announce.go
func (a *Announce) NumContacted() int {
	a.mu.Lock()
	defer a.mu.Unlock()
	return a.numContacted
}
func (a *Announce) NumContacted() int {
	a.mu.Lock()
	defer a.mu.Unlock()
	return a.numContacted
}
// Returns the number of distinct remote addresses the announce has queried.