code: def close(self):
          
          super(Pool, self).close()
          for waiter, waketime in self.outq._waiters:
              scheduler.schedule_exception(PoolClosed(), waiter)
docs: shut down the pool's workers
  
          this method sets the :attr:`closing` attribute, lines up the
          :attr:`closed` attribute to be set once any queued data has been
          processed, and raises a PoolClosed() exception in any coroutines still
          blocked on :meth:`get`.