Hands-On Parallel Programming with C# 8 and .NET Core 3

Registering for a request cancellation using the Callback delegate

This approach makes use of a Callback delegate that gets invoked when the cancellation is requested by the underlying token. We should use this with operations that are blocked in a way that makes it not possible to check the value of CancellationToken in a regular fashion.

Let's have a look at the following code, which downloads files from a remote URL:

private static void DownloadFileWithoutToken(){    WebClient webClient = new WebClient();    webClient.DownloadStringAsync(new      Uri("http://www.google.com"));    webClient.DownloadStringCompleted += (sender, e) =>      {        if (!e.Cancelled)          Console.WriteLine("Download Complete.");        else          Console.WriteLine("Download Cancelled.");     };}

As you ...