This is a useful classification. With the benefit of hindsight--and threading--it would be nice if async signals could just go away, since the kernel can send a

This is a useful classification. With the benefit of hindsight--and threading--it would be nice if async signals could just go away, since the kernel can send a notification message to the application over a file descriptor (see man signalfd(2)) and the application can have a dedicated thread to deal with it at its leisure. That leaves the synchronous signals, which are the kernel's way of telling you that you executed a bad instruction and giving you a chance to do something awfully clever instead of crashing.