// NewEWMA constructs a new EWMA with the given alpha and sampling period.
func NewEWMA(alpha float64, period time.Duration) EWMA {
	return &StandardEWMA{alpha: alpha, period: period, ts: time.Now()}
}
// We imitate the current implementation by specifying 5-second clock ticks.
// Updates that arrive within 5s of each other are accumulated, and the EWMA
// is updated once the next 5s interval begins.
func NewEWMA1() EWMA {
 // create an EWMA with a 5-second sampling period.
	return NewEWMA(1-math.Exp(-5.0/60.0/1), 5*time.Second)
}
m := NewEWMA1()
m.Update(10)
// Returns 0 because a whole sampling period has not yet elapsed, the EWMA is
// still accumulating events.
fmt.Println(m.Snapshot().Rate())
for range time.Tick(5 * time.Seconds) {
 // Rate will begin at 10 and then exponentially decline. Rate is only manually
 // updated whenever Snapshot() or Update() is called, no need for a clock.
 fmt.Println(m1.Snapshot().Rate())
}

// Mark records the occurrence of n events.
func (m *StandardMeter) Mark(n int64) {
	m.mutex.Lock()
	defer m.mutex.Unlock()
	// Synchronize rateMean so that it's only updated after
	// a sampling period elapses.
	if elapsed := time.Since(m.lastMark); elapsed >= 5*time.Second {
		m.lastMark = m.lastMark.Add(elapsed)
		m.count += m.uncounted
		m.uncounted = 0
	}
	m.uncounted += n
	m.a1.Update(n)
	m.a5.Update(n)
	m.a15.Update(n)
}