func()

in middleware/dblock/lock_client.go [71:116]

• 37 lines of code
• 6 McCabe index (conditional complexity)

func (l MysqlLocker) ObtainTimeoutContext(ctx context.Context, key string, timeout int) (*Lock, error) {
	cancellableContext, cancelFunc := context.WithCancel(context.Background())

	dbConn, err := l.db.Conn(ctx)
	if err != nil {
		cancelFunc()
		return nil, fmt.Errorf("failed to get a db connection: %w", err)
	}

	row := dbConn.QueryRowContext(ctx, "SELECT COALESCE(GET_LOCK(?, ?), 2)", key, timeout)

	var res int
	err = row.Scan(&res)
	if err != nil {
		// mysql error does not tell if it was due to context closing, checking it manually
		select {
		case <-ctx.Done():
			cancelFunc()
			return nil, ErrGetLockContextCancelled
		default:
			break
		}
		cancelFunc()
		return nil, fmt.Errorf("could not read mysql response: %w", err)
	} else if res == 2 {
		// Internal MySQL error occurred, such as out-of-memory, thread killed or others (the doc is not clear)
		// Note: some MySQL/MariaDB versions (like MariaDB 10.1) does not support -1 as timeout parameters
		cancelFunc()
		return nil, ErrMySQLInternalError
	} else if res == 0 {
		// MySQL Timeout
		cancelFunc()
		return nil, ErrMySQLTimeout
	}

	lock := &Lock{
		key:             key,
		conn:            dbConn,
		unlocker:        make(chan struct{}, 1),
		lostLockContext: cancellableContext,
		cancelFunc:      cancelFunc,
	}
	go lock.refresher(l.refreshInterval, cancelFunc)

	return lock, nil
}