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The Evolution of Async-Programming on .NET Platform (.Net China, C#)
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The Evolution of Async-Programming on .NET Platform (.Net China, C#)

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  • 1. The Evolution of AsyncProgramming on .NET Platform ZhaoJie @ SNDA Nov, 2010
  • 2. About Me• / / Jeffrey Zhao /•• Blog: http://blog.zhaojie.me/• Twitter: @jeffz_cn• F#, Scala, JavaScript, Python, .NET, mono...• Java (as the language) hater
  • 3. Agenda• Why & How• .NET 1.0• .NET 2.0 / C# 2.0• .NET 3.0 / F#• .NET 4.0 / Reactive Framework• Future / C# vNext
  • 4. Why? Because the essence of Cloud, Web, Mobileis asynchronous computations
  • 5. How? By providing powerful languagefeatures / programming model / libraries
  • 6. .NET 1.0
  • 7. Two Raw Async Models• Begin/End• Event-based• Both are callback-based • Which is just “asynchronous” means
  • 8. Begin/End Async Modeldelegate AsyncCallback(IAsyncResult);interface IAsyncResult { object AsyncState { get; } WaitHandle AsyncWaitHandle { get; } bool CompletedSynchronously { get; } bool IsCompleted { get; }}void BeginXxx(arg1, arg2, ..., AsyncCallback, state);TResult EndXxx(IAsyncResult);
  • 9. Event-based Async Modelclass XxxCompletedEventArgs : EventArgs { Exception Error { get; } TResult Result { get; }}class Worker { event EventHandler<XxxCompletedArgs> XxxCompleted; void XxxAsync(arg1, arg2, ...);}
  • 10. Let’s write a “Transfer” method in 4 different ways
  • 11. Demo 1Sync & Async
  • 12. Code Locality is Broken• Used to expressing algorithms linearly• Async requires logical division of algorithms • No if / using / while / for ...• Very difficult to • Combine multiple asynchronous operations • Deal with exceptions and cancellation
  • 13. .NET 2.0 / C# 2.0
  • 14. “yield” for Iterators IEnumerable<int> Numbers() { yield return 0; yield return 1; yield return 2; }
  • 15. “yield” for Iterators IEnumerable<int> Numbers() {MoveNext() yield return 0; yield return 1; yield return 2; }
  • 16. “yield” for Iterators IEnumerable<int> Numbers() {MoveNext() yield return 0; MoveNext() yield return 1; yield return 2; }
  • 17. “yield” for Iterators IEnumerable<int> Numbers() {MoveNext() yield return 0; MoveNext() yield return 1; MoveNext() yield return 2; }
  • 18. “yield” for Iterators IEnumerable<int> Numbers() {MoveNext() yield return 0; MoveNext() yield return 1; MoveNext() yield return 2;MoveNext() }
  • 19. Demo 2Async with “yield”
  • 20. “yield return” for Async• Coming with new programming patterns• Keep code locality • Good parts: support if / using / while / for ... • But not perfect: cannot use try...catch• The primitives for Fibers - lightweight computation units
  • 21. .NET 3.0 / F#
  • 22. F#• Language by Don Syme, MS Research• Strongly statically typed language• Functional language with OO ability• For industry and education • Open source (Apache 2.0) • Cross-platform supported by Microsoft
  • 23. Concurrency Challenges• Shared State - Immutability• Code Locality - async { ... }• I/O Parallelism - async { ... }• Scaling to Multi-Machine - Agents with async { ... }
  • 24. What’s async { ... }... the principle we go by is, dont expect to seea particular concurrency model put into C#because therere many different concurrencymodel ... its more about finding things arecommon to to all kinds of concurrency ... - Anders Hejlsberg
  • 25. Async Workflowasync {   let! res = <async work> ... }
  • 26. Async Workflow React!async {   let! res = <async work> ... }
  • 27. Async Workflow React!async {   let! res = <async work> ... } an HTTP Response an UI Event a Timer Callback a Query Response a Web Servcie Response a Disk I/O Completion an Agent Message
  • 28. How async { ... } Works async { let! img = AsyncRead "http://..." printfn "loaded!" do! AsyncWrite img @"c:..." printfn "saved!" }
  • 29. How async { ... } Works async { let! img = AsyncRead "http://..." printfn "loaded!" do! AsyncWrite img @"c:..." printfn "saved!" } =async.Delay(fun -> async.Bind(AsyncRead "http://...", (fun img -> printfn "loaded!" async.Bind(AsyncWrite img @"c:...", (fun () -> printfn "saved!" async.Return())))))
  • 30. Demo 3Async in F#
  • 31. F# Async Workflow• Library, not a language feature • Based on Computation Expressions in F#• Support all kinds of language constructions • Error handling: try...catch • Loop: while / for (like “foreach” in C#) • Others: if / use (like “using” in C#), etc.• Easy to • Combine multiple asynchronous operations • Deal with exceptions and cancellation
  • 32. F# Resources http://fsharp.netProgramming F# Expert F# 2.0 Real World FP
  • 33. .NET 4.0 / Reactive Framework
  • 34. Reactive Framework Fundamentally change the way you think about coordinating and orchestrating asynchronous and event-based programming
  • 35. HowBy showing that asynchronous and event-base computations are just push-based collections
  • 36. Interactive Reactive Environment Program
  • 37. Enumerable Collections interface IEnumerable<out T> { IEnumerator<T> GetEnumerator(); } interface IEnumerator<out T> { bool MoveNext(); T Current { get; } }
  • 38. Dualize
  • 39. Observable Collectionsinterface IObservable<out T> { IDisposable Subscribe(IObserver<T> o)}interface IObserver<in T> { void OnCompleted(); void OnNext(T item); void OnError(Exception ex);}
  • 40. IEnumerable & IEnumerator are prototypicalinterfaces for interactive collections andinteractive programs.IObservable & IObserver are prototypicalinterfaces for observable collections andreactive, asynchronous & event-based programs.
  • 41. LINQ to Observable If you are writing LINQ or declarative code in an interactive program...
  • 42. LINQ to Observable If you are writing LINQ or declarative code in an interactive program... You already know how to use it!
  • 43. Again... the principle we go by is, dont expect to seea particular concurrency model put into C#because therere many different concurrencymodel ... its more about finding things arecommon to to all kinds of concurrency ... - Anders Hejlsberg
  • 44. Again... the principle we go by is, dont expect to seea particular concurrency model put into C#because therere many different concurrencymodel ... its more about finding things arecommon to to all kinds of concurrency ... - Anders Hejlsberg
  • 45. Rx in JavaScript• A full featured port for JavaScript • Easy-to-use conversions from existing DOM, XmlHttpRequest, etc • In a download size of less than 7kb (gzipped)• Bindings for various libraries / frameworks • jQuery • MooTools • Dojo • ...
  • 46. Time Flies like an Arrowvar container = $("#container");var mouseMove = container.toObservable("mousemove");for (var i = 0; i < text.length; i++) { (function(i) { var ele = $("<span/>").text(text.charAt(i)); ele.css({position: "absolute"}).appendTo(container); mouseMove.Delay(i * 100).Subscribe(function (ev) { ele.css({ left: ev.clientX + i * 20 + 15 + "px", top: ev.clientY + "px" }); }); })(i);
  • 47. Demo 4Async with Reactive Fx
  • 48. Benefits of Rx• Easy to composite and coordinate async operations• Express the algorithm in functional ways • Helper method: For / While / If / Try / Switch...• Easy to be unit tested• ...
  • 49. Rx & Language Features• Features in C# that Rx uses • Extension method • Lambda expression & closure • Type inference • LINQ query expression• Rx has been implemented in ... • C# & VB • JavaScript • F#
  • 50. Portability• Rx can be easily ported to various languages • Scala • Ruby • Python • modern languages with basic functional features• Almost impossible to implement Rx in Java • Cannot extend a type without breaking code • Missing enough functional features
  • 51. Rx Resources• Matthew Podwysocki • http://codebetter.com/blogs/matthew.podwysocki/• Reactive Framework on MSDN DevLabs • http://msdn.microsoft.com/en-us/devlabs/ ee794896.aspx• Tomáš Petříček • http://tomasp.net/
  • 52. Comparison• F# Async Workflow • Elegant, simple, easy to use • Can only be used at server-side (WebSharper come to rescure?)• Reactive Framework • Can be used at both server-side and client-side. • New async model brings learning cost.
  • 53. Can we use“Async Workflow” in JavaScript?
  • 54. Demo 5Jscex & Jscex.Async
  • 55. C# vNext
  • 56. Sourceasync 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;}
  • 57. CompiledTask<XElement> GetRssAsync(string url) { var $builder = AsyncMethodBuilder<XElement>.Create(); var $state = 0; TaskAwaiter<string> $a1; Action $resume = delegate { try { if ($state == 1) goto L1; var client = new WebClient(); 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;}
  • 58. Conclusion• Async Programming is difficult• New programming language / feature / library / model can help• JavaScript is incredible.
  • 59. Q &A
  • 60. Thanks