The document discusses async programming in .NET using the Async CTP. It explains that async programming is important for multicore processing and handling asynchronous operations like web requests without blocking the UI. The Async CTP allows writing async code using the async and await keywords in C# and VB.NET to simplify asynchronous calls and avoid callbacks. It provides an example of asynchronously downloading and parsing RSS feed XML and compares the old callback-based approach to the new async approach.

1. Async CTP

2. .NET Software engineerEmailkristof@kristofmattei.bekristof.mattei@ordina.beWebsitewww.kristofmattei.beTwitter@Snakiej

3. Why do asynchronous programming?2 reasons: We’re living in a multicore worldOffload work to other processorsWe’re living in a async worldThings take timeWe don’t want the user’s UI to be blocked when we’re doing somethingAccess a webserviceWrite something to disc

4. Synchronous vs. AsynchronousSTOPvar data = DownloadData(...);ProcessData(data);ProcessDataDownloadDataThreadDownloadDataAsyncProcessDataDownloadDataAsync(... , data => {ProcessData(data);});Thread

5. What is the Async CTPSyntactic sugar for .NET 4 at the momentIn C# and VB.NETWill be part of the .NET 5To make easy asynchronous calls without callbacksUses Task, Task<T> or void (fire and forget) to represent ongoing operationsCan be async I/O, backgroundworker, anything you would want to offload.Single object which has status (busy, done, …), exceptions and result

6. Demo

7. New thingsasyncTo define a function that awaits a TaskawaitTo wait for a task to complete

8. How does it work?async Task<XElement> GetRssAsync(stringurl) {var client = newWebClient();var task = client.DownloadStringTaskAsync(url);var text = await task;var xml = XElement.Parse(text);return xml;}

9. async Task<XElement> GetRssAsync(string url) {var client = new WebClient();var task = client.DownloadStringTaskAsync(url);var text = await task;var xml = XElement.Parse(text); return xml;}How does it work?Task<XElement> GetRssAsync(stringurl) {var $builder = AsyncMethodBuilder<XElement>.Create();var $state = 0;TaskAwaiter<string> $a1;Action $resume = delegate {try {if ($state == 1) goto L1;var client = newWebClient();var task = client.DownloadStringTaskAsync(url); $state = 1; $a1 = task.GetAwaiter();if ($a1.BeginAwait($resume)) return; L1: var text = $a1.EndAwait();var xml = XElement.Parse(text); $builder.SetResult(xml); }catch (Exception $ex) { $builder.SetException($ex); } }; $resume();return $builder.Task;}

10. Old vs new demo

11. The old wayCreate WebClientUse the async method with callbackIn the callback consume the result

12. The new async wayShorterEasier to understandNo more callbacksEasier access to exceptions, just wrap it in a try catch block

13. Unifying AsynchronyAsynchronous MethodsTaskAn asynchronous scenarioScrape YouTube for video linksDownload two or more videos concurrentlyCreate a mashup from downloaded videosSave the resulting videoCPUNetworkI/OComposite

14. Unifying AsynchronyTaskCPUNetworkI/OCompositetry {string[] videoUrls = awaitScrapeYoutubeAsync(url); // Network-boundTask<Video> t1 = DownloadVideoAsync(videoUrls[0]);// Start two downloadsTask<Video> t2 = DownloadVideoAsync(videoUrls[1]);Video[] vids = awaitTask.WhenAll(t1, t2); // Wait for bothVideo v = awaitMashupVideosAsync(vids[0], vids[1]); // CPU-boundawaitv.SaveAsync(textbox.Text); // IO-bound}catch (WebException ex) {ReportError(ex);}

15. Set-up2 thingsasync methodor it awaits another async function or it awaits a Task(<T>).The await will essentially execute the task and the code BELOW the await will be the callback of when the task is finishedYou can only do await inside a async functionAsync functions without await will execute synchronously

16. Nice to knowDownload linkSpec linkAsync CTP doesn’t play nice with ReSharperCommand window  Resharper_DisableIt’s a CTPFunction names can change(and everything else too!)Modifies compiler - can break other CTPs

17. Follow Ordina…17Share your thoughts via #SOFTC Follow us on twitter: @OrdinaBEFind the presentationson www.slideshare.net/ordinaBeBe informed at www.linkedin.com/company/ordina-belgium