TimerSettime(), TimerSettime_r()

Updated: April 19, 2023

Arm a timer with the given expiration time, disarm it, or set its tolerance


#include <sys/neutrino.h>

int TimerSettime( timer_t id,
                  int flags,
                  const struct _itimer * itime,
                  struct _itimer * oitime );

int TimerSettime_r( timer_t id,
                    int flags,
                    const struct _itimer * itime,
                    struct _itimer * oitime );


The ID of the timer that you want to modify, as returned by TimerCreate().
Flags that specify what you want to set for the timer; at most one of the following:
  • TIMER_ABSTIME — set an absolute expiration time.
  • TIMER_TOLERANCE — specify the amount of the tolerance to allow the kernel in low-power situations.

If you don't set either of these flags, the function sets a relative expiration time. For more information, see below.

If you're setting an expiration time (i.e., you specify TIMER_ABSTIME or neither bit), you can OR in TIMER_PRECISE to override any default tolerance that was set for the process (see procmgr_timer_tolerance()).

A pointer to an _itimer structure that specifies the expiration time or tolerance, depending on the flag settings. If you specify TIMER_TOLERANCE for that other argument, itime can be NULL.
NULL, or a pointer to an _itimer structure where the function can store the previous data.



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The TimerSettime() and TimerSettime_r() functions either set the expiration time of the timer specified by id, or set the tolerance for that timer, depending on the flags provided.

These functions are identical except in the way they indicate errors. See the Returns section for details.

Note: Instead of using these kernel calls directly, consider calling timer_gettime() or timer_settime().

The _itimer structure contains at least the following members:

The meaning of these fields depends on the flags specified.

Expiration date

If you specify the TIMER_ABSTIME flag, then the nsec member represents an absolute expiration date, in nanoseconds from the start of the Unix Epoch, 00:00:00 January 1, 1970 UTC. If the specified date has already passed, then the expiration event is delivered immediately.

If you don't specify TIMER_ABSTIME or TIMER_TOLERANCE, nsec represents a relative expiration period that's offset from the given clock's current system time, in nanoseconds.

If nsec is zero, then the timer is disarmed.

If interval_nsec is nonzero, then it specifies a repeat rate which is added to the timer once the nsec period has expired. Subsequently, the timer is automatically rearmed, causing it to become repetitive with a period of interval_nsec.

If the timer is already armed when you call TimerSettime(), this call discards the previous setting and sets a new setting.

If the event notification specified by TimerCreate() has a sigev_code of SI_TIMER, then at most one event is queued. In this case, if an event is pending from a previous timer when the timer fires again, a timer overrun occurs. You can use the TimerInfo() kernel call to obtain the number of overruns that have occurred on this timer.

Note: Because of the nature of time measurement, the timer might actually expire after the specified time. For more information, see the Understanding the Microkernel's Concept of Time chapter of the QNX Neutrino Programmer's Guide.

If the oitime argument isn't NULL, the function fills in the structure that it points to with the interval timer period (i.e., the previous amount of time left before the timer was to have expired), or zero if the timer was disarmed at the time of the call. The previous repeat rate is stored in the interval_nsec member.

Timer tolerance

If you specify the TIMER_TOLERANCE flag, then:

(QNX Neutrino 7.0.1 or later) In order to set the tolerance to a value between 0 and the clock period, you need to have the PROCMGR_AID_HIGH_RESOLUTION_TIMER ability enabled. For more information, see procmgr_ability().

You can set the tolerance at any time without affecting the active/inactive status of the timer. For more information, see Tolerant and high-resolution timers in the “Understanding the Microkernel's Concept of Time” chapter of the QNX Neutrino Programmer's Guide.

Blocking states

This call doesn't block.


The only difference between these functions is the way they indicate errors:

If an error occurs, -1 is returned and errno is set. Any other value returned indicates success.
EOK is returned on success. This function does NOT set errno. If an error occurs, any value in the Errors section may be returned.


The timer specified by id doesn't exist.
A fault occurred when the kernel tried to access itime or oitime.
The calling process doesn't have the required permission; see procmgr_ability().


QNX Neutrino

Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes