141 lines
4.1 KiB
Groff
141 lines
4.1 KiB
Groff
.\" $NetBSD: time.9,v 1.1 1995/11/25 21:24:53 perry Exp $
|
|
.\"
|
|
.\" Copyright (c) 1994 Christopher G. Demetriou
|
|
.\" 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 Christopher G. Demetriou
|
|
.\" for the NetBSD Project.
|
|
.\" 3. The name of the author may not be used to endorse or promote products
|
|
.\" derived from this software without specific prior written permission
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd March 22, 1997
|
|
.Dt TIME 9
|
|
.Os FreeBSD
|
|
.Sh NAME
|
|
.Nm boottime ,
|
|
.Nm mono_time ,
|
|
.Nm runtime ,
|
|
.Nm time
|
|
.Nd system time variables
|
|
.Sh SYNOPSIS
|
|
.Bl -item -compact
|
|
.It
|
|
.Va extern struct timeval boottime ;
|
|
.It
|
|
.Va extern volatile struct timeval mono_time ;
|
|
.It
|
|
.Va extern struct timeval runtime ;
|
|
.It
|
|
.Va extern struct timeval time ;
|
|
.El
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Va time
|
|
variable is the system's
|
|
.Dq wall time
|
|
clock.
|
|
It is set at boot by
|
|
.Xr inittodr 9 ,
|
|
and is updated by the
|
|
.Xr settimeofday 2
|
|
system call and by periodic clock interrupts.
|
|
.Pp
|
|
The
|
|
.Va boottime
|
|
variable holds the system boot time. It is set from
|
|
.Va time
|
|
at system boot, and is updated when the system time is adjusted
|
|
with
|
|
.Xr settimeofday 2 .
|
|
.Pp
|
|
The
|
|
.Va runtime
|
|
variable holds the time that the system switched to the
|
|
current process.
|
|
It is set after each context switch,
|
|
and is updated when the system time is adjusted with
|
|
.Xr settimeofday 2 .
|
|
Because
|
|
.Va runtime
|
|
is used for system accounting, it is set with the high-resolution
|
|
.Xr microtime 9
|
|
function, rather than being copied from
|
|
.Va time .
|
|
.Pp
|
|
The
|
|
.Va mono_time
|
|
variable is a monotonically increasing system clock. It is set
|
|
from
|
|
.Va time
|
|
at boot, and is updated by the periodic timer interrupt. (It is
|
|
not updated by
|
|
.Xr settimeofday 2 . )
|
|
.Pp
|
|
All of these variables contain times
|
|
expressed in seconds and microseconds since midnight (0 hour),
|
|
January 1, 1970.
|
|
.Pp
|
|
Clock interrupts should be blocked
|
|
when reading or writing
|
|
.Va time
|
|
or
|
|
.Va mono_time ,
|
|
because those variables are updated by
|
|
.Fn hardclock .
|
|
The
|
|
.Xr gettime 9
|
|
function can be used to read the
|
|
.Va time
|
|
variable in an atomic manner. There is no equivalent
|
|
function for accessing
|
|
.Va mono_time .
|
|
The
|
|
.Va boottime
|
|
and
|
|
.Va runtime
|
|
variables may be read and written without special precautions.
|
|
.Pp
|
|
It should be noted that due to the differences in how the time values
|
|
returned by
|
|
.Xr gettime 9
|
|
and
|
|
.Xr microtime 9
|
|
are updated, comparing the results of the two routines
|
|
may result in a time value that appears to go backwards.
|
|
This can be avoided by consistently using one function or the other
|
|
for use in any given context.
|
|
.Sh SEE ALSO
|
|
.Xr settimeofday 2 ,
|
|
.Xr gettime 9 ,
|
|
.\" .Xr hz 9 ,
|
|
.\" .Xr hardclock 9 ,
|
|
.Xr inittodr 9 ,
|
|
.Xr microtime 9
|
|
.Sh BUGS
|
|
The notion of having a single
|
|
.Va runtime
|
|
variable obviously would not be appropriate in multiprocessor systems.
|