code: public boolean releaseIfHolds(T referenced)
      {
          Ref ref = references.remove(referenced);
          if (ref != null)
              ref.release();
          return ref != null;
      }
docs: Release the retained Ref to the provided object, if held, return false otherwise
  @param referenced the object we retain a Ref to
  @return return true if we held a reference to the object, and false otherwise