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GETITIMER(2)		  FreeBSD System Calls Manual		  GETITIMER(2)

NAME
     getitimer,	setitimer -- get/set value of interval timer

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/time.h>
     #define ITIMER_REAL      0
     #define ITIMER_VIRTUAL   1
     #define ITIMER_PROF      2

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

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

DESCRIPTION
     The system	provides each process with three interval timers, defined in
     <sys/time.h>.  The	getitimer() system call	returns	the current value for
     the timer specified in which in the structure at value.  The setitimer()
     system call sets a	timer to the specified value (returning	the previous
     value of the timer	if ovalue is not a null	pointer).

     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 expira-
     tion.  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 dis-
     ables a timer, regardless of the value of it_interval.  Setting
     it_interval to 0 causes a timer to	be disabled after its next expiration
     (assuming it_value	is non-zero).

     Time values smaller than the resolution of	the system clock are rounded
     up	to this	resolution (typically 10 milliseconds).

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

     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 inter-
     preted programs.  Each time the ITIMER_PROF timer expires,	the SIGPROF
     signal is delivered.  Because this	signal may interrupt in-progress sys-
     tem calls,	programs using this timer must be prepared to restart inter-
     rupted system calls.

     The maximum number	of seconds allowed for it_interval and it_value	in
     setitimer() is 100000000.

NOTES
     Three macros for manipulating time	values are defined in <sys/time.h>.
     The timerclear() macro sets a time	value to zero, timerisset() tests if a
     time value	is non-zero, and timercmp() compares two time values.

RETURN VALUES
     Upon successful completion, the value 0 is	returned; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

ERRORS
     The getitimer() and setitimer() system calls will fail if:

     [EFAULT]		The value argument specified a bad address.

     [EINVAL]		The value argument specified a time that was too large
			to be handled.

SEE ALSO
     gettimeofday(2), select(2), sigaction(2), clocks(7)

HISTORY
     The getitimer() system call appeared in 4.2BSD.

FreeBSD	9.2			 May 16, 1995			   FreeBSD 9.2

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | NOTES | RETURN VALUES | ERRORS | SEE ALSO | HISTORY

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