playground-context-error.go

package main

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

func main() {
	// ctx
	ctx, cancel := context.WithTimeout(context.Background(), time.Hour)

	// This function returns error
	go Perform(ctx)

	// ...
	time.Sleep(time.Second * 5)

	cancel()

	fmt.Println("Ctx canceled")

	// runtime.Goexit makes to crash program in case
	// there is no running routines
	time.Sleep(time.Hour)

	// too bad :(
	runtime.Goexit()
}

// Following function is often found in many examples
// It returns ctx.Err() but for what reason since there is no
// way to catch it in such manner
func Perform(ctx context.Context) error {
	for {
		SomeFunction(ctx)

		select {
			case <-ctx.Done():
				fmt.Println("ctx is canceled, return error")
				return ctx.Err()
			case <-time.After(time.Second): // sleep 1 sec
				fmt.Println("ctx is not canceled, continue immediately")
		}
	}

	return nil
}

func SomeFunction(ctx context.Context) {
	fmt.Println("ping")
}