Graceful shutdown in Go using context.Context and chan os.Signal

graceful_shutdown.go

package main

import (
	"context"
	"errors"
	"fmt"
	"os"
	"os/signal"
	"sync"
	"syscall"
	"time"
)

type Looper interface {
	Loop(context.Context)
}

type Client interface {
	Shutdown()
}

type client struct{}

func (c *client) Shutdown() {
	fmt.Println("gracefully shutdown client")
}

type looper struct {
	someClient Client
}

func main() {
	sigChan := make(chan os.Signal, 1)
	signal.Notify(
		sigChan,
		syscall.SIGHUP,  // kill -SIGHUP XXXX
		syscall.SIGINT,  // kill -SIGINT XXXX or Ctrl+c
		syscall.SIGQUIT, // kill -SIGQUIT XXXX
		syscall.SIGTERM, // kill -SIGTERM XXXX
	)

	ctx, cancel := context.WithCancel(context.Background())
	var wg sync.WaitGroup
	wg.Add(1)

	client := &client{}
	looper := &looper{
		someClient: client,
	}
	go func() {
		defer wg.Done()
		if err := looper.Loop(ctx); err != nil {
			fmt.Println(err.Error())
		}
	}()

	wg.Add(1)
	go func() {
		defer wg.Done()
		<-sigChan
		cancel()
	}()
	wg.Wait()
}

func (l *looper) Loop(ctx context.Context) error {
	return l.loopUseCase(ctx)
}

func (l *looper) loopUseCase(ctx context.Context) error {
	var i int
	for {
		select {
		case <-ctx.Done():
			l.someClient.Shutdown()
			return errors.New("context canceled")
		default:
			i++
			fmt.Println(i)
		}
		time.Sleep(time.Second)
	}
}