Run pattern with error handling in Go

run_error.go

func run(ctx context.Context) error {
	var h Handler
	ctx, cancel := context.WithCancel(ctx)
	eg, ctx := errgroup.WithContext(ctx)

	eg.Go(func() error { return h.Run(ctx) })

	eg.Go(func() error {
		for i := 0; i < 10; i++ {
			select {
			case <-time.After(time.Second):
				log.Print(h.GetVal())
			case <-ctx.Done():
				return ctx.Err()
			}
		}

		cancel()
		return nil
	})

	err := eg.Wait()
	if errors.Is(err, context.Canceled) {
		return nil
	}

	return err
}

type Handler struct {
	val int
	mu  sync.Mutex
}

const (
	LIMIT = 100
	BOMB  = 42
)

func (h *Handler) Run(ctx context.Context) error {
	log.Print("Starting handler")

	for {
		select {
		case <-time.After(100 * time.Millisecond):
			val := rand.Intn(LIMIT)
			if val == BOMB {
				log.Print("returning BOMB from handler")
				return errors.New("BOMB!")
			}

			h.mu.Lock()
			h.val = val
			h.mu.Unlock()

		case <-ctx.Done():
			log.Print("exiting handler")
			return ctx.Err()
		}
	}
}

func (h *Handler) GetVal() int {
	h.mu.Lock()
	defer h.mu.Unlock()
	return h.val
}