registry.go
func (r *Registry) Subscribe(rep Reporter) {
	r.mutex.Lock()
	r.reporters = append(r.reporters, rep)
	r.mutex.Unlock()
}
func (r *Registry) Subscribe(rep Reporter) {
	r.mutex.Lock()
	r.reporters = append(r.reporters, rep)
	r.mutex.Unlock()
}
// Subscribe attaches a reporter to the Registry.