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package kamon.util
import java.util
import java.util.concurrent.ConcurrentLinkedQueue
import akka.actor.{ Actor, ActorRef }
import org.HdrHistogram.WriterReaderPhaser
import scala.annotation.tailrec
/**
* A LazyActorRef accumulates messages sent to an actor that doesn't exist yet. Once the actor is created and
* the LazyActorRef is pointed to it, all the accumulated messages are flushed and any new message sent to the
* LazyActorRef will immediately be sent to the pointed ActorRef.
*
* This is intended to be used during Kamon's initialization where some components need to use ActorRefs to work
* (like subscriptions and the trace incubator) but our internal ActorSystem is not yet ready to create the
* required actors.
*/
class LazyActorRef {
private val _refPhaser = new WriterReaderPhaser
private val _backlog = new ConcurrentLinkedQueue[(Any, ActorRef)]()
@volatile private var _target: Option[ActorRef] = None
def tell(message: Any)(implicit sender: ActorRef = Actor.noSender): Unit = {
val criticalEnter = _refPhaser.writerCriticalSectionEnter()
try {
_target.map(_.tell(message, sender)) getOrElse {
_backlog.add((message, sender))
}
} finally { _refPhaser.writerCriticalSectionExit(criticalEnter) }
}
def point(target: ActorRef): Unit = {
@tailrec def drain(q: util.Queue[(Any, ActorRef)]): Unit = if (!q.isEmpty) {
val (msg, sender) = q.poll()
target.tell(msg, sender)
drain(q)
}
try {
_refPhaser.readerLock()
if (_target.isEmpty) {
_target = Some(target)
_refPhaser.flipPhase(1000L)
drain(_backlog)
} else sys.error("A LazyActorRef cannot be pointed more than once.")
} finally { _refPhaser.readerUnlock() }
}
}
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