Golang context with cancellation on signal receive

sigterm_context.go

func contextWithSigterm(ctx context.Context) context.Context {
	ctxWithCancel, cancel := context.WithCancel(ctx)
	go func() {
		defer cancel()

		signalCh := make(chan os.Signal, 1)
		signal.Notify(signalCh, os.Interrupt, syscall.SIGTERM)

		select {
		case <-signalCh:
		case <-ctx.Done():
		}
	}()

	return ctxWithCancel
}

Why line #11? Isn’t the derived context ctxWithCancel expired anyway if ctx is “Done”?

Why line #11? Isn’t the derived context ctxWithCancel expired anyway if ctx is “Done”?

Yes but the gorutine lines 3 to 13 would not exit until signal is return. Line 11 ensures gorutine exists if parent context is done otherwise there could be small memory leak of signal is never received but context is done by other means.

Ah yes, thank you!

You can use signal.NotifyContext() instead

@stokito Exactly, here's an example taken from https://henvic.dev/posts/signal-notify-context/. Thanks @henvic!

// This example passes a context with a signal to tell a blocking function that
// it should abandon its work after an operating system signal is notified.
func main() {
	// Pass a context with a timeout to tell a blocking function that it
	// should abandon its work after the timeout elapses.
	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
	defer stop()

	select {
	case <-time.After(10 * time.Second):
		fmt.Println("missed signal")
	case <-ctx.Done():
		stop()
		fmt.Println("signal received")
	}
}

You’re welcome!

LOL 😅

@henvic could you please extend the example in your article?

The problem is that the os.Interrupt is an alias to syscall.SIGINT but at least on Linux we also must handle the SIGTERM:

ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)

I had a problem when the systemd service stuck during reloading.

@stokito, thank you for the feedback. I've updated it.