func newNotifier() Notifier {
	return &notifierImpl{
		regCustomers: make(map[int]chan NotifyMsg),
	}
}
newNotifier returns a Notifier object
package outputhost
import (
	"sync"
)
type NotifyType int
const (
	ThrottleDown = iota
	ThrottleUp
	NumNotifyTypes
)
type (
	Notifier interface {
		Register(id int, notifyCh chan NotifyMsg)
		Unregister(id int)
		Notify(id int, notifyMsg NotifyMsg)
	}
	NotifyMsg struct {
		notifyType NotifyType
	}
	notifierImpl struct {
		lk           sync.RWMutex            
		regCustomers map[int]chan NotifyMsg  
	}
)