Question

I’m trying to reproduce this example.
Everything compiles, but when I run it, all my results look like this:

  scala> NameResolver ! ("www.scala-lang.org", self)

  scala> self.receiveWithin(0) { case x => x }
  res0: Any = TIMEOUT // and not Some(www.scala-lang.org/128.178.154.102)

  scala> NameResolver ! ("wwwwww.scala-lang.org", self)

  scala> self.receiveWithin(0) { case x => x }
  res1: Any = TIMEOUT // and not None

Here is my example:

import scala.actors._
import scala.actors.Actor._

case class Plus(x: Int, y: Int)

val concurrentCalculator = actor {
   while(true)
      receive {
         case Plus(x, y) => println(x + y)
         case (Plus(x, y), caller: Actor) => caller ! (x + y)
      }
}

scala> concurrentCalculator ! Plus(2,3)
5

scala> concurrentCalculator ! (Plus(2,3), self)

scala> self.receiveWithin(1000) { case x => x }
res0: Any = TIMEOUT // WTF?

So why am I getting a TIMEOUT instead of a valid result?

Answer 1

You can check that self returns different values on different calls not within a code block, due to the way Scala REPL works (every expression to be evaluated is compiled into a separate class):

scala> self
res3: scala.actors.Actor = scala.actors.ActorProxy@1bb0ff0

scala> self
res4: scala.actors.Actor = scala.actors.ActorProxy@46530

In one block of code it will work even if it isn’t explicitly declared as an actor:

scala> {
     | concurrentCalculator ! (Plus(2,3), self)
     | self.receiveWithin(1000) { case x => x }
     | }
res9: Any = 5