getitimer man page on NetBSD

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GETITIMER(2)		    BSD 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>

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

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

DESCRIPTION
     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 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.  Setting it_interval to 0 causes a timer to be disabled
     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 expires.

	   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 inter‐
			      preters 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
			      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:

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

	   ·   The interaction between setitimer() and alarm(3) or sleep(3) is
	       unspecified by the specification.

RETURN VALUES
     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.

ERRORS
     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.

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

STANDARDS
     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 obsoles‐
     cent, recommending the use of timer_gettime(2) and timer_settime(2)
     instead.

HISTORY
     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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