golang cancel context example

main.go

package main

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

var wg sync.WaitGroup

func fn(ctx context.Context, threadName string, cancel context.CancelFunc) {
	defer cancel()
	defer wg.Done()

	select {
	case <-time.After(time.Duration(rand.Intn(500)) * time.Millisecond):
		fmt.Println(threadName, "done")
	case <-ctx.Done():
		fmt.Println(threadName, "cancelled")
	}
}

func main() {
	// Create a new context
	ctx := context.Background()
	// Create a new context, with its cancellation function
	// from the original context
	ctx, cancel := context.WithCancel(ctx)

	num_threads := 10
	wg.Add(num_threads)

	for i := 0; i < num_threads; i++ {
		go fn(ctx, fmt.Sprintf("thread%d", i), cancel)
	}

	wg.Wait()
}