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+.\" Copyright (c) 1983, 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.
+.\"
+.\"	@(#)1.4.t	8.1 (Berkeley) 6/8/93
+.\"
+.sh "Timers
+.NH 3
+Real time
+.PP
+The system's notion of the current Greenwich time and the current time
+zone is set and returned by the call by the calls:
+.DS
+#include <sys/time.h>
+
+settimeofday(tvp, tzp);
+struct timeval *tp;
+struct timezone *tzp;
+
+gettimeofday(tp, tzp);
+result struct timeval *tp;
+result struct timezone *tzp;
+.DE
+where the structures are defined in \fI<sys/time.h>\fP as:
+.DS
+._f
+struct timeval {
+	long	tv_sec;	/* seconds since Jan 1, 1970 */
+	long	tv_usec;	/* and microseconds */
+};
+
+struct timezone {
+	int	tz_minuteswest;	/* of Greenwich */
+	int	tz_dsttime;	/* type of dst correction to apply */
+};
+.DE
+The precision of the system clock is hardware dependent.
+Earlier versions of UNIX contained only a 1-second resolution version
+of this call, which remains as a library routine:
+.DS
+time(tvsec)
+result long *tvsec;
+.DE
+returning only the tv_sec field from the \fIgettimeofday\fP call.
+.NH 3
+Interval time
+.PP
+The system provides each process with three interval timers,
+defined in \fI<sys/time.h>\fP:
+.DS
+._d
+#define	ITIMER_REAL	0	/* real time intervals */
+#define	ITIMER_VIRTUAL	1	/* virtual time intervals */
+#define	ITIMER_PROF	2	/* user and system virtual time */
+.DE
+The ITIMER_REAL timer decrements
+in real time.  It could be used by a library routine to
+maintain a wakeup service queue.  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
+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 processes to statistically profile
+their execution.
+A SIGPROF signal is delivered when it expires.
+.PP
+A timer value is defined by the \fIitimerval\fP structure:
+.DS
+._f
+struct itimerval {
+	struct	timeval it_interval;	/* timer interval */
+	struct	timeval it_value;	/* current value */
+};
+.DE
+and a timer is set or read by the call:
+.DS
+getitimer(which, value);
+int which; result struct itimerval *value;
+
+setitimer(which, value, ovalue);
+int which; struct itimerval *value; result struct itimerval *ovalue;
+.DE
+The third argument to \fIsetitimer\fP specifies an optional structure
+to receive the previous contents of the interval timer.
+A timer can be disabled by specifying a timer value of 0.
+.PP
+The system rounds argument timer intervals to be not less than the
+resolution of its clock.  This clock resolution can be determined
+by loading a very small value into a timer and reading the timer back to
+see what value resulted.
+.PP
+The \fIalarm\fP system call of earlier versions of UNIX is provided
+as a library routine using the ITIMER_REAL timer.  The process
+profiling facilities of earlier versions of UNIX
+remain because
+it is not always possible to guarantee
+the automatic restart of system calls after 
+receipt of a signal.
+The \fIprofil\fP call arranges for the kernel to begin gathering
+execution statistics for a process:
+.DS
+profil(buf, bufsize, offset, scale);
+result char *buf; int bufsize, offset, scale;
+.DE
+This begins sampling of the program counter, with statistics maintained
+in the user-provided buffer.