Обсуждение: Trying out

Hi,

Here is an experimental patch to try out standard C (and C++) atomics
to implement port/atomics.h, and also add more types and operations.
It's mostly just redirecting our names to the standard ones, except
for our barriers and slightly extended pg_atomic_flag, so there isn't
much left of the code.

Here also is a semi-independent patch to implement storage/spin.h with
pg_atomic_flag.  It keeps a small amount of the architecture-specific
magic, but moves it out to src/port/spin_delay.h.

I'm not saying they're correct, performant or portable yet, that'll
require studying codegen and performance on a bunch of weird and
wonderful systems, but they at least passes basic testing on the usual
suspects and CI systems, except for Windows which needs a newer
toolchain so I haven't tried yet.  It should hopefully just work™ on
VS 2022 (same version that provides <threads.h>, about which more
soon).

All that being the case, it's not far enough along to be a serious
proposal, but I imagine others will be looking into things like this
since we pulled the trigger on C11 and I figured I might as well share
a basic working patch set to avoid duplicated effort...   Hopefully it
works well enough to kick the tyres and try to find the difficult
problems, test it out on weird systems, etc etc.

On 10/11/2025 15:17, Thomas Munro wrote:
> Hi,
> 
> Here is an experimental patch to try out standard C (and C++) atomics
> to implement port/atomics.h, and also add more types and operations.
> It's mostly just redirecting our names to the standard ones, except
> for our barriers and slightly extended pg_atomic_flag, so there isn't
> much left of the code.

>  9 files changed, 166 insertions(+), 1824 deletions(-)
>  ...
>  8 files changed, 176 insertions(+), 881 deletions(-)
>  ...
>  7 files changed, 1 insertion(+), 394 deletions(-)

Nice!

> [PATCH v1 1/4] Add some missing #include <limits.h>.

This seems like a good thing regardless of the other patches.

The "#include <limits.h>" lines in src/backend/lib/dshash.c and 
src/backend/storage/lmgr/condition_variable.c are slightly misplaced: 
system headers should be included between "postgres.h" and other 
postgres headers.

> Here also is a semi-independent patch to implement storage/spin.h with
> pg_atomic_flag.  It keeps a small amount of the architecture-specific
> magic, but moves it out to src/port/spin_delay.h.

Makes sense.

The patch removes 'src/template/solaris'. Is that on purpose? Is that an 
independent cleanup that could be committed immediately?

- Heikki

Heikki Linnakangas <hlinnaka@iki.fi> writes:
> The patch removes 'src/template/solaris'. Is that on purpose? Is that an 
> independent cleanup that could be committed immediately?

Our four Solaris+illumos buildfarm animals would be sad.

            regards, tom lane

On Tue, Nov 11, 2025 at 4:19 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Heikki Linnakangas <hlinnaka@iki.fi> writes:
> > The patch removes 'src/template/solaris'. Is that on purpose? Is that an
> > independent cleanup that could be committed immediately?
>
> Our four Solaris+illumos buildfarm animals would be sad.

Looks like I overdid it while rebasing over the commit that removed
the dead Sun compiler... will put that bit back.

On Tue, Nov 11, 2025 at 2:57 AM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
> > [PATCH v1 1/4] Add some missing #include <limits.h>.
>
> This seems like a good thing regardless of the other patches.

Pushed.

> The patch removes 'src/template/solaris'. Is that on purpose?

Fixed.

It passes with VS 2022 on CI.  I had to skip some assertions about
macros promising lock-free implementation, that it doesn't define in C
mode yet.  They are definitely lock-free though[1], and the macros are
defined for C++, and the same under the covers...  Perhaps
feature/conformance macros won't be defined until a few remaining
pieces (things we don't care about) are accessible from C?  (I see
that Visual Studio 2026 has also just shipped a couple of days ago,
not investigated.)

[1] https://devblogs.microsoft.com/cppblog/c11-atomics-in-visual-studio-2022-version-17-5-preview-2/