On 04/08/2026 17:32, Andres Freund wrote:
On 2026-08-04 16:07:58 +0200, Peter Eisentraut wrote:
On 23.07.26 21:56, Nathan Bossart wrote:
On Wed, Jul 22, 2026 at 09:31:49AM -0400, Nathan Bossart wrote:
Ah. It looks like we could use 0 as the sentinel and simplify the call
sites. They subtract one before calling SetStartupBufferPinWaitBufId() and
add one after calling GetStartupBufferPinWaitBufId().
I added a new prerequisite patch (v2-0004) that does this.
Maybe this is okay, but there are a bunch more places (not touched by your
patches) that mix unsigned atomics operations with actually signed values.
Stuff like PIDs and proc numbers. I think for better overall hygiene and to
simplify broader adoption, perhaps we should introduce support for signed
atomic variables.
I'm quite hesitant to do that, at least without a lot more clear cut examples
where it actually would make the code better. I think it's rarely a good idea
to use signed variables for atomics, because you get undefined behaviour on
overflow, there's problems with bit masking, etc. IME most data in atomically
modified should actually be unsigned and probably should have been unsigned
before the conversion to atomics.
We could provide pg_atomic_read/write_i32() and
pg_atomic_compare_exchange_i32() but leave out fetch-and-add and other
such instructions that have overflow or bit masking issues.
- Heikki
