gistfile1.scala

class HeartMonitor(millisUntilDeclaredDead: Long) extends Actor with FSM[Health, Long] {
  import System.{currentTimeMillis => now}
  val nextTest = 1000L

  notifying {
    case Transition(Stale, Alive) =>
      log.info("HeartMonitor received initial heartbeat")
    case Transition(Dead, Alive) =>
      log.info("HeartMonitor noticed we are back alive again")
    case Transition(_, Dead) =>
      log.error("HeartMonitor thinks we are dead")
  }

  when(Stale) {
    case Beat() => goto(Alive) using now until nextTest
    case SkippedBeat() => stay until nextTest
    case NoBeat() => goto(Dead)
  }

  when(Alive) {
    case Beat() => stay using now until nextTest
    case SkippedBeat() => stay until nextTest
    case NoBeat() => goto(Dead)
  }

  when(Dead) {
    case Beat() => goto(Alive) using now until nextTest
  }

  startWith(Stale, now, Some(nextTest))

  object SkippedBeat {
    def unapply(event: Event) = event match {
      case Event(StateTimeout, lastHeartBeatTimeMillis) if !isDead(lastHeartBeatTimeMillis) => true
      case _ => false
    }
  }

  object NoBeat {
    def unapply(event: Event) = event match {
      case Event(StateTimeout, lastHeartBeatTimeMillis) if isDead(lastHeartBeatTimeMillis) => true
      case _ => false
    }
  }

  object Beat {
    def unapply(event: Event) = event match {
      case Event(heartBeat: HeartBeat, _) => true
      case _ => false
    }
  }

  def isDead(lastHeartBeatTimeMillis: Long): Boolean = {
    now - lastHeartBeatTimeMillis > millisUntilDeclaredDead
  }
}