cancel2.go

package main

import (
	"context"
	"log"
	"sync"
	"time"
)

var wg sync.WaitGroup
var stopEverything = make(chan bool)

func main() {
	//number of workers
	ctx, cancel := context.WithCancel(context.Background())

	wg.Add(6)
	go worker(ctx, 1)
	go worker(ctx, 2)
	go workerWithBug(ctx, 3)
	go worker(ctx, 4)
	go worker(ctx, 5)
	go worker(ctx, 6)

	go func() {
		for {
			select {
			case <-stopEverything:
				log.Printf("Callin cancel()...")
				cancel()
				return
			}
		}
	}()

	wg.Wait()
}

//worker who waits the same amount of seconds as his ID number
func worker(ctx context.Context, id int) {
	longRunningTicker := time.NewTicker(time.Duration(id) * time.Second)
loop:
	for {
		select {

		case <-longRunningTicker.C:
			log.Printf("goroutine #%v: SUCCESS!", id)
			break loop
		case <-ctx.Done():
			log.Printf("RETURNING from goroutine #%v", id)
			break loop
		}
	}

	wg.Done()
}

//worker who waits the same amount of seconds as his ID number
func workerWithBug(ctx context.Context, id int) {
	errorTicker := time.NewTicker(time.Duration(id) * time.Second)

loop:

	for {
		select {

		case <-errorTicker.C:
			stopEverything <- true
			log.Printf("goroutine #%v: FAILED!", id)
			break loop
		case <-ctx.Done():
			log.Printf("RETURNING from goroutine #%v", id)
			break loop
		}
	}

	wg.Done()
}