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 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 inter‐
       preted 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.   Adjust‐
       ments 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.

CONFORMING TO
       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 3.74 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 http://www.kernel.org/doc/man-pages/.



Linux                                       2012-10-15                           TIMER_SETTIME(2)