在asp.net中取消任务

Question

I have a function that generate 35 task for Calculation of invoices.

My code :

  public int CalcGroup()
        {
            try
            {
                CancellationTokenSource cts = new CancellationTokenSource();
                CancellationToken ct = cts.Token;

                for (int i = 0; i < 35 ; i++)
                {

                   var myTask = new Task<long>(() =>   CalcSingle(_personnelIds.Item1), ct, TaskCreationOptions.LongRunning);
                        myTask.Start();

                }
            }
            catch (Exception)
            {
                return 0;
            }
            return 1;
        } 

"CalcSingle() is another function that tasks working on it." and my event for cancel the tasks is :

 protected void btnStopCalc_Click(object sender, EventArgs e)
        {                             
            CancellationTokenSource cts = new CancellationTokenSource();
            cts.Cancel();
         }

It is not working correctly

Answer 1

An excerpt from MSDN:

"A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. An object creates a cancellation token by using a CancellationTokenSource, and then passes the cancellation token to any number of threads or objects that should receive notice of cancellation. The token cannot be used to initiate cancellation. When the owning object calls Cancel on the CancellationTokenSource, the IsCancellationRequested property on every copy of the cancellation token is set to true. The objects that receive the notification can respond in whatever manner is appropriate."

The point is that cancelling via a token only sets the "IsCancelled" property to true, your code in "CalcSingle" needs to poll that property after whatever logical steps in the code and exit gracefully. This is done because .Net does not know whether your code is doing something critical and cancelling a task arbitrarily might leave your execution in a bad state.

look at: https://msdn.microsoft.com/en-us/library/dd997289(v=vs.110).aspx

and this for a good example on how to do it for tasks (TPL): https://msdn.microsoft.com/en-us/library/dd997396(v=vs.110).aspx