private RrdEntry requestEmpty(String path) throws InterruptedException, IOException {
  RrdEntry ref=waitEmpty(path);
  ref.count=1;
  return ref;
}

private RrdEntry requestEmpty ( String path ) throws InterruptedException , IOException { RrdEntry ref = waitEmpty ( path ) ; ref . count = 1 ; return ref ; }
got an empty reference , use it only if slots are available but don ' t hold any lock waiting for it
