server: add USR1 signal handler to dump goroutine (#7587)

tidb-server/main.go

@@ -128,7 +128,6 @@ func main() {
 		fmt.Println(printer.GetTiDBInfo())
 		os.Exit(0)
 	}
-
 	registerStores()
 	loadConfig()
 	overrideConfig()
@@ -433,20 +432,31 @@ func createServer() {
 }
 
 func setupSignalHandler() {
-	sc := make(chan os.Signal, 1)
-	signal.Notify(sc,
+	usrDefSignalChan := make(chan os.Signal, 1)
+	signal.Notify(usrDefSignalChan, syscall.SIGUSR1)
+	go func() {
+		buf := make([]byte, 1<<16)
+		for {
+			sig := <-usrDefSignalChan
+			if sig == syscall.SIGUSR1 {
+				stackLen := runtime.Stack(buf, true)
+				log.Printf("\n=== Got signal [%s] to dump goroutine stack. ===\n%s\n=== Finished dumping goroutine stack. ===\n", sig, buf[:stackLen])
+			}
+		}
+	}()
+
+	closeSignalChan := make(chan os.Signal, 1)
+	signal.Notify(closeSignalChan,
 		syscall.SIGHUP,
 		syscall.SIGINT,
 		syscall.SIGTERM,
 		syscall.SIGQUIT)
-
 	go func() {
-		sig := <-sc
+		sig := <-closeSignalChan
 		log.Infof("Got signal [%s] to exit.", sig)
 		if sig == syscall.SIGQUIT {
 			graceful = true
 		}
-
 		if xsvr != nil {
 			xsvr.Close() // Should close xserver before server.
 		}