RE: [PATCH] eal: introduce atomics abstraction

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> > >
> > > Honnappa, please could you give your view on the future of atomics in
> DPDK?
> > Thanks Thomas, apologies it has taken me a while to get to this discussion.
> >
> > IMO, we do not need DPDK's own abstractions. APIs from stdatomic.h
> (stdatomics as is called here) already serve the purpose. These APIs are well
> understood and documented.
> 
> i agree that whatever atomics APIs we advocate for should align with the
> standard C atomics for the reasons you state including implied semantics.
Another point I want to make is, we need 'xxx_explicit' APIs only, as we want memory ordering explicitly provided at each call site. (This can be discussed later).

> 
> >
> > For environments where stdatomics are not supported, we could have a
> stdatomic.h in DPDK implementing the same APIs (we have to support only
> _explicit APIs). This allows the code to use stdatomics APIs and when we move
> to minimum supported standard C11, we just need to get rid of the file in DPDK
> repo.
> 
> my concern with this is that if we provide a stdatomic.h or introduce names
> from stdatomic.h it's a violation of the C standard.
> 
> references:
>  * ISO/IEC 9899:2011 sections 7.1.2, 7.1.3.
>  * GNU libc manual
>    https://www.gnu.org/software/libc/manual/html_node/Reserved-
> Names.html
> 
> in effect the header, the names and in some instances namespaces introduced
> are reserved by the implementation. there are several reasons in the GNU libc
Wouldn't this apply only after the particular APIs were introduced? i.e. it should not apply if the compiler does not support stdatomics.

> manual that explain the justification for these reservations and if if we think
> about ODR and ABI compatibility we can conceive of others.
> 
> i'll also remark that the inter-mingling of names from the POSIX standard
> implicitly exposed as a part of the EAL public API has been problematic for
> portability.
These should be exposed as EAL APIs only when compiled with a compiler that does not support stdatomics.

> 
> let's discuss this from here. if there's still overwhelming desire to go this route
> then we'll just do our best.
> 
> ty