code: def build_items(self):
          
          while not self.stats_queue.empty():
              item = self.stats_queue.get()
              self.calculate(item)
  
          for key, value in self.stats.iteritems():
              if 'blackbird.queue.length' == key:
                  value = self.queue.qsize()
              item = BlackbirdStatisticsItem(
                  key=key,
                  value=value,
                  host=self.options['hostname']
              )
              if self.enqueue(item=item, queue=self.queue):
                  self.logger.debug(
                      'Inserted {0} to the queue.'.format(item.data)
                  )
docs: get the items from STATS QUEUE
          calculate self.stats
          make new items from self.stats
          put the new items for ITEM QUEUE