Post on 06-May-2015
description
transcript
2.0 Reloaded
Meetu MaltiarEmail: 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 Actorimport akka.actor.{ Actor, Props }
class MyFirstActor extends Actor { def receive = { case msg => println("Hello!!") }}
Create Actors
MyFirstActor is an ActorRefCreate a top level actor
import akka.actor.{ ActorSystem, Props }
val system = ActorSystem("firstApp")val myFirstActor = system.actorOf(Props[MyFirstActor])
Stop Actors
Also stops all actors in hierarchy
system stop myFirstActor
Send: !
fire-forget
myFirstActor ! “Hello”
Ask: ?
Returns a Future[Any]
import akka.pattern.ask
implicit val timeout = Timeout(50000 milliseconds)
val future = myActor ? "hello"
Await.result(future, timeout.duration).asInstanceOf[Int]
Replyimport 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)))
Let It CrashFault Tolerance
Actor Path
val actorRef = system.actorFor("akka://actorPathApp/user/parent/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