code: func (s *clientIOSession) Close() error {
  	s.Lock()
  	s.closed = 1
  
  	if s.conn == nil {
  		return nil
  	}
  
  	err := s.conn.Close()
  	s.conn = nil
  	s.in.Release()
  	s.out.Release()
  	s.Unlock()
  
  	return err
  }
docs: // Close close