metrics: simplify interfaces, convert tests to table-driven

metrics/histogram.go

@@ -1,15 +1,7 @@
 package metrics
 
 type HistogramSnapshot interface {
-	Count() int64
-	Max() int64
-	Mean() float64
-	Min() int64
-	Percentile(float64) float64
-	Percentiles([]float64) []float64
-	StdDev() float64
-	Sum() int64
-	Variance() float64
+	SampleSnapshot
 }
 
 // Histograms calculate distribution statistics from a series of int64 values.
@@ -56,52 +48,6 @@ func NewRegisteredHistogram(name string, r Registry, s Sample) Histogram {
 	return c
 }
 
-// histogramSnapshot is a read-only copy of another Histogram.
-type histogramSnapshot struct {
-	sample *sampleSnapshot
-}
-
-// Count returns the number of samples recorded at the time the snapshot was
-// taken.
-func (h *histogramSnapshot) Count() int64 { return h.sample.Count() }
-
-// Max returns the maximum value in the sample at the time the snapshot was
-// taken.
-func (h *histogramSnapshot) Max() int64 { return h.sample.Max() }
-
-// Mean returns the mean of the values in the sample at the time the snapshot
-// was taken.
-func (h *histogramSnapshot) Mean() float64 { return h.sample.Mean() }
-
-// Min returns the minimum value in the sample at the time the snapshot was
-// taken.
-func (h *histogramSnapshot) Min() int64 { return h.sample.Min() }
-
-// Percentile returns an arbitrary percentile of values in the sample at the
-// time the snapshot was taken.
-func (h *histogramSnapshot) Percentile(p float64) float64 {
-	return h.sample.Percentile(p)
-}
-
-// Percentiles returns a slice of arbitrary percentiles of values in the sample
-// at the time the snapshot was taken.
-func (h *histogramSnapshot) Percentiles(ps []float64) []float64 {
-	return h.sample.Percentiles(ps)
-}
-
-// Snapshot returns the snapshot.
-func (h *histogramSnapshot) Snapshot() HistogramSnapshot { return h }
-
-// StdDev returns the standard deviation of the values in the sample at the
-// time the snapshot was taken.
-func (h *histogramSnapshot) StdDev() float64 { return h.sample.StdDev() }
-
-// Sum returns the sum in the sample at the time the snapshot was taken.
-func (h *histogramSnapshot) Sum() int64 { return h.sample.Sum() }
-
-// Variance returns the variance of inputs at the time the snapshot was taken.
-func (h *histogramSnapshot) Variance() float64 { return h.sample.Variance() }
-
 // NilHistogram is a no-op Histogram.
 type NilHistogram struct{}
 
@@ -120,7 +66,7 @@ func (h *StandardHistogram) Clear() { h.sample.Clear() }
 
 // Snapshot returns a read-only copy of the histogram.
 func (h *StandardHistogram) Snapshot() HistogramSnapshot {
-	return &histogramSnapshot{sample: h.sample.Snapshot().(*sampleSnapshot)}
+	return h.sample.Snapshot()
 }
 
 // Update samples a new value.

metrics/runtimehistogram.go

@@ -78,6 +78,11 @@ func (h *runtimeHistogramSnapshot) Count() int64 {
 	return count
 }
 
+// Size returns the size of the sample at the time the snapshot was taken.
+func (h *runtimeHistogramSnapshot) Size() int {
+	return len(h.Counts)
+}
+
 // Mean returns an approximation of the mean.
 func (h *runtimeHistogramSnapshot) Mean() float64 {
 	if len(h.Counts) == 0 {

metrics/sample.go

@@ -21,7 +21,6 @@ type SampleSnapshot interface {
 	Size() int
 	StdDev() float64
 	Sum() int64
-	Values() []int64
 	Variance() float64
 }
 

metrics/sample_test.go

@@ -87,69 +87,43 @@ func BenchmarkUniformSample1028(b *testing.B) {
 	benchmarkSample(b, NewUniformSample(1028))
 }
 
-func TestExpDecaySample10(t *testing.T) {
-	sw := NewExpDecaySample(100, 0.99)
-	for i := 0; i < 10; i++ {
-		sw.Update(int64(i))
-	}
-	s := sw.Snapshot()
-	if size := s.Count(); size != 10 {
-		t.Errorf("s.Count(): 10 != %v\n", size)
-	}
-	if size := s.Size(); size != 10 {
-		t.Errorf("s.Size(): 10 != %v\n", size)
-	}
-	if l := len(s.Values()); l != 10 {
-		t.Errorf("len(s.Values()): 10 != %v\n", l)
-	}
-	for _, v := range s.Values() {
-		if v > 10 || v < 0 {
-			t.Errorf("out of range [0, 10): %v\n", v)
-		}
+func min(a, b int) int {
+	if a < b {
+		return a
 	}
+	return b
 }
 
-func TestExpDecaySample100(t *testing.T) {
-	sw := NewExpDecaySample(1000, 0.01)
-	for i := 0; i < 100; i++ {
-		sw.Update(int64(i))
+func TestExpDecaySample(t *testing.T) {
+	for _, tc := range []struct {
+		reservoirSize int
+		alpha         float64
+		updates       int
+	}{
+		{100, 0.99, 10},
+		{1000, 0.01, 100},
+		{100, 0.99, 1000},
+	} {
+		sample := NewExpDecaySample(tc.reservoirSize, tc.alpha)
+		for i := 0; i < tc.updates; i++ {
+			sample.Update(int64(i))
 		}
-	s := sw.Snapshot()
-	if size := s.Count(); size != 100 {
-		t.Errorf("s.Count(): 100 != %v\n", size)
+		snap := sample.Snapshot()
+		if have, want := int(snap.Count()), tc.updates; have != want {
+			t.Errorf("have %d want %d", have, want)
 		}
-	if size := s.Size(); size != 100 {
-		t.Errorf("s.Size(): 100 != %v\n", size)
+		if have, want := snap.Size(), min(tc.updates, tc.reservoirSize); have != want {
+			t.Errorf("have %d want %d", have, want)
 		}
-	if l := len(s.Values()); l != 100 {
-		t.Errorf("len(s.Values()): 100 != %v\n", l)
+		values := snap.(*sampleSnapshot).values
+		if have, want := len(values), min(tc.updates, tc.reservoirSize); have != want {
+			t.Errorf("have %d want %d", have, want)
 		}
-	for _, v := range s.Values() {
-		if v > 100 || v < 0 {
-			t.Errorf("out of range [0, 100): %v\n", v)
+		for _, v := range values {
+			if v > int64(tc.updates) || v < 0 {
+				t.Errorf("out of range [0, %d): %v", tc.updates, v)
 			}
 		}
-}
-
-func TestExpDecaySample1000(t *testing.T) {
-	sw := NewExpDecaySample(100, 0.99)
-	for i := 0; i < 1000; i++ {
-		sw.Update(int64(i))
-	}
-	s := sw.Snapshot()
-	if size := s.Count(); size != 1000 {
-		t.Errorf("s.Count(): 1000 != %v\n", size)
-	}
-	if size := s.Size(); size != 100 {
-		t.Errorf("s.Size(): 100 != %v\n", size)
-	}
-	if l := len(s.Values()); l != 100 {
-		t.Errorf("len(s.Values()): 100 != %v\n", l)
-	}
-	for _, v := range s.Values() {
-		if v > 1000 || v < 0 {
-			t.Errorf("out of range [0, 1000): %v\n", v)
-		}
 	}
 }
 
@@ -167,7 +141,7 @@ func TestExpDecaySampleNanosecondRegression(t *testing.T) {
 		sw.Update(20)
 	}
 	s := sw.Snapshot()
-	v := s.Values()
+	v := s.(*sampleSnapshot).values
 	avg := float64(0)
 	for i := 0; i < len(v); i++ {
 		avg += float64(v[i])
@@ -221,10 +195,12 @@ func TestUniformSample(t *testing.T) {
 	if size := s.Size(); size != 100 {
 		t.Errorf("s.Size(): 100 != %v\n", size)
 	}
-	if l := len(s.Values()); l != 100 {
+	values := s.(*sampleSnapshot).values
+
+	if l := len(values); l != 100 {
 		t.Errorf("len(s.Values()): 100 != %v\n", l)
 	}
-	for _, v := range s.Values() {
+	for _, v := range values {
 		if v > 1000 || v < 0 {
 			t.Errorf("out of range [0, 100): %v\n", v)
 		}
@@ -238,7 +214,7 @@ func TestUniformSampleIncludesTail(t *testing.T) {
 		sw.Update(int64(i))
 	}
 	s := sw.Snapshot()
-	v := s.Values()
+	v := s.(*sampleSnapshot).values
 	sum := 0
 	exp := (max - 1) * max / 2
 	for i := 0; i < len(v); i++ {

metrics/timer.go

@@ -89,8 +89,8 @@ func (t *StandardTimer) Snapshot() TimerSnapshot {
 	t.mutex.Lock()
 	defer t.mutex.Unlock()
 	return &timerSnapshot{
-		histogram: t.histogram.Snapshot().(*histogramSnapshot),
-		meter:     t.meter.Snapshot().(*meterSnapshot),
+		histogram: t.histogram.Snapshot(),
+		meter:     t.meter.Snapshot(),
 	}
 }
 
@@ -124,8 +124,8 @@ func (t *StandardTimer) UpdateSince(ts time.Time) {
 
 // timerSnapshot is a read-only copy of another Timer.
 type timerSnapshot struct {
-	histogram *histogramSnapshot
-	meter     *meterSnapshot
+	histogram HistogramSnapshot
+	meter     MeterSnapshot
 }
 
 // Count returns the number of events recorded at the time the snapshot was
@@ -135,6 +135,9 @@ func (t *timerSnapshot) Count() int64 { return t.histogram.Count() }
 // Max returns the maximum value at the time the snapshot was taken.
 func (t *timerSnapshot) Max() int64 { return t.histogram.Max() }
 
+// Size returns the size of the sample at the time the snapshot was taken.
+func (t *timerSnapshot) Size() int { return t.histogram.Size() }
+
 // Mean returns the mean value at the time the snapshot was taken.
 func (t *timerSnapshot) Mean() float64 { return t.histogram.Mean() }