。30             var cts = new CancellationTokenSource(5000);31             var ct = cts.Token;32 33             try34             {35                 Task
          
            t = new Task
           
            (() =>36 {37 //Task.Delay不阻塞线程，任务不会被取消（5秒后早执行完了）38 //Task.Delay(10000);39 40 //阻塞线程，10秒后收到取消通知41 Thread.Sleep(10000);42 return 0;43 });44 t.Start();45 46 //调用扩展方法取消任务47 await t.WithCancellation(ct);48 49 Console.WriteLine("Task completed");50 }51 catch (OperationCanceledException)52 {53 Console.WriteLine("Task cancelled");54 }55 }56 }