如附件。

Compared to sleep(3) and usleep(3), nanosleep() has the advantage of not affecting any signals, it is standardized by POSIX, it provides higher timing resolution, and it allows to continue a sleep that has been interrupted by a signal more easily.

Security issue:
[1] (obsolete) usleep:
  This C routine is considered obsolete (as opposed to the shell command
  by the same name).   The interaction of this function with SIGALRM and
  other timer functions such as sleep(), alarm(), setitimer(), and
  nanosleep() is unspecified. Use nanosleep(2) or setitimer(2) instead.

我不覺得 signal 影響會造成什麼問題，如果從負面的影響來說，而且 nanosleep 多出來的 parameter 會讓 file size 變大。