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  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

       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  speci-
       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 inter-
       val, 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.


       See timer_create(2).

       timer_create(2), timer_getoverrun(2), time(7)

       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.

Linux                             2009-02-20                  TIMER_SETTIME(2)
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