fix(memmetrics): prevent 'now' from accumulating during cleanup (#245)

Co-authored-by: Fernandez Ludovic <[email protected]>

memmetrics/counter.go

@@ -131,9 +131,9 @@ func (c *RollingCounter) getBucket(t time.Time) int {
 func (c *RollingCounter) cleanup() {
 	now := clock.Now().UTC()
 	for i := 0; i < len(c.values); i++ {
-		now = now.Add(time.Duration(-1*i) * c.resolution)
-		if now.Truncate(c.resolution).After(c.lastUpdated.Truncate(c.resolution)) {
-			c.values[c.getBucket(now)] = 0
+		checkPoint := now.Add(time.Duration(-1*i) * c.resolution)
+		if checkPoint.Truncate(c.resolution).After(c.lastUpdated.Truncate(c.resolution)) {
+			c.values[c.getBucket(checkPoint)] = 0
 		} else {
 			break
 		}

memmetrics/counter_test.go

@@ -1,6 +1,7 @@
 package memmetrics
 
 import (
+	"math"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -27,3 +28,25 @@ func TestCloneExpired(t *testing.T) {
 
 	assert.EqualValues(t, 2, out.Count())
 }
+
+func Test_cleanup(t *testing.T) {
+	clock.Freeze(clock.Date(2012, 3, 4, 5, 6, 7, 0, clock.UTC))
+
+	cnt, err := NewCounter(10, clock.Second)
+	require.NoError(t, err)
+
+	cnt.Inc(1)
+
+	for i := 0; i < 9; i++ {
+		clock.Advance(clock.Second)
+		cnt.Inc(int(math.Pow10(i + 1)))
+	}
+
+	assert.EqualValues(t, 1111111111, cnt.Count())
+	assert.Equal(t, []int{1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000, 1, 10, 100}, cnt.values)
+
+	clock.Advance(9 * clock.Second)
+
+	assert.EqualValues(t, 1000000000, cnt.Count())
+	assert.Equal(t, []int{0, 0, 0, 0, 0, 0, 1000000000, 0, 0, 0}, cnt.values)
+}