Reactive programming

Reactive programming

• 1.
  Reactive Programming Nick Hodge Developer,Geek nhodge@mungr.com http://nickhodge.com/ https://gist.github.com/nickhodge for codesnippets
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  Who is NickHodge? • 28 years in IT, mostly as non-Developer • Apple, Adobe, Microsoft • Many small-scale, rapidly built applications • Open source contributor • Functional Reactive Programming Fan
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  Group Experiment: Data-at-rest vs.Data-in-motion • LINQ to IEnumerable (or IQueryable) • “data at rest” • yield • What happens if data changes in midst of foreach() ? • Reactive programming (IObservable) • “data in motion” • Data (or events) are pushed at you
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  Reactive Programming demo required
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  Reactive Programming vs.TPL • Task Parallel Library (TPL) http://msdn.microsoft.com/en- us/concurrency • PLINQ
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  The core ofLINQ is the sequence
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  A sequence isjust some stuff in a particular order
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  What about Rx? Let’stalk about events
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  Limitations of .NETEvents exchange.StockTick += (sender, args) => { if (args.Quote.Symbol == “MSFT”) { // Imperative code } }; exchange.StockTick -= /* what goes here? */;
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  Observable Sequences tothe Rescue IObservable<Quote> stockQuotes = …; var msft = stockQuotes .Where(quote => quote.Symbol == “MSFT”); var subscription = msft.Subscribe(quote => /* … */); subscription.Dispose();
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  Are .NET EventsObsolete? • .NET Events • Code centric • Design-time experience • Not first class • Non-compositional • Lightweight • Rigid execution model (IL) • Observables • Data centric • No design-time experience • First class objects • Rich composition • Slightly more cost • Translatable with expression trees
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  The Event ProcessingLandscape Social media RSS feeds GPS Server management
• 13.
  Reactive Extensions Architecture
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  Event Streams • Towardsa unified programming model • Producers are observable sequences • .NET events, WinRT events, sensor APIs, APM methods, tasks, etc. • Consumers are observers • Hooking up “continuations” or handlers Observable Subscribe Observer
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  Essential Interfaces namespace System { publicinterface IObservable<out T> { IDisposable Subscribe(IObserver<T> observer); } public interface IObserver<in T> { void OnNext(T value); void OnError(Exception error); void OnCompleted(); } }
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  Observable Sources • Singleitems / empty Observable.Return() • Lists and arrays • UI Events • Async methods • Subjects (demo) • Property Changes
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  Cold / Hot •Hot : example MouseMove • Cold: when you subscribe, something happens (it waits)
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  UI Example, Windows8 Universal App
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  This Presentation’s ReferencePresentations • Bart De Smet “Curing Your Event Processing Blues with Reactive Extensions (Rx)” TechEd Europe 2012 http://channel9.msdn.com/events/TechEd/Europe/2012/DEV413 • Paul Betts “Introduction to Reactive Extensions” Norwegian Developer’s Conference 2012 http://vimeo.com/43659034 • Brendan Forster “Reactive UI – Turning MVVM up to 11” http://vimeo.com/97329155
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  Further References, Links •https://rx.codeplex.com/ and https://github.com/Reactive- Extensions/Rx.NET as the starting point • RxJS (and other languages such as Ruby, C++, Python, Java, ObjC) https://github.com/Reactive-Extensions/RxJS • http://www.introtorx.com/ • 101 Rx Examples http://rxwiki.wikidot.com/101samples • http://amzn.to/programming-rx “Programming Reactive Extensions and LINQ”
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  Further Research, Future •“Scalable Information Stream Processing by Bing in Support of Cortana Scenarios” http://channel9.msdn.com/posts/Scalable- Information-Stream-Processing-by-Bing-in-Support-of-Cortana- Scenarios • Actor model, “Microsoft Research project Orleans simplify development of scalable cloud services” http://channel9.msdn.com/Shows/Cloud+Cover/Episode-142- Microsoft-Research-project-Orleans-simplify-development-of- scalable-cloud-services