private function countPlugins()
    {
        if (isset(self::$count)) {
            return self::$count;
        }

        $count = count(glob(WPMU_PLUGIN_DIR . '/*/', GLOB_ONLYDIR | GLOB_NOSORT));

        if (!isset(self::$cache['count']) || $count !== self::$cache['count']) {
            self::$count = $count;
            $this->updateCache();
        }

        return self::$count;
    }