我的IsCancellationRequested值在token.cancel（）之后不会更改。

Question

我正在尝试使用asp：fileupload上传多个文件（C＃，asp.net），并且我希望此过程在单独的线程上执行，并且能够通过单击“取消”按钮来停止该过程，因此我创建了新任务我确实在单独的线程上执行，但是当我将此行放入取消代码tokenSource.Cancel（）时， 如果（tokenSource。IsCancellationRequested）仍然为false，则该过程将持续到结束且不会停止，这是代码：

>

  private CancellationTokenSource tokenSource= new CancellationTokenSource();
    private CancellationToken token;
    protected void submitupload_Click(object sender, EventArgs e)
    {
        fileCollection = Request.Files;
        string confirmValue = Request.Form["confirm_value"];
        if (confirmValue == "Yes" && Selected_folder_name.SelectedIndex > 0)
        {   
            if (FileUpload.HasFile)
               {
                tokenSource = new CancellationTokenSource();
                token = tokenSource.Token;
                Task.Factory.StartNew(() =>
                     {
                       int count = 0;
                       while (!tokenSource.Token.IsCancellationRequested && 
                               count<fileCollection.Count)
                         {
                           HttpPostedFile uploadfile = fileCollection[count];
                        String fileName = Path.GetFileName(uploadfile.FileName);
                 string fileExxtension = Path.GetExtension(uploadfile.FileName);
                 uploadfile.SaveAs(Chosen_Site_Path + @"\" 
       +Selected_folder_name.SelectedItem.Text + @"\" + fileName);
                   count++;
                     }
                  }, token);

                }               
            }
    }
     protected void cancelupload_Click(object sender, EventArgs e)
    {
       tokenSource.Cancel();
    }