From: Jens Gustedt <jens.gustedt@inria.fr>
To: musl@lists.openwall.com
Subject: Re: Deduplicating atomics written in terms of CAS
Date: Mon, 18 May 2015 00:23:07 +0200 [thread overview]
Message-ID: <1431901387.4219.7.camel@inria.fr> (raw)
In-Reply-To: <20150517175918.GQ17573@brightrain.aerifal.cx>
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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. With that we could ensure that actually all
accesses to such an object are through these functions.
The advantage of C11's model for atomic is that this a qualifier, and
then the compiler automatically checks (or ensures) that all accesses
are atomic. We don't have that luxury, here, but we could get a bit
closer to it.
Jens
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next prev parent reply other threads:[~2015-05-17 22:23 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-17 4:55 Rich Felker
2015-05-17 6:00 ` Alexander Monakov
2015-05-17 6:14 ` Rich Felker
2015-05-17 7:37 ` Jens Gustedt
2015-05-17 16:28 ` Rich Felker
2015-05-17 16:59 ` Jens Gustedt
2015-05-17 17:59 ` Rich Felker
2015-05-17 22:23 ` Jens Gustedt [this message]
2015-05-17 22:33 ` Rich Felker
2015-05-17 23:22 ` Jens Gustedt
2015-05-18 10:19 ` Szabolcs Nagy
2015-05-18 11:03 ` Jens Gustedt
2015-05-17 6:49 ` Jens Gustedt
2015-05-17 16:22 ` Rich Felker
2015-05-17 17:19 ` Jens Gustedt
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