timer_gettime man page on Ubuntu

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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 >= 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 non-zero value  (i.e.,  either  sub‐
       field  is non-zero), then timer_settime() arms (starts) the timer, set‐
       ting 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  non-zero,  then  each  time
       that an armed timer expires, the timer is reloaded from the value spec‐
       ified 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	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 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.

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
       This  page  is  part of release 3.23 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				  2009-02-20		      TIMER_SETTIME(2)
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