contextwithtimeout.go

/*
How to use context with timeout to cancel a slow operation.
The same concept can be used with context.WithDeadline()
*/
package main

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

func slowOp() {
	fmt.Println("** Slow op with timeout **")

	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
	defer cancel()

	done := make(chan bool)

	// Do something that will take more time than the timeout
	go func() {
		for i := 0; i < 1000000000000000; i++ {
		}
		done <- true
	}()

	select {
	case <-ctx.Done():
		if ctx.Err() != nil {
			// Handle timeout error
			fmt.Printf("Timeout context: %v\n", ctx.Err())
		}
	case <-done:
		// Never reached...
	}
}

func fastOp() {
	fmt.Println("** Fast op with timeout **")

	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
	defer cancel()

	done := make(chan bool)

	// Do something that will take some time but less than the timeout
	go func() {
		for i := 0; i < 5; i++ {
		}
		done <- true
	}()

	select {
	case <-ctx.Done():
		if ctx.Err() != nil {
			// Never reached...
		}
	case d := <-done:
		// Handle done operation
		fmt.Printf("Operation done: %t \n", d)
	}
}

func main() {
	fastOp()
	slowOp()
}