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().

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 SIGALARM, and the sigev_value member having the value of the timer ID.

If the sigev_notify member of the sigeven structure has the value SIGEV_SIGNAL_THR, the signal number specified in sigev_signo will be sent to the calling thread. When the thread exits, this timer will be deleted automatically.

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:

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), resource_controls(5), standards(5)