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Nathan Whitehorn
7b7ba7857c
Provide a clock through clock_gettime() that returns the current TAI time (UTC without leap seconds) as a complement to CLOCK_REALTIME. This provides compatibility with Linux, which also provides a CLOCK_TAI since kernel 2.6.26, and this seems to be becoming the standard way to acquire TAI time. Unlike Linux, this code will return EINVAL if the TAI offset (set by ntpd, ptpd, etc.) is not known since it seems pathological for CLOCK_TAI to silently give the wrong (UTC) time if the offset is not known as it does on Linux. Reviewed by: imp Differential Revision: https://reviews.freebsd.org/D46268
256 lines
6.1 KiB
Plaintext
256 lines
6.1 KiB
Plaintext
.\" $NetBSD: nanosleep.2,v 1.23 2016/11/14 10:40:59 wiz Exp $
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.\"
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.\" Copyright (c) 1986, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd May 3, 2025
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.Dt NANOSLEEP 2
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.Os
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.Sh NAME
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.Nm nanosleep
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.Nd high resolution sleep
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In time.h
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.Ft int
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.Fo clock_nanosleep
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.Fa "clockid_t clock_id"
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.Fa "int flags"
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.Fa "const struct timespec *rqtp"
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.Fa "struct timespec *rmtp"
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.Fc
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.Ft int
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.Fo nanosleep
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.Fa "const struct timespec *rqtp"
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.Fa "struct timespec *rmtp"
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.Fc
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.Sh DESCRIPTION
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If the
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.Dv TIMER_ABSTIME
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flag is not set in the
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.Fa flags
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argument, then
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.Fn clock_nanosleep
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suspends execution of the calling thread until either the
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time interval specified by the
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.Fa rqtp
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argument has elapsed,
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or a signal is delivered to the calling process and its
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action is to invoke a signal-catching function or to terminate the
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process.
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The clock used to measure the time is specified by the
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.Fa clock_id
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argument.
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.Pp
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If the
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.Dv TIMER_ABSTIME
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flag is set in the
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.Fa flags
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argument, then
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.Fn clock_nanosleep
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suspends execution of the calling thread until either the value
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of the clock specified by the
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.Fa clock_id
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argument reaches the absolute time specified by the
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.Fa rqtp
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argument,
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or a signal is delivered to the calling process and its
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action is to invoke a signal-catching function or to terminate the
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process.
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If, at the time of the call, the time value specified by
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.Fa rqtp
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is less than or equal to the time value of the specified clock, then
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.Fn clock_nanosleep
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returns immediately and the calling thread is not suspended.
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An unmasked signal will terminate the sleep early, regardless of the
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.Dv SA_RESTART
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value on the interrupting signal.
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The
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.Fa rqtp
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and
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.Fa rmtp
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arguments can point to the same object.
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.Pp
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The following
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.Fa clock_id
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values are supported:
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.Pp
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.Bl -item -compact -offset indent
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.It
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CLOCK_MONOTONIC
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.It
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CLOCK_MONOTONIC_FAST
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.It
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CLOCK_MONOTONIC_PRECISE
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.It
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CLOCK_REALTIME
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.It
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CLOCK_REALTIME_FAST
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.It
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CLOCK_REALTIME_PRECISE
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.It
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CLOCK_SECOND
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.It
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CLOCK_TAI
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.It
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CLOCK_UPTIME
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.It
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CLOCK_UPTIME_FAST
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.It
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CLOCK_UPTIME_PRECISE
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.El
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.Pp
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The suspension time may be longer than requested due to the
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scheduling of other activity by the system.
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The clocks with the
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.Dv _FAST
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suffix and the
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.Dv CLOCK_SECOND
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are subject to the allowed time interval deviation specified by the
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.Va kern.timecounter.alloweddeviation
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.Xr sysctl 8
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variable.
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The clocks with the
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.Dv _PRECISE
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suffix are always as precise as possible.
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The
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.Dv CLOCK_MONOTONIC ,
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.Dv CLOCK_REALTIME
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and
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.Dv CLOCK_UPTIME
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are precise by default.
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Setting the
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.Va kern.timecounter.nanosleep_precise
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.Xr sysctl 8
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to a false value would make those clocks to behave like the
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.Dv _FAST
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clocks.
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.Pp
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The
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.Fn nanosleep
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function behaves like
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.Fn clock_nanosleep
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with a
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.Fa clock_id
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argument of
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.Dv CLOCK_REALTIME
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and without the
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.Dv TIMER_ABSTIME
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flag in the
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.Fa flags
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argument.
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.Sh RETURN VALUES
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These functions return zero when the requested time has elapsed.
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.Pp
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If these functions return for any other reason, then
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.Fn clock_nanosleep
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will directly return the error number, and
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.Fn nanosleep
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will return \-1 with the global variable
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.Va errno
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set to indicate the error.
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If a relative sleep is interrupted by a signal and
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.Fa rmtp
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is
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.Pf non- Dv NULL ,
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the timespec structure it references is updated to contain the
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unslept amount (the request time minus the time actually slept).
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.Sh ERRORS
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These functions can fail with the following errors.
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.Bl -tag -width Er
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.It Bq Er EFAULT
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Either
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.Fa rqtp
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or
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.Fa rmtp
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points to memory that is not a valid part of the process
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address space.
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.It Bq Er EINTR
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The function was interrupted by the delivery of a signal.
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.It Bq Er EINVAL
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The
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.Fa rqtp
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argument specified a nanosecond value less than zero
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or greater than or equal to 1000 million.
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.It Bq Er EINVAL
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The
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.Fa flags
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argument contained an invalid flag.
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.It Bq Er EINVAL
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The
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.Fa clock_id
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argument was
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.Dv CLOCK_THREAD_CPUTIME_ID
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or an unrecognized value.
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.It Bq Er ENOTSUP
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The
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.Fa clock_id
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argument was valid but not supported by this implementation of
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.Fn clock_nanosleep .
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.El
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.Sh SEE ALSO
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.Xr clock_gettime 2 ,
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.Xr sigaction 2 ,
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.Xr sleep 3
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.Sh STANDARDS
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These functions conform to
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.St -p1003.1-2008 .
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.Sh HISTORY
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The predecessor of this system call,
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.Fn sleep ,
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appeared in
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.At v3 ,
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but was removed when
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.Xr alarm 3
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was introduced into
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.At v7 .
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The
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.Fn nanosleep
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system call has been available since
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.Nx 1.3
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and was ported to
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.Ox 2.1
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and
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.Fx 3.0 .
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The
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.Fn clock_nanosleep
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system call has been available since
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.Fx 11.1 .
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.Pp
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In
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.Fx 15.0
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the default behavior of
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.Fn clock_nanosleep
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with
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.Dv CLOCK_MONOTONIC ,
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.Dv CLOCK_REALTIME ,
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.Dv CLOCK_UPTIME
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clocks and
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.Fn nanosleep
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has been switched to use precise clock.
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