on_signal
void on_signal(int, short, void *);
signal_set(&ev_sigint, SIGINT, on_signal, NULL);
signal_set(&ev_sighup, SIGHUP, on_signal, NULL);
signal_set(&ev_sigterm, SIGTERM, on_signal, NULL);
signal_set(&ev_sigwinch, SIGWINCH, on_signal, NULL);