package main

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

/**
同一個content可以控制多個goroutine, 確保線程可控, 而不是每新建一個goroutine就要有一個chan去通知他關(guān)閉
有了他代碼更加簡潔
*/

func main() {
 fmt.Println("run demo \n\n\n")
 demo()
}

func demo() {
 ctx, cancel := context.WithTimeout(context.Background(), 9*time.Second)
 go watch(ctx, "[線程1]")
 go watch(ctx, "[線程2]")
 go watch(ctx, "[線程3]")

 index := 0
 for {
  index++
  fmt.Printf("%d 秒過去了 \n", index)
  time.Sleep(1 * time.Second)
  if index > 10 {
   break
  }
 }

 fmt.Println("通知停止監(jiān)控")
 // 其實此時已經(jīng)超時, 協(xié)程已經(jīng)提前退出
 cancel()

 // 防止主進(jìn)程提前退出
 time.Sleep(3 * time.Second)
 fmt.Println("done")
}

func watch(ctx context.Context, name string) {
 for {
  select {
  case <-ctx.Done():
   fmt.Printf("%s 監(jiān)控退出, 停止了...\n", name)
   return
  default:
   fmt.Printf("%s goroutine監(jiān)控中... \n", name)
   time.Sleep(2 * time.Second)
  }
 }
}

func demo2() {
 pCtx, pCancel := context.WithCancel(context.Background())
 pCtx = context.WithValue(pCtx, "parentKey", "parentVale")
 go watch(pCtx, "[父進(jìn)程1]")
 go watch(pCtx, "[父進(jìn)程2]")

 cCtx, cCancel := context.WithCancel(pCtx)
 go watch(cCtx, "[子進(jìn)程1]")
 go watch(cCtx, "[子進(jìn)程2]")
 fmt.Println(pCtx.Value("parentKey"))
 fmt.Println(cCtx.Value("parentKey"))

 time.Sleep(10 * time.Second)
 fmt.Println("子進(jìn)程關(guān)閉")
 cCancel()
 time.Sleep(5 * time.Second)
 fmt.Println("父進(jìn)程關(guān)閉")
 pCancel()

 time.Sleep(3 * time.Second)
 fmt.Println("done")
}

type Context interface {
 Deadline() (deadline time.Time, ok bool)

 Done() <-chan struct{}

 Err() error

 Value(key interface{}) interface{}
}

var (
 background = new(emptyCtx)
 todo  = new(emptyCtx)
)

// 這個是最初始的ctx, 之后的子ctx都是繼承自它
func Background() Context {
 return background
}

// 不清楚context要干嘛, 但是就得有一個ctx的用這個
func TODO() Context {
 return todo
}

func WithCancel(parent Context) (ctx Context, cancel CancelFunc)
func WithDeadline(parent Context, deadline time.Time) (Context, CancelFunc)
func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc)
func WithValue(parent Context, key, val interface{}) Context

func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
 return WithDeadline(parent, time.Now().Add(timeout))
}