I have a class that is read heavy with low contention on writes. I'd like
to be able to access a piece of shared mutable state outside of Actors. The
state itself (AnnouncementRegistry) is immutable. Since it is a single
writer, having a shared @volatile var between the actor and the class seems
to be a good approach, however it also has a code smell to it since I am
closing over external mutable state and using an anonymous actor. Is there
a better approach to what I have below?
class DiscoveryClient(config: DiscoveryConfig, singleRequest: HttpRequest =>
Future[HttpResponse])
(implicit system: ActorSystem, m: Materializer) {
@volatile
private[this] var _registry = AnnouncementRegistry.empty
def registry = _registry
private[this] val client = system.actorOf(Props(new Actor with ActorLogging {
import DiscoveryClient._
private[this] var subscribers = HashSet.empty[ActorRef]
private[this] val killswitch =
ChangeWatcher(config.seeds, singleRequest).to(Sink.foreach(self !
RegistryUpdate(_))).run()
def receive: Receive = uninitialized
private[this] def uninitialized: Receive = {
case Subscribe =>
subscribers += sender
context.watch(sender)
case Terminated(ref) =>
subscribers -= ref
case m @ RegistryUpdate(newRegistry) =>
_registry = newRegistry
context.become(initialized)
subscribers.foreach(_ ! m)
}
private[this] def initialized: Receive = {
case Subscribe =>
subscribers += sender
context.watch(sender)
sender ! RegistryUpdate(_registry)
case Terminated(ref) =>
subscribers -= ref
case m @ RegistryUpdate(newRegistry) =>
_registry = newRegistry
subscribers.foreach(_ ! m)
}
override def postStop(): Unit = killswitch.shutdown()
}), "discovery-client")
}
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