*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->IRIX man pages -> standard/getitimer (2)              



NAME    [Toc]    [Back]

     getitimer,	setitimer - get/set value of interval timer

SYNOPSIS    [Toc]    [Back]

     #include <sys/time.h>

     #define ITIMER_REAL      0	   /* real time	intervals */
     #define ITIMER_VIRTUAL   1	   /* virtual time intervals */
     #define ITIMER_PROF      2	   /* user and system virtual time */

     int getitimer(int which, struct itimerval *value);

     int setitimer(int which, struct itimerval *value,
	       struct itimerval	*ovalue);

DESCRIPTION    [Toc]    [Back]

     The system	provides each process with three interval timers, defined in
     <sys/time.h>.  The	getitimer call returns the current value for the timer
     specified in which, while the setitimer call sets the value of a timer
     (optionally returning the previous	value of the timer).

     A timer value is defined by the itimerval structure:

	  struct itimerval {
	       struct	 timeval it_interval;	  /* timer interval */
	       struct	 timeval it_value;	  /* current value */

     If	it_value is non-zero, it indicates the time to the next	timer
     expiration	and not	the time the timer was set originally.	If it_interval
     is	non-zero, it specifies a value to be used in reloading it_value	when
     the timer expires.	 Setting it_value to 0 disables	a timer.  Setting
     it_interval to 0 causes a timer to	be disabled after its next expiration
     (assuming it_value	is non-zero).

     For ITIMER_VIRTUAL	and ITIMER_PROF, the timer resolution is 100 HZ	(which
     equals 10 milliseconds). Time values that are not a multiple of 100 HZ
     will be rounded to	a multiple.

     For ITIMER_REAL, the timer	resolution is 100 HZ (which equals 10
     milliseconds) for normal processes. For processes with a real time
     scheduling	policy (see sched setscheduler (2)), actual resolution of the
     clock depends on the timer	capability of the underlying hardware (see
     timers (5)).  To avoid a reduction	in overall system performance, normal
     processes are not permitted to use	the high resolution timers, since fast
     itimer requests can add considerable system overhead.

     The ITIMER_REAL timer decrements in real time.  A SIGALRM signal is
     delivered when this timer expires.

									Page 1


     The ITIMER_VIRTUAL	timer decrements in process virtual time.  It runs
     only when the process is executing.  A SIGVTALRM signal is	delivered when
     it	expires.

     The ITIMER_PROF timer decrements both in process virtual time and when
     the system	is running on behalf of	the process.  It is designed to	be
     used by interpreters in statistically profiling the execution of
     interpreted programs.  Each time the ITIMER_PROF timer expires, the
     SIGPROF signal is delivered.  Because this	signal may interrupt inprogress
 system calls, programs using this	timer must be prepared to
     restart interrupted system	calls.

NOTES    [Toc]    [Back]

     Three macros for manipulating time	values are defined in <sys/time.h>.
     timerclear	sets a time value to zero, timerisset tests if a time value is
     non-zero, and timercmp compares two time values (beware that >= and <= do
     not work with this	macro).

SEE ALSO    [Toc]    [Back]

     ftimer(1),	lboot(1M), npri(1), systune(1M), schedctl(2), sigset(2),

FILES    [Toc]    [Back]

     /var/sysgen/mtune/kernel fast itimer configuration	variables.

DIAGNOSTICS    [Toc]    [Back]

     If	the calls succeed, a value of 0	is returned.  If an error occurs, the
     value -1 is returned, and errno will be set.  setitimer and getitimer
     will fail if any of the following are true:

     [EFAULT]	    The	value or ovalue	structure specified a bad address.

     [EINVAL]	    A value structure specified	a time was too large to	be

BUGS    [Toc]    [Back]

     setitimer calls reset the alarm clock (see	alarm(2)) of the calling

     Programs cannot use getitimer(2) to accurately determine how much time
     remains until the timer expires.  On the Challenge/Onyx hardware family,
     it_value is not updated at	a constant rate.

									PPPPaaaaggggeeee 2222
[ Back ]
 Similar pages
Name OS Title
getitimer Linux get or set value of an interval timer
setitimer HP-UX get and set value of interval timer
ualarm HP-UX set the interval timer
getitimer HP-UX get and set value of interval timer
nanosleep Tru64 Suspends a process from execution for the specified timer interval (P1003.1b)
gettimer Tru64 Get value of a per-process timer
timers HP-UX timer operations
timer_gettime HP-UX timer operations
timer_settime HP-UX timer operations
timer_getoverrun HP-UX timer operations
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service