import (
	"errors"
	"testing"
	"time"
)
func takesFiveSecond(stopper <-chan struct{}) error {
	time.Sleep(5 * time.Second)
	return nil
}
func takesTwentySecond(stopper <-chan struct{}) error {
	time.Sleep(20 * time.Second)
	return nil
}
func TestDeadline(t *testing.T) {
	dl := New(10 * time.Second)
  //執(zhí)行takesFiveSecond
  if err := dl.Run(takesFiveSecond); err != nil {
		t.Error(err)
	}
  //執(zhí)行takesTwentySecond
  if err := dl.Run(takesTwentySecond); err == ErrTimedOut {
		t.Error(err)
	}
}

type Deadline struct {
	timeout time.Duration
}
func New(timeout time.Duration) *Deadline {
	return &Deadline{
		timeout: timeout,
	}
}

//1. 可以看到Run函數(shù)有一個入?yún)⑹且粋€函數(shù)，函數(shù)的原型為func (<-chan struct{}))error 也就是說我們傳入work變量就需要定義一個這個的簽名函數(shù)。
//2. Run函數(shù)返回error，這個返回實際是入?yún)ork函數(shù)返回的。
//3.為什么work函數(shù)變量，要有一個chan了？ 這個主要為了能讓work函數(shù)里來控制，Run提前退出
func (d *Deadline) Run(work func(<-chan struct{}) error) error {
	result := make(chan error)
	stopper := make(chan struct{})
  //啟動一個協(xié)程
	go func() {
		value := work(stopper)
		select {
		case result <- value:
		case <-stopper:
		}
	}()
  //這里是判斷是否超時常用手法，通過select監(jiān)聽2個chan,一個讀取結果，一個為超時定時器。
  //如果在timeout時間內(nèi)未讀取到執(zhí)行結果，就觸發(fā)time.After返回超時
	select {
	case ret := <-result:
		return ret
	case <-time.After(d.timeout):
		close(stopper)
		return ErrTimedOut
	}
}

import (
	"context"
	"errors"
	"time"
)
var ErrTimedOut = errors.New("timed out waiting for function to finish")
type ContextTimeOut struct {
	timeout time.Duration
}
// New constructs a new Deadline with the given timeout.
func New(timeout time.Duration) *ContextTimeOut {
	return &ContextTimeOut{
		timeout: timeout,
	}
}
func (d *ContextTimeOut) Run(work func(<-chan struct{}) error) error {
	result := make(chan error)
	stopper := make(chan struct{})
	go func() {
		value := work(stopper)
		select {
		case result <- value:
		case <-stopper:
		}
	}()
	ctx, _ := context.WithTimeout(context.Background(), d.timeout)
	select {
	case ret := <-result:
		return ret
	case <-ctx.Done():
		close(stopper)
		return ErrTimedOut
	}
}