code: def _start(self, tpart):
          
          g = gevent.Greenlet(self.uploader, tpart)
          g.link(self._finish)
  
          # Account for concurrency_burden before starting the greenlet
          # to avoid racing against .join.
          self.concurrency_burden += 1
  
          self.member_burden += len(tpart)
  
          g.start()
docs: Start upload and accout for resource consumption.