MILAN 20/21.11.2015

Talk title: Reactive Extensions 101Tamir Dresher – CodeValue - @tamir_dresher

• Software Architect, Consultant and Instructor

• Software Engineering Lecturer @ Ruppin Academic Center

@tamir_dreshertamirdr@codevalue.nethttp://www.TamirDresher.com.

Your headache relief pill to Asynchronous and Event based applications

AsyncPush

TriggersEvents

Reactive Extensions

Reactive Programming concentrates on the propagation of changes and

their effectssimply put, how to react to

changes and create dataflows that depend on

them

Reactive Programming

5

Socialmedia

High Rate Data

IoTGPS

External Services

UI eve

nts

Your System

So Many Sources…

Source/Producer

Target/Consumer

Producer-Consumer

Source/Producer

Target/Consumer

Source/Producer

Source/Producer

Target/Consumer

Target/Consumer

Producer-Consumer

IEnumerable<Message> LoadMessages(string hashtag){

var statuses = facebook.Search(hashtag);var tweets = twitter.Search(hashtag);var updates = linkedin.Search(hashtag);return statuses.Concat(tweets).Concat(updates);

}

Twitter AppLinkedi

n

Facebook

Pull Model

???? LoadMessages(string hashtag){

facebook.Search(hashtag);twitter.Search(hashtag);linkedin.Search(hashtag);

}

DoSomething( )msg

Push Model

observable observer

Subscribe(observer)

subscription

OnNext(X1)

OnNext(Xn)⁞

X1observable X2 Xn

⁞IDisposable

Observables and Observers

OnCompleted()

OnError(Exception)

observable

observable observer

X1 X2 Xn

⁞

Observables and Observers

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(); }}

Interfaces

MILAN 20/21.11.2015

Creating Observables

IObservable<Message> ObserveMessages(string hashtag){

}

return Observable.Create( async (o) => {

});

var messages = await GetMessagesAsync(hashtag);foreach(var m in messages){ o.OnNext(m);}o.OnCompleted();

Pull To Push

IObservable<Message> ObserveMessages(string hashtag){

}

return Observable.Defer( async () => {

});

var messages = await GetMessagesAsync(hashtag);return message.ToObservable();

Built-in Converters

Observable.Merge(

facebook.ObserveMessages(hashtag),

twitter.ObserveMessages(hashtag),

linkedin.ObserveMessages(hashtag));

Built-in Operators

Observable.Range(1, 10)    .Subscribe(x => Console.WriteLine(x));

Observable.Interval(TimeSpan.FromSeconds(1))    .Subscribe(x => Console.WriteLine(x));

Observable.FromEventPattern(SearchBox, "TextChanged")

1 2 10

⁞1 2 10

⁞1 sec 1 sec

Observables Factories

⁞

MILAN 20/21.11.2015

Observable Queries (Rx Operators)

Filtering Projection Partitioning Joins Grouping Set

Element Generation Quantifiers Aggregation Error HandlingTime and Concurrency

Where

OfType

Select

SelectMany

Materialize

Skip

Take

TakeUntil

CombineLatest

Concat

join

GroupBy

GroupByUntil

Buffer

Distinct

DistinctUntilChanged

Timeout

TimeInterval

ElementAt

First

Single

Range

Repeat

Defer

All

Any

Contains

Sum

Average

Scan

Catch

OnErrorResumeNext

Using

Operator2 Creates an IObservable<T3>

IObservable<T2> Operator<T1>(IObservable<T1> source, parameters);

Operator 1 Subscribe( )

observer

observable… Operator

N

Operator1 Creates an IObservable<T2>

IObservable<T>Original source

observerSubscribe

Composability

g(x)

f(x)

Observable Query Pipeline

Reactive Search

1. At least 3 characters2. Don’t overflow server (0.5 sec delay)3. Don’t send the same string again4. Discard results if another search was

requested

Reactive Search - Rules

Demo

Var textChanged = Observable.FromEventPattern(txt,

“TextChanged”).Select(_=>txt.Text);

textChanged.Where(text=>text.Length>3).Throttle(TimeSpan.FromSeconds(0.5)).DistinctUntilChanged().SelectMany(text => SearchAsync(text)).Switch().Subscribe(/*handle the results*/);

var $input = $('#input'), $results = $('#results');

Rx.Observable.fromEvent($input, 'keyup') .map(e => e.target.value) .filter(text => text.length > 3) .throttle(500 /* ms */) .distinctUntilChanged() .flatMapLatest(searchWikipedia) .subscribe(data => { var res = data[1]; $results.empty(); $.each(res, (_, value) => $('<li>' + value + '</li>').appendTo($results)); }, error => { /* handle any errors */ $results.empty(); $('<li>Error: ' + error + '</li>').appendTo($results);});

MILAN 20/21.11.2015

Abstracting Time and Concurrency

Thread Pool

Task Scheduler

other

Schedulers

public interface IScheduler{ DateTimeOffset Now { get; }

IDisposable Schedule<TState>( TState state, Func<IScheduler, TState, IDisposable> action);

IDisposable Schedule<TState>(TimeSpan dueTime, TState state,Func<IScheduler, TState, IDisposable> action);

IDisposable Schedule<TState>(DateTimeOffset dueTime,

TState state,Func<IScheduler, TState, IDisposable> action);

}

//// Runs a timer on the default scheduler//IObservable<T> Throttle<T>(TimeSpan dueTime);

//// Every operator that introduces concurrency// has an overload with an IScheduler//IObservable<T> Throttle<T>(TimeSpan dueTime, IScheduler scheduler);

Parameterizing Concurrency

textChanged

.Throttle(TimeSpan.FromSeconds(0.5),

DefaultScheduler.Instance).DistinctUntilChanged().SelectMany(text =>

SearchAsync(text)).Switch().Subscribe(/*handle the

results*/);

//// runs the observer callbacks on the specified // scheduler.//IObservable<T> ObserveOn<T>(IScheduler);

//// runs the observer subscription and unsubsciption on// the specified scheduler.//IObservable<T> SubscribeOn<T>(IScheduler)

Changing Execution Context

textChanged.Throttle(TimeSpan.FromSeconds(0.5)).DistinctUntilChanged().SelectMany(text =>

SearchAsync(text)).Switch()

.ObserveOn(DispatcherScheduler.Current).Subscribe(/*handle the results*/);

Changing Execution Context

textChanged.Throttle(TimeSpan.FromSeconds(0.5)).DistinctUntilChanged().SelectMany(text =>

SearchAsync(text)).Switch().ObserveOnDispatcher().Subscribe(/*handle the results*/);

Changing Execution Context

http://blogs.msdn.com/b/rxteam/archive/2012/06/14/testing-rx-queries-using-virtual-time-scheduling.aspx

Virtualizing Time

Your headache relief pill to Asynchronous and Event based applications

AsyncPush

TriggersEvents

Reactive Extensions

Thank You

www.manning.com/dresher www.reactivex.io github.com/Reactive-Extensions

Discount code: ctwcodemot 

MILAN 20/21.11.2015 - Tamir Dresher – Rx 101

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Presenter contact detailst: @tamir_dreshere: tamirdr@codevalue.netb: TamirDresher.comw: www.codevalue.net