// consequences. For example, SIGALRM is a bad choice because the
// signal handler can't tell if it was caused by the real process
// alarm or not (arguably this means the signal is broken, but I
// digress). SIGUSR1 and SIGUSR2 are also bad because those are often
// used in meaningful ways by applications.
//
// 4. We need to deal with platforms without real-time signals (like
// macOS), so those are out.
//