package main

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

func main() {
	wg := &sync.WaitGroup{} // WaitGroup is used to wait for the execution of all running goroutines

	for i := 1; i <= 5; i++ {
		wg.Add(1) // launch several goroutines and increment the counter in WaitGroup for each running goroutine

		go func(id int) {
			worker(id, wg)
		}(i)
	}

	fmt.Println("waiting for all goroutines to complete")
	wg.Wait() // block the execution of the program until the WaitGroup counter becomes equal to 0 again
	fmt.Println("done")
}

func worker(id int, wg *sync.WaitGroup) {
	fmt.Printf("worker %d started\n", id)
	time.Sleep(time.Second) // Sleep simulates a long task
	
    fmt.Printf("worker %d finished\n", id)
	wg.Done() // notify WaitGroup that the worker has completed
}

// $ go run waitgroups.go 
// waiting for all goroutines finished
// worker 4 started
// worker 1 started
// worker 2 started
// worker 3 started
// worker 2 finished
// worker 4 finished
// worker 1 finished
// worker 3 finished
// done