Minimalist Scala Actors

minscalaactors.scala

object Actor {
    import java.util.concurrent.{ConcurrentLinkedQueue, Executor}
    import java.util.concurrent.atomic.{AtomicBoolean}

    sealed trait Instr
    case object Continue extends Instr
    case class Become(b: Any => Instr) extends Instr
    case object Dead extends Instr

    trait Address {
      def !(msg: Any): Unit
    }

  def apply(initial: Any => Instr)(implicit e: Executor): Address = {
    val a: Address = new Address with Runnable {
     private final val mbox = new ConcurrentLinkedQueue[Any]
       private final val on = new AtomicBoolean(false)
       private var behavior: Any => Instr = {
         case i: Instr => i
         case _ => println("Unknown message"); Continue
       }

       final def trySchedule(): Unit = if(!mbox.isEmpty && on.compareAndSet(false, true)) {
         try e.execute(this) catch {
           case anything => assert(on.getAndSet(false)); throw anything
         }
       }

       final def reactTo(msg: Any): Unit = behavior(msg) match {
         case Become(newBeh) => behavior = newBeh
         case Dead     => println("Dead, cannot deal with: " + msg)
         case Continue => //Just remain as you were
       }
      
       final def run() = try reactTo(mbox.poll()) finally {
         assert(on.getAndSet(false))
         trySchedule()
       }

       final override def !(msg: Any): Unit = {
         assert(mbox.offer(msg))
         trySchedule()
       }
     }
     a ! Become(initial)
     a
  }
}