如何从另一个尚未准备好的演员那里要求数据？

Question

class A extends Actor {
  var data = Option.empty[Int]
  val requestors = mutable.Set[ActorRef]

  def receive = {
    case data: Int => 
      this.data = Some(data)
      requestors.foreach {_ ! data}
    case Request => 
      if (data.isEmpty) {
        requestors.add(sender)
        //What should I send back to sender here?
      } else {
        sender ! data.get
      }
  }
}

(actorA ? Request()).map {
  //if the data is not ready here, how can I wait for data?
}

dataActor ! 100

问题是，当请求者请求时，数据可能还没有准备好，所以请求的未来可能会失败。我需要给发送者发送一些东西来保证有数据，但显然Akka似乎没有promiseAkaik。

这里如何落实？

Answer 1

几种可能性。

首先，您可以返回实际的选项(data.get无论如何都是“代码气味”，最好避免）：

 case Request() => data

然后在客户端继续尝试：

 def result: Future[Int] = (actor ? Request()).map { 
    case Some(n) => n
    case None => after(1 second, system.scheduler)(result)
 }

val ready = Promise[Int]()

case data: Int => 
   this.data = data
   ready.complete(data)
case Request() => 
   data.fold(ready.future)(Future.successful)

 val result: Future[Int] = (actor ? Request()).flatMap {
    case f: Future[Int] => f
 }