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NetBSD 6.1.5 - man page for setitimer (netbsd section 2)

GETITIMER(2)			     BSD System Calls Manual			     GETITIMER(2)

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

     Standard C Library (libc, -lc)

     #include <sys/time.h>

     getitimer(int which, struct itimerval *value);

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

     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 in the structure
     at value.	The setitimer() call sets a timer to the specified value, returning the previous
     value of the timer if ovalue is not NULL.

     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.  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 dis-
     abled after its next expiration (assuming it_value is non-zero).

     The which parameter specifies the type of the timer:

	   ITIMER_REAL	      timer decrements in real time.  This timer is affected by
			      adjtime(2) and settimeofday(2).  A SIGALRM signal is delivered when
			      this timer expires.

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

	   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 system calls, programs using this timer must be prepared
			      to restart interrupted system calls.

	   ITIMER_MONOTONIC   timer decrements in monotonic time.  This timer is not affected by
			      adjtime(2) and settimeofday(2).  A SIGALRM signal is delivered when
			      this timer expires.
     Note that:

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

	   o   The interaction between setitimer() and alarm(3) or sleep(3) is unspecified by the

     If the calls succeed, a value of 0 is returned.  If an error occurs, the value -1 is
     returned, and a more precise error code is placed in the global variable errno.

     Both functions may fail if:

     [EFAULT]		The value parameter specified a bad address.

     [EINVAL]		The which parameter was not a known timer type, or the value parameter
			specified a time that was too large to be handled.

     gettimeofday(2), select(2), sigaction(2), itimerval(3), timeradd(3)

     The functions conform to IEEE Std 1003.1-2001 (``POSIX.1'').  The later IEEE Std 1003.1-2008
     (``POSIX.1'') revision however marked both as obsolescent, recommending the use of
     timer_gettime(2) and timer_settime(2) instead.

     The getitimer() function call appeared in 4.2BSD.	The ITIMER_MONOTONIC functionality
     appeared in NetBSD 6.0.

BSD					 October 27, 2011				      BSD

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