code: private void mapAndSetOffset() {
          try {
              final RandomAccessFile backingFile = new RandomAccessFile(this.file, "rw");
              backingFile.setLength(this.size);
              final FileChannel ch = backingFile.getChannel();
              this.addr = (Long) mmap.invoke(ch, 1, 0L, this.size);
  
              ch.close();
              backingFile.close();
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
      }
docs: for the given length and set this.addr to the returned offset