189 lines
4.7 KiB
Groff
189 lines
4.7 KiB
Groff
.\" $NetBSD: timeval.3,v 1.11 2010/06/08 05:50:01 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 June 8, 2010
|
|
.Dt TIMEVAL 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm timeval ,
|
|
.Nm timespec ,
|
|
.Nm itimerval ,
|
|
.Nm itimerspec ,
|
|
.Nm bintime
|
|
.Nd time structures
|
|
.Sh SYNOPSIS
|
|
.In sys/time.h
|
|
.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 .
|
|
.It
|
|
The following structure is used by
|
|
.Xr setitimer 2 ,
|
|
among others:
|
|
.Bd -literal -offset indent
|
|
struct itimerval {
|
|
struct timeval it_interval;
|
|
struct timeval it_value;
|
|
};
|
|
.Ed
|
|
.It
|
|
The following structure is used by
|
|
.Xr timer_settime 2 ,
|
|
among others:
|
|
.Bd -literal -offset indent
|
|
struct itimerspec {
|
|
struct timespec it_interval;
|
|
struct timespec it_value;
|
|
};
|
|
.Ed
|
|
.Pp
|
|
Both
|
|
.Em struct itimerval
|
|
and
|
|
.Em struct itimerspec
|
|
are used to specify when a timer expires.
|
|
Generally,
|
|
.Va it_interval
|
|
specifies the period between successive timer expirations.
|
|
A value zero implies that the alarm will fire only once.
|
|
If
|
|
.Va it_value
|
|
is non-zero, it indicates the time left to the next timer expiration.
|
|
A value zero implies that the timer is disabled.
|
|
.It
|
|
The following structure is used by
|
|
.Xr bintime 9 ,
|
|
among others:
|
|
.Bd -literal -offset indent
|
|
struct bintime {
|
|
time_t sec;
|
|
uint64_t frac;
|
|
};
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Va sec
|
|
member specifies the time in seconds and
|
|
.Va frac
|
|
represents a 64-bit fraction of seconds.
|
|
The
|
|
.Va struct bintime
|
|
is meant to be used in the kernel only.
|
|
It is further described in
|
|
.Xr timecounter 9 .
|
|
.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
|
|
(see
|
|
.Xr hz 9 ) .
|
|
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 3 ,
|
|
.Xr bintime_add 9
|