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

NAME
       getitimer, setitimer - get or set value of an interval timer

SYNOPSIS
       #include	<sys/time.h>

       int getitimer(int which,	struct itimerval *value);
       int  setitimer(int which, const struct itimerval	*value,	struct itimer-
	      val *ovalue);

DESCRIPTION
       The system provides each	 process  with	three  interval	 timers,  each
       decrementing in a distinct time domain.	When any timer expires,	a sig-
       nal is sent to the process, and the timer (potentially) restarts.

       ITIMER_REAL    decrements in real time, and delivers SIGALRM upon expi-
		      ration.

       ITIMER_VIRTUAL decrements  only	when  the  process  is	executing, and
		      delivers SIGVTALRM upon expiration.

       ITIMER_PROF    decrements both when the process executes	and  when  the
		      system  is  executing on behalf of the process.  Coupled
		      with ITIMER_VIRTUAL, this	timer is usually used to  pro-
		      file  the	time spent by the application in user and ker-
		      nel space.  SIGPROF is delivered upon expiration.

       Timer values are	defined	by the following structures:
	    struct itimerval {
		struct timeval it_interval; /* next value */
		struct timeval it_value;    /* current value */
	    };
	    struct timeval {
		long tv_sec;		    /* seconds */
		long tv_usec;		    /* microseconds */
	    };

       The function getitimer fills the	structure indicated by value with  the
       current	setting	 for the timer indicated by which (one of ITIMER_REAL,
       ITIMER_VIRTUAL, or ITIMER_PROF).	 The element it_value is  set  to  the
       amount  of  time	 remaining  on the timer, or zero if the timer is dis-
       abled.  Similarly, it_interval is set to	the reset value.  The function
       setitimer sets the indicated timer to the value in value.  If ovalue is
       nonzero,	the old	value of the timer is stored there.

       Timers decrement	from it_value to zero, generate	a signal, and reset to
       it_interval.   A	 timer	which  is set to zero (it_value	is zero	or the
       timer expires and it_interval is	zero) stops.

       Both tv_sec and tv_usec are significant in determining the duration  of
       a timer.

       Timers  will  never  expire before the requested	time, instead expiring
       some short, constant time afterwards, dependent	on  the	 system	 timer
       resolution  (currently 10ms).  Upon expiration, a signal	will be	gener-
       ated and	the timer reset.  If the timer expires while  the  process  is
       active (always true for ITIMER_VIRT) the	signal will be delivered imme-
       diately when generated.	Otherwise the delivery will  be	 offset	 by  a
       small time dependent on the system loading.

RETURN VALUE
       On  success,  zero is returned.	On error, -1 is	returned, and errno is
       set appropriately.

ERRORS
       EFAULT value or ovalue are not valid pointers.

       EINVAL which is not one of ITIMER_REAL, ITIMER_VIRT, or ITIMER_PROF.

CONFORMING TO
       SVr4, 4.4BSD (This call first appeared in 4.2BSD).

SEE ALSO
       gettimeofday(2),	sigaction(2), signal(2)

BUGS
       Under Linux, the	generation and delivery	of a signal are	distinct,  and
       there each signal is permitted only one outstanding event.  It's	there-
       fore conceivable	that under pathologically heavy	 loading,  ITIMER_REAL
       will  expire  before  the  signal  from	a previous expiration has been
       delivered.  The second signal in	such an	event will be lost.

Linux 0.99.11			  1993-08-05			  GETITIMER(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | SEE ALSO | BUGS

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