对象，它会消耗太多的内存，尝试处理大块...

You're pulling in 300k objects, it'll consume way too much memory, try processing in chunks...

$message = new Message();

$limit = 50;
$offset = 0;
while($devices = self::$entityManager->getRepository('Device')->findBy(array("deviceProperty" => "someValue"), array(), $limit, $offset))
{
   foreach($devices as $device)
   {
       $message->addRecipient($device->getPushToken);
   }
   $offset += $limit;
}