Post on 06-May-2015
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Akka Actors And Futures
Meetu MaltiarPrincipal Consultant
Email: meetu@knoldus.comTwitter:@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
ScatterGatherFirstCompleted
Routers...
val router = system.actorOf(Props[RouterWorkerActor].withRouter(RoundRobinRouter(nrOfInstances = 5)))
Actor Path
val actorRef = system.actorFor("akka://actorPathApp/user/parent/child")
val parent = context.actorFor("..")
val sibling = context.actorFor("../sibling")
val refPath = actorRef.path
Akka FuturesA Future is a data structure
Used to retrieve of some concurrent operation
This operation is performed by an Actor or a dispatcher directly
The result can be accessed synchronously or asynchronously
Execution Context
Futures need ExecutionContext to execute callback and operations
If we have ActorSystem in scope Future will use default dispatcher as ExecutionContext
We can use factory methods provided by ExecutionContext companion object to wrap Executors and ExecutorServices
Use With Actors
There are two ways to get a reply from an Actor. First one is (myActor ! Msg)
The second way is through a Future. Using Actors “?” method will return a Future
The simplest way to use Await method call, though not recommended as the thread blocks till result is obtained.
Future With Akka andAwait
import akka.actor._import akka.pattern.askimport akka.util.duration._import akka.util.Timeoutimport akka.dispatch.Await
object FutureWithAwaitApp extends App { implicit val timeout = Timeout(50000 milliseconds) val system = ActorSystem("future") val echoActor = system.actorOf(Props[EchoActor]) val future = echoActor ? "Hello World" val result = Await.result(future, timeout.duration).asInstanceOf[String] println(result)}
Use Futures Directly
import akka.dispatch._import akka.util.duration._import akka.actor.ActorSystem
object MonadicFutureApplication extends App { implicit val system = ActorSystem("future")
val f1 = Future { "Hello" + "World" } val f2 = f1 map { x => x.length } val result = Await.result(f2, 1 second) println(result)}
Composing Futuresobject MultiMonadicFutureApplication extends App { implicit val system = ActorSystem("future")
val f1 = Future { "Hello" + "World" } val f2 = Future { 3 } val f3 = f1 flatMap { x => f2 map { y => x.length * y } }
val result = Await.result(f3, 1 second)}
Code Samples
https://github.com/meetumaltiar/AkkaKnolX
References
Viktor Klang talk on Akka 2.0 at NE Scala symposium
Akka website akka.io