package main

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

func main() {

    t := time.NewTimer(3 * time.Second)
    fmt.Printf("Start waiting at %v\n", time.Now().Format(time.UnixDate))
    <-t.C
    fmt.Printf("Code executed at %v\n", time.Now().Format(time.UnixDate))

    wg := &sync.WaitGroup{}
    wg.Add(1
 
)
    fmt.Printf("Start waiting for AfterFunc at %v\n", time.Now().Format(time.UnixDate))
    time.AfterFunc(3*time.Second, func() {
        fmt.Printf("Code executed for AfterFunc at %v\n", time.Now().Format(time.UnixDate))
        wg.Done()
    })

    wg.Wait()

    fmt.Printf("Waiting on time.After at %v
 
\n", time.Now().Format(time.UnixDate))
    <-time.After(3 * time.Second)
    fmt.Printf("Code resumed at %v\n", time.Now().Format(time.UnixDate))

}

/*

Start waiting at Thu Mar 22 00:32:42 CST 2018
Code executed at Thu Mar 22 00:32:45 CST 2018
Start waiting for AfterFunc at Thu Mar 22 00:32:45 CST 2018
Code executed for AfterFunc at Thu Mar 22 00:32:48 CST 2018
 

Waiting on time.After at Thu Mar 22 00:32:48 CST 2018
Code resumed at Thu Mar 22 00:32:51 CST 2018

*/

3.10 計算代碼運行的時長