main.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"runtime"
	"sync"
)

func get(url string) {
	resp, err := http.DefaultClient.Get(url)
	if err != nil {
		log.Fatal(err)
	}
	defer resp.Body.Close()

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Fatal(err)
	}

	log.Printf("Goroutine:%d, URL:%s (%d bytes)", runtime.NumGoroutine(), url, len(body))
}

func main() {
	var wg sync.WaitGroup
	for i := 0; i < 100; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			url := fmt.Sprintf("http://placehold.it/%dx%d", i, i)
			get(url)
		}(i)
	}
	wg.Wait()
}