add(sam): basic memory/goroutine monitor

cmd/sam/flags.go

@@ -6,8 +6,9 @@ import (
 )
 
 type configuration struct {
-	httpAddr string
-	dbDSN    string
+	httpAddr        string
+	dbDSN           string
+	monitorInterval int
 }
 
 func flags(prefix string, mountFlags ...func()) configuration {
@@ -19,6 +20,7 @@ func flags(prefix string, mountFlags ...func()) configuration {
 
 	flag.StringVar(&config.httpAddr, p("http-addr"), ":3000", "Listen address for HTTP server")
 	flag.StringVar(&config.dbDSN, p("db-dsn"), "crust:crust@tcp(db1:3306)/crust?collation=utf8mb4_general_ci", "DSN for database connection")
+	flag.IntVar(&config.monitorInterval, "monitor-interval", 300, "Monitor interval (seconds, 0 = disable)")
 
 	for _, mount := range mountFlags {
 		mount()

cmd/sam/main.go

@@ -30,6 +30,7 @@ func main() {
 
 	// log to stdout not stderr
 	log.SetOutput(os.Stdout)
+	NewMonitor(config.monitorInterval)
 
 	// set up database connection
 	factory.Database.Add("default", config.dbDSN)

cmd/sam/monitor.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"runtime"
+	"time"
+)
+
+type Monitor struct {
+	runtime.MemStats
+	NumGoroutine int
+}
+
+func (m Monitor) MarshalJSON() ([]byte, error) {
+	result := struct {
+		Alloc,
+		TotalAlloc,
+		Sys,
+		Mallocs,
+		Frees uint64
+
+		NumGC        uint32
+		NumGoroutine int
+	}{
+		m.MemStats.Alloc,
+		m.MemStats.TotalAlloc,
+		m.MemStats.Sys,
+		m.MemStats.Mallocs,
+		m.MemStats.Frees,
+
+		m.MemStats.NumGC,
+		m.NumGoroutine,
+	}
+	return json.Marshal(result)
+}
+
+func NewMonitor(duration int) {
+	var m Monitor
+	var interval = time.Duration(duration) * time.Second
+	for {
+		<-time.After(interval)
+		runtime.ReadMemStats(&m.MemStats)
+		m.NumGoroutine = runtime.NumGoroutine()
+		b, _ := json.Marshal(m)
+		fmt.Println(string(b))
+	}
+}