Demo: Using context to cancel heavy jobs after timeout

context_demo.go

package main

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

// DemoTimeout .
func DemoTimeout(ctxTimeout time.Duration, workDuration time.Duration) error {
	ctx, _ := context.WithTimeout(context.Background(), ctxTimeout)

	return demoTimeoutInternal(ctx, workDuration)
}

func demoTimeoutInternal(ctx context.Context, workDuration time.Duration) error {
	res := make(chan error)

	go func(ctx context.Context, res chan error, workDuration time.Duration) {
		fmt.Println("goroutine started")
		res <- heavyJob(ctx, workDuration)
		fmt.Println("goroutine finished")
	}(ctx, res, workDuration)

	select {
	case e := <-res:
		fmt.Printf("got res, error: %v\n", e)
		return e
	}
}

func heavyJob(ctx context.Context, duration time.Duration) error {
	fmt.Println("heavy job started")

	select {
	case <-time.After(duration):
		fmt.Println("heavy job completed")
		return nil
	case <-ctx.Done():
		fmt.Printf("heavy job interrupted by ctx.Done: %v\n", ctx.Err())
		return ctx.Err()
	}
}

func main() {
	err := DemoTimeout(1*time.Second, 900*time.Millisecond)
    fmt.Println(err) // <nil>

	err = DemoTimeout(1*time.Second, 1100*time.Millisecond)
    fmt.Println(err) // context deadline exceeded
}