Re: [avr-libc-dev] C11 Atomics and GCC libatomic

[Martin McKee]

I don't comment often, but...

There are, for C++ work, a number of advantages to supporting the
standardized atomic types.  And, we *are* talking here about C++ support
rather than C support, which is rather more lacking in avr-lib-c.  Besides
making code more portable, the standard atomics library works in a well
quantified manner and is, thus, safer for someone that moves between
different platforms.  Plus, the C++ standard atomic functionality has a
much wider range of granularity than the current avr-libc atomic header.
It is possible to protect blocks of code, but, moreover, atomic types allow
for *type-safe* atomic access to single values with only minimal periods of
interrupts being disabled.  Granted, this is entirely possible with a block
critical section, but the code is much more complicated than the direct
value access of the "atomic type."

Finally, the C++ atomics are typically, and this is what Jacob is
describing above, I believe, implemented with a combination of compiler
intrensics and template metaprogramming.  The result is that there is no
function call.  The code is inlined, just like a macro.  As such, there is
no additional cost

I for one would welcome this as an addition to the current library.

Martin Jay McKee

On Fri, Jun 24, 2016 at 10:02 AM, Markus Hitter <address@hidden> wrote:

> Am 24.06.2016 um 16:21 schrieb Jacob Moroni:
>
>> With this library, I was also able to include a portable version of the
>> <stdatomic.h> header which allows for the successful use of C11 atomic
>> types!
>>
>> I would like to get this merged into avr-libc
>>
>
> What's wrong with the atomic macros already existing?
>
> http://www.nongnu.org/avr-libc/user-manual/atomic_8h.html
>
> A function call is rather heavyweight for something as simple as locking
> interrupts.
>
> As the above macros require C99, Teacup Firmware created a similar macro
> set working on C89, too:
>
> https://github.com/Traumflug/Teacup_Firmware/blob/master/memory_barrier.h
>
>
> Markus
>
> --
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> Dipl. Ing. (FH) Markus Hitter
> http://www.jump-ing.de/
>
>
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