timer_settime(2) System Calls Manual timer_settime(2)
NAME
timer_settime, timer_gettime - arm/disarm and fetch state of POSIX per-
process timer
LIBRARY
Real-time library (librt, -lrt)
SYNOPSIS
#include <time.h>
int timer_gettime(timer_t timerid, struct itimerspec *curr_value);
int timer_settime(timer_t timerid, int flags,
const struct itimerspec *restrict new_value,
struct itimerspec *_Nullable restrict old_value);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
timer_settime(), timer_gettime():
_POSIX_C_SOURCE >= 199309L
DESCRIPTION
timer_settime() arms or disarms the timer identified by timerid. The
new_value argument is pointer to an itimerspec structure that specifies
the new initial value and the new interval for the timer. The itimer-
spec structure is described in itimerspec(3type).
Each of the substructures of the itimerspec structure is a timespec(3)
structure that allows a time value to be specified in seconds and
nanoseconds. These time values are measured according to the clock that
was specified when the timer was created by timer_create(2).
If new_value->it_value specifies a nonzero value (i.e., either subfield
is nonzero), then timer_settime() arms (starts) the timer, setting it to
initially expire at the given time. (If the timer was already armed,
then the previous settings are overwritten.) If new_value->it_value
specifies a zero value (i.e., both subfields are zero), then the timer
is disarmed.
The new_value->it_interval field specifies the period of the timer, in
seconds and nanoseconds. If this field is nonzero, then each time that
an armed timer expires, the timer is reloaded from the value specified
in new_value->it_interval. If new_value->it_interval specifies a zero
value, then the timer expires just once, at the time specified by
it_value.
By default, the initial expiration time specified in new_value->it_value
is interpreted relative to the current time on the timer's clock at the
time of the call. This can be modified by specifying TIMER_ABSTIME in
flags, in which case new_value->it_value is interpreted as an absolute
value as measured on the timer's clock; that is, the timer will expire
when the clock value reaches the value specified by new_value->it_value.
If the specified absolute time has already passed, then the timer ex-
pires immediately, and the overrun count (see timer_getoverrun(2)) will
be set correctly.
If the value of the CLOCK_REALTIME clock is adjusted while an absolute
timer based on that clock is armed, then the expiration of the timer
will be appropriately adjusted. Adjustments to the CLOCK_REALTIME clock
have no effect on relative timers based on that clock.
If old_value is not NULL, then it points to a buffer that is used to re-
turn the previous interval of the timer (in old_value->it_interval) and
the amount of time until the timer would previously have next expired
(in old_value->it_value).
timer_gettime() returns the time until next expiration, and the inter-
val, for the timer specified by timerid, in the buffer pointed to by
curr_value. The time remaining until the next timer expiration is re-
turned in curr_value->it_value; this is always a relative value, regard-
less of whether the TIMER_ABSTIME flag was used when arming the timer.
If the value returned in curr_value->it_value is zero, then the timer is
currently disarmed. The timer interval is returned in
curr_value->it_interval. If the value returned in curr_value->it_inter-
val is zero, then this is a "one-shot" timer.
RETURN VALUE
On success, timer_settime() and timer_gettime() return 0. On error, -1
is returned, and errno is set to indicate the error.
ERRORS
These functions may fail with the following errors:
EFAULT new_value, old_value, or curr_value is not a valid pointer.
EINVAL timerid is invalid.
timer_settime() may fail with the following errors:
EINVAL new_value.it_value is negative; or new_value.it_value.tv_nsec is
negative or greater than 999,999,999.
STANDARDS
POSIX.1-2008.
HISTORY
Linux 2.6. POSIX.1-2001.
EXAMPLES
See timer_create(2).
SEE ALSO
timer_create(2), timer_getoverrun(2), timespec(3), time(7)
Linux man-pages 6.9.1 2024-05-02 timer_settime(2)
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