public function addCron(CronInterface $cron, $alias, $priority, $arguments)
    {
        if (!isset($this->crons[$priority])) {
            $this->crons[$priority] = array();
        }
        $cron->setAlias($alias);
        $cron->addArguments($arguments);
        $cron->addPriority($priority);
        $this->crons[$priority][$alias] = $cron;
    }