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post.scala

class UserServiceActor(userDb: Map[Int, User],
                       latch: CountDownLatch,
                       numQueries: Int) extends Actor {
  private var left = numQueries
  def receive = {
    case Request(id) =>
      userDb.get(id) match {
        case Some(u) => sender() ! u
        case None =>
      }
      if (left == 0) {
        latch.countDown()
        context stop self
      }
      left -= 1
  }
}

class UserQueryActor(latch: CountDownLatch,
                     numQueries: Int,
                     numUsersInDB: Int) extends Actor {

  private var left = numQueries
  private val receivedUsers: mutable.Map[Int, User] = mutable.Map()
  private val randGenerator = new Random()
 
  override def receive: Receive = {
    case u: User => {
      receivedUsers.put(u.userId, u)
      if (left == 0) {
        latch.countDown()
        context stop self
      } else {
        sender() ! Request(randGenerator.nextInt(numUsersInDB))
      }
      left -= 1
    }
  }
}