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Strange behavior: Scala Actors 2.7.7 vs. 2.8-Snapshot

Answer 1

+3 A:

There are some problems with the code. Foremost among them, don't do this:

object ActorApplication extends Application

When you use extends Application, the way your code is run imposes a number of restrictions, such as not being optimizable by the JIT and, of particular relevance to your case, threads won't work correctly. I find it harder to explain what happened on 2.7.7 than what happened on 2.8. Instead, just write a normal object, and define the main method.

Other stuff:

gearController ! StartSync()

Don't do this. Always send a message to an actor from inside an actor, and this line is inside ActorApplication constructor, which is not an actor. In situations like this, you can do this:

Actor.actor { gearController ! StartSync() }

Speaking of StartSync, don't do this:

case class StartSync

A class without parameters is meaningless (and deprecated). Instead, do this:

case object StartSync

and drop the parenthesis after StartSync in the places where you use it.

Also, there's nothing wrong with scala.util.Random, though it was easier to misuse it on Scala 2.7 than it is on Scala 2.8, by creating a new Random generator every time you needed a random number (which is what you do in the code). Instead, on Scala 2.8, just this ought to work:

  private var mySpeed = scala.util.Random.nextInt(1000)

Finally, there's nothing wrong with either execution, it's just the scheduler that's different between them. In fact, given that you created a hundred actors, the GearController was receiving a disproportional amount of execution time in the Scala 2.7 version, as Scala doesn't create a thread for every actor.

Now, if you want GearController not to share a thread with the others, you should use while(true)/receive instead of loop/react, like this:

    while(true) {
      receive {
        case StartSync => {

Which will produce a result quite similar to what 2.7 produced.

Daniel 2010-02-08 22:55:48

Thank you Daniel for your helpful answer. I did the changes and my code runs well in Scala 2.8. I'll do a simple Scala-swing-GUI for this simulation and publish it on github.

pmeiclx 2010-02-11 13:02:05

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Strange behavior: Scala Actors 2.7.7 vs. 2.8-Snapshot

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