package main

import (
	"fmt"
	"sync"
)

var (
	wg sync.WaitGroup
)

func print(ch *chan int, i int) {
	defer wg.Done()
	*ch <- i
}

func main() {
  maxInt := 7
	wg.Add(maxInt)

	ch := make(chan int)
	for i := 0; i < maxInt; i++ {
		go print(&ch, i)
		fmt.Println(<-ch) // 这里卡住等待第i个goroutine运行，然后打印
	}
	
	wg.Wait()
	fmt.Println("done")
}