docs: public synchronized void markCompleted(Piece piece) {
      if (this.completedPieces.get(piece.getIndex())) {
        return;
      }
  
      // A completed piece means that's that much data left to download for
      // this torrent.
      myTorrentStatistic.addLeft(-piece.size());
      this.completedPieces.set(piece.getIndex());
      if (completedPieces.cardinality() == getPiecesCount()) {
        logger.info("all pieces are received for torrent {}. Validating...", this);
      }
    }