fix: Add mutex. Fixes #588 (#589)

Signed-off-by: Alex Collins <alex_collins@intuit.com>

runner/sidecar/source/kafka/kafka.go

@@ -27,7 +27,7 @@ type kafkaSource struct {
 	consumer   *kafka.Consumer
 	topic      string
 	wg         *sync.WaitGroup
-	channels   map[int32]chan *kafka.Message
+	channels   *sync.Map // map[int32]chan *kafka.Message
 	process    source.Process
 	totalLag   int64
 }
@@ -78,7 +78,7 @@ func New(ctx context.Context, secretInterface corev1.SecretInterface, cluster, n
 		sourceURN:  sourceURN,
 		consumer:   consumer,
 		topic:      x.Topic,
-		channels:   map[int32]chan *kafka.Message{}, // partition -> messages
+		channels:   new(sync.Map), // partition -> messages
 		wg:         &sync.WaitGroup{},
 		process:    process,
 		totalLag:   pendingUnavailable,
@@ -113,9 +113,9 @@ func (s *kafkaSource) processMessage(ctx context.Context, msg *kafka.Message) er
 
 func (s *kafkaSource) assignedPartition(ctx context.Context, partition int32) {
 	logger := s.logger.WithValues("partition", partition)
-	if _, ok := s.channels[partition]; !ok {
+	if _, ok := s.channels.Load(partition); !ok {
 		logger.Info("assigned partition")
-		s.channels[partition] = make(chan *kafka.Message, 256)
+		s.channels.Store(partition, make(chan *kafka.Message, 256))
 		go wait.JitterUntilWithContext(ctx, func(ctx context.Context) {
 			s.consumePartition(ctx, partition)
 		}, 3*time.Second, 1.2, true)
@@ -142,7 +142,8 @@ func (s *kafkaSource) startPollLoop(ctx context.Context) {
 							s.logger.Info("recovered from panic while queuing message", "recover", fmt.Sprint(r))
 						}
 					}()
-					s.channels[e.TopicPartition.Partition] <- e
+					v, _ := s.channels.Load(e.TopicPartition.Partition)
+					v.(chan *kafka.Message) <- e
 				}()
 			case *kafka.Stats:
 				// https://github.com/edenhill/librdkafka/wiki/Consumer-lag-monitoring
@@ -166,9 +167,10 @@ func (s *kafkaSource) startPollLoop(ctx context.Context) {
 
 func (s *kafkaSource) Close() error {
 	s.logger.Info("closing partition channels")
-	for _, ch := range s.channels {
-		close(ch)
-	}
+	s.channels.Range(func(_, v interface{}) bool {
+		close(v.(chan *kafka.Message))
+		return true
+	})
 	s.logger.Info("waiting for partition consumers to finish")
 	s.wg.Wait()
 	s.logger.Info("closing consumer")
@@ -218,10 +220,11 @@ func (s *kafkaSource) consumePartition(ctx context.Context, partition int32) {
 	ticker := time.NewTicker(time.Second)
 	defer ticker.Stop()
 	for {
+		v, _ := s.channels.Load(partition)
 		select {
 		case <-ticker.C:
 			commitLastUncommitted()
-		case msg, ok := <-s.channels[partition]:
+		case msg, ok := <-v.(chan *kafka.Message):
 			if !ok {
 				return
 			}