docs: void loadBlock(BlockId blockId, ByteBuffer block) throws IOException {
          synchronized (m_accessLock) {
              if (! m_blockPathMap.containsKey(blockId)) {
                  throw new IllegalArgumentException("Request to load block that is not stored: " + blockId);
              }
  
              int origPosition = block.position();
              block.position(0);
              Path blockPath = m_blockPathMap.get(blockId);
              try (SeekableByteChannel channel = Files.newByteChannel(blockPath)) {
                  channel.read(block);
              }
              finally {
                  block.position(origPosition);
              }
          }
      }