Project about Atomic Operations

[Ralf Corsepius]

On 03/26/2012 06:19 PM, Thomas Doerfler wrote:
> Hi,
>
> I am a bit confused about this discussion. I havn't looked into the
> RTEMS/GSOC project related to atomic support, but I agree with Sebastian
> that it doesn't make sense to implement an RTEMS-specific atomic API
> that would replace the C11 standard API.

I agree in sofar as C11 could be a promise about an emerging, future 
standard.

So far, IMO, C11 is too young to be considered stable and established 
standard and to be utilized as foundation of works.

[Remember how long it took until comparable precessors (c89, c99) were 
stable and well established. Their implementation timeframes were 
measured in decades - I'd be surprised, if c11 would be different]

> What might make sense is to
>
> - develop an API for RTEMS synchronization/kernel services which is ON
> TOP of the C11 atomic standard

One option I see, would be to treat c11-atomics as optional and 
conditional and to consider their API as API-template for RTEMS specific 
atomics.

  This would mean, if C11 should be adopted for RTEMS, I'd recomment 
RTEMS to implement an RTEMS-specific wrapper layer, which optionally and 
conditionally may utilize c11-atomics as one potential implementation 
option underneath.

> - develp support routines (maybe in newlib, maybe in RTEMS) that
> implements a synchronization function.

On a wider scope, I think, one would have to analyse whether c11-atomics 
actually meet RTEMS demands and ... whether lowlevel atomic operations 
are actually necessary and/or useful, rsp. if some atomics aren't better 
implemented on higher levels (e.g. using RTEMS score functions).

At least I would rather avoid any low level, RTEMS-specific (esp. ASM) 
atomic operations, because such low level code in longer terms often 
turns into a nightmare.

> Maybe for the discussion the following wiki page might help:
>
> http://gcc.gnu.org/wiki/Atomic
>
> It lists the architectures that GCC directly supports for atomics. All
> other architectures (including ARM, M68K) require library support to get
> atomic operations to work properly. So at least _this_ would be work
> that requires doing.
Well, IMO, The state Atomics in GCC currently is in speaks for itself.
It's an Herculanean effort, which not even the GCC folks are able to 
implement on the broadness which would actually be required.

Ralf