custom channel example change

a channel for each Produce call

examples/producer_custom_channel_example/producer_custom_channel_example.go

@@ -28,16 +28,16 @@ import (
 func main() {
 
 	if len(os.Args) != 3 {
-		fmt.Fprintf(os.Stderr, "Usage: %s <broker> <topic>\n",
+		fmt.Fprintf(os.Stderr, "Usage: %s <bootstrap-servers> <topic>\n",
 			os.Args[0])
 		os.Exit(1)
 	}
 
-	broker := os.Args[1]
+	bootstrapServers := os.Args[1]
 	topic := os.Args[2]
 	totalMsgcnt := 3
 
-	p, err := kafka.NewProducer(&kafka.ConfigMap{"bootstrap.servers": broker})
+	p, err := kafka.NewProducer(&kafka.ConfigMap{"bootstrap.servers": bootstrapServers})
 
 	if err != nil {
 		fmt.Printf("Failed to create producer: %s\n", err)
@@ -66,38 +66,40 @@ func main() {
 		}
 	}()
 
-	// Optional delivery channel, if not specified the Producer object's
-	// .Events channel is used.
-	deliveryChan := make(chan kafka.Event)
-	go func() {
-		for e := range deliveryChan {
-			switch ev := e.(type) {
-			case *kafka.Message:
-				m := ev
-				if m.TopicPartition.Error != nil {
-					fmt.Printf("Delivery failed: %v\n", m.TopicPartition.Error)
-				} else {
-					fmt.Printf("Delivered message to topic %s [%d] at offset %v\n",
-						*m.TopicPartition.Topic, m.TopicPartition.Partition, m.TopicPartition.Offset)
-				}
-
-			default:
-				fmt.Printf("Ignored event: %s\n", ev)
-			}
-		}
-	}()
-
 	msgcnt := 0
 	for msgcnt < totalMsgcnt {
 		value := fmt.Sprintf("Producer example, message #%d", msgcnt)
 
+		deliveryChan := make(chan kafka.Event)
+		go func() {
+			for e := range deliveryChan {
+				switch ev := e.(type) {
+				case *kafka.Message:
+					m := ev
+					if m.TopicPartition.Error != nil {
+						fmt.Printf("Delivery failed: %v\n", m.TopicPartition.Error)
+					} else {
+						fmt.Printf("Delivered message to topic %s [%d] at offset %v\n",
+							*m.TopicPartition.Topic, m.TopicPartition.Partition, m.TopicPartition.Offset)
+					}
+
+				default:
+					fmt.Printf("Ignored event: %s\n", ev)
+				}
+				// in this case the caller knows that this channel is used only
+				// for one Produce call, so it can close it.
+				close(deliveryChan)
+			}
+		}()
+
 		err = p.Produce(&kafka.Message{
 			TopicPartition: kafka.TopicPartition{Topic: &topic, Partition: kafka.PartitionAny},
 			Value:          []byte(value),
 			Headers:        []kafka.Header{{Key: "myTestHeader", Value: []byte("header values are binary")}},
 		}, deliveryChan)
 
 		if err != nil {
+			close(deliveryChan)
 			if err.(kafka.Error).Code() == kafka.ErrQueueFull {
 				// Producer queue is full, waits for it to be freed
 				time.Sleep(time.Second)