CachedFontFace seems to be causing crash

[krbs]

Fyne v2.2.3, Windows 11/21H2, go1.17.11. Crash happens if multiple faces of the same font is used.

Stacktrace:

fatal error: concurrent map writes

goroutine 138 [running]:
runtime.throw({0x21f66c0, 0x48})
        C:/Program Files/Go/src/runtime/panic.go:1198 +0x76 fp=0xc0008bd3e8 sp=0xc0008bd3b8 pc=0x2a83f6
runtime.mapassign(0xc0000f85a0, 0xc0008bd5d8, 0xc0008bd490)
        C:/Program Files/Go/src/runtime/map.go:585 +0x4d6 fp=0xc0008bd468 sp=0xc0008bd3e8 pc=0x280516
fyne.io/fyne/v2/internal/painter.CachedFontFace({0x0, 0x0, 0x0, 0x0, 0x0}, 0xc0008bd5d8)
        C:/Users/go/pkg/mod/fyne.io/fyne/v2@v2.2.3/internal/painter/font.go:70 +0x46d fp=0xc0008bd518 sp=0xc0008bd468 pc=0x7884cd

Safeguarding it with RWMutex resolves it.

        comp := val.(*fontCacheItem)
        comp.facesMutex.RLock()
        face := comp.faces[*opts]
        comp.facesMutex.RUnlock()
        if face == nil {
                f1 := truetype.NewFace(comp.font, opts)
                f2 := truetype.NewFace(comp.fallback, opts)
                face = newFontWithFallback(f1, f2, comp.font, comp.fallback)

                comp.facesMutex.Lock()
                comp.faces[*opts] = face
                comp.facesMutex.Unlock()
        }

type fontCacheItem struct {
        font, fallback *truetype.Font
        faces          map[truetype.Options]font.Face
        facesMutex     sync.RWMutex
}

Race was introduced in this commit: d83ffac

[andydotxyz]

Fixed on develop and release branch, ready for next release (v2.3 or v2.2.4)