Reactive Extensions

Dmitri Nesteruk dmitri@activemesa.com http://activemesa.com http://spbalt.net Based on materials by Scott Weinstein

Multiple data items can be “processed” in either a push or a pull fashion. In a pull paradigm, data is processed at the leisure of the destination. Common examples include: reading from a file summing the numbers in an array iterating though a database query traversing a directory listing paging through an Amazon search

In a push paradigm, data is processed via demands of the source. Common examples include: Device measurements such as time light heat User triggered data such as Mouse & Keyboard events UI events Sales transactions Asynchronous code

In .Net Pulled data is exposed via a single core interface IEnumerable/IEnumerator Pushed data is exposed via Events Ad-hoc delegate callbacks Ad-hoc subscribe/callback interfaces BeginXXX/EndXXX Async pattern 3rd party attempts at Linq for Pushed data (Clinq, Slinq, PushLinq) Each implementation is unique is it’s own way

LINQ provides a composable, and standard way to do list manipulations The Reactive Extensions (RX) attempt to Provide a common interface for Pushed data IObservable/IObserver Enable Linq over Pushed data, providing composiblity and standard operators

Available for free from Domains MS DevLabs Events http://bit.ly/reext APM Support for Web service calls .Net 3.5 SP1 Async workflows .Net 4 Task<T>-based calls Silverlight 3 Applications JavaScript Web page d/l Not part of .Net 4 :( Async file IO Except the interfaces Streaming OLAP

5 assemblies (including PFX) System.CoreEx Feel free to ILmerge Main features System.Interactive Interfaces (IObserver<T>, IObservable<T>) System.Observable Observer conversions LINQ support System.Reactive WinForms & WPF notification support System.Threading (PFX) Infrastructure No particular namespace

Implemented by the object that wants to receive notifications OnNext(T value) Called when a value has been provided OnError(Exception ex) Called in case of an error OnCompleted() When done The contract is OnNext* (OnError|OnCompleted)

Implemented by an object which can be observed IDisposable Subscribe( IObserver<T> obs); Called by the observer to subscribe Typical behavior Adds each observer to a List<IObserver<T>> Calls OnXxx() on each listed observer Dispose() called to unsubscribe More composable – no need for Unsubscribe()

Typically, you would not implement these interfaces Use helper methods to get Observable<T> Use Subscribe() to act as an Observer<T> Observable.FromEvent() Observable.FromAsyncPattern() EnumerableEx.ToObservable() Enumerable → Observable Observable.Interval Generates an event in an interval

Observable.FromXxx lets you create an anonymous observable Subscribe() lets you create an anonymous observer Parameters take An IObserver<T> A combination of Action<T>’s that correspond to OnNext, OnError and OnCompleted

New LINQ combinators Amb Time CombineLatest Presence/absence Delay Value changes Repeat Value patterns Utility TakeUntil/TakeWhile SkipUntil/SkipWhile Mirrored in IEnumerable Scan EnumerableEx Timer Using

Scan CombineLatest Yields running aggregate Combines each pair of values latest values list = { 1, 2, 3 }; o.Scan((a,b) => a+b) yields 1, 3, 6

Merge Zip Collates two streams into Pairwise collection of one items in stream

How observables produce values even when not subscribed var timer = new Timer(1000); var hot = Observable.FromEvent( timer, “Elapsed”); Cold observable produces values onl y on subscriptions var cold = Obsevable.Interval( TimeSpan.FromSeconds(1));

Rx itself http://bit.ly/reext Rx Team Blog http://blogs.msdn.com/RxTeam/ Lots of Rx videos Rx PowerToys http://rxpowertoys.codeplex.com/ Tracing Time machine scheduler Marble diagram generator (.Net 4) Shameless plug: http://bit.ly/rxrus

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Reactive Extensions

by Dmitri Nesteruk on Apr 03, 2010

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Reactive Extensions — Presentation Transcript