func (stor *groupStore) Shutdown(ctx context.Context) error {
	stor.lock.Lock()
	err := stor.shutdown()
	stor.lock.Unlock()
	return err
}
func (stor *groupStore) Shutdown(ctx context.Context) error {
	stor.lock.Lock()
	err := stor.shutdown()
	stor.lock.Unlock()
	return err
}
// Shutdown will close any existing connections; note that Startup may
// automatically get called with any further activity, but it will use a new
// connection. To ensure the groupStore has no further activity, use Close.