Fix go vet issues: example tests, returning a mutex copy

example_consumergroup_test.go

@@ -8,7 +8,7 @@ import (
  "github.com/segmentio/kafka-go"
 )
 
-func ExampleConsumerGroupParallelReaders() {
+func ExampleGeneration_Start_consumerGroupParallelReaders() {
  group, err := kafka.NewConsumerGroup(kafka.ConsumerGroupConfig{
  ID: "my-group",
  Brokers: []string{"kafka:9092"},
@@ -60,7 +60,7 @@ func ExampleConsumerGroupParallelReaders() {
  }
 }
 
-func ExampleConsumerGroupOverwriteOffsets() {
+func ExampleGeneration_CommitOffsets_overwriteOffsets() {
  group, err := kafka.NewConsumerGroup(kafka.ConsumerGroupConfig{
  ID: "my-group",
  Brokers: []string{"kafka:9092"},

example_groupbalancer_test.go

@@ -10,11 +10,11 @@ import (
  "time"
 )
 
-// ExampleAWSRackLocal shows how the RackAffinityGroupBalancer can be used to
-// pair up consumers with brokers in the same AWS availability zone. This code
-// assumes that each brokers' rack is configured to be the name of the AZ in
-// which it is running.
-func ExampleAWSRackLocal() {
+// ExampleNewReader_rackAffinity shows how the RackAffinityGroupBalancer can be
+// used to pair up consumers with brokers in the same AWS availability zone.
+// This code assumes that each brokers' rack is configured to be the name of the
+// AZ in which it is running.
+func ExampleNewReader_rackAffinity() {
  r := NewReader(ReaderConfig{
  Brokers: []string{"kafka:9092"},
  GroupID: "my-group",

writer.go

@@ -867,8 +867,8 @@ func (w *Writer) chooseTopic(msg Message) (string, error) {
 type batchQueue struct {
  queue []*writeBatch
 
- mutex sync.Mutex
- cond sync.Cond
+ mutex *sync.Mutex
+ cond *sync.Cond
 
  closed bool
 }
@@ -915,9 +915,11 @@ func (b *batchQueue) Close() {
 func newBatchQueue(initialSize int) batchQueue {
  bq := batchQueue{
  queue: make([]*writeBatch, 0, initialSize),
+ mutex: &sync.Mutex{},
+ cond: &sync.Cond{},
  }
 
- bq.cond.L = &bq.mutex
+ bq.cond.L = bq.mutex
 
  return bq
 }