场景 1

package main

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

var wg sync.WaitGroup
var notify bool

func f1()  {
   defer wg.Done()
   i := 0
   for   {
      i++
      fmt.Println(i)
      time.Sleep(time.Millisecond*500)
      if notify {
         break
      }
   }
}

func f11()  {
   wg.Add(1)
   go f1()
   time.Sleep(time.Second*5)
   notify = true
   wg.Wait()
}


func main()  {
   f11()
}

场景2

package main

import (
   "fmt"
   "sync"
   "time"
)
var wg sync.WaitGroup
var ch = make(chan bool,1)

func c1(){
   defer wg.Done()

   i := 0
XXXXAAAAA:
   for   {
      i++
      fmt.Println(i)
      time.Sleep(time.Millisecond*500)
      select {
      case x:= <-ch:
         fmt.Println(x)
         break XXXXAAAAA
         //return
      default:

      }
   }

}

func c11() {
   wg.Add(1)
   go c1()
   time.Sleep(time.Second * 5)
   ch <- true
   wg.Wait()
}

func main() {
   c11()
}

场景3

package main

import (
   "context"
   "fmt"
   "sync"
   "time"
)
var wg sync.WaitGroup

func c1(ctx context.Context){
   defer wg.Done()
   go c2(ctx)
      i := 0
XXXXX1:
   for   {
      i++
      fmt.Println("A:",i)
      time.Sleep(time.Millisecond*500)
      select {
      case <- ctx.Done():
         break XXXXX1
      default:

      }
   }

}

func c2(ctx context.Context){
   defer wg.Done()
   i := 0
XXXXX2:
   for   {
      i++
      fmt.Println("B:",i)
      time.Sleep(time.Millisecond*500)
      select {
      case <- ctx.Done():
         break XXXXX2
      default:

      }
   }

}

func c11() {
   ctx,cancel := context.WithCancel(context.Background())
   wg.Add(1)
   go c1(ctx)
   time.Sleep(time.Second * 5)
   cancel()
   wg.Wait()
}

func main() {
   c11()
}