.\" Copyright (c) 2005 David Xu .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice(s), this list of conditions and the following disclaimer as .\" the first lines of this file unmodified other than the possible .\" addition of one or more copyright notices. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice(s), this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY .\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE .\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR .\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, .\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE .\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, .\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .\" $FreeBSD: releng/11.0/lib/libc/sys/timer_create.2 303324 2016-07-25 23:37:47Z jhb $ .\" .Dd July 15, 2016 .Dt TIMER_CREATE 2 .Os .Sh NAME .Nm timer_create .Nd "create a per-process timer (REALTIME)" .Sh LIBRARY .Lb librt .Sh SYNOPSIS .In time.h .In signal.h .Ft int .Fo timer_create .Fa "clockid_t clockid" "struct sigevent *restrict evp" .Fa "timer_t *restrict timerid" .Fc .Sh DESCRIPTION The .Fn timer_create system call creates a per-process timer using the specified clock, .Fa clock_id , as the timing base. The .Fn timer_create system call returns, in the location referenced by .Fa timerid , a timer ID of type .Vt timer_t used to identify the timer in timer requests. This timer ID is unique within the calling process until the timer is deleted. The particular clock, .Fa clock_id , is defined in .In time.h . The timer whose ID is returned is in a disarmed state upon return from .Fn timer_create . .Pp The .Fa evp argument, if .Pf non- Dv NULL , points to a .Vt sigevent structure. This structure, allocated by the application, defines the asynchronous notification to occur when the timer expires. .Pp If .Fa evp->sigev_notify is .Dv SIGEV_SIGNO or .Dv SIGEV_THREAD_ID , the signal specified in .Fa evp->sigev_signo will be sent to the calling process .Pq Dv SIGEV_SIGNO or to the thread whose LWP ID is .Fa evp->sigev_notify_thread_id .Pq Dv SIGEV_THREAD_ID . The information for the queued signal will include: .Bl -column ".Va si_value" .It Sy Member Ta Sy Value .It Va si_code Ta Dv SI_TIMER .It Va si_value Ta the value stored in .Fa evp->sigev_value .It Va si_timerid Ta timer ID .It Va si_overrun Ta timer overrun count .It Va si_errno Ta If timer overrun is .Brq Dv DELAYTIMER_MAX , an error code defined in .In errno.h .El .Pp If the .Fa evp argument is .Dv NULL , the effect is as if the .Fa evp argument pointed to a .Vt sigevent structure with the .Va sigev_notify member having the value .Dv SIGEV_SIGNAL , the .Va sigev_signo having a default signal number .Pq Dv SIGALRM , and the .Va sigev_value member having the value of the timer ID. .Pp This implementation supports a .Fa clock_id of .Dv CLOCK_REALTIME or .Dv CLOCK_MONOTONIC . .Pp If .Fa evp->sigev_notify is .Dv SIGEV_THREAD and .Fa sev->sigev_notify_attributes is not .Dv NULL , if the attribute pointed to by .Fa sev->sigev_notify_attributes has a thread stack address specified by a call to .Fn pthread_attr_setstack or .Fn pthread_attr_setstackaddr , the results are unspecified if the signal is generated more than once. .Sh RETURN VALUES If the call succeeds, .Fn timer_create returns zero and updates the location referenced by .Fa timerid to a .Vt timer_t , which can be passed to the per-process timer calls. If an error occurs, the system call returns a value of \-1 and the global variable .Va errno is set to indicate the error. The value of .Fa timerid is undefined if an error occurs. .Sh ERRORS The .Fn timer_create system call will fail if: .Bl -tag -width Er .It Bq Er EAGAIN The calling process has already created all of the timers it is allowed by this implementation. .It Bq Er EINVAL The specified clock ID is not supported. .It Bq Er EINVAL The specified asynchronous notification method is not supported. .It Bq Er EFAULT Any arguments point outside the allocated address space or there is a memory protection fault. .El .Sh SEE ALSO .Xr clock_getres 2 , .Xr timer_delete 2 , .Xr timer_getoverrun 2 , .Xr sigevent 3 , .Xr siginfo 3 .Sh STANDARDS The .Fn timer_create system call conforms to .St -p1003.1-2004 . .Sh HISTORY Support for .Tn POSIX per-process timer first appeared in .Fx 7.0 .