cmd/watcher: fix termination races

cmd/watcher/main.go

@@ -150,8 +150,11 @@ func (d *daemon) dial(ctx context.Context, network, addr string, dialer net.Dial
 }
 
 func (d *daemon) close() error {
+	d.pMu.Lock()
+	defer d.pMu.Unlock()
 	d.conn.Notify(context.Background(), rpc.Unregister, rpc.NewMessage(rpc.UID{Module: d.uid}, rpc.None{}))
 	return errors.Join(
+		closeCloser(d.detailer),
 		closeCloser(d.timezone),
 		d.conn.Close(),
 	)
@@ -333,11 +336,9 @@ func (d *daemon) replaceDetailer(ctx context.Context, strategy string) {
 		d.log.LogAttrs(ctx, slog.LevelError, "configure", slog.Any("error", err))
 		return
 	}
-	if c, ok := d.detailer.(io.Closer); ok {
-		err = c.Close()
-		if err != nil {
-			d.log.LogAttrs(ctx, slog.LevelWarn, "configure", slog.Any("error", err))
-		}
+	err = closeCloser(d.detailer)
+	if err != nil {
+		d.log.LogAttrs(ctx, slog.LevelWarn, "configure", slog.Any("error", err))
 	}
 	d.log.LogAttrs(ctx, slog.LevelInfo, "configure", slog.String("strategy", det.strategy()))
 	d.detailer = det

cmd/watcher/poll_dbus_linux.go

@@ -7,6 +7,7 @@ package main
 import (
 	"encoding/json"
 	"errors"
+	"sync"
 	"time"
 
 	"github.com/godbus/dbus/v5"
@@ -27,19 +28,31 @@ func newMutterDetailer() (detailer, error) {
 }
 
 type mutterDetailer struct {
+	mu   sync.Mutex
 	conn *dbus.Conn
 	last time.Time
 }
 
 func (*mutterDetailer) strategy() string { return "gnome/mutter" }
 
 func (d *mutterDetailer) Close() error {
-	err := d.conn.Close()
-	d.conn = nil
+	d.mu.Lock()
+	var err error
+	if d.conn != nil {
+		err = d.conn.Close()
+		d.conn = nil
+	}
+	d.mu.Unlock()
 	return err
 }
 
 func (d *mutterDetailer) details() (watcher.Details, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	if d.conn == nil {
+		return watcher.Details{}, errors.New("closed")
+	}
+
 	locked, errLocked := dbusCall[bool](d.conn,
 		"org.gnome.ScreenSaver",
 		"/org/gnome/ScreenSaver",