code: func Warmup(c context.Context) error {
  	state.Lock()
  	defer state.Unlock()
  
  	var merr errors.MultiError
  	for _, cb := range state.callbacks {
  		logging.Infof(c, "Warming up %q", cb.name)
  		if err := cb.Callback(c); err != nil {
  			logging.WithError(err).Errorf(c, "Error when warming up %q", cb.name)
  			merr = append(merr, err)
  		}
  	}
  
  	logging.Infof(c, "Finished warming up")
  	if len(merr) == 0 {
  		return nil
  	}
  	return merr
  }
docs: // Warmup executes all registered warmup callbacks, sequentially.
  //
  // Doesn't abort on individual callback errors, just collects and returns them
  // all.