metrics: remove deprecated uses of math.rand (#26710)

metrics/sample.go

@@ -41,6 +41,7 @@ type ExpDecaySample struct {
 	reservoirSize int
 	t0, t1        time.Time
 	values        *expDecaySampleHeap
+	rand          *rand.Rand
 }
 
 // NewExpDecaySample constructs a new exponentially-decaying sample with the
@@ -59,6 +60,12 @@ func NewExpDecaySample(reservoirSize int, alpha float64) Sample {
 	return s
 }
 
+// SetRand sets the random source (useful in tests)
+func (s *ExpDecaySample) SetRand(prng *rand.Rand) Sample {
+	s.rand = prng
+	return s
+}
+
 // Clear clears all samples.
 func (s *ExpDecaySample) Clear() {
 	s.mutex.Lock()
@@ -168,8 +175,14 @@ func (s *ExpDecaySample) update(t time.Time, v int64) {
 	if s.values.Size() == s.reservoirSize {
 		s.values.Pop()
 	}
+	var f64 float64
+	if s.rand != nil {
+		f64 = s.rand.Float64()
+	} else {
+		f64 = rand.Float64()
+	}
 	s.values.Push(expDecaySample{
-		k: math.Exp(t.Sub(s.t0).Seconds()*s.alpha) / rand.Float64(),
+		k: math.Exp(t.Sub(s.t0).Seconds()*s.alpha) / f64,
 		v: v,
 	})
 	if t.After(s.t1) {
@@ -402,6 +415,7 @@ type UniformSample struct {
 	mutex         sync.Mutex
 	reservoirSize int
 	values        []int64
+	rand          *rand.Rand
 }
 
 // NewUniformSample constructs a new uniform sample with the given reservoir
@@ -416,6 +430,12 @@ func NewUniformSample(reservoirSize int) Sample {
 	}
 }
 
+// SetRand sets the random source (useful in tests)
+func (s *UniformSample) SetRand(prng *rand.Rand) Sample {
+	s.rand = prng
+	return s
+}
+
 // Clear clears all samples.
 func (s *UniformSample) Clear() {
 	s.mutex.Lock()
@@ -511,7 +531,12 @@ func (s *UniformSample) Update(v int64) {
 	if len(s.values) < s.reservoirSize {
 		s.values = append(s.values, v)
 	} else {
-		r := rand.Int63n(s.count)
+		var r int64
+		if s.rand != nil {
+			r = s.rand.Int63n(s.count)
+		} else {
+			r = rand.Int63n(s.count)
+		}
 		if r < int64(len(s.values)) {
 			s.values[int(r)] = v
 		}

metrics/sample_test.go

@@ -80,7 +80,6 @@ func BenchmarkUniformSample1028(b *testing.B) {
 }
 
 func TestExpDecaySample10(t *testing.T) {
-	rand.Seed(1)
 	s := NewExpDecaySample(100, 0.99)
 	for i := 0; i < 10; i++ {
 		s.Update(int64(i))
@@ -102,7 +101,6 @@ func TestExpDecaySample10(t *testing.T) {
 }
 
 func TestExpDecaySample100(t *testing.T) {
-	rand.Seed(1)
 	s := NewExpDecaySample(1000, 0.01)
 	for i := 0; i < 100; i++ {
 		s.Update(int64(i))
@@ -124,7 +122,6 @@ func TestExpDecaySample100(t *testing.T) {
 }
 
 func TestExpDecaySample1000(t *testing.T) {
-	rand.Seed(1)
 	s := NewExpDecaySample(100, 0.99)
 	for i := 0; i < 1000; i++ {
 		s.Update(int64(i))
@@ -150,7 +147,6 @@ func TestExpDecaySample1000(t *testing.T) {
 // The priority becomes +Inf quickly after starting if this is done,
 // effectively freezing the set of samples until a rescale step happens.
 func TestExpDecaySampleNanosecondRegression(t *testing.T) {
-	rand.Seed(1)
 	s := NewExpDecaySample(100, 0.99)
 	for i := 0; i < 100; i++ {
 		s.Update(10)
@@ -183,8 +179,7 @@ func TestExpDecaySampleRescale(t *testing.T) {
 
 func TestExpDecaySampleSnapshot(t *testing.T) {
 	now := time.Now()
-	rand.Seed(1)
+	s := NewExpDecaySample(100, 0.99).(*ExpDecaySample).SetRand(rand.New(rand.NewSource(1)))
-	s := NewExpDecaySample(100, 0.99)
 	for i := 1; i <= 10000; i++ {
 		s.(*ExpDecaySample).update(now.Add(time.Duration(i)), int64(i))
 	}
@@ -195,8 +190,7 @@ func TestExpDecaySampleSnapshot(t *testing.T) {
 
 func TestExpDecaySampleStatistics(t *testing.T) {
 	now := time.Now()
-	rand.Seed(1)
+	s := NewExpDecaySample(100, 0.99).(*ExpDecaySample).SetRand(rand.New(rand.NewSource(1)))
-	s := NewExpDecaySample(100, 0.99)
 	for i := 1; i <= 10000; i++ {
 		s.(*ExpDecaySample).update(now.Add(time.Duration(i)), int64(i))
 	}
@@ -204,7 +198,6 @@ func TestExpDecaySampleStatistics(t *testing.T) {
 }
 
 func TestUniformSample(t *testing.T) {
-	rand.Seed(1)
 	s := NewUniformSample(100)
 	for i := 0; i < 1000; i++ {
 		s.Update(int64(i))
@@ -226,7 +219,6 @@ func TestUniformSample(t *testing.T) {
 }
 
 func TestUniformSampleIncludesTail(t *testing.T) {
-	rand.Seed(1)
 	s := NewUniformSample(100)
 	max := 100
 	for i := 0; i < max; i++ {
@@ -244,7 +236,7 @@ func TestUniformSampleIncludesTail(t *testing.T) {
 }
 
 func TestUniformSampleSnapshot(t *testing.T) {
-	s := NewUniformSample(100)
+	s := NewUniformSample(100).(*UniformSample).SetRand(rand.New(rand.NewSource(1)))
 	for i := 1; i <= 10000; i++ {
 		s.Update(int64(i))
 	}
@@ -254,8 +246,7 @@ func TestUniformSampleSnapshot(t *testing.T) {
 }
 
 func TestUniformSampleStatistics(t *testing.T) {
-	rand.Seed(1)
+	s := NewUniformSample(100).(*UniformSample).SetRand(rand.New(rand.NewSource(1)))
-	s := NewUniformSample(100)
 	for i := 1; i <= 10000; i++ {
 		s.Update(int64(i))
 	}
@@ -327,7 +318,7 @@ func testUniformSampleStatistics(t *testing.T, s Sample) {
 	if ps[1] != 7380.5 {
 		t.Errorf("75th percentile: 7380.5 != %v\n", ps[1])
 	}
-	if math.Abs(ps[2]-9986.429999999998) > epsilonPercentile {
+	if math.Abs(9986.429999999998-ps[2]) > epsilonPercentile {
 		t.Errorf("99th percentile: 9986.429999999998 != %v\n", ps[2])
 	}
 }