Date: Sun, 23 Nov 2014 11:38:50 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH] Add stdatomic.h for clang>=3.1 and gcc>=4.1 On Sun, Nov 23, 2014 at 05:29:03PM +0100, Jens Gustedt wrote: > > > For the discussion about the second case for the type, this is the > > > question if there are archs that implement TAS operations with other > > > values than 0 for "unset" and 1 for "set". There seem to be archs out > > > there that implement TAS with other values, I vaguely remember having > > > heard about some risk arch (??). Actually this also is the reason why > > > the standard defines this type in such a weird manner, and why per the > > > standard it needs a dedicated initialization macro, default > > > initialization with 0 doesn't do in all cases. > > > > These are not archs we can support with musl, so they wouldn't be > > relevant. And they're not archs that could support POSIX without a > > kernel stop-the-world approach for implementing CAS, or syscalls for > > every synchronization action. > > Could you be more specific? Is it that you know that all the arch in > question and conclude about their behavior from you knowledge about > them? > > Without more specific information I don't see any reason, that an arch > that has such specialized super-fast TAS with weird values couldn't > have a CAS that behaves "normal". But then I also don't see any reason > for such a TAS design in any case ... If you have a CAS, you don't use the broken TAS to implement TAS. You just use the CAS. Rich
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