package main

import (
	"fmt"
	"math/rand"
	"sync"
	"time"
)

const N = 1000

func CallMe() error {
	n := rand.Intn(N)
	if n == 888 {
		return fmt.Errorf("lucky: %d", n)
	}
	<-time.After(time.Duration(n) * time.Millisecond)
	fmt.Printf("Waited: %d\n", n)
	return nil
}

func main() {
	// run 1000 goroutine for CallMe, program exit after all goroutines exit.
	var wg sync.WaitGroup
	for i := 0; i < 1000; i++ {
		wg.Add(1)
		go func(){
			CallMe() 
			wg.Done()
		}
	}
	wg.Wait()

}
// 2. follow-up: when CallMe hit the lucky number 888, it returns an error immediately.
//    we hope the program can gracefully exit when any of the goroutine returns an error,
//    without waiting. You can change CallMe function.