问为什么这个顽固的演员不能工作？

EN

import akka.persistence._
import akka.actor.{Actor, ActorRef, ActorSystem, Props, ActorLogging}


class Counter extends PersistentActor with ActorLogging {

  import Counter._

  var state: State = new State(0)

  override def receiveRecover: Receive = {
    case RecoveryCompleted => println("Recovery completed.")
    case SnapshotOffer(_, snapshot: State) => state = snapshot
    case op: Operation => updateState(op)
  }


  override def persistenceId: String = "counter-persistent"

  override def receiveCommand: Receive = {
    case op: Operation =>
      println(s"Counter receive ${op}")
      persist(op) {
        op => updateState(op)
      }
    case "print" => println(s"The current state of couter is ${state}")
    case SaveSnapshotFailure(_, reason) => println(s"save snapshot failed, reason: ${reason}")
    case SaveSnapshotSuccess(_) => println(s"snapshot saved")
  }

  def updateState(op: Operation): Unit = op match {
    case Increment(n) =>
      state = state.inc(n)
      takeSnapshot
    case Decrement(n) =>
      state = state.dec(n)
      takeSnapshot
  }

  def takeSnapshot: Unit = {
    //    if (state % 5 == 0) saveSnapshot()
    saveSnapshot()
  }
}


object Counter {

  sealed trait Operation {
    val count: Int
  }

  case class Increment(override val count: Int) extends Operation

  case class Decrement(override val count: Int) extends Operation

  final case class State(n: Int) {
    def inc(x: Int) = State(n + x)

    def dec(x: Int) = State(n - x)
  }

}







object Persistent extends App {

  import Counter._

  val system = ActorSystem("persistent-actors")

  val counter = system.actorOf(Props[Counter])

  counter ! Increment(3)
  counter ! Increment(5)
  counter ! Decrement(3)
  counter ! "print"

  Thread.sleep(1000)

  system.terminate()

}

akka {
  persistence {
    journal {
      plugin = "akka.persistence.journal.leveldb",
      leveldb {
        dir = "target/example/journal",
        native = false
      }
    },
    snapshot-store {
      plugin = "akka.persistence.snapshot-store.local",
      local {
        dir = "target/example/snapshots"
      }
    }
  }
}

Recovery completed.
Counter receive Increment(3)
Counter receive Increment(5)
Counter receive Decrement(3)
The current state of couter is State(5)
snapshot saved
snapshot saved
snapshot saved

Recovery completed.
Counter receive Increment(3)
Counter receive Increment(5)
Counter receive Decrement(3)
The current state of couter is State(5)
snapshot saved
snapshot saved
snapshot saved