Re: fix more casting away of qualifiers

Hi,

On 2026-11-03 11:41:34 +0100, Peter Eisentraut wrote:
> On 19.10.26 13:55, Andres Freund wrote:
> > I don't think the volatiles moved into PMSignalData are particularly
> > useful. They're precisely one of the cases where volatile is just pretending
> > to do things correctly.
>
> > Tom, is there any reason this doesn't use barriers? I assume it's just
> > because the code is "too old"?
>
> I played around with this a little bit. Using memory barriers here makes
> for very difficult to follow code, because the interacting parts are spread
> over a bunch of different functions, and so you don't get the idiomatic
>
> do one thing
> barrier
> do another thing
>
> code.
>
> If we're going to touch it, would it better to try to write this with
> atomics (with barrier semantics, as appropriate)? What is the current
> thinking on whether the barrier macros or atomics should be used?

I don't quite get it, tbh. If you can move to atomics, you need to do just
about the same analysis, no? I think using atomics is just fine, but normally
for me the analysis is about the same amount of work. Sometimes atomics are a
bit simpler, sometimes barriers, but more often than not the difference is
marginal. Sometimes explicit barrier use can be a bit faster on x86 (because
the barriers operate on non-contended memory).

Greetings,

Andres Freund