package main

import "sync"

//某些操作只需要在高并发场景中做一次，例如加载配置文件
//这种场景下用到sync.once

var waitGroup sync.WaitGroup
var once sync.Once

func send(ch1 chan<- int) {
	defer waitGroup.Done()
	for i := 0; i < 100; i++ {
		ch1 <- i
	}
	close(ch1)
}
func getV(ch1 <-chan int, ch2 chan<- int) {
	defer waitGroup.Done()
	for {
		x, ok := <-ch1
		if !ok {
			break
		}
		ch2 <- x * x
	}
	once.Do(func() { close(ch2) })
}

func main() {
	a := make(chan int, 100)
	b := make(chan int, 100)
	waitGroup.Add(3)
	go send(a)
	go getV(a, b)
	go getV(a, b)
	waitGroup.Wait()
	for ret := range b {
		println(ret)
	}

}