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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
199 lines
4.9 KiB
Groff
199 lines
4.9 KiB
Groff
.\" Copyright (c) 2005 David Xu <davidxu@FreeBSD.org>
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.\" 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(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
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.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd July 15, 2016
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.Dt TIMER_CREATE 2
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.Os
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.Sh NAME
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.Nm timer_create
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.Nd "create a per-process timer (REALTIME)"
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.Sh LIBRARY
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.Lb librt
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.Sh SYNOPSIS
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.In time.h
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.In signal.h
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.Ft int
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.Fo timer_create
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.Fa "clockid_t clockid" "struct sigevent *restrict evp"
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.Fa "timer_t *restrict timerid"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn timer_create
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system call creates a per-process timer using the specified clock,
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.Fa clock_id ,
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as the timing base.
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The
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.Fn timer_create
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system call returns, in the location referenced by
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.Fa timerid ,
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a timer ID of type
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.Vt timer_t
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used to identify the timer in timer requests.
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This timer ID is unique within the calling process until the timer is deleted.
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The particular clock,
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.Fa clock_id ,
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is defined in
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.In time.h .
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The timer whose ID is returned is in a disarmed state upon return from
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.Fn timer_create .
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.Pp
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The
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.Fa evp
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argument, if
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.Pf non- Dv NULL ,
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points to a
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.Vt sigevent
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structure.
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This structure,
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allocated by the application, defines the asynchronous notification to occur
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when the timer expires.
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.Pp
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If
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.Fa evp->sigev_notify
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is
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.Dv SIGEV_SIGNO
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or
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.Dv SIGEV_THREAD_ID ,
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the signal specified in
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.Fa evp->sigev_signo
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will be sent to the calling process
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.Pq Dv SIGEV_SIGNO
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or to the thread whose LWP ID is
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.Fa evp->sigev_notify_thread_id
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.Pq Dv SIGEV_THREAD_ID .
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The information for the queued signal will include:
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.Bl -column ".Va si_value"
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.It Sy Member Ta Sy Value
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.It Va si_code Ta Dv SI_TIMER
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.It Va si_value Ta
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the value stored in
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.Fa evp->sigev_value
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.It Va si_timerid Ta timer ID
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.It Va si_overrun Ta timer overrun count
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.It Va si_errno Ta
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If timer overrun is
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.Brq Dv DELAYTIMER_MAX ,
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an error code defined in
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.In errno.h
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.El
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.Pp
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If the
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.Fa evp
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argument is
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.Dv NULL ,
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the effect is as if the
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.Fa evp
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argument pointed to a
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.Vt sigevent
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structure with the
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.Va sigev_notify
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member having the value
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.Dv SIGEV_SIGNAL ,
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the
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.Va sigev_signo
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having a default signal number
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.Pq Dv SIGALRM ,
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and the
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.Va sigev_value
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member having
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the value of the timer ID.
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.Pp
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This implementation supports a
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.Fa clock_id
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of
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.Dv CLOCK_REALTIME ,
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.Dv CLOCK_TAI ,
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or
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.Dv CLOCK_MONOTONIC .
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.Pp
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If
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.Fa evp->sigev_notify
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is
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.Dv SIGEV_THREAD
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and
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.Fa sev->sigev_notify_attributes
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is not
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.Dv NULL ,
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if the attribute pointed to by
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.Fa sev->sigev_notify_attributes
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has
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a thread stack address specified by a call to
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.Fn pthread_attr_setstack
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or
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.Fn pthread_attr_setstackaddr ,
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the results are unspecified if the signal is generated more than once.
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.Sh RETURN VALUES
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If the call succeeds,
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.Fn timer_create
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returns zero and updates the location referenced by
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.Fa timerid
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to a
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.Vt timer_t ,
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which can be passed to the per-process timer calls.
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If an error
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occurs, the system call returns a value of \-1
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and the global variable
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.Va errno
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is set to indicate the
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error.
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The value of
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.Fa timerid
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is undefined if an error occurs.
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.Sh ERRORS
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The
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.Fn timer_create
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The calling process has already created all of the timers it is allowed by
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this implementation.
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.It Bq Er EINVAL
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The specified clock ID is not supported.
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.It Bq Er EINVAL
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The specified asynchronous notification method is not supported.
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.It Bq Er EFAULT
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Any arguments point outside the allocated address space or there is a
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memory protection fault.
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.El
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.Sh SEE ALSO
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.Xr clock_getres 2 ,
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.Xr timer_delete 2 ,
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.Xr timer_getoverrun 2 ,
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.Xr sigevent 3 ,
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.Xr siginfo 3
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.Sh STANDARDS
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The
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.Fn timer_create
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system call conforms to
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.St -p1003.1-2004 .
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.Sh HISTORY
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Support for
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.Tn POSIX
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per-process timer first appeared in
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.Fx 7.0 .
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