code: func (e *Environment) Stop() {
  	e.mu.Lock()
  
  	if !e.stopped {
  		e.stopped = true
  		close(e.stopCh)
  	}
  
  	e.mu.Unlock()
  }
docs: // Stop just declares no further Go will be called.
  //
  // Calling Stop is optional if and only if Cancel is guaranteed
  // to be called at some point.  For instance, if the program runs
  // until SIGINT or SIGTERM, Stop is optional.