Add Reset(map[string]string) to Metric interface

Change-Id: I289cf8796adbd6ff55f23bba7730145329de00e1

prometheus/counter.go

@@ -65,6 +65,14 @@ func (metric *counter) Set(labels map[string]string, value float64) float64 {
 	return value
 }
 
+func (metric *counter) Reset(labels map[string]string) {
+	metric.mutex.Lock()
+	defer metric.mutex.Unlock()
+
+	signature := labelsToSignature(labels)
+	delete(metric.values, signature)
+}
+
 func (metric *counter) ResetAll() {
 	metric.mutex.Lock()
 	defer metric.mutex.Unlock()

prometheus/counter_test.go

@@ -70,6 +70,24 @@ func testCounter(t tester) {
 				value: `{"type":"counter","value":[{"labels":{},"value":5}]}`,
 			},
 		},
+		{
+			in: input{
+				steps: []func(g Counter){
+					func(g Counter) {
+						g.Set(map[string]string{"handler": "/foo"}, 13)
+					},
+					func(g Counter) {
+						g.Set(map[string]string{"handler": "/bar"}, 17)
+					},
+					func(g Counter) {
+						g.Reset(map[string]string{"handler": "/bar"})
+					},
+				},
+			},
+			out: output{
+				value: `{"type":"counter","value":[{"labels":{"handler":"/foo"},"value":13}]}`,
+			},
+		},
 		{
 			in: input{
 				steps: []func(g Counter){

prometheus/gauge.go

@@ -72,6 +72,14 @@ func (metric *gauge) Set(labels map[string]string, value float64) float64 {
 	return value
 }
 
+func (metric *gauge) Reset(labels map[string]string) {
+	metric.mutex.Lock()
+	defer metric.mutex.Unlock()
+
+	signature := labelsToSignature(labels)
+	delete(metric.values, signature)
+}
+
 func (metric *gauge) ResetAll() {
 	metric.mutex.Lock()
 	defer metric.mutex.Unlock()

prometheus/gauge_test.go

@@ -70,6 +70,24 @@ func testGauge(t tester) {
 				value: `{"type":"gauge","value":[{"labels":{},"value":5}]}`,
 			},
 		},
+		{
+			in: input{
+				steps: []func(g Gauge){
+					func(g Gauge) {
+						g.Set(map[string]string{"handler": "/foo"}, 13)
+					},
+					func(g Gauge) {
+						g.Set(map[string]string{"handler": "/bar"}, 17)
+					},
+					func(g Gauge) {
+						g.Reset(map[string]string{"handler": "/bar"})
+					},
+				},
+			},
+			out: output{
+				value: `{"type":"gauge","value":[{"labels":{"handler":"/foo"},"value":13}]}`,
+			},
+		},
 		{
 			in: input{
 				steps: []func(g Gauge){

prometheus/histogram.go

@@ -296,6 +296,23 @@ func (h *histogram) Purge() {
 	h.lastPurge = time.Now()
 }
 
+func (h *histogram) Reset(labels map[string]string) {
+	h.mutex.Lock()
+	defer h.mutex.Unlock()
+
+	signature := labelsToSignature(labels)
+	value, ok := h.values[signature]
+
+	if !ok {
+		return
+	}
+
+	for _, bucket := range value.buckets {
+		bucket.Reset()
+	}
+	delete(h.values, signature)
+}
+
 func (h *histogram) ResetAll() {
 	h.mutex.Lock()
 	defer h.mutex.Unlock()

prometheus/metric.go

@@ -16,6 +16,8 @@ import (
 type Metric interface {
 	// Produce a JSON representation of the metric.
 	json.Marshaler
+	// Reset removes any stored values associated with a given labelset.
+	Reset(labels map[string]string)
 	// Reset the parent metrics and delete all child metrics.
 	ResetAll()
 	// Produce a human-consumable representation of the metric.