akka.event.EventStreamUnsubscriber.scala Maven / Gradle / Ivy
The newest version!
/**
* Copyright (C) 2009-2016 Lightbend Inc.
*/
package akka.event
import akka.actor._
import akka.event.Logging.simpleName
import java.util.concurrent.atomic.AtomicInteger
/**
* INTERNAL API
*
* Watches all actors which subscribe on the given eventStream, and unsubscribes them from it when they are Terminated.
*
* Assumptions note:
* We do not guarantee happens-before in the EventStream when 2 threads subscribe(a) / unsubscribe(a) on the same actor,
* thus the messages sent to this actor may appear to be reordered - this is fine, because the worst-case is starting to
* needlessly watch the actor which will not cause trouble for the stream. This is a trade-off between slowing down
* subscribe calls * because of the need of linearizing the history message sequence and the possibility of sometimes
* watching a few actors too much - we opt for the 2nd choice here.
*/
protected[akka] class EventStreamUnsubscriber(eventStream: EventStream, debug: Boolean = false) extends Actor {
import EventStreamUnsubscriber._
override def preStart() {
if (debug) eventStream.publish(Logging.Debug(simpleName(getClass), getClass, s"registering unsubscriber with $eventStream"))
eventStream initUnsubscriber self
}
def receive = {
case Register(actor) ⇒
if (debug) eventStream.publish(Logging.Debug(simpleName(getClass), getClass, s"watching $actor in order to unsubscribe from EventStream when it terminates"))
context watch actor
case UnregisterIfNoMoreSubscribedChannels(actor) if eventStream.hasSubscriptions(actor) ⇒
// do nothing
// hasSubscriptions can be slow, but it's better for this actor to take the hit than the EventStream
case UnregisterIfNoMoreSubscribedChannels(actor) ⇒
if (debug) eventStream.publish(Logging.Debug(simpleName(getClass), getClass, s"unwatching $actor, since has no subscriptions"))
context unwatch actor
case Terminated(actor) ⇒
if (debug) eventStream.publish(Logging.Debug(simpleName(getClass), getClass, s"unsubscribe $actor from $eventStream, because it was terminated"))
eventStream unsubscribe actor
}
}
/**
* INTERNAL API
*
* Provides factory for [[akka.event.EventStreamUnsubscriber]] actors with **unique names**.
* This is needed if someone spins up more [[EventStream]]s using the same [[akka.actor.ActorSystem]],
* each stream gets it's own unsubscriber.
*/
private[akka] object EventStreamUnsubscriber {
private val unsubscribersCount = new AtomicInteger(0)
final case class Register(actor: ActorRef)
final case class UnregisterIfNoMoreSubscribedChannels(actor: ActorRef)
private def props(eventStream: EventStream, debug: Boolean) =
Props(classOf[EventStreamUnsubscriber], eventStream, debug)
def start(system: ActorSystem, stream: EventStream) = {
val debug = system.settings.config.getBoolean("akka.actor.debug.event-stream")
system.asInstanceOf[ExtendedActorSystem]
.systemActorOf(props(stream, debug), "eventStreamUnsubscriber-" + unsubscribersCount.incrementAndGet())
}
}