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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 >= 199309

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 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
       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 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  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 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_settime(2), timer_getoverrun(2), time(7)

COLOPHON

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