exit_handler
if (set_signal_handler(SIGHUP, exit_handler) != 0 ||
set_signal_handler(SIGINT, exit_handler) != 0 ||
set_signal_handler(SIGTERM, exit_handler) != 0 ||
if (restore_signal_handler(SIGHUP, exit_handler) == -1 ||
restore_signal_handler(SIGINT, exit_handler) == -1 ||
restore_signal_handler(SIGTERM, exit_handler) == -1 ||