docs: private DataBlock getWriteDataBlock() throws IOException {
          if (writableBlocks.size() != 0) {
              return writableBlocks.get(0);
          }
  
          lock.lock();
          try {
              if (writableBlocks.size() != 0) {
                  return writableBlocks.get(0);
              }
              DataBlock dataBlock = new DataBlock(storeConfig);
              NAME_BLOCK_MAP.put(dataBlock.getFileId(), dataBlock);
              writableBlocks.add(dataBlock);
              return dataBlock;
          } finally {
              lock.unlock();
          }
      }