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_VIRTUAL
user CPU usage clock


CLOCK_PROF
user and system CPU usage 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.


EPERM
The specified clock ID, clock_id, is CLOCK_HIGHRES and the
{PRIV_PROC_CLOCK_HIGHRES} is not asserted in the effective set
of the calling process.


ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-------------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------------+
|Interface Stability | Committed |
+--------------------+-------------------------+
|MT-Level | MT-Safe with exceptions |
+--------------------+-------------------------+
|Standard | See standards(5). |
+--------------------+-------------------------+

SEE ALSO


exec(2), fork(2), time(2), clock_settime(3C), signal(3C),
signal.h(3HEAD), timer_delete(3C), timer_settime(3C), attributes(5),
privileges(5), standards(5)


September 15, 2015 TIMER_CREATE(3C)