SLEEP(3) BSD Programmer's Manual SLEEP(3)
sleep - suspend process execution for interval of seconds
The sleep() function suspends execution of the calling process for
seconds of time. System activity or time spent in processing the call
may lengthen the sleep by a second.
If a timer is already running on the process its state is saved. If the
value seconds is more than or equal to the remaining clock time for the
saved timer, the sleep time is set to the remaining clock time. The
state of the previous timer is restored after seconds has passed.
This function is implemented using setitimer(2); it requires eight sys-
tem calls each time it is invoked. A similar but less compatible func-
tion can be obtained with a single select(2); such a function would not
restart after signals, but would not interfere with other uses of
setitimer(2), sigpause(2), usleep(3)
A sleep() function appeared in Version 7 AT&T UNIX.
4.4BSD June 4, 1993 1