Context

type Context interface {
   Deadline() (deadline time.Time, ok bool)
   Done() <-chan struct{}
   Err() error
   Value(key interface{}) interface{}
}

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

package main

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

func main() {
   ctx, cancel := context.WithCancel(context.Background())
   go Watch(ctx, "goroutine1")
   go Watch(ctx, "goroutine2")

   time.Sleep(6 * time.Second)   // 让goroutine1和goroutine2执行6s
   fmt.Println("end watching!!!")
   cancel()  // 通知goroutine1和goroutine2关闭
   time.Sleep(1 * time.Second)
}

func Watch(ctx context.Context, name string) {
   for {
      select {
      case <-ctx.Done():
         fmt.Printf("%s exit!\n", name) // 主goroutine调用cancel后，会发送一个信号到ctx.Done()这个channel，这里就会收到信息
         return
      default:
         fmt.Printf("%s watching...\n", name)
         time.Sleep(time.Second)
      }
   }
}

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