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

       timer_settime, timer_gettime - arm/disarm and fetch state of POSIX per-
       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 pointer to an itimerspec structure that specifies
       the new initial value and the new interval for the timer.  The  itimer-
       spec 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-
       fying  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 speci-
       fied 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 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	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.

       POSIX.1-2001, POSIX.1-2008.

       See timer_create(2).

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

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Linux				  2015-08-08		      TIMER_SETTIME(2)