sleep, alarm - delay, ask for delayed note
int sleep(long millisecs)
long alarm(unsigned long millisecs)
Sleep suspends the current process for the number of milliseconds spec‐
ified by the argument. The actual suspension time may be a little more
or less than the requested time. If millisecs is 0, the process gives
up the CPU if another process is waiting to run, returning immediately
if not. Sleep returns -1 if interrupted, 0 otherwise.
Alarm causes an alarm note (see notify(2)) to be sent to the invoking
process after the number of milliseconds given by the argument. Suc‐
cessive calls to alarm reset the alarm clock. A zero argument clears
the alarm. The return value is the amount of time previously remaining
in the alarm clock.
These functions set errstr.