[cairo] cairo_font_face_t not freeing

Bill Spitzak spitzak at gmail.com
Thu May 18 17:20:20 UTC 2017

I don't understand how it even works as intended. What destroys the
h_font passed to cairo_win32_font_face_create_for_hfont when the
font_face is destroyed (for instance in the current implementation
when it is thrown out of the lru cache)? If it is done automatically
then there is no way your code can destroy the h_font as it may be
doubly-destroyed. If it is reference-counted then there should be
absolutely no problem with the current cache, you or that font library
can "destroy" the h_font all it wants. If, as you imply, it leaks,
then there is no way to fix this cleanly, and any solution would
require *ALL* programs, including "toy" ones, to maintain a callback
that says when an h_font is no longer in use.

Can an h_font be shared between mulitple font_face? What if you use it
twice in two different cairo contexts?

Does cairo_win32_font_face_create_for_hfont find a previous use of the
same h_font in the cache? If not then it seems plausible that use of
this constructor function would also indicate that the font should not
be put in the cache in order to fix this problem.

On Thu, May 18, 2017 at 5:22 AM, Fred Bca <fredbca21 at gmail.com> wrote:
> This looks like the issue that I encountered last year with the
> holdovers cache. The cairo font cache works fine and is necessary for
> performance, BUT it also keeps a list of fonts that have been recently
> released which are not used anymore (+ a most recently used font).
> While this can be useful at the application level, I
> don't think that it belongs to cairo as is, since it keeps some fonts
> alive forever, with no control over it as far as I know.
> More information and a patch for a quick fix can be found here:
> https://lists.cairographics.org/archives/cairo/2016-April/027349.html
> It would be nice if we can come up with a solution to fix this that is
> accepted by the community. A compile-time option or runtime API to
> disable / control this behavior for example?
> On Sun, May 7, 2017 at 4:13 PM, Louis M <prog at tioui.com> wrote:
>> On 05/05/2017 10:42 AM, Uli Schlachter wrote:
>>> I'm not completely sure how this cache works, but I doubt that it "keeps
>>> to things" indefinitely. It might even just be a most-recently-used
>>> cache so that it only ever keeps one font alive - I'm not sure.
>> Ok, Thanks. This is reassuring. I will try to do some testing.
>> Good day,
>> Louis M
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