4.1cBSD/usr/man/man2/getitimer.2

.TH GETITIMER 2 2/12/83
.SH NAME
getitimer, setitimer \- get/set value of interval timer
.SH SYNOPSIS
.nf
.ft B
#include <time.h>
.PP
.ft B
getitimer(which, value)
int which;
struct itimerval *value;
.PP
.ft B
setitimer(which, value)
int which;
struct itimerval *value;
.fi
.SH DESCRIPTION
The system provides each process with three interval timers,
defined in
.RI < time.h >
as:
.PP
.nf
.RS
.DT
#define	ITIMER_REAL   	0	/* real time intervals */
#define	ITIMER_VIRTUAL	1	/* virtual time intervals */
#define	ITIMER_PROF   	2	/* user and system virtual time */
.RE
.fi
.PP
The
.I getitimer
call returns the current value for the timer specified in
.IR which ,
while the
.I setitimer
call sets the value of a timer.  A timer may be disabled by
setting it to a value of 0.
.PP
A timer value is defined by the 
.I itimerval
structure:
.PP
.nf
.RS
.DT
struct itimerval {
	struct	timeval itimer_interval;	/* timer interval */
	struct	timeval itimer_value;	/* current value */
};
.RE
.fi
.PP
The ITIMER_REAL timer decrements in real time.  A SIGALRM signal is
delivered when this timer expires.
.PP
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.
.PP
Thee 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 to statistically profile their executions.
A SIGPROF signal is delivered when it expires.
Because this signal may interrupt some in-progress system calls,
programs must be prepared to deal with this interruption to run
with this timer enabled.
.SH "RETURN VALUE
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 \fIerrno\fP.
.SH "ERRORS
The possible errors are:
.TP 15
[EFAULT]
The \fIvalue\fP structure specified a bad address.
.SH "SEE ALSO"
signal(2), getimeofday(2)