Date: Sun, 17 May 2015 18:33:27 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: Deduplicating atomics written in terms of CAS On Mon, May 18, 2015 at 12:23:07AM +0200, Jens Gustedt wrote: > Am Sonntag, den 17.05.2015, 13:59 -0400 schrieb Rich Felker: > > > Ah sorry, I probably went too fast. My last paragraph would be for all > > > atomic operations, so in particular 32 bit. A macro "a_load" would > > > make intentions clearer and would perhaps allow to implement an > > > optional compile time check to see if we use any object consistently > > > as atomic or not. > > > > The reason I'm mildly against this is that all current reads of > > atomics, except via the return value of a_cas or a_fetch_add, are > > relaxed-order. We don't care if we see a stale value; if staleness > > could be a problem, the caller takes care of that in an efficient way. > > Having a_load that's relaxed-order whereas all the existing atomics > > are seq_cst order would be an inconsistent API design. > > I still wasn't clear enough, sorry. My idea was not that such a > function or macro should change anything on the binary code that is > produced, at least for production builds. I just thought to > encapsulate all atomic accesses into a type and functions that allow > to have a compile check. I understand that. But if it were called a_load, its semantics (no synchronization/relaxed order) would be inconsistent with all other a_* atomics which are seq_cst. That's what I don't like. Rich
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