询问演员并让他在 Akka 2 中达到特定状态时做出回应

Question

我对 Akka 很陌生，所以我的问题可能看起来很简单：

我有一个叫workerA 的演员，它使用FSM，因此可以处于Finished 和Computing 这两种状态：

sealed trait State
case object Finished extends State
case object Computing extends State

sealed trait Data
case object Uninitialized extends Data
case class Todo(target: ActorRef, queue: immutable.Seq[Any]) extends Data

当workerA 接收到GetResponse 时，它应该回答它是否处于状态Finished。

这样做的正确方法是什么？我知道我们应该避免在这种范式中被阻塞，但这里只关注顶级参与者。 谢谢

Answer 1

我不一定确定您是否需要 FSM。当您有许多状态以及这些状态之间的许多可能（并且可能很复杂）的状态转换时，FSM 是一个非常好的工具。就您而言，如果我理解正确，您基本上有两种状态；收集数据并完成。似乎也只有一个状态转换，从gathering -> finished 开始。如果这一切都正确，那么我建议您只需使用become 来解决您的问题。

我在下面有一些代码来展示我所描述的一个简单的例子。基本思想是主角将一些工作分给一些工人，然后等待结果。如果有人在工作完成时询问结果，演员会隐藏该请求，直到工作完成。完成后，演员将回复任何要求结果的人。代码如下：

case object GetResults
case class Results(ints:List[Int])
case object DoWork

class MainActor extends Actor with Stash{
  import context._

  override def preStart = {
    val a = actorOf(Props[WorkerA], "worker-a")
    val b = actorOf(Props[WorkerB], "worker-b")
    a ! DoWork
    b ! DoWork
  }

  def receive = gathering(Nil, 2)

  def gathering(ints:List[Int], count:Int):Receive = {
    case GetResults => stash()
    case Results(i) =>      
      val results = i ::: ints
      val newCount = count - 1
      if (newCount == 0){
        unstashAll()
        become(finished(results))        
        child("worker-a") foreach (stop(_))
        child("worker-b") foreach (stop(_))
      }
      else
        become(gathering(results, newCount))
  } 

  def finished(results:List[Int]):Receive = {
    case GetResults => sender ! results
  }
}

class WorkerA extends Actor{
  def receive = {
    case DoWork =>

      //Only sleeping to simulate work.  Not a good idea in real code
      Thread sleep 3000
      val ints = for(i <- 2 until 100 by 2) yield i
      sender ! Results(ints.toList)
  }
}

class WorkerB extends Actor{
  def receive = {
    case DoWork =>

      //Only sleeping to simulate work.  Not a good idea in real code
      Thread sleep 2000  
      val ints = for(i <- 1 until 100 by 2) yield i
      sender ! Results(ints.toList)      
  }
}

那么你可以如下测试：

val mainActor = system.actorOf(Props[MainActor])
val fut = mainActor ? GetResults
fut onComplete (println(_))

Answer 2

您可以对 FSM 状态进行模式匹配：

// insert pattern matching stuff instead of ...

class MyActor extends Actor with FSM[State, Message] {
  startWith(Finished, WaitMessage(null))

  when(Finished) {
    case Event(Todo(... =>
      // work
      goto(Computing) using Todo(...)
    case Event(GetResponse(... =>
      // reply: sender ! msg // or similar
  }

  /* the rest is optional. You can use onTransition below to send yourself a message to    report status of the job: */
  when(Busy) {
    case Event(Finished(... =>
      // reply to someone: sender ! msg // or similar
      goto(Finished)
  }

  onTransition {
    case Finished -> Computing =>
      // I prefer to run stuff here in a future, and then send a message to myself to signal the end of the job:
      self ! Finished(data)
  }

更具体地解决问题的编辑：

class MyActor extends Actor with FSM[State, Message] {
  startWith(Finished, WaitMessage(null))

  when(Finished) {
    case Event(Todo(... =>
      // work
      goto(Computing) using Todo(...)
    case Event(GetResponse(... =>
      // reply: sender ! msg // or similar
      stay
  }

  initialize()
}