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Reactive programming

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Nick Hodge
Nick Hodge

This document discusses reactive programming and introduces the Reactive Extensions (Rx) library. It provides an overview of Rx and how it addresses limitations of traditional .NET events by treating all data sources as observable sequences. Rx allows composing and transforming event streams in a declarative way using LINQ-like operators. The document demonstrates how to work with observable sequences and observers in Rx and contrasts it with other approaches like the Task Parallel Library.

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Reactive Programming Nick Hodge Developer, Geek nhodge@mungr.com http://nickhodge.com/ https://gist.github.com/nickhodge for codesnippets
Who is Nick Hodge? • 28 years in IT, mostly as non-Developer • Apple, Adobe, Microsoft • Many small-scale, rapidly built applications • Open source contributor • Functional Reactive Programming Fan
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
Reactive Programming demo required
Reactive Programming vs. TPL • Task Parallel Library (TPL) http://msdn.microsoft.com/en- us/concurrency • PLINQ
The core of LINQ is the sequence
A sequence is just some stuff in a particular order
What about Rx? Let’s talk about events
Limitations of .NET Events exchange.StockTick += (sender, args) => { if (args.Quote.Symbol == “MSFT”) { // Imperative code } }; exchange.StockTick -= /* what goes here? */;
Observable Sequences to the Rescue IObservable<Quote> stockQuotes = …; var msft = stockQuotes .Where(quote => quote.Symbol == “MSFT”); var subscription = msft.Subscribe(quote => /* … */); subscription.Dispose();
Are .NET Events Obsolete? • .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
The Event Processing Landscape Social media RSS feeds GPS Server management
Reactive Extensions Architecture
Event Streams • Towards a 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
Essential Interfaces namespace System { public interface IObservable<out T> { IDisposable Subscribe(IObserver<T> observer); } public interface IObserver<in T> { void OnNext(T value); void OnError(Exception error); void OnCompleted(); } }
Observable Sources • Single items / empty Observable.Return() • Lists and arrays • UI Events • Async methods • Subjects (demo) • Property Changes
Cold / Hot • Hot : example MouseMove • Cold: when you subscribe, something happens (it waits)
UI Example, Windows 8 Universal App
This Presentation’s Reference Presentations • 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
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”
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

More Related Content

Reactive programming

  • 1. Reactive Programming Nick Hodge Developer, Geek nhodge@mungr.com http://nickhodge.com/ https://gist.github.com/nickhodge for codesnippets
  • 2. Who is Nick Hodge? • 28 years in IT, mostly as non-Developer • Apple, Adobe, Microsoft • Many small-scale, rapidly built applications • Open source contributor • Functional Reactive Programming Fan
  • 3. 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
  • 5. Reactive Programming vs. TPL • Task Parallel Library (TPL) http://msdn.microsoft.com/en- us/concurrency • PLINQ
  • 6. The core of LINQ is the sequence
  • 7. A sequence is just some stuff in a particular order
  • 8. What about Rx? Let’s talk about events
  • 9. Limitations of .NET Events exchange.StockTick += (sender, args) => { if (args.Quote.Symbol == “MSFT”) { // Imperative code } }; exchange.StockTick -= /* what goes here? */;
  • 10. Observable Sequences to the Rescue IObservable<Quote> stockQuotes = …; var msft = stockQuotes .Where(quote => quote.Symbol == “MSFT”); var subscription = msft.Subscribe(quote => /* … */); subscription.Dispose();
  • 11. Are .NET Events Obsolete? • .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
  • 12. The Event Processing Landscape Social media RSS feeds GPS Server management
  • 14. Event Streams • Towards a 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
  • 15. Essential Interfaces namespace System { public interface IObservable<out T> { IDisposable Subscribe(IObserver<T> observer); } public interface IObserver<in T> { void OnNext(T value); void OnError(Exception error); void OnCompleted(); } }
  • 16. Observable Sources • Single items / empty Observable.Return() • Lists and arrays • UI Events • Async methods • Subjects (demo) • Property Changes
  • 17. Cold / Hot • Hot : example MouseMove • Cold: when you subscribe, something happens (it waits)
  • 18. UI Example, Windows 8 Universal App
  • 19. This Presentation’s Reference Presentations • 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
  • 20. 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”
  • 21. 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

Editor's Notes

  1. We no longer write sync software LINQ: the core of LINQ clojure/Haskell is a sequence (Ienumerable)  things in a particular order MoveNext() MoveNext() Yield/return LINQ : from sequence, and create a pipeline .Select .Where .ForEach (except last, deferred computation)
  2. An order LINQ describe what we are going to do with the data when get it it … without having the data THIS IS A MONAD Monad : chain together functions that describe what you want to do with the data
  3. In the C# world, events are not composable Events are first class elements of the language OnMouseUp + OnMouseDown != OnDoubleClick (delegates) Timer, hook onmouseup/onmousedown, Booleans, state … erg Events fight with different states Event is some stuff in a particular order (time  ) List; happened Events; future or going to happen
  4. Taking what you know about LINQ, applying to events IEnumerable : lists IObservable, stream of events Idisposable, can stop the subscription early. (only if doing early, unless complete on its own) GC will cleanup Iobservable == list, LINQ works .Subscribe is the foreach. Nothing happens until you .Subscribe
  5. .NET event to an observable Special one: Subject<T> push around by hand INotifyPropertyChanged == events