fix(RollingCounter): prevent 'now' from accumulating during cleanup

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

@@ -27,3 +27,22 @@ func TestCloneExpired(t *testing.T) {
 
 	assert.EqualValues(t, 2, out.Count())
 }
+
+func TestCleanup(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(1)
+	}
+	// cnt will be  [1 1 1 1 1 1 1 1 1 1]
+
+	clock.Advance(9 * clock.Second)
+	assert.EqualValues(t, 1, cnt.Count())
+	// cnt will be  [0 0 0 0 0 0 1 0 0 0]
+	// old behavior [1 1 0 1 0 0 1 1 1 0]
+}