Re: Trying out <stdatomic.h>

On Tue, 20 Oct 2026 20:56:45 -0400, shihao zhong <zhong950419(at)gmail(dot)com> wrote:
> Hi Greg,

Hi Shihao,

Thanks very much for testing this on macOS arm64 and for two very
specific reports -- both were real, and both are fixed in v9 attached
(rebased on master df64d6e984b).

>
> 1. The header has a C++23 branch, and that branch fails to build
> when an extension includes it inside extern "C", which is the usual
> way:
>
> extern "C" {
> #include "postgres.h"
> #include "storage/lwlock.h"
> }
>
> clang 17 failed with "templates must have C++ linkage".

Confirmed and fixed.

> 2. pg_atomic_test_set_flag_impl uses atomic_fetch_and_explicit(). On
> x86 clang turns that into a lock cmpxchg loop, while master uses a
> single xchg.
>
> Maybe use atomic_exchange_explicit(ptr, 0, memory_order_acquire) ?

Adopted, thank you. Exchange is the better way to write it regardless.

> Thanks,
> Shihao

best.

-greg