don't show zero 'db_size' on start

cmd/opera/launcher/metrics/metrics.go

@@ -3,40 +3,45 @@ package metrics
 import (
 	"os"
 	"path/filepath"
+	"sync"
 	"sync/atomic"
 	"time"
 
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/metrics"
 )
 
-var (
-	dbDir        atomic.Value
-	dbSize       atomic.Int64
-	dbSizeMetric = metrics.NewRegisteredFunctionalGauge("db_size", nil, func() int64 {
-		return dbSize.Load()
-	})
-)
+var once sync.Once
 
 func SetDataDir(datadir string) {
-	was := dbDir.Swap(datadir)
-	if was != nil {
-		panic("SetDataDir() only once!")
-	}
-	go measureDbDir()
+	once.Do(func() {
+		go measureDbDir("db_size", datadir)
+	})
 }
 
-func measureDbDir() {
+func measureDbDir(name, datadir string) {
+	var (
+		dbSize  atomic.Int64
+		gauge   metrics.Gauge
+		rescan = (len(datadir) > 0 && datadir != "inmemory")
+	)
 	for {
 		time.Sleep(time.Second)
 
-		datadir, ok := dbDir.Load().(string)
-		if !ok || len(datadir) == 0 || datadir == "inmemory" {
-			dbSize.Store(0)
-		} else {
+		if rescan {
 			size := sizeOfDir(datadir)
 			dbSize.Store(size)
 		}
+
+		if gauge == nil {
+			gauge = metrics.NewRegisteredFunctionalGauge(name, nil, func() int64 {
+				return dbSize.Load()
+			})
+		}
+
+		if !rescan {
+			break
+		}
 	}
 }
 

demo/start.sh

@@ -25,6 +25,7 @@ do
 	--nat extip:127.0.0.1 \
 	--http --http.addr="127.0.0.1" --http.port=${RPCP} --http.corsdomain="*" --http.api="eth,debug,net,admin,web3,personal,txpool,ftm,dag" \
 	--ws --ws.addr="127.0.0.1" --ws.port=${WSP} --ws.origins="*" --ws.api="eth,debug,net,admin,web3,personal,txpool,ftm,dag" \
+	--metrics --metrics.addr=127.0.0.1 --metrics.port=$(($RPCP+1100)) \
 	--verbosity=3 --tracing >> opera$i.log 2>&1)&
 
     echo -e "\tnode$i ok"