Question

Let’s say you have a gui component and 10 threads all tell it to repaint at sufficiently the same time as they all arrive before a single paint operation takes place. Instead of naively wasting resources repainting 10 times, just merge/ignore all but the last one and repaint once (or more likely, twice–once for the first, and once for the last). My understanding is that the Swing repaint manager does this.

Is there a way to accomplish this same type of behavior in a Scala Actor? Is there a way to look at the queue and merge messages, or ignore all but the last of a certain type or something?

Answer 1

Something like this?:

act = 
  loop { 
    react {
      case Repaint(a, b) => if (lastRepaint + minInterval < System.currentTimeMillis) {
          lastRepaint = System.currentTimeMillis
          repaint(a, b)
    }
  }

If you want to repaint whenever the actor’s thread gets a chance, but no more, then:
(UPDATE: repainting using the last message arguments)

act =
  loop {
    react {
      case r@Repaint(_, _) =>  
        var lastMsg = r
        def findLast: Unit = {
          reactWithin(0) {
            case r@Repaint(_, _) => 
              lastMsg = r
            case TIMEOUT => repaint(lastMsg.a, lastMsg.b)
          }
        }
        findLast
    }
  }