Fix data race in drivers

pkg/driver/audiotest/dummy.go

@@ -44,9 +44,11 @@ func (d *dummy) AudioRecord(p prop.Media) (audio.Reader, error) {
 	nextReadTime := time.Now()
 	var phase int
 
+	closed := d.closed
+
 	reader := audio.ReaderFunc(func(samples [][2]float32) (int, error) {
 		select {
-		case <-d.closed:
+		case <-closed:
 			return 0, io.EOF
 		default:
 		}

pkg/driver/camera/camera_linux.go

@@ -123,6 +123,8 @@ func (c *camera) VideoRecord(p prop.Media) (video.Reader, error) {
 		return nil, err
 	}
 
+	cam := c.cam
+
 	ctx, cancel := context.WithCancel(context.Background())
 	c.cancel = cancel
 	var buf []byte
@@ -138,7 +140,7 @@ func (c *camera) VideoRecord(p prop.Media) (video.Reader, error) {
 				return nil, io.EOF
 			}
 
-			err := c.cam.WaitForFrame(5) // 5 seconds
+			err := cam.WaitForFrame(5) // 5 seconds
 			switch err.(type) {
 			case nil:
 			case *webcam.Timeout:
@@ -148,7 +150,7 @@ func (c *camera) VideoRecord(p prop.Media) (video.Reader, error) {
 				return nil, err
 			}
 
-			b, err := c.cam.ReadFrame()
+			b, err := cam.ReadFrame()
 			if err != nil {
 				// Camera has been stopped.
 				return nil, err

pkg/driver/screen/x11_linux.go

@@ -66,10 +66,11 @@ func (s *screen) VideoRecord(p prop.Media) (video.Reader, error) {
 	s.tick = time.NewTicker(time.Duration(float32(time.Second) / p.FrameRate))
 
 	var dst image.RGBA
+	reader := s.reader
 
 	r := video.ReaderFunc(func() (image.Image, error) {
 		<-s.tick.C
-		return s.reader.Read().ToRGBA(&dst), nil
+		return reader.Read().ToRGBA(&dst), nil
 	})
 	return r, nil
 }

pkg/driver/videotest/dummy.go

@@ -99,16 +99,18 @@ func (d *dummy) VideoRecord(p prop.Media) (video.Reader, error) {
 	}
 	random := rand.New(rand.NewSource(0))
 
-	d.tick = time.NewTicker(time.Duration(float32(time.Second) / p.FrameRate))
+	tick := time.NewTicker(time.Duration(float32(time.Second) / p.FrameRate))
+	d.tick = tick
+	closed := d.closed
 
 	r := video.ReaderFunc(func() (image.Image, error) {
 		select {
-		case <-d.closed:
+		case <-closed:
 			return nil, io.EOF
 		default:
 		}
 
-		<-d.tick.C
+		<-tick.C
 
 		copy(yy, yyBase)
 		copy(cb, cbBase)