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;
>