Creating a lazy actor router in Akka with timeout - akka

Question

I have spent the last two days learning Actors, and I want to create an expiring cache. Now we use a tenant model so I want each tenant to be represented by an actor. I would like these actors to be created when required, and timeout after a period of being idle.
To solve this I have mocked up the following as I am unaware of a provided solution, and am looking for any critique or validation of the approach.
//A simple Message carrying just the name of the actor
case class Message(name:String)
//Actor that will expire after a timeout period and stop itself
class ExpireActor extends Actor {
val id = Random.nextInt(1000)
context.setReceiveTimeout(100 milliseconds)
def receive ={
case Message(_) => println("Message: " + id + " " + System.currentTimeMillis())
case ReceiveTimeout => {
println("Timeout: " + id + " " + System.currentTimeMillis())
self ! PoisonPill
}
}
}
//Router for creating actors on demand
case class LazyRouter() extends RouterConfig {
def routerDispatcher: String = Dispatchers.DefaultDispatcherId
def supervisorStrategy: SupervisorStrategy = SupervisorStrategy.defaultStrategy
def createRoute(routeeProvider: RouteeProvider): Route = {
{
case (sender, Message(name)) ⇒
routeeProvider.context
.child(name)
.map(a => List(Destination(sender, a)))
.getOrElse{
synchronized {
routeeProvider.context
.child(name) //Dont want to call sync until I have to, so need to check existence again
.map(a => List(Destination(sender, a)))
.getOrElse{
val ref = routeeProvider.context.actorOf(Props[ExpireActor], name)
routeeProvider.registerRoutees(List(ref))
List(Destination(sender, ref))
}
}
}
}
}
}

Answer 1

I'm not sure I'm fully on board with your approach. Actors are very lightweight. When they are not doing anything they are not costing you anything CPU wise. Why not just pre-create all of the cache actors (for each possible tenant) before hand so the router does not have to have that scary synchronized block around whether or not it needs to create the routee. Then, instead of stopping the actors when they are idle for a specific amount of time, just clear out their internal state (which I'm assuming is the cached data) if you want to free up that memory. This will greatly simplify your code and make it more reliable (and probably faster to boot).