Example_routinesCustomContext.go

package main

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

type myCtx struct {
	context.Context
}

func (d *myCtx) Done() <-chan struct{} {
	c := make(chan struct{})
	return c
}

func Example_routinesCustomContext() {
	fmt.Println("routines before", runtime.NumGoroutine())
	_, cancel := context.WithCancel(&myCtx{Context: context.Background()})
	fmt.Println("routines, ctx is just created", runtime.NumGoroutine())
	cancel()
	runtime.GC() // updates the goroutines counter faster than sleep
	fmt.Println("routines, ctx is cancelled", runtime.NumGoroutine())
	// Output:
	// routines before 2
	// routines, ctx is just created 3
	// routines, ctx is cancelled 2
}