Akka 2.0 Reloaded

2.0 Reloaded

Meetu Maltiar
Email: meetu@knoldus.com
Twitter:@meetumaltiar

Akka 2.0
Akka name comes from Sami mythology is actually
name of a goddess of wisdom and beauty.

Akka incidentally means sister in Telugu!!

The Problem
It is way too hard to build
=> correct highly concurrent systems
=> truly scalable systems
=> self-healing, fault-tolerant systems

What is Akka?
Right abstraction with actors for concurrent, fault-tolerant
and scalable applications

For Fault-Tolerance uses “let it crash” model

Abstraction for transparent distribution for load

Introducing Actors
Actor is an entity encapsulating behavior, state and a
mailbox to receive messages

For a message received by Actor a thread is allocated to it

Then Actors behavior is applied to the message and
potentially some state is changed or messages is passed to
other Actors

Introducing Actors..
There is elasticity between message processing and
addition of new messages. New messages can be added
while actor execution is happening.

When processing of messages is completed thread is
deallocated from the actor. It can be reallocated a thread at
a later time

Create Application
import akka.actor.ActorSystem

val system =
ActorSystem("firstApp")

My First Actor
import akka.actor.{ Actor, Props }

class MyFirstActor extends Actor {
def receive = {
case msg => println("Hello!!")
}
}

Create Actors
import akka.actor.{ ActorSystem, Props }

val system = ActorSystem("firstApp")
val myFirstActor =
system.actorOf(Props[MyFirstActor])

MyFirstActor is an ActorRef
Create a top level actor

Stop Actors
system stop myFirstActor

Also stops all actors in hierarchy

Send: !
myFirstActor ! “Hello”

fire-forget

Ask: ?
import akka.pattern.ask

implicit val timeout = Timeout(50000 milliseconds)

val future = myActor ? "hello"

Await.result(future, timeout.duration).asInstanceOf[Int]

Returns a Future[Any]

Reply
import akka.actor.Actor

class LongWorkingActor extends Actor {
def receive = {
case number: Int =>
sender ! (“Hi I received ” + number)
}
}

Routers
RoundRobin
Random
SmallestMailBox
BroadCast
ScatterGaherFirstCompleted

Routers...

val router =
system.actorOf(
Props[RouterWorkerActor].
withRouter(RoundRobinRouter(nrOfInstances = 5)))

Actor Path
val actorRef =
system.actorFor("akka://actorPathApp/user/pa
rent/child")

val parent = context.actorFor("..")

val sibling = context.actorFor("../sibling")

val refPath = actorRef.path

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

Manage Failure
class FaultTolerantService extends Actor {
def receive = {
case msg => println(msg)
}

override def preRestart(reason: Throwable, message: Option[Any]) = {
// clean up before restart
}

override def postRestart(reason: Throwable) = {
// init after restart
}
}

Code Samples

https://github.com/meetumaltiar/AkkaKnolX

References

Viktor Klang talk on Akka 2.0 at NE Scala symposium

Akka website akka.io

Akka 2.0 Reloaded

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