Again, the issue for the mm is https://github.com/golang/go/issues/5045 <https://github.com/golang/go/issues/5045> but if you read the comments it appears the the de-facto standard is that the atomics do provide “happens before”, but it is not specified that this has to be the case.
> On Nov 11, 2019, at 8:02 PM, burak serdar <bser...@computer.org> wrote: > > On Sun, Nov 10, 2019 at 7:08 AM Lars Seipel <lars.sei...@gmail.com> wrote: >> >> On Sat, Nov 09, 2019 at 11:00:04AM -0600, Robert Engels wrote: >>> No. Because in the absence on a memory barrier the writes may not be >>> flushed meaning you cannot reason about any value ever being changed. >>> atomics provide the memory barrier, but the mm still does not specify a >>> “happens before” relationship (but without this they are fairly useless). >> >> Visibility is implied by the definition of "no concurrent access". >> >> This case is fully handled by the current memory model: > > > You cannot define a "happens-before" relationship using only atomics > with the current memory model. The happens-before relationship, the > way it is written, relies on one goroutine blocking until the other > comes to a point where "things happen" before the block is released. > There is no blocking with atomics, hence there is no point in time > where one goroutine can be sure of things happened in the other > goroutine. > > The only guarantee with atomics is that when one goroutine reads a > value, it will read the last written value. There are no guarantees on > other values. According to the mm, things that happened before that > final write may not be observable to other goroutines. > > > >> >>> Also, if e1 does not happen before e2 and does not happen after e2, then >>> we say that e1 and e2 happen concurrently. >> >> […] >> >>> That is, r is guaranteed to observe w if both of the following hold: >>> >>> 1. w happens before r. >>> 2. Any other write to the shared variable v either happens before w or >>> after r. >> [https://golang.org/ref/mem#tmp_2] >> >> -- >> 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/20191110140757.GB83577%40horsthansen.slrz.net. -- 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/439AC344-C698-4281-87BB-8C33839FB6C5%40ix.netcom.com.
