bug#21028: Performance regression in revision af1a69f4d17a482c359d98c00ef86fac835b5fac (Apr 2014).

[Clément Pit--Claudel]

On 2016-10-27 10:38, Eli Zaretskii wrote:
>> From: Clément Pit--Claudel <clement.pit@gmail.com>
>> Date: Wed, 26 Oct 2016 13:15:14 -0400
>>
>> Note: inhibit-compact-font-caches doesn't solve this problem (was it 
>> supposed to?).  Reverting the commit in the title causes other crashes 
>> (24790).
> 
> The problem with reverting that commit is that you reverted too much.
> The part of the commit shown below cannot be reverted, because the
> code it fixed was inserting invalid data types into the font cache,
> which then caused rare segfaults such as the one you had recently.

Indeed! Thanks for explaining Eli :) Based on your instructions I:

* Started from a clean checkout
* Reverted af1a69f4d17a482c359d98c00ef86fac835b5fac
* Applied the patch below

And indeed:

* Performance is great (bug #21028 is gone)
* I don't observe segfaults anymore (I can't reproduce bug #24790)

> So put back that part of the changeset, and if your performance
> problems are still solved by the rest, we might just revert the other
> part on master, because no one seems to be able to reproduce the
> problem with empty vectors in the font cache, which that part was
> supposed to fix.

That would be great.

Thanks!
Clément.

> diff --git a/src/font.c b/src/font.c
> index b49664b..e99141b 100644
> --- a/src/font.c
> +++ b/src/font.c
> @@ -2804,7 +2803,6 @@ font_matching_entity (struct frame *f, Lisp_Object 
> *attrs, Lisp_Object spec)
>       && (NILP (ftype) || EQ (driver_list->driver->type, ftype)))
>        {
>       Lisp_Object cache = font_get_cache (f, driver_list->driver);
> -     Lisp_Object copy;
>  
>       ASET (work, FONT_TYPE_INDEX, driver_list->driver->type);
>       entity = assoc_no_quit (work, XCDR (cache));
> @@ -2813,9 +2811,14 @@ font_matching_entity (struct frame *f, Lisp_Object 
> *attrs, Lisp_Object spec)
>       else
>         {
>           entity = driver_list->driver->match (f, work);
> -         copy = copy_font_spec (work);
> -         ASET (copy, FONT_TYPE_INDEX, driver_list->driver->type);
> -         XSETCDR (cache, Fcons (Fcons (copy, entity), XCDR (cache)));
> +         if (!NILP (entity))
> +           {
> +             Lisp_Object copy = copy_font_spec (work);
> +             Lisp_Object match = Fvector (1, &entity);
> +
> +             ASET (copy, FONT_TYPE_INDEX, driver_list->driver->type);
> +             XSETCDR (cache, Fcons (Fcons (copy, match), XCDR (cache)));
> +           }
>         }
>       if (! NILP (entity))
>         break;
>

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