time::hires.3

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.\" ========================================================================
.\"
.IX Title "Time::HiRes 3"
.TH Time::HiRes 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Time::HiRes \- High resolution alarm, sleep, gettimeofday, interval timers
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 3
\&  use Time::HiRes qw( usleep ualarm gettimeofday tv_interval nanosleep
\&                      clock_gettime clock_getres clock_nanosleep clock
\&                      stat );
\&
\&  usleep ($microseconds);
\&  nanosleep ($nanoseconds);
\&
\&  ualarm ($microseconds);
\&  ualarm ($microseconds, $interval_microseconds);
\&
\&  $t0 = [gettimeofday];
\&  ($seconds, $microseconds) = gettimeofday;
\&
\&  $elapsed = tv_interval ( $t0, [$seconds, $microseconds]);
\&  $elapsed = tv_interval ( $t0, [gettimeofday]);
\&  $elapsed = tv_interval ( $t0 );
\&
\&  use Time::HiRes qw ( time alarm sleep );
\&
\&  $now_fractions = time;
\&  sleep ($floating_seconds);
\&  alarm ($floating_seconds);
\&  alarm ($floating_seconds, $floating_interval);
\&
\&  use Time::HiRes qw( setitimer getitimer );
\&
\&  setitimer ($which, $floating_seconds, $floating_interval );
\&  getitimer ($which);
\&
\&  use Time::HiRes qw( clock_gettime clock_getres clock_nanosleep
\&                      ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF ITIMER_REALPROF );
\&
\&  $realtime   = clock_gettime(CLOCK_REALTIME);
\&  $resolution = clock_getres(CLOCK_REALTIME);
\&
\&  clock_nanosleep(CLOCK_REALTIME, 1.5e9);
\&  clock_nanosleep(CLOCK_REALTIME, time()*1e9 + 10e9, TIMER_ABSTIME);
\&
\&  my $ticktock = clock();
\&
\&  use Time::HiRes qw( stat );
\&
\&  my @stat = stat("file");
\&  my @stat = stat(FH);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`Time::HiRes\*(C'\fR module implements a Perl interface to the
\&\f(CW\*(C`usleep\*(C'\fR, \f(CW\*(C`nanosleep\*(C'\fR, \f(CW\*(C`ualarm\*(C'\fR, \f(CW\*(C`gettimeofday\*(C'\fR, and
\&\f(CW\*(C`setitimer\*(C'\fR/\f(CW\*(C`getitimer\*(C'\fR system calls, in other words, high
resolution time and timers. See the \*(L"\s-1EXAMPLES\s0\*(R" section below and the
test scripts for usage; see your system documentation for the
description of the underlying \f(CW\*(C`nanosleep\*(C'\fR or \f(CW\*(C`usleep\*(C'\fR, \f(CW\*(C`ualarm\*(C'\fR,
\&\f(CW\*(C`gettimeofday\*(C'\fR, and \f(CW\*(C`setitimer\*(C'\fR/\f(CW\*(C`getitimer\*(C'\fR calls.
.PP
If your system lacks \f(CW\*(C`gettimeofday()\*(C'\fR or an emulation of it you don't
get \f(CW\*(C`gettimeofday()\*(C'\fR or the one-argument form of \f(CW\*(C`tv_interval()\*(C'\fR.
If your system lacks all of \f(CW\*(C`nanosleep()\*(C'\fR, \f(CW\*(C`usleep()\*(C'\fR,
\&\f(CW\*(C`select()\*(C'\fR, and \f(CW\*(C`poll\*(C'\fR, you don't get \f(CW\*(C`Time::HiRes::usleep()\*(C'\fR,
\&\f(CW\*(C`Time::HiRes::nanosleep()\*(C'\fR, or \f(CW\*(C`Time::HiRes::sleep()\*(C'\fR.
If your system lacks both \f(CW\*(C`ualarm()\*(C'\fR and \f(CW\*(C`setitimer()\*(C'\fR you don't get
\&\f(CW\*(C`Time::HiRes::ualarm()\*(C'\fR or \f(CW\*(C`Time::HiRes::alarm()\*(C'\fR.
.PP
If you try to import an unimplemented function in the \f(CW\*(C`use\*(C'\fR statement
it will fail at compile time.
.PP
If your subsecond sleeping is implemented with \f(CW\*(C`nanosleep()\*(C'\fR instead
of \f(CW\*(C`usleep()\*(C'\fR, you can mix subsecond sleeping with signals since
\&\f(CW\*(C`nanosleep()\*(C'\fR does not use signals.  This, however, is not portable,
and you should first check for the truth value of
\&\f(CW&Time::HiRes::d_nanosleep\fR to see whether you have nanosleep, and
then carefully read your \f(CW\*(C`nanosleep()\*(C'\fR C \s-1API\s0 documentation for any
peculiarities.
.PP
If you are using \f(CW\*(C`nanosleep\*(C'\fR for something else than mixing sleeping
with signals, give some thought to whether Perl is the tool you should
be using for work requiring nanosecond accuracies.
.PP
Remember that unless you are working on a \fIhard realtime\fR system,
any clocks and timers will be imprecise, especially so if you are working
in a pre-emptive multiuser system.  Understand the difference between
\&\fIwallclock time\fR and process time (in UNIX-like systems the sum of
\&\fIuser\fR and \fIsystem\fR times).  Any attempt to sleep for X seconds will
most probably end up sleeping \fBmore\fR than that, but don't be surpised
if you end up sleeping slightly \fBless\fR.
.PP
The following functions can be imported from this module.
No functions are exported by default.
.IP "gettimeofday ()" 4
.IX Item "gettimeofday ()"
In array context returns a two-element array with the seconds and
microseconds since the epoch.  In scalar context returns floating
seconds like \f(CW\*(C`Time::HiRes::time()\*(C'\fR (see below).
.ie n .IP "usleep ( $useconds )" 4
.el .IP "usleep ( \f(CW$useconds\fR )" 4
.IX Item "usleep ( $useconds )"
Sleeps for the number of microseconds (millionths of a second)
specified.  Returns the number of microseconds actually slept.
Can sleep for more than one second, unlike the \f(CW\*(C`usleep\*(C'\fR system call.
Can also sleep for zero seconds, which often works like a \fIthread yield\fR.
See also \f(CW\*(C`Time::HiRes::usleep()\*(C'\fR, \f(CW\*(C`Time::HiRes::sleep()\*(C'\fR, and
\&\f(CW\*(C`Time::HiRes::clock_nanosleep()\*(C'\fR.
.Sp
Do not expect \fIusleep()\fR to be exact down to one microsecond.
.ie n .IP "nanosleep ( $nanoseconds )" 4
.el .IP "nanosleep ( \f(CW$nanoseconds\fR )" 4
.IX Item "nanosleep ( $nanoseconds )"
Sleeps for the number of nanoseconds (1e9ths of a second) specified.
Returns the number of nanoseconds actually slept (accurate only to
microseconds, the nearest thousand of them).  Can sleep for more than
one second.  Can also sleep for zero seconds, which often works like
a \fIthread yield\fR.  See also \f(CW\*(C`Time::HiRes::sleep()\*(C'\fR,
\&\f(CW\*(C`Time::HiRes::usleep()\*(C'\fR, and \f(CW\*(C`Time::HiRes::clock_nanosleep()\*(C'\fR.
.Sp
Do not expect \fInanosleep()\fR to be exact down to one nanosecond.
Getting even accuracy of one thousand nanoseconds is good.
.ie n .IP "ualarm ( $useconds\fR [, \f(CW$interval_useconds ] )" 4
.el .IP "ualarm ( \f(CW$useconds\fR [, \f(CW$interval_useconds\fR ] )" 4
.IX Item "ualarm ( $useconds [, $interval_useconds ] )"
Issues a \f(CW\*(C`ualarm\*(C'\fR call; the \f(CW$interval_useconds\fR is optional and
will be zero if unspecified, resulting in \f(CW\*(C`alarm\*(C'\fR\-like behaviour.
.Sp
\&\fIualarm\fR\|(0) will cancel an outstanding \fIualarm()\fR.
.Sp
Note that the interaction between alarms and sleeps is unspecified.
.IP "tv_interval" 4
.IX Item "tv_interval"
tv_interval ( \f(CW$ref_to_gettimeofday\fR [, \f(CW$ref_to_later_gettimeofday\fR] )
.Sp
Returns the floating seconds between the two times, which should have
been returned by \f(CW\*(C`gettimeofday()\*(C'\fR. If the second argument is omitted,
then the current time is used.
.IP "time ()" 4
.IX Item "time ()"
Returns a floating seconds since the epoch. This function can be
imported, resulting in a nice drop-in replacement for the \f(CW\*(C`time\*(C'\fR
provided with core Perl; see the \*(L"\s-1EXAMPLES\s0\*(R" below.
.Sp
\&\fB\s-1NOTE\s0 1\fR: This higher resolution timer can return values either less
or more than the core \f(CW\*(C`time()\*(C'\fR, depending on whether your platform
rounds the higher resolution timer values up, down, or to the nearest second
to get the core \f(CW\*(C`time()\*(C'\fR, but naturally the difference should be never
more than half a second.  See also \*(L"clock_getres\*(R", if available
in your system.
.Sp
\&\fB\s-1NOTE\s0 2\fR: Since Sunday, September 9th, 2001 at 01:46:40 \s-1AM\s0 \s-1GMT\s0, when
the \f(CW\*(C`time()\*(C'\fR seconds since epoch rolled over to 1_000_000_000, the
default floating point format of Perl and the seconds since epoch have
conspired to produce an apparent bug: if you print the value of
\&\f(CW\*(C`Time::HiRes::time()\*(C'\fR you seem to be getting only five decimals, not
six as promised (microseconds).  Not to worry, the microseconds are
there (assuming your platform supports such granularity in the first
place).  What is going on is that the default floating point format of
Perl only outputs 15 digits.  In this case that means ten digits
before the decimal separator and five after.  To see the microseconds
you can use either \f(CW\*(C`printf\*(C'\fR/\f(CW\*(C`sprintf\*(C'\fR with \f(CW"%.6f"\fR, or the
\&\f(CW\*(C`gettimeofday()\*(C'\fR function in list context, which will give you the
seconds and microseconds as two separate values.
.ie n .IP "sleep ( $floating_seconds )" 4
.el .IP "sleep ( \f(CW$floating_seconds\fR )" 4
.IX Item "sleep ( $floating_seconds )"
Sleeps for the specified amount of seconds.  Returns the number of
seconds actually slept (a floating point value).  This function can
be imported, resulting in a nice drop-in replacement for the \f(CW\*(C`sleep\*(C'\fR
provided with perl, see the \*(L"\s-1EXAMPLES\s0\*(R" below.
.Sp
Note that the interaction between alarms and sleeps is unspecified.