As sleep() would only detect a minimum of 1 second of sleeping, using
nanosleep() solves this problem. But we now required to define
POSIX_C_SOURCE >= 199309
As OpenBSD manual for pause(3) stated, this function is made obsolete by
sigsuspend(2).
We may think it will be removed in future for this *nix.
On linux, this require defining _POSIX_C_SOURCE to 1.