package main
import (
    "fmt"
    "sync"
)
var num int
func add(h chan int, wg *sync.WaitGroup) {
    defer wg.Done()
    h <- 1
    num += 1
    <-h
}
func main() {
    ch := make(chan int, 1)
    wg := &sync.WaitGroup{}
    for i := 0; i < 100; i++ {
        wg.Add(1)
        go add(ch, wg)
    }
    wg.Wait()
    fmt.Println("num:", num)
}