private static void reapCollectedRefs() {
    while (true) {
      final Reference<?> ref = ourRefQueue.poll();
      if (ref == null) break;
      if (!(ref instanceof WeakReferenceDisposable)) continue;
      Disposer.dispose((Disposable)ref);  // the referent is gone, remove from the Disposer tree
    }
  }
private static void reapCollectedRefs()