响应式编程及框架

Reactive Programming and FrameworkZhao Jie - SNDA - Sep. 2010

About me

赵劼 / 老赵 / Jeffrey Zhao / 赵姐夫

日写代码三百行，不辞长作程序员

Blog: http://blog.zhaojie.me/

Twitter: @jeffz_cn

F#, Scala, JavaScript, Python, .NET, mono...

Java (as the language) hater

http://blog.zhaojie.me

http://blog.zhaojie.me

What?

Fundamentally change the way you think about coordinating and

orchestrating asynchronous and event-based programming

Why?

Because the essence ofCloud, Web, Mobile

is asynchronous computations

How?

By showing that asynchronous and event-base computations are just

push-based collections

Interactive & Reactive

a := b + c

Environment

Program

Interactive Reactive

Let’s implement both interfaces with...

Enumerable Collections

interface IEnumerable<out T>{ IEnumerator<T> GetEnumerator();}

interface IEnumerator<out T>{ bool MoveNext(); T Current { get; }}

EnumeratorGetEnumerator()

1

MoveNext()2

true/falseConsumer pulls

successive elements from the collection

3

Current

interface IEnumerable<out T>{ // void -‐> enumerator IEnumerator<T> GetEnumerator();}

interface IObservable<out T>{ // observer -‐> void IDisposable Subscribe(IObserver<T> o)}

Dualize Enumerable Collections

Dualize Enumerable Collections

interface IEnumerator<out T>{ bool MoveNext(); // void -‐> bool T Current { get; } // void -‐> T // throws Exception}

interface IObserver<in T>{ void OnCompleted(bool done); // bool -‐> void T Current { set; } // T -‐> void void OnError(Exception ex); // accepts Exception}

Observable Collections

interface IObservable<out T>{ IDisposable Subscribe(IObserver<T> o)}

interface IObserver<in T>{ void OnCompleted(); void OnNext(T item); void OnError(Exception ex);}

ObserverSubscribe(o)

1

OnCompleted()

3

XProducer pushes

successive elements from the collection

2

OnNext(e)

IEnumerable & IEnumerator areprototypical interfaces for interactive collections and interactive programs.

IObservable & IObserver are prototypical interfaces for observable collections and reactive, asynchronous & event-based programs.

Iterator

Observer

Iterator / ObserverPatterns in Java

class Observable { void addObserver(Observer o);

void deleteObserver(Observer o); void deleteObservers(); int countObservers(); void notifyObservers(); void notifyObservers(Object arg); void setChanged(); void clearChanged(); boolean hasChanged();}

interface Observer { void update(Observable o, Object arg);}

interface Iterable<T> { Iterator<T> iterator();}

interface Iterator<T> { T next();

boolean hasNext(); void remove();}

LINQ to Observable

If you are writingLINQ or declarative codein an interactive program...

LINQ to Observable

If you are writingLINQ or declarative codein an interactive program...

You already know how to use it!

LINQ to Observable

... the principle we go by is, don't expect to see a particular concurrency model put into C# because there're many different concurrency model ... it's more about finding things are common to to all kinds of concurrency ...

- Anders Hejlsberg

LINQ to Object

Standard query operatorsSelectWhereSelectMany...

Extended query operatorsZipAggregate...

LINQ to Observable

Standard query operatorsSelectWhereSelectMany...

Extended query operatorsZipThrottle...

How to move a ball by keyboard (ASDW)?

Imperative Impl.void OnKeyPress(object sender, KeyPressEventArgs e){ if (isPlaying) { if (e.KeyChar == 'a' && ball.Left > 0) { ball.Left -‐= 5; } else if (e.KeyChar == 'w' && ball.Top > 0) { ball.Top -‐= 5; } else ... } else ...}

Declarative Impl.// filter the KeyPress events when playingvar keyPress = GetKeyPress().Where(_ => isPlaying);

// filter the events to move leftvar moveLeft = from ev in keyPress where ev.EventArgs.KeyChar == 'a' where ball.Left > 0 select ev;moveLeft.Subscribe(_ => ball.Left -‐= 5);

// filter the events to move topvar moveTop = from ev in keyPress where ev.EventArgs.KeyChar == 'w' where ball.Top > 0 select ev;moveTop.Subscribe(_ => ball.Top -‐= 5);

Mouse drag and draw

var mouseMove = GetMouseMove();var mouseDiff = mouseMove.Zip(mouseMove.Skip(1), (prev, curr) => new { PrevPos = new Point( prev.EventArgs.X, prev.EventArgs.Y), CurrPos = new Point( curr.EventArgs.X, curr.EventArgs.Y) });

var mouseDrag = from _ in GetMouseDown() from diff in mouseDiff.TakeUntil(GetMouseUp()) select diff;

mouseDrag.Subscribe(d => DrawLine(d.PrevPos, d.CurrPos));

Everything in Web is Asynchronous

User actions

AJAX requests

Animations

...

Reactive Framework in JavaScript

A full featured port for JavaScriptEasy-to-use conversions from existing DOM, XmlHttpRequest, etcIn a download size of less than 7kb (gzipped)

Bindings for various libraries / frameworksjQueryMooToolsDojo...

Mouse drag and drawin JavaScript

Wikipedia lookup

Time flies like an arrow

Benefits of Rx

Easy to composite and coordinate async operations

Easy to express the algorithm (code locality)

Easy to be unit tested

...

Rx & Language Features

Features in C# that Rx usesExtension methodLambda expression & closureType inferenceLINQ query expression

Rx has been implemented in ...C# & VBJavaScriptF#

Port to other Languages

Rx can be easily ported to various languagesScalaRubyPythonmodern languages with basic functional features

Almost impossible to implement Rx in JavaCannot extend a type without breaking codeMissing enough functional features

Resources

Matthew Podwysockihttp://codebetter.com/blogs/matthew.podwysocki/

Reactive Framework on MSDN DevLabshttp://msdn.microsoft.com/en-us/devlabs/ee794896.aspx

Tomáš Petříčekhttp://tomasp.net/

http://codebetter.com/blogs/matthew.podwysocki/

http://codebetter.com/blogs/matthew.podwysocki/

http://msdn.microsoft.com/en-us/devlabs/ee794896.aspx




http://tomasp.net

http://tomasp.net

响应式编程及框架

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