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.TH NANOSLEEP "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.

.SH NAME
nanosleep
\(em high resolution sleep
.SH SYNOPSIS
.LP
.nf
#include <time.h>
.P
int nanosleep(const struct timespec *\fIrqtp\fP, struct timespec *\fIrmtp\fP);
.fi
.SH DESCRIPTION
The
\fInanosleep\fR()
function shall cause the current thread to be suspended from execution
until either the time interval specified by the
.IR rqtp
argument has elapsed or a signal is delivered to the calling thread,
and its action is to invoke a signal-catching function or to terminate
the process. The suspension time may be longer than requested because
the argument value is rounded up to an integer multiple of the sleep
resolution or because of the scheduling of other activity by the
system. But, except for the case of being interrupted by a signal, the
suspension time shall not be less than the time specified by
.IR rqtp ,
as measured by the system clock CLOCK_REALTIME.
.P
The use of the
\fInanosleep\fR()
function has no effect on the action or blockage of any signal.
.SH "RETURN VALUE"
If the
\fInanosleep\fR()
function returns because the requested time has elapsed, its return
value shall be zero.
.P
If the
\fInanosleep\fR()
function returns because it has been interrupted by a signal, it
shall return a value of \(mi1 and set
.IR errno
to indicate the interruption. If the
.IR rmtp
argument is non-NULL, the
.BR timespec
structure referenced by it is updated to contain the amount of time
remaining in the interval (the requested time minus the time actually
slept). The
.IR rqtp
and
.IR rmtp
arguments may point to the same object. If the
.IR rmtp
argument is NULL, the remaining time is not returned.
.P
If
\fInanosleep\fR()
fails, it shall return a value of \(mi1 and set
.IR errno
to indicate the error.
.SH ERRORS
The
\fInanosleep\fR()
function shall fail if:
.TP
.BR EINTR
The
\fInanosleep\fR()
function was interrupted by a signal.
.TP
.BR EINVAL
The
.IR rqtp
argument specified a nanosecond value less than zero or greater than or
equal to 1\|000 million.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
It is common to suspend execution of a thread for an interval in order
to poll the status of a non-interrupting function. A large number of
actual needs can be met with a simple extension to
\fIsleep\fR()
that provides finer resolution.
.P
In the POSIX.1\(hy1990 standard and SVR4, it is possible to implement such a routine,
but the frequency of wakeup is limited by the resolution of the
\fIalarm\fR()
and
\fIsleep\fR()
functions. In 4.3 BSD, it is possible to write such a routine using
no static storage and reserving no system facilities. Although it is
possible to write a function with similar functionality to
\fIsleep\fR()
using the remainder of the
.IR timer_* (\|)
functions, such a function requires the use of signals and the
reservation of some signal number. This volume of POSIX.1\(hy2008 requires that
\fInanosleep\fR()
be non-intrusive of the signals function.
.P
The
\fInanosleep\fR()
function shall return a value of 0 on success and \(mi1 on failure or if
interrupted. This latter case is different from
\fIsleep\fR().
This was done because the remaining time is returned via an argument
structure pointer,
.IR rmtp ,
instead of as the return value.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIclock_nanosleep\fR\^(\|)",
.IR "\fIsleep\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<time.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .

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