Properly make core_text::font::Font be Send and Sync The Apple documentation says: > All individual functions in Core Text are thread-safe. Font objects (CTFont, > CTFontDescriptor, and associated objects) can be used simultaneously by > multiple operations, work queues, or threads. However, the layout objects > (CTTypesetter, CTFramesetter, CTRun, CTLine, CTFrame, and associated objects) > should be used in a single operation, work queue, or thread. https://developer.apple.com/documentation/coretext