change topicArns to map safe for concurrent access (#3459)

Co-authored-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>

pubsub/aws/snssqs/snssqs.go

@@ -234,8 +234,10 @@ func (s *snsSqs) getTopicArn(parentCtx context.Context, topic string) (string, e
 	return *getTopicOutput.Attributes["TopicArn"], nil
 }
 
-// get the topic ARN from the topics map. If it doesn't exist in the map, try to fetch it from AWS, if it doesn't exist
+// Get the topic ARN from the topics map. If it doesn't exist in the map, try to fetch it from AWS, if it doesn't exist
 // at all, issue a request to create the topic.
+// NOTE: This method potentially reads and writes to the topicArns map, which may end up being accessed by multiple goroutines concurrently,
+// therefore it is necessary for its caller to lock the topic.
 func (s *snsSqs) getOrCreateTopic(ctx context.Context, topic string) (topicArn string, sanitizedTopic string, err error) {
 	sanitizedTopic = nameToAWSSanitizedName(topic, s.metadata.Fifo)
 
@@ -840,6 +842,9 @@ func (s *snsSqs) Publish(ctx context.Context, req *pubsub.PublishRequest) error
 		return errors.New("component is closed")
 	}
 
+	s.topicsLocker.Lock(req.Topic)
+	defer s.topicsLocker.Unlock(req.Topic)
+
 	topicArn, _, err := s.getOrCreateTopic(ctx, req.Topic)
 	if err != nil {
 		s.logger.Errorf("error getting topic ARN for %s: %v", req.Topic, err)