Date: Tue, 19 Apr 2022 17:49:13 +0800
From: Julien Rouhaud <rjuju123@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Nathan Bossart <nathandbossart@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>,
	Andres Freund <andres@anarazel.de>,
	Michael Paquier <michael@paquier.xyz>,
	"Bossart, Nathan" <bossartn@amazon.com>,
	Fujii Masao <masao.fujii@oss.nttdata.com>,
	"wangsh.fnst@fujitsu.com" <wangsh.fnst@fujitsu.com>,
	Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
	Greg Sabino Mullane <htamfids@gmail.com>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Subject: Re: make MaxBackends available in _PG_init
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Hi,

On Mon, Apr 18, 2022 at 08:17:04PM -0400, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
> > I'm looking for a clean way to ERROR if someone attempts to call
> > RequestAddinShmemSpace() or RequestNamedLWLockTranche() outside of the
> > hook.  Currently, we are using static variables in ipci.c and lwlock.c to
> > silently ignore invalid requests.  I could add a new 'extern bool' called
> > 'process_shmem_requests_in_progress', but extensions could easily hack
> > around that to allow requests in _PG_init().  Maybe I am overthinking all
> > this and that is good enough.
> 
> If they do that and it breaks something, that's their fault not ours.
> (It's not like there's not $BIGNUM ways for a C-language module to
> break the backend, anyway.)

Agreed.  Similarly the process_shared_preload_libraries_in_progress flag could
be modified by extension, and that wouldn't be any better.

> BTW, I'd make such errors FATAL, as it's unlikely that we can recover
> cleanly from an error during initialization of a loadable module.
> The module's likely to be only partially initialized/hooked in.

While at it, should we make process_shmem_requests_in_progress true when the
new hook is called?  The hook should only be called when that's the case, and
extension authors may feel like asserting it.