code: func (s *Session) Close() {
  	s.m.Lock()
  	if s.cluster_ != nil {
  		debugf("Closing session %p", s)
  		s.unsetSocket()
  		s.cluster_.Release()
  		s.cluster_ = nil
  	}
  	s.m.Unlock()
  }
docs: // Close terminates the session.  It's a runtime error to use a session
  // after it has been closed.