188 lines
4.7 KiB
Groff
188 lines
4.7 KiB
Groff
.\" $NetBSD: timeval.3,v 1.10 2010/05/20 05:37:58 jruoho Exp $
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.\"
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.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jukka Ruohonen.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd May 20, 2010
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.Dt TIMEVAL 3
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.Os
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.Sh NAME
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.Nm timeval ,
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.Nm timespec ,
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.Nm itimerval ,
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.Nm itimerspec ,
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.Nm bintime
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.Nd time structures
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.Sh SYNOPSIS
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.In sys/time.h
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.Ft void
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.Fn TIMEVAL_TO_TIMESPEC "struct timeval *tv" "struct timespec *ts"
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.Ft void
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.Fn TIMESPEC_TO_TIMEVAL "struct timeval *tv" "struct timespec *ts"
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.Sh DESCRIPTION
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The
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.In sys/time.h
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header, included by
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.In time.h ,
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defines various structures related to time and timers.
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.Bl -enum -offset 1n
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.It
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The following structure is used by
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.Xr gettimeofday 2 ,
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among others:
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.Bd -literal -offset indent
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struct timeval {
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time_t tv_sec;
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suseconds_t tv_usec;
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};
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.Ed
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.Pp
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The
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.Va tv_sec
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member represents the elapsed time, in whole seconds.
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The
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.Va tv_usec
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member captures rest of the elapsed time,
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represented as the number of microseconds.
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.It
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The following structure is used by
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.Xr nanosleep 2 ,
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among others:
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.Bd -literal -offset indent
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struct timespec {
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time_t tv_sec;
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long tv_nsec;
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};
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.Ed
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.Pp
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The
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.Va tv_sec
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member is again the elapsed time in whole seconds.
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The
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.Va tv_nsec
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member represents the rest of the elapsed time in nanoseconds.
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.Pp
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A microsecond is equal to one millionth of a second,
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1000 nanoseconds, or 1/1000 milliseconds.
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To ease the conversions, the macros
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.Fn TIMEVAL_TO_TIMESPEC
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and
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.Fn TIMESPEC_TO_TIMEVAL
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can be used to convert between
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.Em struct timeval
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and
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.Em struct timespec .
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.It
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The following structure is used by
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.Xr setitimer 2 ,
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among others:
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.Bd -literal -offset indent
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struct itimerval {
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struct timeval it_interval;
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struct timeval it_value;
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};
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.Ed
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.It
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The following structure is used by
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.Xr timer_settime 2 ,
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among others:
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.Bd -literal -offset indent
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struct itimerspec {
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struct timespec it_interval;
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struct timespec it_value;
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};
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.Ed
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.Pp
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Both
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.Em struct itimerval
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and
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.Em struct itimerspec
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are used to specify when a timer expires.
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Generally,
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.Va it_interval
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specifies the period between successive timer expirations.
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A value zero implies that the alarm will fire only once.
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If
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.Va it_value
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is non-zero, it indicates the time left to the next timer expiration.
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A value zero implies that the timer is disabled.
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.It
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The following structure is used by
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.Xr bintime 9 ,
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among others:
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.Bd -literal -offset indent
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struct bintime {
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time_t sec;
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uint64_t frac;
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};
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.Ed
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.Pp
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The
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.Va sec
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member specifies the time in seconds and
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.Va frac
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represents a 64-bit fraction of seconds.
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The
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.Va struct bintime
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is meant to be used in the kernel only.
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It is further described in
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.Xr timecounter 9 .
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.El
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.Sh EXAMPLES
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It can be stressed that the traditional
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.Tn UNIX
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.Va timeval
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and
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.Va timespec
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structures represent elapsed time, measured by the system clock
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(see
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.Xr hz 9 ) .
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The following sketch implements a function suitable
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for use in a context where the
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.Va timespec
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structure is required for a conditional timeout:
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.Bd -literal -offset indent
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static void
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example(struct timespec *spec, time_t minutes)
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{
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struct timeval elapsed;
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(void)gettimeofday(&elapsed, NULL);
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_DIAGASSERT(spec != NULL);
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TIMEVAL_TO_TIMESPEC(&elapsed, spec);
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/* Add the offset for timeout in minutes. */
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spec->tv_sec = spec->tv_sec + minutes * 60;
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}
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.Ed
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.Pp
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A better alternative would use the more precise
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.Xr clock_gettime 2 .
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.Sh SEE ALSO
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.Xr timeradd 3
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