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.Dd March 22, 1997 33.Dt TIME 9 34.Os FreeBSD 35.Sh NAME 36.Nm boottime , 37.Nm mono_time , 38.Nm runtime , 39.Nm time 40.Nd system time variables 41.Sh SYNOPSIS 42.Va extern struct timeval boottime; 43.br 44.Va extern volatile struct timeval mono_time; 45.br 46.Va extern struct timeval runtime; 47.br 48.Va extern struct timeval time; 49.Sh DESCRIPTION 50The 51.Va time 52variable is the system's 53.Dq wall time 54clock. 55It is set at boot by 56.Xr inittodr 9 , 57and is updated by the 58.Xr settimeofday 2 59system call and by periodic clock interrupts. 60.Pp 61The 62.Va boottime 63variable holds the system boot time. It is set from 64.Va time 65at system boot, and is updated when the system time is adjusted 66with 67.Xr settimeofday 2 . 68.Pp 69The 70.Va runtime 71variable holds the time that the system switched to the 72current process. 73It is set after each context switch, 74and is updated when the system time is adjusted with 75.Xr settimeofday 2 . 76Because 77.Va runtime 78is used for system accounting, it is set with the high-resolution 79.Xr microtime 9 80function, rather than being copied from 81.Va time . 82.Pp 83The 84.Va mono_time 85variable is a monotonically increasing system clock. It is set 86from 87.Va time 88at boot, and is updated by the periodic timer interrupt. (It is 89not updated by 90.Xr settimeofday 2 .) 91.Pp 92All of these variables contain times 93expressed in seconds and microseconds since midnight (0 hour), 94January 1, 1970. 95.Pp 96Clock interrupts should be blocked 97when reading or writing 98.Va time 99or 100.Va mono_time , 101because those variables are updated by 102.Fn hardclock . 103The 104.Xr gettime 9 105function can be used to read the 106.Va time 107variable in an atomic manner. There is no equivalent 108function for accessing 109.Va mono_time. 110The 111.Va boottime 112and 113.Va runtime 114variables may be read and written without special precautions. 115.Pp 116It should be noted that due to the differences in how the time values 117returned by 118.Xr gettime 9 119and 120.Xr microtime 9 121are updated, comparing the results of the two routines 122may result in a time value that appears to go backwards. 123This can be avoided by consistently using one function or the other 124for use in any given context. 125.Sh SEE ALSO 126.Xr settimeofday 2 , 127.Xr gettime 9 , 128.\" .Xr hz 9 , 129.\" .Xr hardclock 9 , 130.Xr inittodr 9 , 131.Xr microtime 9 132.Sh BUGS 133The notion of having a single 134.Va runtime 135variable obviously would not be appropriate in multiprocessor systems. 136