Tamir DresherSenior Software ArchitectNovember 2015

Reactiveness All The Way

About Me

• Software architect, consultant and instructor• Software Engineering Lecturer @ Ruppin Academic Center• Reactive Extensions in Action (Manning)

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

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Software Architecture is like Pasta

By @benorama

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Socialmedia

Stock tickers

RSS feeds

GPS

Server managementUI e

vents

Your System

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Being Reactive

Responsive

Resilience

React to users

React to failures

http://www.reactivemanifesto.org/

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Resiliency

You know you have a distributed system when the crash of a computer you’ve never heard of stops

you from getting any work done.

- Leslie Lamport -

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Being Reactive

Responsive

Resilience

React to users

React to failures

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Being Reactive

Responsive

Resilience

Message Driven

React to users

React to failures

React to messages

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Being Reactive

Responsive

Elastic Resilience

Message Driven

React to users

React to failuresReact to load

React to messages

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Being Reactive

Responsive

Elastic Resilience

Message Driven

React to users

React to failuresReact to load

React to messages

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Reacting to Changes (notifications) with Rx• Observables• Observers• Operators• www.ReactiveX.io

g(x)

f(x)UI eve

nts

Stock tickers

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Rx Example

1. At least 4 characters2. Don’t overflow server (0.5 sec delay)3. Don’t send the same string again4. Discard results if another search was requested

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Rx Example

Rx.Observable.fromEvent($('#input'),'keyup') .map(e => e.target.value) .filter(text => text.length > 3) .throttle(500 /* ms */) .distinctUntilChanged() .flatMapLatest(searchWikipedia) .subscribe( data => { /* handle the results */}, error => { /* handle any errors */});

Observable.FromEventPattern(txtBox,“TextChanged”) .Select(_ => txtBox.Text); .Where(txt => txt.Length > 3); .Throttle(TimeSpan.FromSeconds(0.5)) .DistinctUntilChanged() .Select(text => SearchAsync(text)) .Switch() .Subscribe(

results => { /* handle the results */ },ex => { /* handle any errors */ } );

RxJS Rx.NET

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Back Pressure

3 per sec 1 per sec

http://www.reactive-streams.org/

Publisher Subscriber

demand

• “Push” behavior when consumer is faster

• “Pull” behavior when producer is faster

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The Actor Model (Hewitt et al. 1973)

Alice

Mailbox

Bob

Sally

Mailbox

Mailbox

“the Actor model retained more of what I thought

were the good features of the object idea.”

Alan Kay Object Orientation pioneer and Smalltalk co-designer

AliceParent

BobParent

SallyParent

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Akka Exampleclass SimpleActor extends Actor { override def receive: Receive = { case x => println("Received message: " + x) }}

object Main extends App { val system = ActorSystem(“actor-system") val anActor: ActorRef = system.actorOf(Props[SimpleActor]) anActor ! "Hello world" }

akka { actor.deployment { /simpleActor { remote = "akka://actor-system@127.0.0.1:3232" } }}

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Akka Parental Supervision

override val supervisorStrategy = OneForOneStrategy(maxNrOfRetries = 10, withinTimeRange = 1 minute) { case _: ArithmeticException => Resume case _: NullPointerException => Restart case _: IllegalArgumentException => Stop case _: Exception => Escalate }

1. OneForOneStrategy – affect only the failing child2. AllForOneStrategy – affects the failing child & it’s siblings

Child

Parent

Child

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Summary

manning.com/dresherDiscount code: ctwswarch

http://www.reactivemanifesto.org/

Actor Model

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