package main

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

//协程并发控制,只执行一次
var num = 0
var once = sync.Once{}

func main() {
    for i := 0; i <= 100; i++ {

        go once.Do(addNum)
    }

    time.Sleep(time.Second*10)
    fmt.Println(num)
}

func addNum() {

    num = num + 1
}