Re: make MaxBackends available in _PG_init

On Tue, Apr 19, 2022 at 05:49:13PM +0800, Julien Rouhaud wrote:
> 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.

Okay, I did it this way in v5.

-- 
Nathan Bossart
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