package main

import (
	"fmt"
	"math/rand"
	"sync"
	"time"
)

//waitGroup

func f() {
	//生成随机数
	rand.New(rand.NewSource(time.Now().UnixNano()))
	for i := 0; i < 5; i++ {
		r1 := rand.Int()
		r2 := rand.Intn(10)
		fmt.Println(r1, r2)
	}

}

func f1(i int) {
	defer wg.Done() //任务结束后计数器-1
	time.Sleep(time.Second * time.Duration(rand.Intn(3)))
	fmt.Println(i)

}

var wg sync.WaitGroup

func main() {
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go f1(i)
	}
	//如何知道这10个goroutine都结束了
	wg.Wait() //等待wg的计数器减为0

}