.\"	$NetBSD: getitimer.2,v 1.6 1995/10/12 15:40:54 jtc Exp $
.\"
.\" Copyright (c) 1983, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)getitimer.2	8.2 (Berkeley) 12/11/93
.\"
.Dd December 11, 1993
.Dt GETITIMER 2
.Os BSD 4.2
.Sh NAME
.Nm getitimer ,
.Nm setitimer
.Nd get/set value of interval timer
.Sh SYNOPSIS
.Fd #include <sys/time.h>
.Pp
.Fd #define ITIMER_REAL		0
.Fd #define ITIMER_VIRTUAL	1
.Fd #define ITIMER_PROF		2
.Ft int
.Fo getitimer
.Fa "int which"
.Fa "struct itimerval *value"
.Fc
.Ft int
.Fo setitimer
.Fa "int which"
.Fa "const struct itimerval *restrict value"
.Fa "struct itimerval *restrict ovalue"
.Fc
.Sh DESCRIPTION
The system provides each process with three interval timers,
defined in
.Ao Pa sys/time.h Ac .
The
.Fn getitimer
call returns the current value for the timer specified in
.Fa which
in the structure at
.Fa value .
The
.Fn setitimer
call sets a timer to the specified
.Fa value
(returning the previous value of the timer if
.Fa ovalue
is non-nil).
.Pp
A timer value is defined by the 
.Fa itimerval
structure:
.Bd -literal -offset indent
struct itimerval {
	struct	timeval it_interval;	/* timer interval */
	struct	timeval it_value;	/* current value */
};
.Ed
.Pp
If
.Fa it_value
is non-zero, it indicates the time to the next timer expiration. 
If
.Fa it_interval
is non-zero, it specifies a value to be used in reloading 
.Fa it_value
when the timer expires.
Setting 
.Fa it_value
to 0 disables a timer.  Setting 
.Fa it_interval
to 0 causes a timer to be disabled after its next expiration (assuming
.Fa it_value
is non-zero).
.Pp
Time values smaller than the resolution of the
system clock are rounded up to this resolution
(typically 10 milliseconds).
.Pp
The
.Dv ITIMER_REAL
timer decrements in real time.  A
.Dv SIGALRM
signal is
delivered when this timer expires.
.Pp
The
.Dv ITIMER_VIRTUAL
timer decrements in process virtual time.
It runs only when the process is executing.  A
.Dv SIGVTALRM
signal
is delivered when it expires.
.Pp
The
.Dv 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
.Dv ITIMER_PROF
timer expires, the
.Dv 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.
.Sh NOTES
Three macros for manipulating time values are defined in
.Ao Pa sys/time.h Ac .
.Fa Timerclear
sets a time value to zero,
.Fa timerisset
tests if a time value is non-zero, and
.Fa timercmp
compares two time values (beware that >= and <= do not
work with this macro).
.Sh RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and the global integer variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn getitimer
and
.Fn setitimer
will fail if:
.Bl -tag -width Er
.\" ==========
.It Bq Er EFAULT
The
.Fa value
parameter specified a bad address.
.\" ==========
.It Bq Er EINVAL
The
.Fa value
parameter specified a time that was too large to be handled
or not in the canonical form.
.\" ==========
.It Bq Er EINVAL
The
.Fa which
parameter was invalid.
.El
.Sh SEE ALSO
.Xr gettimeofday 2 ,
.Xr select 2 ,
.Xr sigaction 2
.Sh HISTORY
The
.Fn getitimer
function call appeared in
.Bx 4.2 .