code: def release(self, conn):
          
          self._in_use.remove(conn)
          if conn.reader.at_eof() or conn.reader.exception():
              self._do_close(conn)
          else:
              self._pool.put_nowait(conn)
docs: Releases connection back to the pool.
  
          :param conn: ``namedtuple`` (reader, writer)