code: function listQueues()
      {
          try {
              $csr = $this->collection->aggregate(
                  [
                      [
                          '$group' => [
                              '_id'   => '$queue',
                          ],
                      ],
                  ]
                  , [
                      // override typeMap option
                      'typeMap' => self::$typeMap,
                  ]
              );
          } catch (\Exception $e) {
              throw new exReadError('Error While Write To Mongo Client.', $e->getCode(), $e);
          }
  
          $list = [];
          foreach ($csr as $item)
              $list[] = $item['_id'];
  
          return $list;
      }
docs: Get Queues List
  
  @return string[]
  @throws exIOError