multidownloader.go

package main

import (
	"fmt"
	"sync"
)

type job struct {
	id  int
	url string
}

const total int = 100

func main() {

	c := make(chan job)
	done := make(chan struct{})
	wg := sync.WaitGroup{}

	go func() {
		for {
			resp := <-c
			go func() {
				// Do the job
				fmt.Println(resp.id, "=>", resp.url)

				// The job is done!
				wg.Done() // make sure do this before writing in channel
				done <- struct{}{}
			}()
		}
	}()

	jobs := make([]job, total)

	// Fill the jobs here
	for i := range jobs {
		jobs[i] = job{id: i, url: fmt.Sprintf("the url number %d", i)}
	}
	//now pass the job to worker
	for i := range jobs {
		wg.Add(1)

		if i < 10 { // 10 is the limit
			c <- jobs[i]
		} else {
			c <- jobs[i]
			<-done
		}
	}

	wg.Wait()
}