scala - Akka Actor - 发件人指向死信

Question

考虑以下示例:

case class Payload(message: String, async: Boolean)

class EchoActor extends Actor {
  override def receive: Receive = {
    case Payload(message, async) =>
      if (async) Future {
        println(s"from: $sender")
        sender ! message
      } else {
        println(s"from: $sender")
        sender ! message
      }
  }
}

def main(args: Array[String]): Unit = {
  val system = ActorSystem("demo")
  val echo = system.actorOf(Props[EchoActor])
  implicit val timeout = Timeout(2 seconds)

  (echo ? Payload("Hello", async = false)).mapTo[String].foreach(println(_))
  (echo ? Payload("Async Hello", async = true)).mapTo[String].foreach(println(_))

  StdIn.readLine()
  system.terminate()
}

控制台输出:

from: Actor[akka://demo/temp/$a]
Hello
from: Actor[akka://demo/deadLetters]
[INFO] [04/13/2017 19:56:58.516] [demo-akka.actor.default-dispatcher-4] [akka://demo/deadLetters] Message [java.lang.String] from Actor[akka://demo/user/$a#2112869650] to Actor[akka://demo/deadLetters] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.

即当从另一个线程访问时，发送者指向 deadLetters。

这背后的原因是什么？是bug吗？

虽然，我们可以保存对实际发件人的引用以使其工作:

if (async) {
  val currentSender = sender()
  Future {
    println(s"from: $currentSender")
    currentSender ! message
  }
}

但是...没有更好的方法吗？

Answer 1

这不是错误，而是记录在案的行为 -

http://doc.akka.io/docs/akka/2.5.0/scala/actors.html#Send_messages

使用 Future 意味着调用一个匿名函数，该函数不是 Actor 类的实例，因此您的 sender() 引用映射到deadLetters 邮箱