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.Dd June 4, 1993
.Dt SLEEP 3
.Os
.Sh NAME
.Nm sleep
.Nd suspend process execution for interval of seconds
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft unsigned int
.Fn sleep "unsigned int seconds"
.Sh DESCRIPTION
The
.Fn sleep
function suspends execution of the calling process until either the
number of seconds specified by
.Fa 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.
.Pp
If a timer is already running on the process its state is saved.
If the value
.Fa 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
.Fa seconds
has passed.
.Pp
This function is implemented using
.Xr setitimer 2 ;
it requires eight system calls each time it is invoked.
A similar but less compatible function can be obtained with a single
.Xr select 2 ;
such a function would not restart after signals, but would not interfere
with other uses of
.Xr setitimer .
.Sh RETURN VALUE
If the 
.Fn sleep
function returns because the requested time has elapsed, the value
returned will be zero.  If the 
.Fn 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.
.Sh SEE ALSO
.Xr setitimer 2 ,
.Xr sigaction 2 ,
.Xr sigsuspend 2 ,
.Xr alarm 3 ,
.Xr pause 3 ,
.Xr usleep 3
.Sh STANDARDS
The 
.Fn sleep 
function conforms to 
.St -p1003.1-90 .
.Sh HISTORY
A
.Fn sleep
function appeared in
.At v7 .