I find continuously adding and calling done on a waitgroup a bit odd. The
waiting goroutine can continue as soon as the count is zero so there is a
race between adds and dones.
On Sat, 4 Nov 2017, 10:01 , <2891132l...@gmail.com> wrote:
> 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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