metrics: spin up meter ticker routine when enabling metric system (#31400)

Addresses https://github.com/ethereum/go-ethereum/issues/31244

metrics/meter.go

@@ -131,19 +131,15 @@ var arbiter = meterTicker{meters: make(map[*Meter]struct{})}
 type meterTicker struct {
 	mu sync.RWMutex
 
-	started bool
-	meters  map[*Meter]struct{}
+	once   sync.Once
+	meters map[*Meter]struct{}
 }
 
-// add adds another *Meter ot the arbiter, and starts the arbiter ticker.
+// add a *Meter to the arbiter
 func (ma *meterTicker) add(m *Meter) {
 	ma.mu.Lock()
 	defer ma.mu.Unlock()
 	ma.meters[m] = struct{}{}
-	if !ma.started {
-		ma.started = true
-		go ma.loop()
-	}
 }
 
 // remove removes a meter from the set of ticked meters.
@@ -153,7 +149,7 @@ func (ma *meterTicker) remove(m *Meter) {
 	ma.mu.Unlock()
 }
 
-// loop ticks meters on a 5 second interval.
+// loop ticks meters on a 5-second interval.
 func (ma *meterTicker) loop() {
 	ticker := time.NewTicker(5 * time.Second)
 	for range ticker.C {
@@ -167,3 +163,8 @@ func (ma *meterTicker) loop() {
 		ma.mu.RUnlock()
 	}
 }
+
+// startMeterTickerLoop will start the arbiter ticker.
+func startMeterTickerLoop() {
+	arbiter.once.Do(func() { go arbiter.loop() })
+}

metrics/metrics.go

@@ -30,6 +30,7 @@ func Enabled() bool {
 // the program, before any metrics collection will happen.
 func Enable() {
 	metricsEnabled = true
+	startMeterTickerLoop()
 }
 
 var threadCreateProfile = pprof.Lookup("threadcreate")