code: def manual_close(self):
          
          if self.is_closed():
              return False
  
          # Obtain reference to the connection in-use by the calling thread.
          conn = self.connection()
  
          # A connection will only be re-added to the available list if it is
          # marked as "in use" at the time it is closed. We will explicitly
          # remove it from the "in use" list, call "close()" for the
          # side-effects, and then explicitly close the connection.
          self._in_use.pop(self.conn_key(conn), None)
          self.close()
          self._close(conn, close_conn=True)
docs: Close the underlying connection without returning it to the pool.