SLEEP(3)

NAME
sleep - suspend process execution for interval of seconds

SYNOPSIS
#include <unistd.h>
unsigned int
sleep(unsigned int seconds);

DESCRIPTION
The sleep() function suspends execution of the calling process until either the number of seconds specified by seconds have elapsed or a signal is delivered to the calling process and its action is to invoke a signal-catching function or to terminate the process. The suspension time may be longer than requested due to the scheduling of other activity by the system.

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 system calls each time it is invoked. A similar but less compatible function 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.

RETURN VALUE
If the sleep() function returns because the requested time has elapsed, the value returned will be zero. If the sleep() function returns due to the delivery of a signal, the value returned will be the unslept amount (the request time minus the time actually slept) in seconds.

SEE ALSO
setitimer(2), sigaction(2), sigsuspend(2), alarm(3), pause(3), usleep(3)

STANDARDS
The sleep() function conforms to p1003.1-90.

HISTORY
A sleep() function appeared in AT&T UNIX.