Akka/Scala：映射 Future 与 pipelineTo

In Akka参与者，在发送一个Future结果给另一个演员：

A. 映射Future发挥作用tell结果给演员。

B. 定义一个onSuccess未来的回调，其中tell结果给演员。

C. 管道Future结果给演员pipeTo.

其中一些选项已在上一个问题中讨论过：

Akka：向 Actor 发送未来消息 https://stackoverflow.com/questions/16401376/akka-send-a-future-message-to-an-actor

这三种方法中哪一种是首选方法，为什么？

Also,我想知道，如果receive应该是类型Any => Unit, then 为什么代码可以编译当在某些情况下的偏函数receive返回一个Future, not Unit?

这是我上面提到的三个选项的代码示例：

import akka.actor.{Actor, ActorRef, ActorSystem, Props}
import akka.pattern.ask
import akka.util.Timeout
import akka.pattern.pipe

import scala.concurrent.Future
import scala.concurrent.duration._
import scala.language.postfixOps
import scala.util.Success

class ActorIncrement extends Actor {

  def receive = {
    case i: Int =>
      println(s"increment $i")
      sender ! i + 1
  }
}

class ActorEven extends Actor {

  def receive = {
    case i: Int =>
      println(s"$i is even")
  }
}


class ActorOdd extends Actor {

  def receive = {
    case i: Int =>
      println(s"$i is odd")
  }
}

class MyActor(actorIncrement: ActorRef, actorEven: ActorRef, actorOdd: ActorRef) extends Actor {
  import scala.concurrent.ExecutionContext.Implicits.global

  implicit val timeout = Timeout(5 seconds)

  def receive = {
    case i: Int if i % 2 == 0 =>
      println(s"receive a: $i")
      actorIncrement ? i map {
        case j: Int =>
          println(s"$j from increment a")
          actorOdd ! j
      }
    case i: Int =>
      println(s"receive b: $i")
      val future: Future[Any] = actorIncrement ? i
      future onSuccess {
        case i: Int =>
          println(s"$i from increment b")
          actorEven ! i
      }

    case s: String =>
      println(s"receive c: $s")
      (actorIncrement ? s.toInt).mapTo[Int] filter(_ % 2 == 0) andThen { case Success(i: Int) => println(s"$i from increment c") } pipeTo actorEven
  }
}

object TalkToActor extends App {

  // Create the 'talk-to-actor' actor system
  val system = ActorSystem("talk-to-actor")

  val actorIncrement = system.actorOf(Props[ActorIncrement], "actorIncrement")
  val actorEven = system.actorOf(Props[ActorEven], "actorEven")
  val actorOdd = system.actorOf(Props[ActorOdd], "actorOdd")

  val myActor = system.actorOf(Props(new MyActor(actorIncrement, actorEven, actorOdd)), "myActor")

  myActor ! 2
  myActor ! 7
  myActor ! "11"

  Thread.sleep(1000)

  //shutdown system
  system.terminate()
}

如果你看看如何pipeTo定义于akka.pattern.PipeToSupport,

def pipeTo(recipient: ActorRef)(implicit sender: ActorRef = 
  Actor.noSender): Future[T] = {
    future andThen {
      case Success(r) ⇒ recipient ! r
      case Failure(f) ⇒ recipient ! Status.Failure(f)
    }
  }
}

如你看到的...pipeTo与仅仅添加没有什么不同andThen打电话给你的Future它要么发送未来结果，要么发送Status.Failure给管道演员的消息，以防您Future fails.

现在主要的区别在于这个Status.Failure故障处理。如果您不使用pipeTo，你可以用任何你想要的方式来处理你的失败。