Re: [PATCH] Use DatumGetUInt32() for dsm_attach() in test_shm_mq_main()

On Thu, Jun 26, 2025 at 01:46:10PM -0700, Jianghua Yang wrote:
> Just to follow up - in our production system (pg_cron extension),
> we´ve encountered real issues caused by passing a `Datum` to
> `dsm_attach()` using `DatumGetInt32()` instead of `DatumGetUInt32()`.
>
> Here's a sample of the errors observed in our logs:
>
>
> ERROR: unable to map dynamic shared memory segment
> WARNING: one or more background workers failed to start
>
>
> These errors trace back to failures in `dsm_attach()`, where the
> segment handle value was incorrectly interpreted due to sign extension
> from `int32`.

I think there might be something else going on. I added a debug log in
test_shm_mq, and it looks like it regularly uses handles with the high bit
set. I also wrote a test program and consulted the C standard, which seem
to confirm that passing a signed integer to a function with an unsigned
parameter leaves the high bit set.

--
nathan