TIMER_SETTIME(2)                                    Linux Programmer's Manual                                   TIMER_SETTIME(2)



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 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()

       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  dis-
       armed.

       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 expi-
       ration  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 buf-
       fer 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.

CONFORMING TO
       POSIX.1-2001

EXAMPLE
       See timer_create(2).

SEE ALSO
       timer_create(2), timer_settime(2), timer_getoverrun(2), time(7)

COLOPHON
       This page is part of release 3.25 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)