Actor in Scala have multiple way of implementations. Here we are going to discuss about multiple ways of actors implementations.
Typesafe Stack combines the Scala language with the Akka framework.
Nowthough Scala has actors in its standard library, Akka uses its own implementation. And, if we look for other implementations, We can find that Lift and Scalaz have implementations too!
Design Philosophy of Actor
Scalaz Actors
Minimal complexity. Maximal generality, modularity and extensibility.
Lift Actors
Lift is an expressive and elegant framework for writing web applications. It stresses the importance of security, maintainability, scalability and performance, while allowing for high levels of developer productivity.
minimal complexity, Garbage Collection by JVM rather than worrying about an explicit lifecycle. Error handling behaviour consistent with other Scala & Java programs,
object ScheduledTask extends LiftActor {
case class DoNow()
case class StopIt()
private var stopped = false
def messageHandler = {
case DoNow if !stopped =>
Schedule.schedule(this, DoNow, 10 minutes)
// ... do useful work here
case StopIt =>
stopped = true
}
}Scala Actors
Provide the full Erlang actor model in Scala, lightweight/small memory footprint.
Akka Actors
Akka Actors have simple and transparently distributable, high performance, lightweight and highly adaptable.
The Actor Model provides a higher level of abstraction for writing concurrent and distributed systems. It alleviates the developer from having to deal with explicit locking and thread management, making it easier to write correct concurrent and parallel systems
object HelloMain {
final case class SayHello(str: String)
def apply(): Behavior[SayHi] =
Behaviors.setup { context =>
val greets = context.spawn(HelloWorld(), "greets")
Behaviors.receiveMessage { msg =>
val replyTo = context.spawn(HelloWorldBot(max = 3), msg.name)
greeter ! HelloWorld.Greeting(msg.name, replyTo)
Behaviors.same
}
}
}Level of state isolation
If user defines public methods on their Actors, are they callable from the outside?
- Scalaz Actors: n/a. Actor is a sealed trait.
- Lift Actor : Yes
- Scala Actors: Yes
- Akka Actors: No, actor instance is shielded behind an ActorRef.
Message processing
Supports nested receives?
- Scalaz Actors: —
- Lift : Yes (with a little hand coding).
- Scala Actors: both thread-based receive and event-based react.
- Akka Actors: No, nesting receives can lead to memory leaks and degraded performance over time.
Message send modes
Scalaz Actors Lift Actors Scala Actors Akka Actors
Fire-forget a ! message actor ! msg actor ! msg actorRef ! msg
a(message)
Send-receive-reply actor !? msg actor !? msg actorRef !! msg
actor !! msg
Send-receive-future actor !! msg actorRef !!! msg
Send-result-of- promise(message). future.onComplete( f => to ! f.result )
future to(actor)
Compose actor with actor comap f No No No
function
