code: func (m *StandardMeter) Mark(n int64) {
  	m.lock.Lock()
  	defer m.lock.Unlock()
  	if m.stopped {
  		return
  	}
  	m.snapshot.count += n
  	m.a1.Update(n)
  	m.a5.Update(n)
  	m.a15.Update(n)
  	m.updateSnapshot()
  }
docs: // Mark records the occurrence of n events.