multi-eq hash tables

multi-eq hash tables

[Stefan Monnier]

> -(defconst tool-bar-keymap-cache (make-hash-table))
> +(defconst tool-bar-keymap-cache (make-hash-table :test #'equal))
> +
> +(defun tool-bar--cache-key ()
> +  (cons (frame-terminal) (sxhash-eq tool-bar-map)))

I've seen such needs in the past.
Maybe we should introduce something like:

    (define-hash-table-test shallow-equal
      (lambda (x1 x2) (while (and (consp x1) (consp x2) (eql (car x1) (car x2)))
                        (setq x1 (cdr x1)) (setq x2 (cdr x2)))
                      (equal x1 x2)))
      ...)

and we could even improve the weakness support so that `key` used with
such a hashtable would mean that as soon as one of the values in the
key's list can be GC'd then the entry is removed.

This way we could have our hash table such that entries are flushed by
the GC when a terminal disappears or when one of the tool-bar-map
objects dies (instead of the current code which prevents us from GC'ing
the terminal objects and the old tool bar maps).


        Stefan

Re: multi-eq hash tables

[Lars Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> Maybe we should introduce something like:
>
>     (define-hash-table-test shallow-equal
>       (lambda (x1 x2) (while (and (consp x1) (consp x2) (eql (car x1) (car x2)))
>                         (setq x1 (cdr x1)) (setq x2 (cdr x2)))
>                       (equal x1 x2)))
>       ...)

Yes, that would be excellent.

> and we could even improve the weakness support so that `key` used with
> such a hashtable would mean that as soon as one of the values in the
> key's list can be GC'd then the entry is removed.
>
> This way we could have our hash table such that entries are flushed by
> the GC when a terminal disappears or when one of the tool-bar-map
> objects dies (instead of the current code which prevents us from GC'ing
> the terminal objects and the old tool bar maps).

Hm, interesting...  It's slightly niche, though.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

RE: [External] : multi-eq hash tables

[Drew Adams]

I don't mean to divert, here.  Just thought this
might be related.

Is there perhaps a bug here?  Seems like it.

https://emacs.stackexchange.com/q/71607/105

How to use markers as keys in a hash map? (was: multi-eq hash tables)

[Stefan Monnier]

Drew Adams [2022-05-03 19:30:09] wrote:
> I don't mean to divert, here.

And yet!

> Just thought this might be related.

Not really.

> Is there perhaps a bug here?

There might have been, but it seems to be fixed in `master` because
I can't reproduce it.  Can you?


        Stefan

RE: [External] : How to use markers as keys in a hash map? (was: multi-eq hash tables)

[Drew Adams]

> > I don't mean to divert, here.
> 
> And yet!

Sorry.

> > Just thought this might be related.
> 
> Not really.
> 
> > Is there perhaps a bug here?
> 
> There might have been,

I guess you're confirming that the behavior
described is/was incorrect - a bug.


> but it seems to be fixed in `master` because
> I can't reproduce it.  Can you?

I don't build Emacs.  I see it on Emacs 26.3 and 27.2.

I let the OP know that it seems to be fixed in Emacs 29.

https://emacs.stackexchange.com/a/71643/105