Akka

concurrency and parallelism

Andraž Bajt / @edofic

Concurrency vs Parallelism

Concurrency: two tasks running

Parallelism: two things running at the same time

Threads

Good for OS/processor
Bad for programmer
Deadlocks, race conditions, synchronization
"Impossible" to get right

Callbacks

Node.js is popular
Impure
Error handling
Unreadable

The Actor Model

Carl Hewitt 1973
Erricoson Erlang in 80s

Different take on OO

Sample

Defining actors


import akka.actor._

case class DoStuff(s: String)

class Worker extends Actor {
  def receive = {
    case DoStuff(s) => doStuff(s)
    case msg: String => println(msg)
    case 42 => sender ! "You'll need a bigger computer for that"
  }

  def doStuff(s: String) = ... //some blocking operation
}

Sample

Usage


import akka.actor._
import akka.pattern.ask

val sys = ActorSystem()
val worker = sys.actorOf(Props[Worker])

worker ! DoStuff("details")
worker ! "hello world"
val question: Future[Question] = worker ? 42

Routing


import akka.routing.RoundRobin
val worker = sys.actorOf(
  Props[Worker] withRouter RoundRobin(5),
  "myWorker"
)

Config

Exact same code!


akka.actor.deployment {
  /myWorker {
    router = random-router
    nr-of-instances = 17
  }
}

Going remote

Just change the config

remote deploy
remote actor lookup

Cluster

cluster aware routers
no code changes

Call now and get these for free

Typed actors
Logging
Event bus
Scheduling
Dataflow model
Agents
Transactions
IO
...

See http://akka.io/