Fix issue #2543 segfault in font dealloc after reinit

[REW1L]

TTF_Quit frees all the resources allocated by freetype. However pointers to FT_Face from TTF_Font are not set to NULL after this. Therefore when font_dealloc tries to call TTF_CloseFont, FT_Done_Face is called on already freed object and segmentation fault appears.

It can be so when Font module quits and then GC is called. (test is provided)

Solution provided is a little hack for setting font->face to NULL. It will tell TTF_CloseFont that face has been already freed and all that's left is to free allocated SDL resources.

Also I had to introduce a field current_ttf_generation to the PyFontObject to understand if object passed to the font_dealloc function is being destructed after TTF_Quit.

[REW1L]

This should fix #2543

[illume]

I wonder if this is enough to stop the problem instead?

TTF_CloseFont(font);
font=NULL;

[REW1L]

Because of tp_free further we are able not to aware about font. Therefore setting font to NULL is just redundant. Also font_dealloc is called only once after TTF_Quit to get a segfault inside a function TTF_CloseFont.

[illume]

Ok, thanks for the explanation :)

[ankith26]

I am still not so clear about what

int **face_pp = font;
*face_pp = NULL;

does, exactly. Can you please explain this bit?
Anyways, I guess it is some weird hack, and I see it works because the tests pass :)

[ghost]

@illume: Is there a timeline for this being released? I'm using pygame as part of a project and want to be able to update the supervisor as it's approaching deadlines.

Thanks for the quick patch @REW1L

[Starbuck5]

Thanks for looking into this @REW1L, sorry it's been dormant on our end for so long.

Perhaps this should be turned into a more abstract "font object invalidation system," since something like this also segfaults:

import pygame
import gc
 
pygame.font.init()
font = pygame.font.Font(None, 20)
pygame.font.quit()
pygame.font.init()

font.render("hello", True, "white")
print("rendered") # never happens, segfaults on the render

But I still have some experimenting around this to do, I think. This is a weird situation / bug.

[ankith26]

This PR looks good to me! Thanks for the PR 👍
Yeah since this fixes a segfault, it would be great to have this merged in ASAP, for v2.0.3

@REW1L there is a merge conflict that needs to be fixed before this being merged, if you want to fix it, you can go ahead! Or I can do it too if you'd like :)

[illume]

I (hopefully) fixed the merge conflict. If it passes tests, we can merge it :)

[illume]

👍 🎉 Thanks