Metrics interface and Prometheus implementation (#1929)

* Metrics interface

* Prometheus implementation

* NoOp implementation

Co-authored-by: chris <chris@Profanity.local>

metrics/prometheus/metric_family.go

@@ -0,0 +1,109 @@
+package prometheus
+
+import (
+	"sync"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// metricFamily stores our cached metrics:
+type metricFamily struct {
+	counters           map[string]*prometheus.CounterVec
+	gauges             map[string]*prometheus.GaugeVec
+	timings            map[string]*prometheus.SummaryVec
+	defaultLabels      prometheus.Labels
+	mutex              sync.Mutex
+	prometheusRegistry *prometheus.Registry
+	timingObjectives   map[float64]float64
+}
+
+// newMetricFamily returns a new metricFamily (useful in case we want to change the structure later):
+func (r *Reporter) newMetricFamily() metricFamily {
+	return metricFamily{
+		counters:           make(map[string]*prometheus.CounterVec),
+		gauges:             make(map[string]*prometheus.GaugeVec),
+		timings:            make(map[string]*prometheus.SummaryVec),
+		defaultLabels:      r.convertTags(r.options.DefaultTags),
+		prometheusRegistry: r.prometheusRegistry,
+		timingObjectives:   r.options.TimingObjectives,
+	}
+}
+
+// getCounter either gets a counter, or makes a new one:
+func (mf *metricFamily) getCounter(name string, labelNames []string) *prometheus.CounterVec {
+	mf.mutex.Lock()
+	defer mf.mutex.Unlock()
+
+	// See if we already have this counter:
+	counter, ok := mf.counters[name]
+	if !ok {
+
+		// Make a new counter:
+		counter = prometheus.NewCounterVec(
+			prometheus.CounterOpts{
+				Name:        name,
+				ConstLabels: mf.defaultLabels,
+			},
+			labelNames,
+		)
+
+		// Register it and add it to our list:
+		mf.prometheusRegistry.MustRegister(counter)
+		mf.counters[name] = counter
+	}
+
+	return counter
+}
+
+// getGauge either gets a gauge, or makes a new one:
+func (mf *metricFamily) getGauge(name string, labelNames []string) *prometheus.GaugeVec {
+	mf.mutex.Lock()
+	defer mf.mutex.Unlock()
+
+	// See if we already have this gauge:
+	gauge, ok := mf.gauges[name]
+	if !ok {
+
+		// Make a new gauge:
+		gauge = prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name:        name,
+				ConstLabels: mf.defaultLabels,
+			},
+			labelNames,
+		)
+
+		// Register it and add it to our list:
+		mf.prometheusRegistry.MustRegister(gauge)
+		mf.gauges[name] = gauge
+	}
+
+	return gauge
+}
+
+// getTiming either gets a timing, or makes a new one:
+func (mf *metricFamily) getTiming(name string, labelNames []string) *prometheus.SummaryVec {
+	mf.mutex.Lock()
+	defer mf.mutex.Unlock()
+
+	// See if we already have this timing:
+	timing, ok := mf.timings[name]
+	if !ok {
+
+		// Make a new timing:
+		timing = prometheus.NewSummaryVec(
+			prometheus.SummaryOpts{
+				Name:        name,
+				ConstLabels: mf.defaultLabels,
+				Objectives:  mf.timingObjectives,
+			},
+			labelNames,
+		)
+
+		// Register it and add it to our list:
+		mf.prometheusRegistry.MustRegister(timing)
+		mf.timings[name] = timing
+	}
+
+	return timing
+}