The way I read the memory model, this program can print 01, 00, and 11, but not 10. This is because goroutine creation creates a synchronized before relationship between x=1 and x=0, so even though there is a race, x=0 happens before x=1.
On Fri, Dec 2, 2022 at 6:56 AM のびしー <nobishi...@gmail.com> wrote: > > I believe your example is basically equivalent to the ones in > https://go.dev/ref/mem#badsync which also contains an explanation of how > the memory model implies this > > @Wagner > Thanks for your opinion, I think so too. I was not confident that my > example is equivalent to https://go.dev/ref/mem#badsync, since my example > reads from the same variable. > > > > Programs that modify data being simultaneously accessed by multiple > goroutines must serialize such access. > @peterGo > > I know that my example has data races. But the Go Memory Model guarantees > a limited number of outcomes for programs with races(unless runtime reports > the race and terminates). My question is about the limited outcomes. > > 2022年12月2日(金) 22:02 Axel Wagner <axel.wagner...@googlemail.com>: > >> I believe your example is basically equivalent to the ones in >> https://go.dev/ref/mem#badsync which also contains an explanation of how >> the memory model implies this (or rather, how it does not imply the >> opposite). >> >> On Fri, Dec 2, 2022, 13:11 のびしー <nobishi...@gmail.com> wrote: >> >>> Hello, I have another question regarding the Go Memory Model. >>> >>> (1) Can this program print "10", according to the Memory Model? >>> (2) If that is forbidden, which part of the Go Memory Model excludes >>> such behavior? >>> >>> https://go.dev/play/p/Fn5I0fjSiKj >>> >>> ```go >>> package main >>> >>> var x int = 0 >>> >>> func main() { >>> go func() { >>> x = 1 >>> }() >>> print(x) // first read: 1 >>> print(x) // second read: 0 >>> } >>> ``` >>> >>> I draw a picture of the happens-before relation of this program here: >>> >>> >>> https://gist.github.com/nobishino/8150346c30101e2ca409ed83c6c25add?permalink_comment_id=4388680#gistcomment-4388680 >>> >>> I think the answer to (1) is yes. >>> Both reads are concurrent with x = 1, so each read can observe both x = >>> 0 and x = 1. >>> And there is no constraint between the results of the first read and the >>> second read. >>> So the second read can observe x = 0 even if the first read observes x = >>> 0. >>> >>> But I'm not very sure. Is this understanding correct? >>> >>> -- >>> 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+unsubscr...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/CAGoET5HyPxEhBETGWNPuYpDgXbm0JM3jeaKFdoQdtc5eGUR0Uw%40mail.gmail.com >>> <https://groups.google.com/d/msgid/golang-nuts/CAGoET5HyPxEhBETGWNPuYpDgXbm0JM3jeaKFdoQdtc5eGUR0Uw%40mail.gmail.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+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/CAGoET5Fk6Wwd7JOJOY%3DJVix9NymsP3yJ_P%2BaDPgtPTorL-X_Wg%40mail.gmail.com > <https://groups.google.com/d/msgid/golang-nuts/CAGoET5Fk6Wwd7JOJOY%3DJVix9NymsP3yJ_P%2BaDPgtPTorL-X_Wg%40mail.gmail.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+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAMV2Rqphhx8S0sZDv%3Dj1rskhPvCBstzLo%2BAscz5X7pMnNFzWNQ%40mail.gmail.com.
