> Also notice that the random time you pick for cancelTime can be longer
than the different random time you sleep inside the goroutine (i.e. the
function which you pass to DoChan). Hence the goroutine can return a
result, before the cancelTime is reached.
Although the goroutine can return a result before cancelTime arrives, the
returned result should not be err because I haven't had time to call
cancel().
在2022年9月21日星期三 UTC+8 20:18:30<Brian Candler> 写道：
> Notice that DoChan starts a goroutine for the task...
>
> go g.doCall(c, key, fn)
>
> ... and then returns immediately.
>
> Also notice that the random time you pick for cancelTime can be longer
> than the different random time you sleep inside the goroutine (i.e. the
> function which you pass to DoChan). Hence the goroutine can return a
> result, before the cancelTime is reached.
>
> Try this modification:
>
> --- main.go.orig 2022-09-21 13:14:10.000000000 +0100
> +++ main.go 2022-09-21 13:13:43.000000000 +0100
> @@ -144,7 +144,7 @@
> defer wg.Done()
>
> ch, _ := g.DoChan(key, func() (interface{}, error) {
> - time.Sleep(randTimeout())
> + time.Sleep(5000 * time.Millisecond)
> if ctx.Err() == context.Canceled {
> return nil, fmt.Errorf("callUUID=[%d] err=[%s]",
> uuid, ctx.Err())
> }
> @@ -152,7 +152,7 @@
> })
>
> // randomly choose a timeout to cancel
> - cancelTime := time.After(randTimeout())
> + cancelTime := time.After(10 * time.Millisecond)
> select {
> case <-cancelTime:
> // cancel only if no other goroutines share
>
> On Wednesday, 21 September 2022 at 10:01:22 UTC+1 atomic wrote:
>
>> Thanks for your reply, but I still don't understand why time.Sleep is
>> causing my test program to panic.
>>
>> In fact, this is a real online environment problem. My application uses
>> http.Client.Do(), but it occasionally has errors: [lookup xxxxx on
>> xxxxx: dial udp xxxxx: operation was canceled], after looking at the code,
>> I found that it may be There is a problem with ForgetUnshared, lookupIPAddr
>> uses ForgetUnshared:
>> https://github.com/golang/go/blob/4a4127bccc826ebb6079af3252bc6bfeaec187c4/src/net/lookup.go#L336
>>
>> 在2022年9月21日星期三 UTC+8 16:17:35<cuong.m...@gmail.com> 写道：
>>
>>> Hello,
>>>
>>> You use time.Sleep in your program, so the behavior is not predictable.
>>> In fact, I get it success or panic randomly.
>>>
>>> You can see https://go-review.googlesource.com/c/sync/+/424114 to see a
>>> predictable test of ForgetUnshared .
>>>
>>> On Wednesday, September 21, 2022 at 1:45:24 PM UTC+7 atomic wrote:
>>>
>>>> hello
>>>>
>>>> I find that the `src/internal/singleflight/singleflight.go
>>>> ForgetUnshared()` method returns results that are not always expected
>>>>
>>>> For this I wrote a test code, I copied the code in the
>>>> src/internal/singleflight/singleflight.go file to the main package, and
>>>> wrote a main function to test it, if ForgetUnshared() returns correctly,
>>>> this code It should not panic, but the fact that it will panic every time
>>>> it runs, is there something wrong with my understanding of
>>>> ForgetUnshared()?
>>>>
>>>> The test code cannot be run in goplay, so I posted a link:
>>>> https://gist.github.com/dchaofei/e07547bce17d94c3e05b1b2a7230f62f
>>>>
>>>> The go version I use for testing is 1.16, 1.19.1
>>>>
>>>> result:
>>>> ```
>>>> $ go run cmd/main.go
>>>> panic: callUUID=[9314284969 <(931)%20428-4969>] err=[context canceled]
>>>> currentUUId=[6980556786]
>>>> ```
>>>>
>>>
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