ConcurrentHashMap getOrElseProduce()

getOrElseProduce.scala

import akka.dispatch.Future._

def getOrElseProduce(key: K, producer: => V): Future[V] = {
  val f = empty[V]()
  putIfAbsent(key, f) match {
    case null => f completeWithResult producer
    case value => value
  }
}