public function getAllRunningSchedules($host = null)
    {
        $collection = Mage::getModel('cron/schedule')->getCollection();
        $collection->addFieldToFilter('status', Aoe_Scheduler_Model_Schedule::STATUS_RUNNING);
        if (!is_null($host)) {
            $collection->addFieldToFilter('host', $host);
        }
        return $collection;
    }