freebsd-dev/lib/libc/gen/sleep.3
Joshua Peck Macdonald 8098023dde Added a note about the return value. Its been so long I can't
remember who suggested the 'caveat' section.  Sorry.
1996-04-05 05:35:57 +00:00

103 lines
3.6 KiB
Groff

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.\" @(#)sleep.3 8.1 (Berkeley) 6/4/93
.\"
.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 u_int
.Fn sleep "u_int seconds"
.Sh DESCRIPTION
The
.Fn sleep
function
suspends execution of the calling process
for
.Fa seconds
of time.
System activity or time spent in processing the
call may lengthen the sleep by a second.
.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 2 .
.Sh RETURN VALUES
The
.Fn sleep
function returns the number of seconds remaining to complete the operation. If
sleep is interrupted or cannot allocate a timer it may will return the value
needed to be passed to a subsequent sleep to complete the necessary delay.
.Fn sleep
repeatedly until it returns zero may busy-wait until a timer
is available.
.Sh SEE ALSO
.Xr setitimer 2 ,
.Xr sigpause 2 ,
.Xr usleep 3
.Sh CAVEAT
In practice the FreeBSD implementation will not be interrupted: it will
always return the original argument or zero. Code that depends on
sleep being interrupted (using it as a timed pause, for example) needs
to be recoded to use
.Xr select 2
or some other delay mechanism. Code that
calls
.Fn sleep
repeatedly until it returns zero may busy-wait until a timer
is available.
.Sh HISTORY
A
.Fn sleep
function appeared in
.At v7 .