flush method
Implementation
Future<void> flush() async {
final buffer = utf8.encode(json.encode(_subject));
final length = buffer.length;
RandomAccessFile file = await _getRandomFile();
_randomAccessFile = await file.lock();
_randomAccessFile = await _randomAccessFile!.setPosition(0);
_randomAccessFile = await _randomAccessFile!.writeFrom(buffer);
_randomAccessFile = await _randomAccessFile!.truncate(length);
_randomAccessFile = await file.unlock();
_madeBackup();
}