Start-Closer pattern in Go

start_close.go

func run(ctx context.Context) error {
	var h Handler
	h.Start(ctx)
	defer h.Close()

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

	log.Print("exiting")

	return nil
}

type Handler struct {
	val    int
	mu     sync.Mutex
	wg     sync.WaitGroup
	cancel context.CancelFunc
}

func (h *Handler) Start(ctx context.Context) {
	log.Print("Starting handler")
	ctx, h.cancel = context.WithCancel(ctx)
	h.wg.Add(1)

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

			case <-ctx.Done():
				h.wg.Done()
				return
			}
		}
	}()
}

func (h *Handler) Close() {
	h.cancel()
	h.wg.Wait()
	log.Print("Handler closed")
}

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