timer_settime(2) - Linux manual page (original) (raw)
timersettime(2) System Calls Manual timersettime(2)
NAME top
timer_settime, timer_gettime - arm/disarm and fetch state of POSIX
per-process timerLIBRARY top
Real-time library (_librt_, _-lrt_)SYNOPSIS top
**#include <time.h>**
**int timer_gettime(timer_t** _timerid_**, struct itimerspec ***_currvalue_**);**
**int timer_settime(timer_t** _timerid_**, int** _flags_**,**
**const struct itimerspec *restrict** _newvalue_**,**
**struct itimerspec *_Nullable restrict** _oldvalue_**);**Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
**timer_settime**(), **timer_gettime**():
_POSIX_C_SOURCE >= 199309LDESCRIPTION top
**timer_settime**() arms or disarms the timer identified by _timerid_.
The _newvalue_ argument is pointer to an _itimerspec_ structure that
specifies the new initial value and the new interval for the
timer. The _itimerspec_ structure is described in
[itimerspec(3type)](../man3/itimerspec.3type.html).
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)](../man2/timer%5Fcreate.2.html).
If _newvalue->itvalue_ 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 _newvalue->itvalue_ specifies a zero value
(i.e., both subfields are zero), then the timer is disarmed.
The _newvalue->itinterval_ 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 _newvalue->itinterval_. If
_newvalue->itinterval_ specifies a zero value, then the timer
expires just once, at the time specified by _itvalue_.
By default, the initial expiration time specified in
_newvalue->itvalue_ 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
_newvalue->itvalue_ 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
_newvalue->itvalue_. If the specified absolute time has already
passed, then the timer expires immediately, and the overrun count
(see [timer_getoverrun(2)](../man2/timer%5Fgetoverrun.2.html)) 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 _oldvalue_ is not NULL, then it points to a buffer that is used
to return the previous interval of the timer (in
_oldvalue->itinterval_) and the amount of time until the timer
would previously have next expired (in _oldvalue->itvalue_).
**timer_gettime**() returns the time until next expiration, and the
interval, for the timer specified by _timerid_, in the buffer
pointed to by _currvalue_. The time remaining until the next timer
expiration is returned in _currvalue->itvalue_; this is always a
relative value, regardless of whether the **TIMER_ABSTIME** flag was
used when arming the timer. If the value returned in
_currvalue->itvalue_ is zero, then the timer is currently
disarmed. The timer interval is returned in
_currvalue->itinterval_. If the value returned in
_currvalue->itinterval_ is zero, then this is a "one-shot" timer.RETURN VALUE top
On success, **timer_settime**() and **timer_gettime**() return 0. On
error, -1 is returned, and _[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
These functions may fail with the following errors:
**EFAULT** _newvalue_, _oldvalue_, or _currvalue_ is not a valid pointer.
**EINVAL** _timerid_ is invalid.
**timer_settime**() may fail with the following errors:
**EINVAL** _newvalue.itvalue_ is negative; or
_newvalue.itvalue.tvnsec_ is negative or greater than
999,999,999.STANDARDS top
POSIX.1-2008.HISTORY top
Linux 2.6. POSIX.1-2001.EXAMPLES top
See [timer_create(2)](../man2/timer%5Fcreate.2.html).SEE ALSO top
[timer_create(2)](../man2/timer%5Fcreate.2.html), [timer_getoverrun(2)](../man2/timer%5Fgetoverrun.2.html), **timespec**(3), [time(7)](../man7/time.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 timersettime(2)
Pages that refer to this page:getitimer(2), syscalls(2), timer_create(2), timer_delete(2), timerfd_create(2), timer_getoverrun(2), itimerspec(3type), timer_t(3type), timespec(3type), ualarm(3), usleep(3), signal-safety(7), time_namespaces(7)