main.go

package main

import (
	"flag"
	"fmt"
	"github.com/mholt/certmagic"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"sync"
	"time"
)

var (
	fs = &certmagic.FileStorage{Path: filepath.Join(os.TempDir(), "certmagic-test")}
)

func main() {
	name := flag.String("name", "parent", "")
	crash := flag.Bool("crash", false, "")
	flag.Parse()
	wg := &sync.WaitGroup{}
	if *name == "parent" {
		for i := 1; i <= 2; i++ {
			wg.Add(1)
			go spawn(wg, fmt.Sprintf("child/%d", i))
		}
	}
	for i := 1; i <= 2; i++ {
		wg.Add(1)
		go lock(wg, fmt.Sprint(*name, "/", i))
	}
	if *crash {
		time.Sleep(100 * time.Millisecond)
		log.Fatal(*name, "crashed...")
	}
	wg.Wait()
}

func spawn(wg *sync.WaitGroup, name string) {
	defer wg.Done()

	exe, err := os.Executable()
	if err != nil {
		log.Fatalln("Executable:", err)
	}
	cmd := exec.Command(exe, "-name", name)
	cmd.Stderr = os.Stderr
	cmd.Run()
}

func lock(wg *sync.WaitGroup, name string) {
	defer wg.Done()

	k := "hello/world"
	log.Println(name, "lock")
	err := fs.Lock(k)
	if err != nil {
		log.Fatalln(name, "Lock:", err)
	}
	defer func() { log.Println(name, "unlock", fs.Unlock(k)) }()
	log.Println(name, "locked...")
	time.Sleep(100 * time.Millisecond)
}