code: func (t *StandardTimer) Snapshot() Timer {
  	t.mutex.Lock()
  	defer t.mutex.Unlock()
  	return &TimerSnapshot{
  		histogram: t.histogram.Snapshot().(*HistogramSnapshot),
  		meter:     t.meter.Snapshot().(*MeterSnapshot),
  	}
  }
docs: // Snapshot returns a read-only copy of the timer.