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.\"	$NetBSD: nanosleep.2,v 1.21 2016/06/16 12:48:09 ryoon Exp $
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.\"     @(#)sleep.3	8.1 (Berkeley) 6/4/93
.\"
.Dd June 16, 2016
.Dt NANOSLEEP 2
.Os
.Sh NAME
.Nm nanosleep
.Nd high resolution sleep
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In time.h
.Ft int
.Fn clock_nanosleep "clockid_t clock_id" "int flags" "const struct timespec *rqtp" "struct timespec *rmtp"
.Ft int
.Fn nanosleep "const struct timespec *rqtp" "struct timespec *rmtp"
.Sh DESCRIPTION
If the
.Dv TIMER_ABSTIME
flag is not set in the
.Fa flags
argument, then
.Fn clock_nanosleep
suspends execution of the calling thread until either the number of
seconds and nanoseconds specified in the
.Fa rqtp
argument have elapsed using the clock in the
.Fa clock_id
argument, or a signal is delivered to the calling process and its
action is to invoke a signal catching function or to terminate the
process.
.Pp
If the
.Dv TIMER_ABSTIME
flag is set in the
.Fa flags
argument, then
.Fn clock_nanosleep
suspends execution of the calling thread until either the value
of the clock specified in the
.Fa clock_id
argument reaches the value of the
.Fa rqtp
argument in seconds and nanoseconds,
or a signal is delivered to the calling process and its
action is to invoke a signal catching function or to terminate the
process.
.Pp
The suspension time may be longer than requested due to the
scheduling of other activity by the system.
.Pp
The
.Fn nanosleep
function behaves like
.Fn clock_nanosleep
with the
.Fa clock_id
argument equal to
.Dv CLOCK_MONOTONIC
and the
.Fa flags
argument having
.Dv TIMER_ABSTIME
not set.
.Pp
The
.Em struct timespec
is described in
.Xr timespec 3 .
The
.Fa clock_id
specified is the time source, which is described in
.Xr clock_gettime 2 .
.Sh RETURN VALUES
If the
.Fn clock_nanosleep
or the
.Fn nanosleep
functions return because the requested time has elapsed, the value
returned will be zero.
.Pp
If the
.Fn clock_nanosleep
or the
.Fn nanosleep
functions return due to the delivery of a signal, then
.Fn clock_nanosleep
will return directly the error number, and
.Fn nanosleep
will return \-1, and the global variable
.Va errno
will be set to indicate the interruption.
If
.Fa rmtp
is
.Pf non- Dv NULL ,
the timespec structure it references is updated to contain the
unslept amount (the request time minus the time actually slept).
.Sh ERRORS
If any of the following conditions occur, the
.Fn nanosleep
function shall return \-1 and set
.Va errno
to the corresponding value, and the
.Fn clock_nanosleep
function shall return the error number directly.
.Bl -tag -width Er
.It Bq Er EFAULT
Either
.Fa rqtp
or
.Fa rmtp
points to memory that is not a valid part of the process
address space.
.It Bq Er EINTR
.Nm
was interrupted by the delivery of a signal.
.It Bq Er EINVAL
.Fa rqtp
specified a nanosecond value less than zero or greater than 1000 million.
.It Bq Er ENOSYS
.Nm
is not supported by this implementation.
.It Bq Er ENOTSUP
for
.Fn clock_nanosleep ,
the clock specified in the
.Fa clock_id
argument is not supported.
.El
.Sh SEE ALSO
.Xr clock_gettime 2 ,
.Xr sleep 3 ,
.Xr timespec 3
.Sh STANDARDS
The
.Fn nanosleep
function conforms to
.St -p1003.1b-93 .
The
.Fn clock_nanosleep
function conforms to
.St -p1003.1j-2000 .
.Sh BUGS
The
.Nx
kernel is not tickless, so the maximum sleep resolution is determined
by the value of
.Dv HZ
which is by default
.Dv 100
in most architectures.
This means that a request to sleep for less than
.Dv 10ms
(1 /
.Dv HZ
seconds), is rounded up to that.