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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | EXAMPLE | SEE ALSO | COLOPHON |
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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 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 sub‐
field is nonzero), then timer_settime() arms (starts) the timer, set‐
ting 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 spec‐
ifies 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 abso‐
lute timer based on that clock is armed, then the expiration of the
timer will be appropriately adjusted. Adjustments to the CLOCK_REAL‐
TIME 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.
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, POSIX.1-2008.
See timer_create(2).
timer_create(2), timer_getoverrun(2), time(7)
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 TIMER_SETTIME(2)
Pages that refer to this page: getitimer(2), syscalls(2), timer_create(2), timer_delete(2), timerfd_create(2), timer_getoverrun(2), ualarm(3), usleep(3), signal-safety(7)
Copyright and license for this manual page
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