Thank you very much.Sorry I still have some question:what's the function of
wg? what does the sentense "wg.Add(2) " mean?? I found that if I change 2
into 1,the result is differnet.
在 2017年11月3日星期五 UTC+8上午4:45:47，snmed写道：
>
> Hi
>
> Here is the code:
>
> Version 1:
> package main
>
> import (
> "fmt"
> "sync"
> )
>
> var a string
> var once sync.Once
>
> func setup() {
> a = "hello,world\n"
> }
> func doprint() {
> once.Do(setup)
> fmt.Print(a)
> }
> func twoprint() <-chan struct{} {
> var wg sync.WaitGroup
> wg.Add(2)
> ch := make(chan struct{})
>
> go func() {
> doprint()
> wg.Done()
> }()
> go func() {
> doprint()
> wg.Done()
> }()
>
> go func() {
> wg.Wait()
> close(ch)
> }()
>
> return ch
> }
>
> func main() {
> ch := twoprint()
> <-ch
> }
>
>
> Version 2:
> package main
>
> import (
> "fmt"
> "sync"
> )
>
> var a string
> var once sync.Once
>
> func setup() {
> a = "hello,world\n"
> }
> func doprint() {
> once.Do(setup)
> fmt.Print(a)
> }
> func twoprint() {
> var wg sync.WaitGroup
> wg.Add(2)
>
> go func() {
> doprint()
> wg.Done()
> }()
> go func() {
> doprint()
> wg.Done()
> }()
>
> wg.Wait()
> }
>
> func main() {
> twoprint()
> }
>
>
> Cheers snmed
>
>
> Am Donnerstag, 2. November 2017 10:37:15 UTC+1 schrieb 28911...@gmail.com:
>>
>> Sorry,I try my best to open the website but it can't work.Can you write
>> it ??Thank you so much.
>>
>> 在 2017年10月30日星期一 UTC+8下午4:29:44，snmed写道：
>>>
>>> Hi
>>>
>>> There are several ways to solve it, here are two of them:
>>>
>>> https://play.golang.org/p/wJwkI7HQwv
>>> https://play.golang.org/p/nasUcgBeG4
>>>
>>> I prefer the first one, because so I can decide if i want to wait for
>>> the end of twoprint or not.
>>>
>>> Cheers
>>>
>>> Am Montag, 30. Oktober 2017 06:43:45 UTC+1 schrieb 28911...@gmail.com:
>>>>
>>>> Yes, you're right.So how to solve it??
>>>>
>>>> 在 2017年10月30日星期一 UTC+8下午12:37:49，Dave Cheney写道：
>>>>>
>>>>> Hello. I’m guessing that your tried calling twoprint(), but you’ve
>>>>> probably found that nothing is printed to the screen before your program
>>>>> exits.
>>>>>
>>>>> Is that correct?
>>>>
>>>>
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