ResolveIconGlyph() guarded its cache with a mutex, but the work under that
lock reached SharedFactory(), whose lazy DWriteCreateFactory() call was
unsynchronized -- and UiFontFamily()/ApplyUiFontFallback() call the same
helper without that mutex from render paths. Two window threads could both
see a null factory, both create one into the same ComPtr, leak one and race
on the raw pointer. Give SharedFactory() a lock of its own.
IconFonts() memoized its result in a function-local static initialized
exactly once. If SharedFactory() returned null or GetSystemFontCollection()
failed on that first call, the empty list was cached for the process
lifetime and every icon degraded to its text label permanently, with no
retry -- while SharedFactory() itself retried on each call, making the
failure mode asymmetric and hard to diagnose. Keep the list only once the
probe finds a font, and skip the ResolveIconGlyph cache while it is empty
so the retry is actually reachable.
fanlusky
43576b75ca