metrics: pull library and introduce ResettingTimer and InfluxDB reporter (#15910)

* go-metrics: fork library and introduce ResettingTimer and InfluxDB reporter.

* vendor: change nonsense/go-metrics to ethersphere/go-metrics

* go-metrics: add tests. move ResettingTimer logic from reporter to type.

* all, metrics: pull in metrics package in go-ethereum

* metrics/test: make sure metrics are enabled for tests

* metrics: apply gosimple rules

* metrics/exp, internal/debug: init expvar endpoint when starting pprof server

* internal/debug: tiny comment formatting fix

metrics/gauge_float64.go

@@ -0,0 +1,127 @@
+package metrics
+
+import "sync"
+
+// GaugeFloat64s hold a float64 value that can be set arbitrarily.
+type GaugeFloat64 interface {
+	Snapshot() GaugeFloat64
+	Update(float64)
+	Value() float64
+}
+
+// GetOrRegisterGaugeFloat64 returns an existing GaugeFloat64 or constructs and registers a
+// new StandardGaugeFloat64.
+func GetOrRegisterGaugeFloat64(name string, r Registry) GaugeFloat64 {
+	if nil == r {
+		r = DefaultRegistry
+	}
+	return r.GetOrRegister(name, NewGaugeFloat64()).(GaugeFloat64)
+}
+
+// NewGaugeFloat64 constructs a new StandardGaugeFloat64.
+func NewGaugeFloat64() GaugeFloat64 {
+	if !Enabled {
+		return NilGaugeFloat64{}
+	}
+	return &StandardGaugeFloat64{
+		value: 0.0,
+	}
+}
+
+// NewRegisteredGaugeFloat64 constructs and registers a new StandardGaugeFloat64.
+func NewRegisteredGaugeFloat64(name string, r Registry) GaugeFloat64 {
+	c := NewGaugeFloat64()
+	if nil == r {
+		r = DefaultRegistry
+	}
+	r.Register(name, c)
+	return c
+}
+
+// NewFunctionalGauge constructs a new FunctionalGauge.
+func NewFunctionalGaugeFloat64(f func() float64) GaugeFloat64 {
+	if !Enabled {
+		return NilGaugeFloat64{}
+	}
+	return &FunctionalGaugeFloat64{value: f}
+}
+
+// NewRegisteredFunctionalGauge constructs and registers a new StandardGauge.
+func NewRegisteredFunctionalGaugeFloat64(name string, r Registry, f func() float64) GaugeFloat64 {
+	c := NewFunctionalGaugeFloat64(f)
+	if nil == r {
+		r = DefaultRegistry
+	}
+	r.Register(name, c)
+	return c
+}
+
+// GaugeFloat64Snapshot is a read-only copy of another GaugeFloat64.
+type GaugeFloat64Snapshot float64
+
+// Snapshot returns the snapshot.
+func (g GaugeFloat64Snapshot) Snapshot() GaugeFloat64 { return g }
+
+// Update panics.
+func (GaugeFloat64Snapshot) Update(float64) {
+	panic("Update called on a GaugeFloat64Snapshot")
+}
+
+// Value returns the value at the time the snapshot was taken.
+func (g GaugeFloat64Snapshot) Value() float64 { return float64(g) }
+
+// NilGauge is a no-op Gauge.
+type NilGaugeFloat64 struct{}
+
+// Snapshot is a no-op.
+func (NilGaugeFloat64) Snapshot() GaugeFloat64 { return NilGaugeFloat64{} }
+
+// Update is a no-op.
+func (NilGaugeFloat64) Update(v float64) {}
+
+// Value is a no-op.
+func (NilGaugeFloat64) Value() float64 { return 0.0 }
+
+// StandardGaugeFloat64 is the standard implementation of a GaugeFloat64 and uses
+// sync.Mutex to manage a single float64 value.
+type StandardGaugeFloat64 struct {
+	mutex sync.Mutex
+	value float64
+}
+
+// Snapshot returns a read-only copy of the gauge.
+func (g *StandardGaugeFloat64) Snapshot() GaugeFloat64 {
+	return GaugeFloat64Snapshot(g.Value())
+}
+
+// Update updates the gauge's value.
+func (g *StandardGaugeFloat64) Update(v float64) {
+	g.mutex.Lock()
+	defer g.mutex.Unlock()
+	g.value = v
+}
+
+// Value returns the gauge's current value.
+func (g *StandardGaugeFloat64) Value() float64 {
+	g.mutex.Lock()
+	defer g.mutex.Unlock()
+	return g.value
+}
+
+// FunctionalGaugeFloat64 returns value from given function
+type FunctionalGaugeFloat64 struct {
+	value func() float64
+}
+
+// Value returns the gauge's current value.
+func (g FunctionalGaugeFloat64) Value() float64 {
+	return g.value()
+}
+
+// Snapshot returns the snapshot.
+func (g FunctionalGaugeFloat64) Snapshot() GaugeFloat64 { return GaugeFloat64Snapshot(g.Value()) }
+
+// Update panics.
+func (FunctionalGaugeFloat64) Update(float64) {
+	panic("Update called on a FunctionalGaugeFloat64")
+}