Run pattern in Go

run.go

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

	var wg sync.WaitGroup
	wg.Add(1)

	go func() {
		h.Run(ctx)
		wg.Done()
	}()

	defer func() {
		cancel()
		wg.Wait()
	}()

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

	return nil
}

type Handler struct {
	val int
	mu  sync.Mutex
}

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

	for {
		select {
		case <-time.After(100 * time.Millisecond):
			h.mu.Lock()
			h.val = rand.Int()
			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
}