code: func (m *CirconusMetrics) NewHistogram(metric string) *Histogram {
  	m.hm.Lock()
  	defer m.hm.Unlock()
  
  	if hist, ok := m.histograms[metric]; ok {
  		return hist
  	}
  
  	hist := &Histogram{
  		name: metric,
  		hist: circonusllhist.New(),
  	}
  
  	m.histograms[metric] = hist
  
  	return hist
  }
docs: // NewHistogram returns a histogram instance.