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/CAMV2Rqrs2TQWZhDt2uece7OSr8k9ShrT_Anzv4Wp-mLTbFwh%2Bw%40mail.gmail.com.
