src/Pure/System/event_bus.scala

more precise treatment of prover definedness;

/*  Title:      Pure/System/event_bus.scala
    Author:     Makarius

Generic event bus with multiple receiving actors.
*/

package isabelle

import scala.actors.Actor, Actor._
import scala.collection.mutable.ListBuffer


class Event_Bus[Event]
{
  /* receivers */

  private val receivers = new ListBuffer[Actor]

  def += (r: Actor) { synchronized { receivers += r } }
  def + (r: Actor): Event_Bus[Event] = { this += r; this }

  def += (f: Event => Unit) {
    this += actor { loop { react { case x => f(x.asInstanceOf[Event]) } } }
  }

  def + (f: Event => Unit): Event_Bus[Event] = { this += f; this }

  def -= (r: Actor) { synchronized { receivers -= r } }
  def - (r: Actor) = { this -= r; this }


  /* event invocation */

  def event(x: Event) { synchronized { receivers.foreach(_ ! x) } }


  /* await global condition -- triggered via bus events */

  def await(cond: => Boolean)
  {
    case object Wait
    val a = new Actor {
      def act {
        if (cond) react { case Wait => reply(()); exit(Wait) }
        else {
          loop {
            react {
              case trigger if trigger != Wait =>
                if (cond) { react { case Wait => reply(()); exit(Wait) } }
            }
          }
        }
      }
    }
    this += a
    a.start
    a !? Wait
    this -= a
  }
}