Re: [C11-atomic] Miscellaneous fixes 1/n

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Fri, 18 Oct 2013, Andrew MacLeod wrote:

> right.  We may re-visit it when we finalize the ABI changes for c++...  Use of
> the attribute in c++ will ensure that C and C++ both treat an atomic object
> the same...  My original discussions with lawrence and jeffrey over atomics
> concerned the desire to "upsize" an _Atomic object to the next highest size
> that supports lock-free operations. (ie, a 6 byte object becomes an 8 byte
> atomic object). The __attribute__ is really to ensure we can share the code

I'm thinking of upsizing as something that's best done only for special 
cases such as maybe hppa - that the normal case is that if you request a 
6-byte atomic object, it's not lock-free.  I think users generally expect 
to need to choose appropriate types for their atomic operations.  
(Indeed, we could even merge without the hook, potentially, on the basis 
that atomic_flag is the sole type that needs to be lock-free and so all 
that's required is a suitable target-specific definition of that type in 
stdatomic.h.  And there's a case for not putting the hook on mainline 
until it's needed.  So maybe the attributes and hook can be completely 
avoided on that basis.)

-- 
Joseph S. Myers
joseph@codesourcery.com