Feedback-ID: i675e48f3:Fastmail
Date: Sun, 23 Nov 2025 10:22:47 -0500
From: Greg Burd <greg@burd.me>
Reply-To: Greg Burd <greg@burd.me>
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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Subject: Re: Trying out <stdatomic.h>
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On Mon, Nov 10, 2025, at 8:17 AM, 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=5Fatomic=5Fflag, so there isn=
't
> much left of the code.
>
> Here also is a semi-independent patch to implement storage/spin.h with
> pg=5Fatomic=5Fflag.  It keeps a small amount of the architecture-specif=
ic
> magic, but moves it out to src/port/spin=5Fdelay.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=E2=84=A2=
 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.
>
> Attachments:
> * v1-0001-Add-some-missing-include-limits.h.patch
> * v1-0002-Redefine-port-atomics.h-on-top-of-stdatomic.h.patch
> * v1-0003-Use-atomics-API-to-implement-spinlocks.patch
> * v1-0004-Remove-configure-meson-checks-for-atomics.patch

Hello Thomas,

=46irst off, thanks for working on this set of changes.  I like your chan=
ges in general, except for removing Solaris/Illumos (but I get it).  ;-P

As mentioned on a separate thread about fixing ARM64 support when buildin=
g with MSVC on Win11 =5B1=5D I tried out this patch.  The reply on that t=
hread had an issue with =5Fmm=5Fpause() in spin=5Fdelay(), it turns out w=
e need to use =5F=5Fyield() =5B2=5D.  I went ahead and fixed that, so ign=
ore that patch on the other thread =5B1=5D.  The new patch attached that =
layers on top of your work and supports that platform, there was one mino=
r change that was required:


=23ifdef =5FMSC=5FVER

	/*
	 * If using Visual C++ on Win64, inline assembly is unavailable.  Use a
	 * =5Fmm=5Fpause intrinsic instead of rep nop. =46or ARM64, use the =5F=5F=
yield()
	 * intrinsic which emits the YIELD instruction as a hint to the processo=
r.
	 */
=23if defined(=5FM=5FARM64)
	=5F=5Fyield();
=23elif defined(=5FWIN64)
	=5Fmm=5Fpause();
=23else
	/* See comment for gcc code. Same code, MASM syntax */
	=5F=5Fasm		rep nop;
=23endif
=23endif							/* =5FMSC=5FVER */


Visual Studio 2026 (Community)
cl (msvc 19.50.35718 =22Microsoft (R) C/C++ Optimizing Compiler Version 1=
9.50.35718 for ARM64=22)
link 14.50.35718.0


tests are passing, best.

-greg

=5B1=5D https://www.postgresql.org/message-id/3c576ad7-d2da-4137-b791-582=
1da7cc370%40app.fastmail.com
=5B2=5D https://learn.microsoft.com/en-us/cpp/intrinsics/arm64-intrinsics=
=3Fview=3Dmsvc-180
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