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TIMER_SETTIME(2) Linux Programmer's Manual TIMER_SETTIME(2)
timer_settime, timer_gettime - arm/disarm and fetch state of POSIX per-process
timer
#include <time.h>
int timer_settime(timer_t timerid, int flags,
const struct itimerspec *new_value,
struct itimerspec * old_value);
int timer_gettime(timer_t timerid, struct itimerspec *curr_value);
Link with -lrt.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
timer_settime(), timer_gettime(): _POSIX_C_SOURCE >= 199309L
timer_settime() arms or disarms the timer identified by timerid. The
new_value argument is an itimerspec structure that specifies the new initial
value and the new interval for the timer. The itimerspec structure is defined
as follows:
struct timespec {
time_t tv_sec; /* Seconds */
long tv_nsec; /* Nanoseconds */
};
struct itimerspec {
struct timespec it_interval; /* Timer interval */
struct timespec it_value; /* Initial expiration */
};
Each of the substructures of the itimerspec structure is a timespec 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 expires 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 returns 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 interval, for
the timer specified by timerid, in the buffer pointed to by curr_value. The
time remaining until the next timer expiration is returned in
curr_value->it_value; this is always a relative value, regardless 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_interval is zero, then this is a "one-shot" timer.
On success, timer_settime() and timer_gettime() return 0. On error, -1 is
returned, and errno is set to indicate the error.
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.
These system calls are available since Linux 2.6.
POSIX.1-2001.
See timer_create(2).
timer_create(2), timer_getoverrun(2), time(7)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2009-02-20 TIMER_SETTIME(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface