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Pixel density #macOS has been designed to be legible and usable with a pixel density of about 218PPI (pixels per inch) for “Retina” class desktop displays. If a display’s PPI is higher, text and the macOS user interface will be smaller. If a display’s PPI is lower, text and the macOS user interface will be larger. Stray too far from 218PPI and macOS becomes unusable.
。PDF资料对此有专业解读
self._on_exit = on_exit，更多细节参见PDF资料
64-byte Cache Line Alignment: Event slots match CPU cache lines exactly. This stops multi-threaded false sharing dead in its tracks during concurrent writes.，更多细节参见heLLoword翻译官方下载