subscription: refactor subscription recreation

Decouple client and subscription code during subscription recreation.
During this operation both the state of the client and the subscription
have to be updated while holding a lock in the client.

The previous implementation had both classes call each other. The
control flow in the new implementation is only from the client to
the subscription.

client_sub.go

@@ -89,7 +89,7 @@ func (c *Client) SubscriptionIDs() []uint32 {
 }
 
 // recreateSubscriptions creates new subscriptions
-// with the same parameters to replace the previous ones
+// with the same parameters to replace the previous one
 func (c *Client) recreateSubscription(ctx context.Context, id uint32) error {
 	c.subMux.Lock()
 	defer c.subMux.Unlock()
@@ -98,7 +98,10 @@ func (c *Client) recreateSubscription(ctx context.Context, id uint32) error {
 	if !ok {
 		return ua.StatusBadSubscriptionIDInvalid
 	}
-	return sub.recreate_NeedsSubMuxLock(ctx)
+
+	sub.recreate_delete(ctx)
+	c.forgetSubscription_NeedsSubMuxLock(ctx, id)
+	return sub.recreate_create(ctx)
 }
 
 // transferSubscriptions ask the server to transfer the given subscriptions

subscription.go

@@ -391,29 +391,31 @@ func (p *SubscriptionParameters) setDefaults() {
 	}
 }
 
-// recreate_NeedsSubMuxLock creates a new subscription based on the previous subscription
-// parameters and monitored items.
-func (s *Subscription) recreate_NeedsSubMuxLock(ctx context.Context) error {
-	dlog := debug.NewPrefixLogger("sub %d: recreate: ", s.SubscriptionID)
-
-	if s.SubscriptionID == terminatedSubscriptionID {
-		dlog.Printf("subscription is not in a valid state")
-		return nil
+// recreate_delete is called by the client when it is trying to
+// recreate an existing subscription. This function deletes the
+// existing subscription from the server.
+func (s *Subscription) recreate_delete(ctx context.Context) error {
+	dlog := debug.NewPrefixLogger("sub %d: recreate_delete: ", s.SubscriptionID)
+	req := &ua.DeleteSubscriptionsRequest{
+		SubscriptionIDs: []uint32{s.SubscriptionID},
 	}
+	var res *ua.DeleteSubscriptionsResponse
+	_ = s.c.Send(ctx, req, func(v ua.Response) error {
+		return safeAssign(v, &res)
+	})
+	dlog.Print("subscription deleted")
+	return nil
+}
+
+// recreate_create is called by the client when it is trying to
+// recreate an existing subscription. This function creates a
+// new subscription with the same parameters as the previous one.
+func (s *Subscription) recreate_create(ctx context.Context) error {
+	dlog := debug.NewPrefixLogger("sub %d: recreate_create: ", s.SubscriptionID)
 
+	s.paramsMu.Lock()
 	params := s.params
-	{
-		req := &ua.DeleteSubscriptionsRequest{
-			SubscriptionIDs: []uint32{s.SubscriptionID},
-		}
-		var res *ua.DeleteSubscriptionsResponse
-		_ = s.c.Send(ctx, req, func(v ua.Response) error {
-			return safeAssign(v, &res)
-		})
-		dlog.Print("subscription deleted")
-	}
-	s.c.forgetSubscription_NeedsSubMuxLock(ctx, s.SubscriptionID)
-	dlog.Printf("subscription forgotton")
+	s.paramsMu.Unlock()
 
 	req := &ua.CreateSubscriptionRequest{
 		RequestedPublishingInterval: float64(params.Interval / time.Millisecond),