Horton

Re: `pg_ctl init` crashes when run concurrently; semget(2) suspected

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Gavin Panella <gavinpanella@gmail.com>
Cc: pgsql-hackers@postgresql.org
Date: 2025-08-10T21:54:03Z
Lists: pgsql-hackers

Attachments

I wrote:
> This is from current macOS, but equivalent text appears on Linux and
> in the POSIX spec.  So it's just luck that nobody has reported the
> same problem elsewhere --- unless maybe there is some macOS-specific
> behavior making it more likely that different installs would try the
> same key.

Hmm, no, there is a platform dependency here.  I made the attached
test program to see what happens when there's a key collision,
and on Linux I get

semget(SEMAS_PER_SET) failed: File exists
semget(SEMAS_PER_SET + 1) failed: File exists

but macOS and NetBSD give

semget(SEMAS_PER_SET) failed: File exists
semget(SEMAS_PER_SET + 1) failed: Invalid argument

I didn't try other BSDen; this might be a NetBSD-ism that Apple
inherited, or maybe it's common among the BSDen.  I don't see any
text in POSIX specifying which errno is to be returned in this case,
so we can't really argue that the behavior is wrong.

			regards, tom lane

Commits

  1. Don't treat EINVAL from semget() as a hard failure.

  2. Give up on running with NetBSD/OpenBSD's default semaphore settings.