fix: data race in seriesIterator, use atomic int (grafana#12223)

Author: poyzannur

pkg/iter/sample_iterator.go

@@ -3,6 +3,7 @@ package iter
 import (
 	"container/heap"
 	"context"
+	"go.uber.org/atomic"
 	"io"
 	"sync"
 
@@ -521,7 +522,7 @@ func NewSampleQueryResponseIterator(resp *logproto.SampleQueryResponse) SampleIt
 }
 
 type seriesIterator struct {
-	i      int
+	i      *atomic.Int32
 	series logproto.Series
 }
 
@@ -567,14 +568,14 @@ func NewMultiSeriesIterator(series []logproto.Series) SampleIterator {
 // NewSeriesIterator iterates over sample in a series.
 func NewSeriesIterator(series logproto.Series) SampleIterator {
 	return &seriesIterator{
-		i:      -1,
+		i:      atomic.NewInt32(-1),
 		series: series,
 	}
 }
 
 func (i *seriesIterator) Next() bool {
-	i.i++
-	return i.i < len(i.series.Samples)
+	i.i.Inc()
+	return int(i.i.Load()) < len(i.series.Samples)
 }
 
 func (i *seriesIterator) Error() error {
@@ -590,7 +591,7 @@ func (i *seriesIterator) StreamHash() uint64 {
 }
 
 func (i *seriesIterator) Sample() logproto.Sample {
-	return i.series.Samples[i.i]
+	return i.series.Samples[i.i.Load()]
 }
 
 func (i *seriesIterator) Close() error {