[haiku-commits] Re: BRANCH pdziepak-github.lock_elision [a18aae1] in src/system/libroot/os/arch: m68k x86 x86_64 arm ppc
- From: François Revol <revol@xxxxxxx>
- To: haiku-commits@xxxxxxxxxxxxx
- Date: Tue, 23 Jul 2013 00:36:59 +0200
On 23/07/2013 00:30, Axel Dörfler wrote:
> On 07/23/2013 12:03 AM, Pawel Dziepak wrote:
>>>> would be a good idea (while atomic_set{,64}_aligned() becomes
>>>> atomic_set{,64}().).
>>> Can't it return the old value as well to join the club? :-)
>> Unfortunately, no. On x86(_64) to atomically set a value all we need
>> is a simple mov instruction since all writes and reads to naturally
>> aligned memory locations are guaranteed to be atomic. If we want to
>> get the old value we need to use xchg instruction, which is more
>> expensive than a simple mov. That's why I though about having both
>> atomic_set() and atomic_xchg().
>
> Ah, now I see where you're coming from.
> Since we added those calls ourselves, we're free to define how they
> work, at least, and having them both sounds beneficial.
>
> However, 'xchg' would pretty much violate our coding style guide (and
> sounds x86 specific, too), so atomic_exchange() or even
> atomic_get_and_set() would be preferable.
> I think atomic_set(), and atomic_set64() should be consistent, though,
> so whatever you end up naming that exchange function, it should probably
> exist in 32 and 64 bit versions.
Since atomic_set() returns previous value as per the current API, you
might want to use another name for the non-returning version indeed, how
about atomic_put() ?
François.
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