On Sat, Mar 8, 2025 at 3:41 PM Andres Freund <and...@anarazel.de> wrote: > > On 2025-03-08 08:02:41 -0500, Andres Freund wrote: > > From the C/C++ standard atomics model it doesn't make sense to say that a > > failed CAS has release semantics, as there simply isn't a write that could > > be > > ordered! What their barriers guarantee is ordering between multiple memory > > operation, you can't order multiple writes if you don't have multiple > > writes... The synchronization in the C/C++ model is only established > > between > > accesses of the same variable and there's no write in the case of a failed > > CAS, so there's nothing that could establish a release-acquire ordering. > > > > Unfortunately that model doesn't mesh well with barriers that aren't > > attached > > to read/modify operations. Which is what we ended up with... > > Adding a full barrier to failed CAS would be a rather large overhead, > undesirable in just about any sane algorithm. As a consequence, I think what > we ought to do is to redefine the barrier semantics to only imply an acquire > barrier in case CAS fails.
Thank you, I'm good with this solution. Can I leave this on you? I'm not feeling myself strong to word this correctly. ------ Regards, Alexander Korotkov Supabase
