wait_groups.go

// 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 or we can use them as global variable.
func worker(id int, wg *sync.WaitGroup) {
// On return, notify the WaitGroup that we’re done.
   defer wg.Done()
   fmt.Printf("Worker %d starting\n", id)
// Sleep to simulate an expensive task.
   time.Sleep(time.Second)
   fmt.Printf("Worker %d done\n", id)
}

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()
}