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 FreeBSD 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.Va extern struct timeval boottime; 45.br 46.Va extern volatile struct timeval mono_time; 47.br 48.Va extern struct timeval runtime; 49.br 50.Va extern struct timeval time; 51.Sh DESCRIPTION 52The 53.Va time 54variable is the system's 55.Dq wall time 56clock. 57It is set at boot by 58.Xr inittodr 9 , 59and is updated by the 60.Xr settimeofday 2 61system call and by periodic clock interrupts. 62.Pp 63The 64.Va boottime 65variable holds the system boot time. It is set from 66.Va time 67at system boot, and is updated when the system time is adjusted 68with 69.Xr settimeofday 2 . 70.Pp 71The 72.Va runtime 73variable holds the time that the system switched to the 74current process. 75It is set after each context switch, 76and is updated when the system time is adjusted with 77.Xr settimeofday 2 . 78Because 79.Va runtime 80is used for system accounting, it is set with the high-resolution 81.Xr microtime 9 82function, rather than being copied from 83.Va time . 84.Pp 85The 86.Va mono_time 87variable is a monotonically increasing system clock. It is set 88from 89.Va time 90at boot, and is updated by the periodic timer interrupt. (It is 91not updated by 92.Xr settimeofday 2 .) 93.Pp 94All of these variables contain times 95expressed in seconds and microseconds since midnight (0 hour), 96January 1, 1970. 97.Pp 98Clock interrupts should be blocked 99when reading or writing 100.Va time 101or 102.Va mono_time , 103because those variables are updated by 104.Fn hardclock . 105The 106.Xr gettime 9 107function can be used to read the 108.Va time 109variable in an atomic manner. There is no equivalent 110function for accessing 111.Va mono_time. 112The 113.Va boottime 114and 115.Va runtime 116variables may be read and written without special precautions. 117.Pp 118It should be noted that due to the differences in how the time values 119returned by 120.Xr gettime 9 121and 122.Xr microtime 9 123are updated, comparing the results of the two routines 124may result in a time value that appears to go backwards. 125This can be avoided by consistently using one function or the other 126for use in any given context. 127.Sh SEE ALSO 128.Xr settimeofday 2 , 129.Xr gettime 9 , 130.\" .Xr hz 9 , 131.\" .Xr hardclock 9 , 132.Xr inittodr 9 , 133.Xr microtime 9 134.Sh BUGS 135The notion of having a single 136.Va runtime 137variable obviously would not be appropriate in multiprocessor systems. 138