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 jos...@codesourcery.com
