Fix tests, lock topic as short as possible

server/topic.go

@@ -44,11 +44,12 @@ func (t *topic) Unsubscribe(id int) {
 // Publish asynchronously publishes to all subscribers
 func (t *topic) Publish(v *visitor, m *message) error {
 	go func() {
-		t.mu.Lock()
-		defer t.mu.Unlock()
-		if len(t.subscribers) > 0 {
-			log.Debug("%s Forwarding to %d subscriber(s)", logMessagePrefix(v, m), len(t.subscribers))
-			for _, s := range t.subscribers {
+		// We want to lock the topic as short as possible, so we make a shallow copy of the
+		// subscribers map here. Actually sending out the messages then doesn't have to lock.
+		subscribers := t.subscribersCopy()
+		if len(subscribers) > 0 {
+			log.Debug("%s Forwarding to %d subscriber(s)", logMessagePrefix(v, m), len(subscribers))
+			for _, s := range subscribers {
 				if err := s(v, m); err != nil {
 					log.Warn("%s Error forwarding to subscriber", logMessagePrefix(v, m))
 				}
@@ -60,9 +61,20 @@ func (t *topic) Publish(v *visitor, m *message) error {
 	return nil
 }
 
-// Subscribers returns the number of subscribers to this topic
-func (t *topic) Subscribers() int {
+// SubscribersCount returns the number of subscribers to this topic
+func (t *topic) SubscribersCount() int {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 	return len(t.subscribers)
 }
+
+// subscribersCopy returns a shallow copy of the subscribers map
+func (t *topic) subscribersCopy() map[int]subscriber {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	subscribers := make(map[int]subscriber)
+	for k, v := range t.subscribers {
+		subscribers[k] = v
+	}
+	return subscribers
+}