使用context关闭协程以及协程中的协程

package main

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

var wg sync.WaitGroup

func worker2(ctx context.Context) {
    LOOP:
        for {
            fmt.Printf("worker2\n")
            time.Sleep(time.Second)
            select {
            case <- ctx.Done():
                break LOOP
            default:
            }
        }
}


func worker(ctx context.Context) {
    go worker2(ctx)
    LOOP:
        for {
            fmt.Printf("worker\n")
            time.Sleep(time.Second)
            select {
            case <- ctx.Done():
                break LOOP
            default:

            }
        }
    wg.Done()
}

func main() {
    ctx := context.Background()
    ctx, cancel := context.WithCancel(ctx)
    wg.Add(1)
    go worker(ctx)
    //time.Sleep(time.Second*3)
    cancel()
    wg.Wait()
}