Responder.run does not work with Futures #3458

scabug · 2010-05-20T13:53:43Z

Calling Responder.run on Futures does not work.

Running this

import actors.Actor._
import actors.Futures._
import Responder._

println("Result:" + run( constant(42) ) )

println("Result: " +  run( future{Thread.sleep(1000); 42} ) )

actor{ println("Result: " +  run( future{Thread.sleep(1000); 42} ) ) }

in the REPL yields

Welcome to Scala version 2.8.0.RC2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_20).

scala> import actors.Actor._
scala> import actors.Futures._
scala> import Responder._

scala> println("Result:" + run( constant(42) ) )
Result:Some(42)

scala> println("Result: " +  run( future{Thread.sleep(1000); 42} ) )
scala.actors.SuspendActorControl

scala.actors.ActorProxy@2026c088: caught java.lang.InterruptedException
java.lang.InterruptedException
	at scala.actors.ActorProxy.exit(ActorProxy.scala:33)
	at scala.actors.Reactor$$$$anonfun$$2.apply(Reactor.scala:253)
	at scala.actors.Reactor$$$$anonfun$$2.apply(Reactor.scala:253)
    ...

scala> actor{ println("Result: " +  run( future{Thread.sleep(1000); 42} ) ) }
res3: scala.actors.Actor = scala.actors.Actor$$$$anon$$1@69beea90
    ... NO OUTPUT ...

So running the future works neither in the main thread, nor inside an
actor. This is because Responder.run calls respond on the future,
which never returns for Futures:

object Responder {
  ...
  def run[A](r: Responder[A]): Option[A] = {
    var result: Option[A] = None
    r.foreach(x => result = Some(x))
    result
  }
  ...
}

abstract class Responder[+A] {
  ...
  def foreach(k: A => Unit) { respond(k) }
  ...
}

An ugly workaround would be to define

def run2[A](r: Responder[A]): Option[A] = r match {
  case f: actors.Future[_] => Some[A](f())
  case r => run(r)
}

using apply() in case of futures. Then this works:

scala> println("Result: " +  run2( future{Thread.sleep(1000); 42} ) )
Result: Some(42)

Proposed solution:

Obviously, run needs to do different things for different kinds
of Responders. But actually, Future provides the same functionality
with apply() that Responder.run() does for "normal" Responders.

An elegant solution would be to simply add an apply() method
to Responder, too, and have Responder.run just call apply on
the responder in question:

object Responder {
  ...
  def run[A](r: Responder[A]): Option[A] = Option(r())
  ...
}

abstract class Responder[+A] {
  ...
  def apply(): A = {
    var result: Option[A] = None
    r.foreach(x => result = Some(x))
    result orNull
  }
  ...
}

I'm not sure if the Option stuff in apply is strictly necessary, I just tried to preserve the current implementation of run as much as possible.

This would require very litte code changes. It also shouldn't break anything, should it?

scabug · 2010-05-20T13:53:43Z

Imported From: https://issues.scala-lang.org/browse/SI-3458?orig=1
Reporter: @oschulz

scabug · 2010-05-21T06:23:45Z

@oschulz said:
On second thought, apply() returning null wasn't such a bright
idea - sorry. So, I propose this instead:

class NoResponse(msg: String) extends RuntimeException(msg)

object Responder {
  ...
  def run[A](r: Responder[A]): Option[A] = {
    try { Some(r()) }
    catch { case e: NoResponse => None }
  }
  ...
}

abstract class Responder[+A] {
  ...
  def apply(): A = {
    var result: Option[A] = None
    foreach { x => result = Some(x) }
    result getOrElse { throw new NoResponse("NoResponse") }
  }
  ...
}

scabug · 2015-07-17T22:04:21Z

@SethTisue said:
Scala actors are deprecated and unmaintained

scabug closed this as completed Jul 17, 2015

scabug added the won't fix label Apr 7, 2017

scabug assigned phaller Apr 7, 2017

scabug mentioned this issue Apr 7, 2017

Future.foreach throws scala.actors.SuspendActorControl #5574

Closed

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Responder.run does not work with Futures #3458

Responder.run does not work with Futures #3458

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scabug commented Jul 17, 2015

Responder.run does not work with Futures #3458

Responder.run does not work with Futures #3458

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