}
    }
  }

  static class LoadingValueReference<K, V> implements ValueReference<K, V> {
    volatile ValueReference<K, V> oldValue;

    // TODO(fry): rename get, then extend AbstractFuture instead of containing SettableFuture
    final SettableFuture<V> futureValue = SettableFuture.create();
    final Stopwatch stopwatch = Stopwatch.createUnstarted();

    public LoadingValueReference() {