golang限制函数同时调用次数

package main

import (
	"fmt"
	"time"
)

// cocurrency number of the do func
const cnum = 3

func main() {
	var jobs = make(chan bool, cnum)

	for {
		for i := 0; i < 10; i++ {
			go frqLimit(do, jobs, i)
		}
		time.Sleep(4e9)
	}

}

func frqLimit(f func(), jobChan chan bool, i int) {
	select {
	case jobChan <- true:
		f()
		<-jobChan
	default:
		fmt.Println("job channel is full. pass ", i)
	}
	fmt.Println("jobs", i, "exit")
}

func do() {
	time.Sleep(3e9)
	fmt.Println("job done")
}