golang nesting conexts with cancel

nested_context_with_cancel.go

package main

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

func main() {
	rollUp()
	skipLowest()
	closeRoot()
}

func closeRoot() {
	root, cancel_root := context.WithCancel(context.Background())
	child_1, _ := context.WithCancel(root)
	child_2, _ := context.WithCancel(child_1)

	go func() {
		<-time.After(250 * time.Millisecond)
		cancel_root()
	}()

	select {
	case <-child_2.Done():
		fmt.Println("child_2 done!")
	}

	select {
	case <-child_1.Done():
		fmt.Println("child_1 done!")
		fmt.Println("stopping root")
	}

	select {
	case <-root.Done():
		fmt.Println("root done!")
	}
}

func skipLowest() {
	root, cancel_root := context.WithCancel(context.Background())
	child_1, cancel_1 := context.WithCancel(root)
	child_2, _ := context.WithCancel(child_1)

	go func() {
		<-time.After(250 * time.Millisecond)
		cancel_1()
	}()

	select {
	case <-child_2.Done():
		fmt.Println("child_2 done!")
	}

	select {
	case <-child_1.Done():
		fmt.Println("child_1 done!")
		fmt.Println("stopping root")
		cancel_root()
	}

	select {
	case <-root.Done():
		fmt.Println("root done!")
	}
}

func rollUp() {
	root, cancel_root := context.WithCancel(context.Background())
	child_1, cancel_1 := context.WithCancel(root)
	child_2, cancel_2 := context.WithCancel(child_1)

	go func() {
		<-time.After(250 * time.Millisecond)
		cancel_2()
	}()

	select {
	case <-child_2.Done():
		fmt.Println("child_2 done!")
		fmt.Println("stopping child_1")
		cancel_1()
	}

	select {
	case <-child_1.Done():
		fmt.Println("child_1 done!")
		fmt.Println("stopping root")
		cancel_root()
	}

	select {
	case <-root.Done():
		fmt.Println("root done!")
	}
}

To demonstrate creating child contexts from a root context and how cancelling the various contexts impact one another.

This works because we do not get a runtime panic: all goroutines are asleep - deadlock!