\" $NetBSD: timeval.3,v 1.12 2011/04/12 08:39:26 jruoho Exp $
\"
\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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\" This code is derived from software contributed to The NetBSD Foundation
\" by Jukka Ruohonen.
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Dd April 12, 2011
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;
/* 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 tm 3 ,
Xr bintime_add 9
