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Re: [PATCH 2/4] Add atomic operations similar to those provided by C11.
- From: Torvald Riegel <triegel at redhat dot com>
- To: "Joseph S. Myers" <joseph at codesourcery dot com>
- Cc: GLIBC Devel <libc-alpha at sourceware dot org>
- Date: Wed, 29 Oct 2014 23:13:29 +0100
- Subject: Re: [PATCH 2/4] Add atomic operations similar to those provided by C11.
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- References: <1414617613 dot 10085 dot 23 dot camel at triegel dot csb> <1414619416 dot 10085 dot 46 dot camel at triegel dot csb> <Pine dot LNX dot 4 dot 64 dot 1410292156440 dot 15119 at digraph dot polyomino dot org dot uk>
On Wed, 2014-10-29 at 22:00 +0000, Joseph S. Myers wrote:
> On Wed, 29 Oct 2014, Torvald Riegel wrote:
>
> > This patch adds atomic operations similar to C11.
> >
> > The function naming is essentially the C11 names, but with the memory
> > order argument removed and added as a suffix. For example, C11's
> > atomic_store_explicit(&foo, 23, memory_order_release)
> > becomes
> > atomic_store_relaxed (&foo, 23);
>
> As previously discussed, I'm concerned about the explicit relaxed loads
> and stores being defined in terms of __atomic_* (see
> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63273>). Unless and until
> __atomic_* implements relaxed atomics as plain loads/stores not inhibiting
> optimization (as far as compatible with standard semantics), as evidenced
> by the change not significantly changing code generated for uses in glibc,
> I think the glibc implementation should be using plain loads and stores
> rather than __atomic_*.
Yes, see Patch 4/4 for how this looks with pthread_once. (You review
faster than I can write emails -- nice! :)
I've chosen to keep the builtins for relaxed loads/stores for now, but
we can revisit later when we have transformed more code.