// To wait for multiple goroutines to finish, we can
// use a *wait group*.

package main

import (
	"fmt"
	"sync"
	"time"
)

// This is the function we'll run in every goroutine.
// Note that a WaitGroup must be passed to functions by
// pointer.
func worker(id int, wg *sync.WaitGroup) {
	fmt.Printf("Worker %d starting\n", id)

	// Sleep to simulate an expensive task.
	time.Sleep(time.Second)
	fmt.Printf("Worker %d done\n", id)

	// Notify the WaitGroup that this worker is done.
	wg.Done()
}

func main() {

	// This WaitGroup is used to wait for all the
	// goroutines launched here to finish.
	var wg sync.WaitGroup

	// Launch several goroutines and increment the WaitGroup
	// counter for each.
	for i := 1; i <= 5; i++ {
		wg.Add(1)
		go worker(i, &wg)
	}

	// Block until the WaitGroup counter goes back to 0;
	// all the workers notified they're done.
	wg.Wait()
}