data race in AddTime

[arl]

There is a data race in Tachymeter.AddTime

// AddTime adds a time.Duration to Tachymeter.
func (m *Tachymeter) AddTime(t time.Duration) {
	m.Times[(atomic.AddUint64(&m.Count, 1)-1)%m.Size] = t
}

m.Count is atomically incremented, but accessing m.Times slice isn't. As such, calling AddTime() from multiple goroutines does triggers a data race. The higher the number of goroutines and/or the smaller the value of m.Size, the higher the probability of a data race occurring.

[jamiealquiza]

Thanks for opening this (sorry, late - I didn't previously notice this). Will fix this.

[jamiealquiza]

Also, did you confirm this in any way that you could share? Calling the AddUint64 from multiple goroutines ensures unique index numbers. You could however write fast enough with a very small m.Times slice that a goroutine that's wrapped around (since this is a sliding window) writes to an index from the previous window. I haven't thought it through yet whether this has undesired consequences.