NAME¶
timer_settime, timer_gettime - arm/disarm and fetch state of POSIX per-process
timer
SYNOPSIS¶
#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
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
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 points to a buffer that is used to
return 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.
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.
VERSIONS¶
These system calls are available since Linux 2.6.
POSIX.1-2001.
EXAMPLE¶
See
timer_create(2).
SEE ALSO¶
timer_create(2),
timer_getoverrun(2),
time(7)
COLOPHON¶
This page is part of release 3.44 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/.