private @NotNull Int2IntMultimap valueHashToId() throws IOException {
    try {
      if (valueHashToId == null) {
        valueHashToId = valueHashToIdFuture.get();
      }
      return valueHashToId;
    }
    catch (InterruptedException e) {
      throw new IOException(e);
    }
    catch (ExecutionException e) {
      throw new IOException(e.getCause());
    }
  }
private @NotNull Int2IntMultimap valueHashToId()