package main

import (
	"fmt"
	"sync"
)

var wg = new(sync.WaitGroup)
var once = new(sync.Once)

//consumerNum := int32
//var consumer = atomic.N

func f1(ch chan int) {
	defer wg.Done()
	for i := 0; i < 100; i++ {
		ch <- i
	}

	// 使用完必须 close 不然将导致死锁
	close(ch)
}

func f2(in chan int, out chan int) {
	defer wg.Done()
	for i := range in {
		out <- i * i
	}

	once.Do(func() {
		// 使用完必须 close 不然将导致死锁
		close(out)
	})
}

func main() {
	ch := make(chan int, 20)
	ch2 := make(chan int, 5)
	wg.Add(2)
	go f1(ch)
	go f2(ch, ch2)

	for i := range ch2 {
		fmt.Println(i)
	}

	wg.Wait()
}