Re: MPS: weak hash tables

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Pip Cet <pipcet@protonmail.com> writes:

> I believe we should leave our options open as far as modifying MPS
> goes: my understanding is we could, if we really wanted to (but
> IANAL),

IANAL either, but I think one could:

 This is the license under which the Memory Pool System Kit is made
 available by Ravenbrook Limited. This license is generally known as
 the `BSD 2-clause license`_.  It is `GPL compatible`_ and
 `OSI approved`_.

> but I'd strongly prefer to discuss that only if and when scratch/igc
> is merged. Everything else is premature.

Ok.

>> I have a vague memory that the docs say somewhere that a finalizer can
>> decline finalization by creating a strong reference, but I can't find it
>> anymore, as usual. Could we use that somehow, maybe?
>
> https://memory-pool-system.readthedocs.io/en/latest/topic/finalization.html#topic-finalization:
>
> The client program may choose to keep the finalized block alive by keeping a strong reference to the finalized object after discarding the finalization message.
>
> This process is known as resurrection and in some finalization systems
> requires special handling, but in the MPS this just is just the usual
> result of the rule that strong references keep objects alive.

Thanks.

> We could use that for key-or-value hash tables, but those aren't
> really my priority.
>
> I don't see a way to use it for the more usual weak hash tables, but
> maybe I'm missing something.

Ok, maybe if we let it ripe a bit, an idea emerges.

>> > > It would be nice if the ugliness could be encapsulated so that one
>> > > doesn't have to see it all the time, as far as that it possible in C
>> > > :-). Or conditionalized, maybe, because with Helmut's idea (which I find
>> > > the right one), we're using and additional word for weak references.
>> > 
>> > How hard would it be to "just" add struct igc_headers to the remaining
>> > non-headered objects? I don't really want to reopen the "get rid of
>> > pure space" discussion again, but that's probably the hard part?
>> 
>> I'd say it's not hard to add the headers to pure space. (Let me briefly
>> sprinkle in that pure space should die :-)). There is a function
>> pure_alloc that is used to allocate objects in pure space, AFAIK.
>
> git merge scratch/no-purespace :-)

Long done, in a repos lightyears away :-).