TIMER_CREATE(3C) Standard C Library Functions TIMER_CREATE(3C)
NAME
timer_create - create a timer
SYNOPSIS
#include <signal.h>
#include <time.h>
int timer_create(
clockid_t clock_id,
struct sigevent *restrict evp,
timer_t *restrict timerid);
DESCRIPTION
The
timer_create() function creates a timer using the specified clock,
clock_id, as the timing base. The
timer_create() function returns, in the
location referenced by
timerid, a timer
ID of type
timer_t used to
identify the timer in timer requests. This timer
ID will be unique within
the calling process until the timer is deleted. The particular clock,
clock_id, is defined in <
time.h>. The timer whose
ID is returned will be
in a disarmed state upon return from
timer_create(), and can be started
using
timer_settime(3C).
The
evp argument, if non-null, points to a
sigevent structure. This
structure, allocated by the application, defines the asynchronous
notification that will occur when the timer expires (see
signal.h(3HEAD) for event notification details). If the
evp argument is
NULL, the effect
is as if the
evp argument pointed to a
sigevent structure with the
sigev_notify member having the value
SIGEV_SIGNAL, the
sigev_signo having
the value
SIGALRM, and the
sigev_value member having the value of the
timer
ID.
The system defines a set of clocks that can be used as timing bases for
per-process timers. The following values for
clock_id are supported:
CLOCK_REALTIME wall clock
CLOCK_HIGHRES non-adjustable, high-resolution clock
For timers created with a
clock_id of
CLOCK_HIGHRES, the system will
attempt to use an optimal hardware source. This may include, but is not
limited to, per-CPU timer sources. The actual hardware source used is
transparent to the user and may change over the lifetime of the timer.
For example, if the caller that created the timer were to change its
processor binding or its processor set, the system may elect to drive the
timer with a hardware source that better reflects the new binding.
Timers based on a
clock_id of
CLOCK_HIGHRES are ideally suited for
interval timers that have minimal jitter tolerance.
Timers are not inherited by a child process across a
fork(2) and are
disarmed and deleted by a call to one of the
exec functions (see
exec(2)).
RETURN VALUES
Upon successful completion,
timer_create() returns
0 and updates the
location referenced by
timerid to a
timer_t, which can be passed to the
per-process timer calls. If an error occurs, the function returns
-1 and
sets
errno to indicate the error. The value of
timerid is undefined if an
error occurs.
ERRORS
The
timer_create() function will fail if:
EAGAIN The system lacks sufficient signal queuing resources to honor
the request, or the calling process has already created all of
the timers it is allowed by the system.
EINVAL The specified clock
ID,
clock_id, is not defined.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-------------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------------+
|Interface Stability | Committed |
+--------------------+-------------------------+
|MT-Level | MT-Safe with exceptions |
+--------------------+-------------------------+
|Standard | See
standards(7). |
+--------------------+-------------------------+
SEE ALSO
exec(2),
fork(2),
time(2),
clock_settime(3C),
signal(3C),
timer_delete(3C),
timer_settime(3C),
signal.h(3HEAD),
attributes(7),
standards(7) October 4, 2021
TIMER_CREATE(3C)