sclass TestPhantomCleanUp {
  settable bool withGC = true;
  settable double maxWait = 60.0; // how many seconds
  
  gettable bool referenceWasCleared;
  gettable Duration delayBeforeClearance;
  
  run {
    temp new RunnablesReferenceQueue queue;
    
    class MyPhantomRef<A> extends PhantomReference<A> is Runnable {
      new Flag flag;
    
      *(A a, RunnablesReferenceQueue queue) {
        super(a, queue!);
      }
    
      run {
        print("Behold the phantom!");
        flag.raise();
      }
    }
    
    var ref = new MyPhantomRef<S>(new S("copy of a string"), queue);
    if (withGC) timedGC();
    long time = sysNow();
    printWithMS("Waiting...");
    if (ref.flag.waitUntilUp(toMS_int(maxWait))) {
      delayBeforeClearance = msToDuration(sysNow()-time);
      referenceWasCleared = true;
      printWithMS("Cool! Reference was cleared after "
        + renderElapsedSecondsPleasantly(delayBeforeClearance));
    } else
      printWithMS("Ouch");
  }
}