1.\" $NetBSD: time.9,v 1.1 1995/11/25 21:24:53 perry Exp $ 2.\" 3.\" Copyright (c) 1994 Christopher G. Demetriou 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by Christopher G. Demetriou 17.\" for the NetBSD Project. 18.\" 3. The name of the author may not be used to endorse or promote products 19.\" derived from this software without specific prior written permission 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31.\" 32.\" $FreeBSD$ 33.\" 34.Dd March 22, 1997 35.Dt TIME 9 36.Os 37.Sh NAME 38.Nm boottime , 39.Nm mono_time , 40.Nm runtime , 41.Nm time 42.Nd system time variables 43.Sh SYNOPSIS 44.Bl -item -compact 45.It 46.Va extern struct timeval boottime ; 47.It 48.Va extern volatile struct timeval mono_time ; 49.It 50.Va extern struct timeval runtime ; 51.It 52.Va extern struct timeval time ; 53.El 54.Sh DESCRIPTION 55The 56.Va time 57variable is the system's 58.Dq wall time 59clock. 60It is set at boot by 61.Xr inittodr 9 , 62and is updated by the 63.Xr settimeofday 2 64system call and by periodic clock interrupts. 65.Pp 66The 67.Va boottime 68variable holds the system boot time. 69It is set from 70.Va time 71at system boot, and is updated when the system time is adjusted 72with 73.Xr settimeofday 2 . 74.Pp 75The 76.Va runtime 77variable holds the time that the system switched to the 78current process. 79It is set after each context switch, 80and is updated when the system time is adjusted with 81.Xr settimeofday 2 . 82Because 83.Va runtime 84is used for system accounting, it is set with the high-resolution 85.Xr microtime 9 86function, rather than being copied from 87.Va time . 88.Pp 89The 90.Va mono_time 91variable is a monotonically increasing system clock. 92It is set 93from 94.Va time 95at boot, and is updated by the periodic timer interrupt. (It is 96not updated by 97.Xr settimeofday 2 . ) 98.Pp 99All of these variables contain times 100expressed in seconds and microseconds since midnight (0 hour), 101January 1, 1970. 102.Pp 103Clock interrupts should be blocked 104when reading or writing 105.Va time 106or 107.Va mono_time , 108because those variables are updated by 109.Fn hardclock . 110The 111.Xr gettime 9 112function can be used to read the 113.Va time 114variable in an atomic manner. 115There is no equivalent function for accessing 116.Va mono_time . 117The 118.Va boottime 119and 120.Va runtime 121variables may be read and written without special precautions. 122.Pp 123It should be noted that due to the differences in how the time values 124returned by 125.Xr gettime 9 126and 127.Xr microtime 9 128are updated, comparing the results of the two routines 129may result in a time value that appears to go backwards. 130This can be avoided by consistently using one function or the other 131for use in any given context. 132.Sh SEE ALSO 133.Xr settimeofday 2 , 134.Xr gettime 9 , 135.\" .Xr hardclock 9 , 136.\" .Xr hz 9 , 137.Xr inittodr 9 , 138.Xr microtime 9 139.Sh BUGS 140The notion of having a single 141.Va runtime 142variable obviously would not be appropriate in multiprocessor systems. 143