dbjoqbqueue: wait for listener to become ready before returning from New

Otherwise, there might be an already waiting dequeuer and if something is
enqueued before `sqlListen` is called, we will lost this notification.

Also, a small log message was added when shutting down the listener.

Signed-off-by: Ondřej Budai <ondrej@budai.cz>

internal/jobqueue/dbjobqueue/dbjobqueue.go

@@ -186,12 +186,16 @@ func New(url string) (*DBJobQueue, error) {
 		stopListener: cancel,
 	}
 
-	go q.listen(listenContext)
+	listenerReady := make(chan struct{})
+	go q.listen(listenContext, listenerReady)
+
+	// wait for the listener to become ready
+	<-listenerReady
 
 	return q, nil
 }
 
-func (q *DBJobQueue) listen(ctx context.Context) {
+func (q *DBJobQueue) listen(ctx context.Context, ready chan<- struct{}) {
 	conn, err := q.pool.Acquire(ctx)
 	if err != nil {
 		panic(fmt.Errorf("error connecting to database: %v", err))
@@ -209,11 +213,14 @@ func (q *DBJobQueue) listen(ctx context.Context) {
 		panic(fmt.Errorf("error listening on jobs channel: %v", err))
 	}
 
+	ready <- struct{}{}
+
 	for {
 		_, err = conn.Conn().WaitForNotification(ctx)
 		if err != nil {
 			// shutdown the listener if the context is canceled
 			if errors.Is(err, context.Canceled) {
+				logrus.Info("Shutting down the listener")
 				return
 			}