Use go to implement a simple workflow

workflow_demo.go

func callA() string {
	time.Sleep(time.Millisecond * 300)
	return "Hello A"
}

func callB() string {
	time.Sleep(time.Millisecond * 100)
	return "Hello B"
}

func callC() string {
	time.Sleep(time.Millisecond * 200)
	return "Hello C"
}

func main() {
	a_is_done := make(chan bool)
	b_is_done := make(chan bool)
	go func() {
		log.Println(callA())
		a_is_done <- true
	}()
	go func() {
		log.Println(callB())
		go func() {
			log.Println(callC())
		}()
		b_is_done <- true
	}()
	t := time.Now()
	<-a_is_done //wait for A to finish or timeout
	select {
	case <-b_is_done:
	case <-time.After(time.Duration(time.Millisecond*200) - time.Now().Sub(t)): //todo: duration <= 0
	}
}

a在5s内保证返回这个，是不是缺了一个select呢？