Question

What does function eventloop do in Scala Actors and what is it useful for?

Answer 1

eventloop works similarly to loop and react being combined. The difference between loop and eventloop is that loop, in fact, doesn’t call the body recursively (to prevent stack overflow for thread-based actors), but schedules handling (react/receive) of a next message from the mailbox, and finishes execution of a current handler throwing an exception, to clear up the call stack.

eventloop recursively handles the messages using react – in case of react it’s safe (and stack doesn’t get overflown), because the body of react (but not receive!) always ends with an exception, in the most cases, and the next loop scheduled, to guarantee a fair access to the thread pool form all actors. Therefore, eventloop can be used only with event-driven actors.

import scala.actors._
import Actor._

class EventLoop extends Actor {
   def act = eventloop{
      case msg => println("Received " + msg)
   }
}