A Bad and Good Example for Handling Goroutine shutdowns with Context

main.go

// A GOOD example for dealing with worker goroutine shutdowns
// run: https://play.golang.org/p/hdwaMQY_K9Q
package main

import (
	"context"
	"fmt"
	"time"
)

func main() {
	ctx, cancel := context.WithCancel(context.Background())

	var w worker
	w.start(ctx)
	time.Sleep(100 * time.Millisecond) // let worker run a little

	cancel() // signal shutdown
	<-w.quit // wait for shutdown
}

type worker struct {
	quit chan struct{}
}

func (w *worker) start(ctx context.Context) {
	w.quit = make(chan struct{})
	go func() {
		for {
			select {
			case <-ctx.Done():
				w.shutdown()
				return

			default:
				w.work()
			}

		}
	}()
	return
}

func (w *worker) shutdown() {
	fmt.Println("shutdown...")
	time.Sleep(1 * time.Second)   // busy
	fmt.Println("success...bye!") // we will see!
	close(w.quit)
}

func (w *worker) work() {
	fmt.Println("busy, busy...")
	time.Sleep(10 * time.Millisecond)
}

main_bad.go

// A BAD example for dealing with worker goroutine shutdowns
// run: https://play.golang.org/p/d8O01dopuHr
package main

import (
	"context"
	"fmt"
	"time"
)

func main() {
	ctx, cancel := context.WithCancel(context.Background())

	var w worker
	w.start(ctx)
	time.Sleep(100 * time.Millisecond) // let worker run a little

	cancel() // signal shutdown
	// Note: cancel() does not block. =>  Main exits; worker crashes.
}

type worker struct{}

func (w *worker) start(ctx context.Context) {
	go func() {
		for {
			select {
			case <-ctx.Done():
				w.shutdown()
				return

			default:
				w.work()

			}
		}
	}()
}

func (w *worker) shutdown() {
	fmt.Println("shutdown...")
	time.Sleep(1 * time.Second)   // busy
	fmt.Println("success...bye!") // we won't see
}

func (w *worker) work() {
	fmt.Println("busy, busy...")
	time.Sleep(10 * time.Millisecond)
}