private function acquireLock($workerName, Job $job)
 {
     $affectedRows = $this->_em->getConnection()->executeUpdate("UPDATE jms_jobs SET workerName = :worker WHERE id = :id AND workerName IS NULL", array('worker' => $workerName, 'id' => $job->getId()));
     if ($affectedRows > 0) {
         $job->setWorkerName($workerName);
         return true;
     }
     return false;
 }