getting cozy with actors - developermarch...what is akka? actors ••simple & high performance...

Getting Cozy with Actors

Pain-free Concurrency in Java

Balaji Srinivasaraghavan

Goal

• Relational Database = JPA/Hibernate• REST = JAX-RS

• Method calls = built into the language

•Concurrency = Executor Service ?? L

©2017 PayPal Inc. Confidential and proprietary.

Modelling with Java

• Static aspects of a system− Object oriented modelling•Mirrors the real world

• Dynamic aspects of a system− Concurrency & communication− Threads – hardware model


Threads

• Good−Default pattern for concurrency−Reasonably well understood, 20 years old

• Bad−Inter-thread communication is a mess−Locks are hard to design & reason about−20 years old−Explicit concurrency

• Hardware model - world as a processor see’s it• Impedance mismatch between object oriented

models


Hardware Environment• Age of multi-core processors• Per core performance improvements begin

to flat line in ‘05

• “Free lunch is over”


Can we do better?

• Yes, let’s look other models• Functional programming• no shared mutable state• immutable POJOs

• Dataflow programming• model programs as a series of

transformations & connections• implicit concurrency

• Actor model• treats "actors" as the universal

primitive of concurrent computation


public class Person {public final String name;

public Person(String name) {this.name = name;

}}

Object

Java Actor

Object MailboxMailbox

MessageMessage

Message

Actors


everything is an object everything is an actor


Actor

MailboxMailbox

StateMessageMessageMessage

• Actors have • State

• OO: class attributes

• Mailbox

• OO: method params

• Behavior

• State is internal & not shared, accessed through message passing

Behavior


Actor Model


What is Akka?

••simple & high performance concurrencyActors

••Feature rich non-blocking HTTP server & clientHTTP

••location transparency, resilienceCluster / Remoting

••back-pressured data flowsStreams


Java library that provides:

Dispatcher



public class Greeter extends AbstractActor {private String greeting = ”Hello";

public Greeter() {receive(ReceiveBuilder

.match(WhoToGreet.class, message -> greeting = ”Hello, " + message.who)

.match(Greet.class, message -> sender().tell(new Greeting(greeting), self()))

.build());}

}

Actor Operations - Define



public class Greeter extends AbstractActor {private String greeting = ”Hello";

public Greeter() {receive(ReceiveBuilder

.match(WhoToGreet.class, message -> greeting = ”Hello, " + message.who)

.match( Greet.class, message -> sender().tell(new Greeting(greeting), self()))

.build());}

}

Actor Operations – Send Messages



Still harder than it needs to be…

Threads Executors Actors Streams

Level of Abstraction

Streams

• Defines a data flow• Programmer focuses on − transformations− composition

• Framework focuses on − Concurrency− Data movement− Creates actors internally


Akka Streams


• A high-level DSL for defining stream processing graphs

• Machinery for transforming graphs into actors

• Non blocking all the way

• Backpressure enabled

Stream Example


messageQueueSource

.map(message -> parse(message))

.filter(Try::isSuccess) // filter out unparseable

.mapAsync(5, tweet -> detectBot(tweet.get())) //cpu bound

.filter(result -> result.isBot)

.groupedWithin(100, FiniteDuration.create(1, TimeUnit.SECONDS))

.runForeach(Step2BotDetection::writeFraudReport, materializer);

* from https://github.com/ktoso/akka-streams-alpakka-talk-demos-2016

Use Cases

• Actors−maintain state across requests− natural fit for orchestration/façade services− clustering, distributed data designs

• Streams− batch processing of large data sets− structuring complex business logic− streaming data sources e.g. HTTP, Kafka, Oracle− low latency HTTP services


PayPal Open Source


Akka/Spray for Large-Scale Production Deployments

• Unicomplex micro-container

• TestKit

• Enriched HttpClient

• Patterns

• Pipeline

Attributions & Bibliography


• Asynchronous stream processing with AkkaStreams by Johan Andrén JFokus,Stockholm, 2017-02-08

• Akka Actor Introduction – Gene

• Reactive Microservices Architecture ByJonas Bonér

• Akka Docs

• Lightbend Documentation & Case Studies

Thanks

www.modsummit.com

www.developersummit.com

http://www.modsummit.com/

http://www.developersummit.com/

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