public function run()
    {
        // check if cron instances is defined
        if (!isset($this->configs['instances']) || !Any::isArray($this->configs['instances'])) {
            return null;
        }

        // get timestamp
        $time = time();
        $log = [];

        // each every one instance
        foreach ($this->configs['instances'] as $callback => $delay) {
            if (((int)$this->configs['log'][$callback] + $delay) <= $time) {
                // prepare cron initializing
                list($class, $method) = explode('::', $callback);
                if (class_exists($class) && method_exists($class, $method)) {
                    // make static callback
                    forward_static_call([$class, $method]);
                    $log[] = $callback;
                }
                // update log information
                $this->configs['log'][$callback] = $time + $delay;
            }
        }

        // write updated configs
        App::$Properties->writeConfig('Cron', $this->configs);
        return $log;
    }