pop method

@override Future<Job?> pop([ String queue = 'default' ])

Pops the next available job from the queue atomically.

Implementations MUST guarantee that no two workers can receive the same job (distributed lock / atomic dequeue). Returns null if the queue is empty or no jobs are available.

Implementation

@override
Future<Job?> pop([String queue = 'default']) async {
  // Atomic dequeue with distributed locking:
  // SELECT ... FOR UPDATE SKIP LOCKED ensures no two workers get the same row.
  final result = await _db.query('''
    UPDATE $_table
    SET status = 'processing', reserved_by = @workerId
    WHERE id = (
      SELECT id FROM $_table
      WHERE queue = @queue
        AND status = 'pending'
        AND (available_at IS NULL OR available_at <= NOW())
      ORDER BY created_at ASC
      LIMIT 1
      FOR UPDATE SKIP LOCKED
    )
    RETURNING *
  ''', {
    'queue': queue,
    'workerId': workerId,
  });

  if (result.rows.isEmpty) return null;

  final row = _JobRow.fromRow(result.rows.first);
  return _hydrateJob(row);
}