Behavior control (become / unbecome)

1. Become() 을 사용하지 않고 구현

• mutable variable 로 상태 관리

import akka.actor.{Actor, ActorSystem, Props}

object AkkaTest {
  object Kid {
    def props() = Props(new Kid())
    case object KidAccept
    case object KidReject

    val HAPPY = "happy"
    val SAD = "sad"
  }

  object Mom {
    def props() = Props(new Mom())

    case class Food(food: String)
    case class Ask(message: String)

    val VEGETABLE = "vegetable"
    val CHOCOLATE = "chocolate"
  }

  class Kid extends Actor {
    import Kid._
    import Mom._

    var state: String = HAPPY

    override def receive: Receive = {
      case Food(VEGETABLE) => state = SAD
      case Food(CHOCOLATE) => state = HAPPY
      case Ask(_) =>
        if (state == HAPPY) sender() ! KidAccept
        else sender() ! KidReject
    }
  }

  class Mom extends Actor {
    import Kid._

    override def receive: Receive = {
      case KidAccept => println("My kid is happy")
      case KidReject => println("My kid is sad")
    }
  }

  def main(args: Array[String]): Unit = {
    val actorSystem: ActorSystem = ActorSystem(name = "actorCapabilitiesDemo")

    val kidActor = actorSystem.actorOf(Kid.props(), "kidActor")
    val momActor = actorSystem.actorOf(Mom.props(), "momActor")

    import Mom._
    kidActor.tell(Ask("Do you want to play?"), momActor)
    kidActor.tell(Food(VEGETABLE), momActor)
    kidActor.tell(Ask("Do you want to play?"), momActor)
  }
}

 

결과

My kid is happy
My kid is sad

 

2. Become() 을 사용해 구현

import akka.actor.{Actor, ActorSystem, Props}

object AkkaMain {
  object Kid {
    def props() = Props(new Kid())
    case object KidAccept
    case object KidReject

    val HAPPY = "happy"
    val SAD = "sad"
  }

  object Mom {
    def props() = Props(new Mom())

    case class Food(food: String)
    case class Ask(message: String)

    val VEGETABLE = "vegetable"
    val CHOCOLATE = "chocolate"
  }

  class Kid extends Actor {
    import Kid._
    import Mom._

    var state: String = HAPPY

    override def receive: Receive = {
      case Food(VEGETABLE) => state = SAD
      case Food(CHOCOLATE) => state = HAPPY
      case Ask(_) =>
        if (state == HAPPY) sender() ! KidAccept
        else sender() ! KidReject
    }

    // state == HAPPY 인 상태에서
    def happyReceive: Receive = {
      case Food(VEGETABLE) => context.become(sadReceive)
      case Food(CHOCOLATE) => // 현재 상태 그대로 유지
      case Ask(_)          => sender() ! KidAccept
    }

    // state == SAD 상태에서
    def sadReceive: Receive = {
      case Food(VEGETABLE) => // 현재 상태 그대로 유지
      case Food(CHOCOLATE) => context.become(happyReceive)
      case Ask(_)          => sender() ! KidReject
    }
  }

  class Mom extends Actor {
    import Kid._

    override def receive: Receive = {
      case KidAccept => println("My kid is happy")
      case KidReject => println("My kid is sad")
    }
  }

  def main(args: Array[String]): Unit = {
    val actorSystem: ActorSystem = ActorSystem(name = "actorCapabilitiesDemo")

    val kidActor = actorSystem.actorOf(Kid.props(), "kidActor")
    val momActor = actorSystem.actorOf(Mom.props(), "momActor")

    import Mom._
    kidActor.tell(Ask("Do you want to play?"), momActor)
    kidActor.tell(Food(VEGETABLE), momActor)
    kidActor.tell(Ask("Do you want to play?"), momActor)
  }
}

 

참고

context.become() 의 두번째 파라미터 discardOld 값이 False 로 지정되면 (default: True) behavior(Receive) 가 stack 된다. 이상태에서 가장 상위의 behavior 하나가 선택되어 동작한다. context.become() 이 호출되면 가장 상위의 behavior 가 제거되고, 바로 아래 있던 behavior 로 동작한다. unbecome() 을 남용하면 코드가 매우 복잡해 질 수 있을 것 같다. become() 은 https://wefree.tistory.com/289 상황 처럼 사용하면 유용할 것 같다.