package main

import (
	"fmt"
	"strconv"
	"sync"
	"time"
)

/*
限制并发数量的用法
*/
func main() {
	wg := sync.WaitGroup{}
	// 最多允许的并发数量
	limit := make(chan struct{}, 20)
	for i := 0; i < 100; i++ {
		wg.Add(1)
		limit <- struct{}{}
		go func(num int) {
			defer func() {
				<-limit
				wg.Done()
			}()
			dosth(num)
		}(i)
	}
	wg.Wait()
}

func dosth(i int) {
	fmt.Println("do sth-->", strconv.Itoa(i))
	// 模拟耗时1s
	time.Sleep(time.Second)
}