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 speci-
       fies 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 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 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 3.53 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								    2012-10-15							  TIMER_SETTIME(2)