Add histogram support to Snapshot (#38)

scope.go

@@ -459,7 +459,18 @@ func (s *scope) Snapshot() Snapshot {
 			}
 		}
 		ss.tm.RUnlock()
-		// TODO: histograms in snapshot
+		ss.hm.RLock()
+		for key, h := range ss.histograms {
+			name := ss.fullyQualifiedName(key)
+			id := KeyForPrefixedStringMap(name, tags)
+			snap.histograms[id] = &histogramSnapshot{
+				name:      name,
+				tags:      tags,
+				values:    h.snapshotValues(),
+				durations: h.snapshotDurations(),
+			}
+		}
+		ss.hm.RUnlock()
 	}
 	s.registry.RUnlock()
 
@@ -505,6 +516,9 @@ type Snapshot interface {
 
 	// Timers returns a snapshot of timer values since last report execution
 	Timers() map[string]TimerSnapshot
+
+	// Histograms returns a snapshot of histogram samples since last report execution
+	Histograms() map[string]HistogramSnapshot
 }
 
 // CounterSnapshot is a snapshot of a counter
@@ -543,6 +557,21 @@ type TimerSnapshot interface {
 	Values() []time.Duration
 }
 
+// HistogramSnapshot is a snapshot of a histogram
+type HistogramSnapshot interface {
+	// Name returns the name
+	Name() string
+
+	// Tags returns the tags
+	Tags() map[string]string
+
+	// Values returns the sample values by upper bound for a valueHistogram
+	Values() map[float64]int64
+
+	// Durations returns the sample values by upper bound for a durationHistogram
+	Durations() map[time.Duration]int64
+}
+
 // mergeRightTags merges 2 sets of tags with the tags from tagsRight overriding values from tagsLeft
 func mergeRightTags(tagsLeft, tagsRight map[string]string) map[string]string {
 	if tagsLeft == nil && tagsRight == nil {
@@ -574,16 +603,18 @@ func copyStringMap(stringMap map[string]string) map[string]string {
 }
 
 type snapshot struct {
-	counters map[string]CounterSnapshot
-	gauges   map[string]GaugeSnapshot
-	timers   map[string]TimerSnapshot
+	counters   map[string]CounterSnapshot
+	gauges     map[string]GaugeSnapshot
+	timers     map[string]TimerSnapshot
+	histograms map[string]HistogramSnapshot
 }
 
 func newSnapshot() *snapshot {
 	return &snapshot{
-		counters: make(map[string]CounterSnapshot),
-		gauges:   make(map[string]GaugeSnapshot),
-		timers:   make(map[string]TimerSnapshot),
+		counters:   make(map[string]CounterSnapshot),
+		gauges:     make(map[string]GaugeSnapshot),
+		timers:     make(map[string]TimerSnapshot),
+		histograms: make(map[string]HistogramSnapshot),
 	}
 }
 
@@ -599,6 +630,10 @@ func (s *snapshot) Timers() map[string]TimerSnapshot {
 	return s.timers
 }
 
+func (s *snapshot) Histograms() map[string]HistogramSnapshot {
+	return s.histograms
+}
+
 type counterSnapshot struct {
 	name  string
 	tags  map[string]string
@@ -652,3 +687,26 @@ func (s *timerSnapshot) Tags() map[string]string {
 func (s *timerSnapshot) Values() []time.Duration {
 	return s.values
 }
+
+type histogramSnapshot struct {
+	name      string
+	tags      map[string]string
+	values    map[float64]int64
+	durations map[time.Duration]int64
+}
+
+func (s *histogramSnapshot) Name() string {
+	return s.name
+}
+
+func (s *histogramSnapshot) Tags() map[string]string {
+	return s.tags
+}
+
+func (s *histogramSnapshot) Values() map[float64]int64 {
+	return s.values
+}
+
+func (s *histogramSnapshot) Durations() map[time.Duration]int64 {
+	return s.durations
+}

scope_test.go

@@ -21,6 +21,7 @@
 package tally
 
 import (
+	"math"
 	"sync"
 	"sync/atomic"
 	"testing"
@@ -560,11 +561,14 @@ func TestSnapshot(t *testing.T) {
 	s.Gauge("bzzt").Update(2)
 	s.Timer("brrr").Record(1 * time.Second)
 	s.Timer("brrr").Record(2 * time.Second)
+	s.Histogram("fizz", ValueBuckets{0, 2, 4}).RecordValue(1)
+	s.Histogram("fizz", ValueBuckets{0, 2, 4}).RecordValue(5)
+	s.Histogram("buzz", DurationBuckets{time.Second * 2, time.Second * 4}).RecordDuration(time.Second)
 	child.Counter("boop").Inc(1)
 
 	snap := s.Snapshot()
-	counters, gauges, timers :=
-		snap.Counters(), snap.Gauges(), snap.Timers()
+	counters, gauges, timers, histograms :=
+		snap.Counters(), snap.Gauges(), snap.Timers(), snap.Histograms()
 
 	assert.EqualValues(t, 1, counters["foo.beep+env=test"].Value())
 	assert.EqualValues(t, commonTags, counters["foo.beep+env=test"].Tags())
@@ -578,6 +582,24 @@ func TestSnapshot(t *testing.T) {
 	}, timers["foo.brrr+env=test"].Values())
 	assert.EqualValues(t, commonTags, timers["foo.brrr+env=test"].Tags())
 
+	assert.EqualValues(t, map[float64]int64{
+		0:               0,
+		2:               1,
+		4:               0,
+		math.MaxFloat64: 1,
+	}, histograms["foo.fizz+env=test"].Values())
+	assert.EqualValues(t, map[time.Duration]int64(nil), histograms["foo.fizz+env=test"].Durations())
+	assert.EqualValues(t, commonTags, histograms["foo.fizz+env=test"].Tags())
+
+	assert.EqualValues(t, map[float64]int64(nil), histograms["foo.buzz+env=test"].Values())
+	assert.EqualValues(t, map[time.Duration]int64{
+		0:               0,
+		time.Second * 2: 1,
+		time.Second * 4: 0,
+		math.MaxInt64:   0,
+	}, histograms["foo.buzz+env=test"].Durations())
+	assert.EqualValues(t, commonTags, histograms["foo.buzz+env=test"].Tags())
+
 	assert.EqualValues(t, 1, counters["foo.boop+env=test,service=test"].Value())
 	assert.EqualValues(t, map[string]string{
 		"env":     "test",

stats.go

@@ -375,6 +375,32 @@ func (h *histogram) RecordStopwatch(stopwatchStart time.Time) {
 	h.RecordDuration(d)
 }
 
+func (h *histogram) snapshotValues() map[float64]int64 {
+	if h.htype == durationHistogramType {
+		return nil
+	}
+
+	vals := make(map[float64]int64, len(h.buckets))
+	for i := range h.buckets {
+		vals[h.buckets[i].valueUpperBound] = h.buckets[i].samples.value()
+	}
+
+	return vals
+}
+
+func (h *histogram) snapshotDurations() map[time.Duration]int64 {
+	if h.htype == valueHistogramType {
+		return nil
+	}
+
+	durations := make(map[time.Duration]int64, len(h.buckets))
+	for i := range h.buckets {
+		durations[h.buckets[i].durationUpperBound] = h.buckets[i].samples.value()
+	}
+
+	return durations
+}
+
 type histogramBucket struct {
 	h                    *histogram
 	samples              *counter