Tribblix: manual page: timer

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.