simplify classic dns server

common/signal/notifier.go

@@ -1,26 +1,34 @@
 package signal
 
+import "sync"
+
 // Notifier is a utility for notifying changes. The change producer may notify changes multiple time, and the consumer may get notified asynchronously.
 type Notifier struct {
-	c chan struct{}
+	sync.Mutex
+	waiters []chan struct{}
 }
 
 // NewNotifier creates a new Notifier.
 func NewNotifier() *Notifier {
-	return &Notifier{
-		c: make(chan struct{}, 1),
-	}
+	return &Notifier{}
 }
 
 // Signal signals a change, usually by producer. This method never blocks.
 func (n *Notifier) Signal() {
-	select {
-	case n.c <- struct{}{}:
-	default:
+	n.Lock()
+	for _, w := range n.waiters {
+		close(w)
 	}
+	n.waiters = make([]chan struct{}, 0, 8)
+	n.Unlock()
 }
 
 // Wait returns a channel for waiting for changes. The returned channel never gets closed.
 func (n *Notifier) Wait() <-chan struct{} {
-	return n.c
+	n.Lock()
+	defer n.Unlock()
+
+	w := make(chan struct{})
+	n.waiters = append(n.waiters, w)
+	return w
 }