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.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 .