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.\" $NetBSD: timeval.3,v 1.12 2011/04/12 08:39:26 jruoho Exp $
.\"
.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jukka Ruohonen.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd April 12, 2011
.Dt TIMEVAL 3bsd
.Os
.Sh NAME
.Nm timeval ,
.Nm timespec
.Nd time structures
.Sh LIBRARY
.ds str-Lb-libbsd Utility functions from BSD systems (libbsd, \-lbsd)
.Lb libbsd
.Sh SYNOPSIS
.In sys/time.h
(See
.Xr libbsd 7
for include usage.)
.Ft void
.Fn TIMEVAL_TO_TIMESPEC "struct timeval *tv" "struct timespec *ts"
.Ft void
.Fn TIMESPEC_TO_TIMEVAL "struct timeval *tv" "struct timespec *ts"
.Sh DESCRIPTION
The
.In sys/time.h
header, included by
.In time.h ,
defines various structures related to time and timers.
.Bl -enum -offset 1n
.It
The following structure is used by
.Xr gettimeofday 2 ,
among others:
.Bd -literal -offset indent
struct timeval {
time_t tv_sec;
suseconds_t tv_usec;
};
.Ed
.Pp
The
.Va tv_sec
member represents the elapsed time, in whole seconds.
The
.Va tv_usec
member captures rest of the elapsed time,
represented as the number of microseconds.
.It
The following structure is used by
.Xr nanosleep 2 ,
among others:
.Bd -literal -offset indent
struct timespec {
time_t tv_sec;
long tv_nsec;
};
.Ed
.Pp
The
.Va tv_sec
member is again the elapsed time in whole seconds.
The
.Va tv_nsec
member represents the rest of the elapsed time in nanoseconds.
.Pp
A microsecond is equal to one millionth of a second,
1000 nanoseconds, or 1/1000 milliseconds.
To ease the conversions, the macros
.Fn TIMEVAL_TO_TIMESPEC
and
.Fn TIMESPEC_TO_TIMEVAL
can be used to convert between
.Em struct timeval
and
.Em struct timespec .
.El
.Sh EXAMPLES
It can be stressed that the traditional
.Tn UNIX
.Va timeval
and
.Va timespec
structures represent elapsed time, measured by the system clock.
The following sketch implements a function suitable
for use in a context where the
.Va timespec
structure is required for a conditional timeout:
.Bd -literal -offset indent
static void
example(struct timespec *spec, time_t minutes)
{
struct timeval elapsed;
(void)gettimeofday(&elapsed, NULL);
_DIAGASSERT(spec != NULL);
TIMEVAL_TO_TIMESPEC(&elapsed, spec);
/* Add the offset for timeout in minutes. */
spec->tv_sec = spec->tv_sec + minutes * 60;
}
.Ed
.Pp
A better alternative would use the more precise
.Xr clock_gettime 2 .
.Sh SEE ALSO
.Xr timeradd 3bsd
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