1 .\" $NetBSD: time.9,v 1.1 1995/11/25 21:24:53 perry Exp $
3 .\" Copyright (c) 1994 Christopher G. Demetriou
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16 .\" This product includes software developed by Christopher G. Demetriou
17 .\" for the NetBSD Project.
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32 .\" $FreeBSD: src/share/man/man9/time.9,v 1.3.2.5 2001/08/17 13:08:54 ru Exp $
33 .\" $DragonFly: src/share/man/man9/time.9,v 1.2 2003/06/17 04:37:01 dillon Exp $
43 .Nd system time variables
47 .Va extern struct timeval boottime ;
49 .Va extern volatile struct timeval mono_time ;
51 .Va extern struct timeval runtime ;
53 .Va extern struct timeval time ;
58 variable is the system's
65 system call and by periodic clock interrupts.
69 variable holds the system boot time. It is set from
71 at system boot, and is updated when the system time is adjusted
77 variable holds the time that the system switched to the
79 It is set after each context switch,
80 and is updated when the system time is adjusted with
84 is used for system accounting, it is set with the high-resolution
86 function, rather than being copied from
91 variable is a monotonically increasing system clock. It is set
94 at boot, and is updated by the periodic timer interrupt. (It is
96 .Xr settimeofday 2 . )
98 All of these variables contain times
99 expressed in seconds and microseconds since midnight (0 hour),
102 Clock interrupts should be blocked
103 when reading or writing
107 because those variables are updated by
111 function can be used to read the
113 variable in an atomic manner. There is no equivalent
114 function for accessing
120 variables may be read and written without special precautions.
122 It should be noted that due to the differences in how the time values
127 are updated, comparing the results of the two routines
128 may result in a time value that appears to go backwards.
129 This can be avoided by consistently using one function or the other
130 for use in any given context.
134 .\" .Xr hardclock 9 ,
139 The notion of having a single
141 variable obviously would not be appropriate in multiprocessor systems.