Wow, i am from other language and i thought `string` is immutable or something like that, so thread-safe for this operation. learned something new!!! Thanks On Thursday, March 21, 2024 at 11:42:24 PM UTC+8 Ethan Reesor wrote:
> I hadn't used the race detector before. I do see a race warning for > (*URL).String() among an embarrassing number of other results. I'm going to > update (*URL).String() to use atomic.Pointer to remove the race. > > Thanks, > Ethan > > On Thu, Mar 21, 2024 at 8:59 AM 'Axel Wagner' via golang-nuts < > golan...@googlegroups.com> wrote: > >> On Thu, Mar 21, 2024 at 2:48 PM 王李荣 <wanglir...@gmail.com> wrote: >> >>> hi Axel, >>> >>> is not modifying `u.memoize.str` thread-safe? the len and the data >>> point should become visible at same time? >>> >> >> What makes you think that? To be clear, there are no benign data races. >> Even a data-race on a variable smaller than a word is still a data-race, >> unless you do it holding a lock or using atomic instructions. But strings >> are *larger* than single words. >> >> To demonstrate that the effect I am talking about is real, look at this >> code: https://go.dev/play/p/LzRq9-OH-Xb >> >> >>> >>> 在2024年3月16日星期六 UTC+8 06:29:06<Axel Wagner> 写道： >>> >>>> Have you tried running the code with the race detector enabled? I >>>> suspect that you are concurrently modifying `u.memoize.str` by calling >>>> `u.String()` from multiple goroutines. And the non-zero length of the >>>> string header written by one goroutine becomes visible to the other one, >>>> before the modification to the data pointer. >>>> >>>> On Fri, Mar 15, 2024 at 11:15 PM Ethan Reesor <ethan....@gmail.com> >>>> wrote: >>>> >>>>> From this CI job >>>>> <https://gitlab.com/accumulatenetwork/accumulate/-/jobs/6398114923>: >>>>> >>>>> panic: runtime error: invalid memory address or nil pointer dereference >>>>> [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x51d8b7] >>>>> goroutine 1589381 [running]: >>>>> strings.EqualFold({0xc000beec20?, 0x0?}, {0x0?, 0xacace7?}) >>>>> /usr/local/go/src/strings/strings.go:1111 +0x37 >>>>> >>>>> gitlab.com/accumulatenetwork/accumulate/pkg/url.(*URL).Equal(0xc000a74e40?, >>>>> >>>>> 0xc00094c540) >>>>> /builds/accumulatenetwork/accumulate/pkg/url/url.go:472 +0x10c >>>>> >>>>> This is in a docker container based on the go:1.22 image, so the panic >>>>> appears to be happening here: >>>>> >>>>> func EqualFold(s, t string) bool { >>>>> // ASCII fast path >>>>> i := 0 >>>>> for ; i < len(s) && i < len(t); i++ { >>>>> sr := s[i] >>>>> tr := t[i] // <-- line 1111 >>>>> >>>>> (*URL).Equal >>>>> <https://gitlab.com/accumulatenetwork/accumulate/-/blob/5b1cb612d76d4163a101303e51a6fd352224cdab/pkg/url/url.go#L465> >>>>> : >>>>> >>>>> func (u *URL) Equal(v *URL) bool { >>>>> if u == v { >>>>> return true >>>>> } >>>>> if u == nil || v == nil { >>>>> return false >>>>> } >>>>> return strings.EqualFold(u.String(), v.String()) >>>>> } >>>>> >>>>> (*URL).String >>>>> <https://gitlab.com/accumulatenetwork/accumulate/-/blob/5b1cb612d76d4163a101303e51a6fd352224cdab/pkg/url/url.go#L240> >>>>> : >>>>> >>>>> func (u *URL) String() string { >>>>> if u.memoize.str != "" { >>>>> return u.memoize.str >>>>> } >>>>> >>>>> u.memoize.str = u.format(nil, true) >>>>> return u.memoize.str >>>>> } >>>>> >>>>> (*URL).format >>>>> <https://gitlab.com/accumulatenetwork/accumulate/-/blob/5b1cb612d76d4163a101303e51a6fd352224cdab/pkg/url/url.go#L189> >>>>> : >>>>> >>>>> func (u *URL) format(txid []byte, encode bool) string { >>>>> var buf strings.Builder >>>>> // ... write to the builder >>>>> return buf.String() >>>>> } >>>>> >>>>> How is this possible? Based on `addr=0x0` in the panic I think this is >>>>> a nil pointer panic, as opposed to some other kind of segfault. The only >>>>> way I can reproduce panic-on-string-index is with >>>>> `(*reflect.StringHeader)(unsafe.Pointer(&s)).Data >>>>> = 0`, but I don't see how that can be happening here. I'm saving the >>>>> string >>>>> but I'm not doing anything weird with it. And the string header is a >>>>> value >>>>> type so code that manipulates the returned string shouldn't modify the >>>>> original. And I'm definitely not doing any kind of unsafe string >>>>> manipulation like that in my code, anywhere. The only reference to unsafe >>>>> anywhere in my code is for parameters for calling GetDiskFreeSpaceExW >>>>> (Windows kernel32.dll call). >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "golang-nuts" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to golang-nuts...@googlegroups.com. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/golang-nuts/d6f6bb75-45e9-4a38-9bbd-d332e7f3e57cn%40googlegroups.com >>>>> >>>>> <https://groups.google.com/d/msgid/golang-nuts/d6f6bb75-45e9-4a38-9bbd-d332e7f3e57cn%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> -- >>> You received this message because you are subscribed to the Google >>> Groups "golang-nuts" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to golang-nuts...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/31f77ff2-cf11-4b3e-9b14-874b6cc41da3n%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/golang-nuts/31f77ff2-cf11-4b3e-9b14-874b6cc41da3n%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- >> > You received this message because you are subscribed to a topic in the >> Google Groups "golang-nuts" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/golang-nuts/Dgy0fyb4Shw/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> golang-nuts...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/CAEkBMfG8v0qO_NP4PipEBL%3Dd_Ase9ntWi4EL1dQE_6ubeZQnww%40mail.gmail.com >> >> <https://groups.google.com/d/msgid/golang-nuts/CAEkBMfG8v0qO_NP4PipEBL%3Dd_Ase9ntWi4EL1dQE_6ubeZQnww%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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