Start and stop background tasks in SBT

gistfile1.scala

  val runner = AttributeKey[Runner]("runner")
  val start = TaskKey[Unit]("start", "start web runner")
  val stop = TaskKey[Unit]("stop", "stop web runner")

  trait Startable {
    def start()
    def stop()
  }

  class Runner {
    private var currentSubject:Option[Startable] = None

    def start(subject: Startable) {
      stop()
      subject.start()
      currentSubject = Some(subject)
    }
    def stop() {
      currentSubject foreach { _.stop() }
      currentSubject = None
    }
  }

  implicit def stateToRunner(s: State) = s.get(runner).get

  def onRecompile(s: State) {
    println("recompiled! " + s)
  }

  val webSettings = Seq(
    start <<= (state, fullClasspath in Runtime, scalaInstance in Runtime) map { (s, cp:Classpath, si:ScalaInstance) =>
      val loader = ClasspathUtilities.makeLoader(cp map {_.data}, si)

      val klass = loader.loadClass("com.btas.Launcher")

      s.start(new Startable {
        def start() { klass.getDeclaredMethod("start").invoke(null) }
        def stop() { klass.getDeclaredMethod("stop").invoke(null) }
      })

    },
    stop <<= state map { (s:State) =>
      s.stop()
    },
    onLoad in Global := { (state) => state.put(runner, new Runner) }
  )

Hi,
I'm looking for running some tasks in background, this code seems to do what i'm looking for.
But how to use it ? how to call start and stop methods ?