code: TreeMap<Integer,BuildReference<R>> all() {
          if (!fullyLoaded) {
              synchronized (this) {
                  if (!fullyLoaded) {
                      Index copy = copy();
                      for (Integer number : numberOnDisk) {
                          if (!copy.byNumber.containsKey(number))
                              load(number, copy);
                      }
                      index = copy;
                      fullyLoaded = true;
                  }
              }
          }
          return index.byNumber;
      }
docs: /*package