Refactor cloudwatch: Reset().Walk() on every Send(), like influx impl…

… does.

Note there is a breaking API change, as the cloudwatch object now has optional parameters.

metrics/cloudwatch/cloudwatch.go

@@ -2,6 +2,7 @@ package cloudwatch
 
 import (
 	"fmt"
+	"os"
 	"sync"
 	"time"
 
@@ -12,81 +13,131 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/metrics"
 	"github.com/go-kit/kit/metrics/generic"
+	"github.com/go-kit/kit/metrics/internal/lv"
 )
 
 const (
 	maxConcurrentRequests = 20
 )
 
+type Percentiles []struct {
+	s string
+	f float64
+}
+
 // CloudWatch receives metrics observations and forwards them to CloudWatch.
 // Create a CloudWatch object, use it to create metrics, and pass those metrics as
 // dependencies to the components that will use them.
 //
 // To regularly report metrics to CloudWatch, use the WriteLoop helper method.
 type CloudWatch struct {
-	mtx                   sync.RWMutex
-	sem                   chan struct{}
-	namespace             string
-	numConcurrentRequests int
-	svc                   cloudwatchiface.CloudWatchAPI
-	counters              map[string]*counter
-	gauges                map[string]*gauge
-	histograms            map[string]*histogram
+	mtx        sync.RWMutex
+	sem        chan struct{}
+	namespace  string
+	svc        cloudwatchiface.CloudWatchAPI
+	counters   *lv.Space
+	gauges     *lv.Space
+	histograms *lv.Space
+	*cwoptions
+}
+
+type cwoptions struct {
+	percentiles           Percentiles
 	logger                log.Logger
+	numConcurrentRequests int
+}
+
+type option func(*cwoptions)
+
+func (s *cwoptions) apply(opt option) {
+	if opt != nil {
+		opt(s)
+	}
+}
+
+func WithLogger(logger log.Logger) option {
+	return func(o *cwoptions) {
+		o.logger = logger
+	}
+}
+
+func WithPercentiles(p Percentiles) option {
+	return func(o *cwoptions) {
+		validated := Percentiles{}
+		for _, entry := range p {
+			if entry.f < 0 || entry.f > 1 {
+				continue // illegal entry
+			}
+			validated = append(validated, entry)
+		}
+		o.percentiles = validated
+	}
+}
+
+func WithConcurrentRequests(n int) option {
+	return func(o *cwoptions) {
+		if n > maxConcurrentRequests {
+			n = maxConcurrentRequests
+		}
+		o.numConcurrentRequests = n
+	}
 }
 
 // New returns a CloudWatch object that may be used to create metrics.
 // Namespace is applied to all created metrics and maps to the CloudWatch namespace.
-// NumConcurrent sets the number of simultaneous requests to Amazon.
-// A good default value is 10 and the maximum is 20.
 // Callers must ensure that regular calls to Send are performed, either
 // manually or with one of the helper methods.
-func New(namespace string, svc cloudwatchiface.CloudWatchAPI, numConcurrent int, logger log.Logger) *CloudWatch {
-	if numConcurrent > maxConcurrentRequests {
-		numConcurrent = maxConcurrentRequests
+func New(namespace string, svc cloudwatchiface.CloudWatchAPI, options ...option) *CloudWatch {
+	useOptions := &cwoptions{
+		numConcurrentRequests: 10,
+		logger:                log.NewLogfmtLogger(os.Stderr),
+		percentiles: Percentiles{
+			{"50", 0.50},
+			{"90", 0.90},
+			{"95", 0.95},
+			{"99", 0.99},
+		},
+	}
+
+	for _, opt := range options {
+		useOptions.apply(opt)
 	}
 
 	return &CloudWatch{
-		sem:                   make(chan struct{}, numConcurrent),
-		namespace:             namespace,
-		numConcurrentRequests: numConcurrent,
+		sem:        make(chan struct{}, useOptions.numConcurrentRequests),
+		namespace:  namespace,
 		svc:        svc,
-		counters:   map[string]*counter{},
-		gauges:     map[string]*gauge{},
-		histograms: map[string]*histogram{},
-		logger:     logger,
+		counters:   lv.NewSpace(),
+		gauges:     lv.NewSpace(),
+		histograms: lv.NewSpace(),
+		cwoptions:  useOptions,
 	}
 }
 
 // NewCounter returns a counter. Observations are aggregated and emitted once
 // per write invocation.
 func (cw *CloudWatch) NewCounter(name string) metrics.Counter {
-	cw.mtx.Lock()
-	defer cw.mtx.Unlock()
-	c := &counter{c: generic.NewCounter(name)}
-	cw.counters[name] = c
-	return c
-}
-
-// NewGauge returns a gauge. Observations are aggregated and emitted once per
-// write invocation.
-func (cw *CloudWatch) NewGauge(name string) metrics.Gauge {
-	cw.mtx.Lock()
-	defer cw.mtx.Unlock()
-	g := &gauge{g: generic.NewGauge(name)}
-	cw.gauges[name] = g
-	return g
-}
-
-// NewHistogram returns a histogram. Observations are aggregated and emitted as
-// per-quantile gauges, once per write invocation. 50 is a good default value
-// for buckets.
-func (cw *CloudWatch) NewHistogram(name string, buckets int) metrics.Histogram {
-	cw.mtx.Lock()
-	defer cw.mtx.Unlock()
-	h := &histogram{h: generic.NewHistogram(name, buckets)}
-	cw.histograms[name] = h
-	return h
+	return &Counter{
+		name: name,
+		obs:  cw.counters.Observe,
+	}
+}
+
+// NewGauge returns an gauge.
+func (cw *CloudWatch) NewGauge(name string) *Gauge {
+	return &Gauge{
+		name: name,
+		obs:  cw.gauges.Observe,
+		add:  cw.gauges.Add,
+	}
+}
+
+// NewHistogram returns a histogram.
+func (cw *CloudWatch) NewHistogram(name string) *Histogram {
+	return &Histogram{
+		name: name,
+		obs:  cw.histograms.Observe,
+	}
 }
 
 // WriteLoop is a helper method that invokes Send every time the passed
@@ -110,42 +161,46 @@ func (cw *CloudWatch) Send() error {
 
 	var datums []*cloudwatch.MetricDatum
 
-	for name, c := range cw.counters {
+	cw.counters.Reset().Walk(func(name string, lvs lv.LabelValues, values []float64) bool {
+		value := sum(values)
 		datums = append(datums, &cloudwatch.MetricDatum{
 			MetricName: aws.String(name),
-			Dimensions: makeDimensions(c.c.LabelValues()...),
-			Value:      aws.Float64(c.c.Value()),
+			Dimensions: makeDimensions(lvs...),
+			Value:      aws.Float64(value),
 			Timestamp:  aws.Time(now),
 		})
-	}
+		return true
+	})
 
-	for name, g := range cw.gauges {
+	cw.gauges.Reset().Walk(func(name string, lvs lv.LabelValues, values []float64) bool {
+		value := last(values)
 		datums = append(datums, &cloudwatch.MetricDatum{
 			MetricName: aws.String(name),
-			Dimensions: makeDimensions(g.g.LabelValues()...),
-			Value:      aws.Float64(g.g.Value()),
+			Dimensions: makeDimensions(lvs...),
+			Value:      aws.Float64(value),
 			Timestamp:  aws.Time(now),
 		})
-	}
+		return true
+	})
 
-	for name, h := range cw.histograms {
-		for _, p := range []struct {
-			s string
-			f float64
-		}{
-			{"50", 0.50},
-			{"90", 0.90},
-			{"95", 0.95},
-			{"99", 0.99},
-		} {
+	cw.histograms.Reset().Walk(func(name string, lvs lv.LabelValues, values []float64) bool {
+		histogram := generic.NewHistogram(name, 50)
+
+		for _, v := range values {
+			histogram.Observe(v)
+		}
+
+		for _, p := range cw.percentiles {
+			value := histogram.Quantile(p.f)
 			datums = append(datums, &cloudwatch.MetricDatum{
 				MetricName: aws.String(fmt.Sprintf("%s_%s", name, p.s)),
-				Dimensions: makeDimensions(h.h.LabelValues()...),
-				Value:      aws.Float64(h.h.Quantile(p.f)),
+				Dimensions: makeDimensions(lvs...),
+				Value:      aws.Float64(value),
 				Timestamp:  aws.Time(now),
 			})
 		}
-	}
+		return true
+	})
 
 	var batches [][]*cloudwatch.MetricDatum
 	for len(datums) > 0 {
@@ -179,64 +234,98 @@ func (cw *CloudWatch) Send() error {
 	return firstErr
 }
 
+func sum(a []float64) float64 {
+	var v float64
+	for _, f := range a {
+		v += f
+	}
+	return v
+}
+
+func last(a []float64) float64 {
+	return a[len(a)-1]
+}
+
 func min(a, b int) int {
 	if a < b {
 		return a
 	}
 	return b
 }
 
-// counter is a CloudWatch counter metric.
-type counter struct {
-	c *generic.Counter
+type observeFunc func(name string, lvs lv.LabelValues, value float64)
+
+// Counter is a counter. Observations are forwarded to a node
+// object, and aggregated (summed) per timeseries.
+type Counter struct {
+	name string
+	lvs  lv.LabelValues
+	obs  observeFunc
 }
 
-// With implements counter
-func (c *counter) With(labelValues ...string) metrics.Counter {
-	c.c = c.c.With(labelValues...).(*generic.Counter)
-	return c
+// With implements metrics.Counter.
+func (c *Counter) With(labelValues ...string) metrics.Counter {
+	return &Counter{
+		name: c.name,
+		lvs:  c.lvs.With(labelValues...),
+		obs:  c.obs,
+	}
 }
 
-// Add implements counter.
-func (c *counter) Add(delta float64) {
-	c.c.Add(delta)
+// Add implements metrics.Counter.
+func (c *Counter) Add(delta float64) {
+	c.obs(c.name, c.lvs, delta)
 }
 
-// gauge is a CloudWatch gauge metric.
-type gauge struct {
-	g *generic.Gauge
+// Gauge is a gauge. Observations are forwarded to a node
+// object, and aggregated (the last observation selected) per timeseries.
+type Gauge struct {
+	name string
+	lvs  lv.LabelValues
+	obs  observeFunc
+	add  observeFunc
 }
 
-// With implements gauge
-func (g *gauge) With(labelValues ...string) metrics.Gauge {
-	g.g = g.g.With(labelValues...).(*generic.Gauge)
-	return g
+// With implements metrics.Gauge.
+func (g *Gauge) With(labelValues ...string) metrics.Gauge {
+	return &Gauge{
+		name: g.name,
+		lvs:  g.lvs.With(labelValues...),
+		obs:  g.obs,
+		add:  g.add,
+	}
 }
 
-// Set implements gauge
-func (g *gauge) Set(value float64) {
-	g.g.Set(value)
+// Set implements metrics.Gauge.
+func (g *Gauge) Set(value float64) {
+	g.obs(g.name, g.lvs, value)
 }
 
-// Add implements gauge
-func (g *gauge) Add(delta float64) {
-	g.g.Add(delta)
+// Add implements metrics.Gauge.
+func (g *Gauge) Add(delta float64) {
+	g.add(g.name, g.lvs, delta)
 }
 
-// histogram is a CloudWatch histogram metric
-type histogram struct {
-	h *generic.Histogram
+// Histogram is an Influx histrogram. Observations are aggregated into a
+// generic.Histogram and emitted as per-quantile gauges to the Influx server.
+type Histogram struct {
+	name string
+	lvs  lv.LabelValues
+	obs  observeFunc
 }
 
-// With implements histogram
-func (h *histogram) With(labelValues ...string) metrics.Histogram {
-	h.h = h.h.With(labelValues...).(*generic.Histogram)
-	return h
+// With implements metrics.Histogram.
+func (h *Histogram) With(labelValues ...string) metrics.Histogram {
+	return &Histogram{
+		name: h.name,
+		lvs:  h.lvs.With(labelValues...),
+		obs:  h.obs,
+	}
 }
 
-// Observe implements histogram
-func (h *histogram) Observe(value float64) {
-	h.h.Observe(value)
+// Observe implements metrics.Histogram.
+func (h *Histogram) Observe(value float64) {
+	h.obs(h.name, h.lvs, value)
 }
 
 func makeDimensions(labelValues ...string) []*cloudwatch.Dimension {