HashDBM constructor

HashDBM(RandomAccessFile file, { int buckets = 10007, bool flush = true, bool crc = false, bool readonly = false, bool versioned = false, })

Open a new database. Optional parameters are: buckets which sets the number of hash buckets to use, flush which when set to true will force data to disk every time it is changed, crc which will enable CRC checks on underlying records if set to true, and readonly which opens the database with a shared lock and prevents mutations. The defaults are generally good enough.

Implementation

HashDBM(RandomAccessFile file,
    {int buckets = 10007,
    bool flush = true,
    bool crc = false,
    bool readonly = false,
    bool versioned = false})
    : _file = file,
      _flush = flush,
      _readonly = readonly,
      _header = HashHeader(buckets) {
  _file.lockSync(readonly ? FileLock.shared : FileLock.exclusive);
  _finalizer.attach(this, _file);

  final length = file.lengthSync();
  final existing = length >= _header.length;
  if (existing) {
    _header.read(_file);
  } else if (readonly) {
    throw DBMException(
        403, 'Cannot open a new file in readonly mode');
  }
  if (_header.magic != HashHeader.MAGIC) {
    throw DBMException(500, 'HashHeader magic mismatch: ${_header.magic}');
  }
  if (!_header.validate()) {
    throw DBMException(500, 'Header CRC mismatch');
  }

  // Format version validation
  final ver = _header.version;
  if (existing) {
    if (versioned) {
      if (ver == HashHeader.VERSION_PLAIN) {
        // Upgrade plain file to versioned format
        _header.version = HashHeader.VERSION_VERSIONED;
      } else if (ver != HashHeader.VERSION_VERSIONED) {
        throw DBMException(
            500, 'Unknown format version: 0x${ver.toRadixString(16)}');
      }
    } else {
      if (ver == HashHeader.VERSION_VERSIONED) {
        throw DBMException(403,
            'File is a versioned database; open with VersionedHashDBM');
      } else if (ver != HashHeader.VERSION_PLAIN) {
        throw DBMException(
            500, 'Unknown format version: 0x${ver.toRadixString(16)}');
      }
    }
  } else if (versioned) {
    _header.version = HashHeader.VERSION_VERSIONED;
  }

  if (!readonly) {
    // Update with current time
    _header.modified = DateTime.now().millisecondsSinceEpoch;
    _header.seal();
    _header.write(_file);
  }

  // Create the memory pool
  _memoryPool = MemoryPool(_file, _header.memPoolOffset);

  // Create the record pool
  _recordPool = HashRecordPool(
      _file, _memoryPool.end + 1, _memoryPool, _header.numBuckets,
      crc: crc);
}