concurrency.go

package main

import (
	"bytes"
	"fmt"
	"runtime"
	"strconv"
	"time"
)

func main() {
        fmt.Println(getGID())

	concurrency := 4
	sem := make(chan bool, concurrency)
	urls := []string{"url1", "url2", "url3", "url4", "url5", "url6", "url7", "url8", "url9", "url10"}
	for _, url := range urls {
		sem <- true
		go func(url string) {
			defer func() { <-sem }()
			fmt.Println("Hello, playground", url, getGID())
			time.Sleep(10 * time.Second)

		}(url)
	}
	//for i := 0; i < cap(sem); i++ {
	//	sem <- true
	//}

}

func getGID() uint64 {
	b := make([]byte, 64)
	b = b[:runtime.Stack(b, false)]
	b = bytes.TrimPrefix(b, []byte("goroutine "))
	b = b[:bytes.IndexByte(b, ' ')]
	n, _ := strconv.ParseUint(string(b), 10, 64)
	return n
}