Changing resource pack that overrides a font crashes JVM

Could you please attach a sample resource pack to this issue?

Code analysis (23w18a)

Yarn names are used here: 23w18+build.1 for 23w18a. The decompiled code shown below has been generated using Fabric’s fork of CFR.

FontManager#reload has this chunk of code, closing each loaded font storage, then closing each font:

this.fontStorages.values().forEach(FontStorage::close);
        this.fontStorages.clear();
        this.fonts.forEach(Font::close);
        this.fonts.clear();

Looking at {{FontStorage}}’s code, we find the following:

@Override
    public void close() {
        this.closeFonts();
        this.closeGlyphAtlases();
    }

    private void closeFonts() {
        for (Font font : this.fonts) {
            font.close();
        }
        this.fonts.clear();
    }

    private void closeGlyphAtlases() {
        for (GlyphAtlasTexture glyphAtlasTexture : this.glyphAtlases) {
            glyphAtlasTexture.close();
        }
        this.glyphAtlases.clear();
    }

The problem is that the font storage objects in FontManager#fontStorages refer to the same fonts as the ones in FontManager#fonts. This causes some fonts to be closed more than once. BitmapFont}}’s implementation of {{Font#close protects against multiple calls, but TrueTypeFont}}’s implementation does not – calling {{close more than once on a TrueTypeFont causes a double free, resulting in a JVM crash.

Likewise, FontManager#close also causes the same type of double free.

A possible solution would be to have FontStorage not be responsible for closing its fonts. Alternatively, each subclass of Font could protect against multiple closes, but this is a hacky solution in my opinion.

I’ve attached a sample resource pack. You should be able to reproduce this bug by reloading resources several times with this pack loaded.