Monitor restarts itself when the service updated its binary on disk

cmd/gpu-turnstile/main.go

@@ -1034,6 +1034,9 @@ type statusSnapshot struct {
 	UptimeS     int64              `json:"uptime_s"`
 	Downstreams []statusDownstream `json:"downstreams"`
 	Lock        statusLock         `json:"lock"`
+	// MonitorNote is set client-side (never over the wire) when the
+	// monitor's own binary differs from the service's version.
+	MonitorNote string `json:"-"`
 }
 
 // statusProvider assembles the one-line JSON snapshot for CmdStatus.

cmd/gpu-turnstile/monitor.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"os/exec"
 	"strings"
 	"time"
 
@@ -21,7 +22,10 @@ const (
 )
 
 // monitorCommand renders a live status view of the running service,
-// refreshed every second from the control channel. Ctrl+C quits.
+// refreshed every second from the control channel. When the service
+// reports a different version and the executable on disk changed (the
+// updater replaced it), the monitor restarts itself onto the new binary.
+// Ctrl+C quits.
 func monitorCommand() int {
 	if !stdoutIsTerminal() {
 		fmt.Fprintln(os.Stderr, "gpu-turnstile: --monitor needs an interactive terminal")
@@ -30,12 +34,26 @@ func monitorCommand() int {
 	enableVirtualTerminal()
 	fmt.Print("\x1b[2J") // clear once; frames then redraw in place
 	defer fmt.Print(cReset + "\n")
+	exe, _ := os.Executable()
+	var exeStamp time.Time
+	if st, err := os.Stat(exe); err == nil {
+		exeStamp = st.ModTime()
+	}
 	for {
 		frame := renderWaiting()
 		if reply, err := control.Ask(control.CmdStatus); err == nil {
 			if msg, ok := strings.CutPrefix(reply, "OK "); ok {
 				var snap statusSnapshot
 				if json.Unmarshal([]byte(msg), &snap) == nil {
+					if snap.Version != "" && snap.Version != version {
+						if exeChanged(exe, exeStamp) {
+							fmt.Print("\x1b[2J\x1b[H")
+							fmt.Printf("gpu-turnstile: service updated to %s — restarting the monitor\n", snap.Version)
+							restartSelf(exe, "--monitor")
+							return 0
+						}
+						snap.MonitorNote = fmt.Sprintf("note: the service runs %s, this monitor is %s", snap.Version, version)
+					}
 					frame = renderMonitor(snap, termWidth())
 				}
 			}
@@ -45,6 +63,24 @@ func monitorCommand() int {
 	}
 }
 
+// exeChanged reports whether the executable on disk was replaced since the
+// recorded stamp (the updater swaps it via rename, which changes ModTime).
+func exeChanged(exe string, stamp time.Time) bool {
+	if exe == "" || stamp.IsZero() {
+		return false
+	}
+	st, err := os.Stat(exe)
+	return err == nil && !st.ModTime().Equal(stamp)
+}
+
+// restartSelf starts a fresh copy of this executable with the given args on
+// the same console; the caller exits right after.
+func restartSelf(exe string, args ...string) {
+	cmd := exec.Command(exe, args...)
+	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
+	cmd.Start() //nolint:errcheck // best effort: on failure we just exit
+}
+
 func renderWaiting() string {
 	return cDim + " gpu-turnstile — waiting for a running service…" + cReset + "\x1b[K\n"
 }
@@ -81,6 +117,9 @@ func renderMonitor(snap statusSnapshot, width int) string {
 		b.WriteString(fmt.Sprintf(" Queue: %s%d image job(s) waiting%s\x1b[K\n",
 			cYellow, snap.Lock.ImageQueue, cReset))
 	}
+	if snap.MonitorNote != "" {
+		b.WriteString(" " + cYellow + snap.MonitorNote + cReset + "\x1b[K\n")
+	}
 	return b.String()
 }