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Time::HiRes(3)
NAME
Time::HiRes - High resolution alarm, sleep, gettimeofday, interval timers
SYNOPSIS
use Time::HiRes qw( usleep ualarm gettimeofday tv_interval );
usleep ($microseconds);
ualarm ($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, $floating_interval);
use Time::HiRes qw( setitimer getitimer
ITIMER_REAL ITIMER_VIRTUAL ITIMER_PROF ITIMER_REALPROF );
setitimer ($which, $floating_seconds, $floating_interval );
getitimer ($which);
DESCRIPTION
The "Time::HiRes" module implements a Perl interface to the "usleep",
"ualarm", "gettimeofday", and "setitimer"/"getitimer" system calls, in
other words, high resolution time and timers. See the "EXAMPLES" section
below and the test scripts for usage; see your system documentation for the
description of the underlying "nanosleep" or "usleep", "ualarm",
"gettimeofday", and "setitimer"/"getitimer" calls.
If your system lacks "gettimeofday()" or an emulation of it you don't get
"gettimeofday()" or the one-argument form of "tv_interval()". If your
system lacks all of "nanosleep()", "usleep()", and "select()", you don't
get "Time::HiRes::usleep()" or "Time::HiRes::sleep()". If your system
lacks both "ualarm()" and "setitimer()" you don't get
"Time::HiRes::ualarm()" or "Time::HiRes::alarm()".
If you try to import an unimplemented function in the "use" statement it
will fail at compile time.
If your subsecond sleeping is implemented with "nanosleep()" instead of
"usleep()", you can mix subsecond sleeping with signals since "nanosleep()"
does not use signals. This, however is unportable, and you should first
check for the truth value of &Time::HiRes::d_nanosleep to see whether you
have nanosleep, and then carefully read your "nanosleep()" C API
documentation for any peculiarities. (There is no separate interface to
call "nanosleep()"; just use "Time::HiRes::sleep()" or
"Time::HiRes::usleep()" with small enough values.)
Unless using "nanosleep" for mixing sleeping with signals, give some
thought to whether Perl is the tool you should be using for work requiring
nanosecond accuracies.
The following functions can be imported from this module. No functions are
exported by default.
gettimeofday ()
In array context returns a two-element array with the seconds and
microseconds since the epoch. In scalar context returns floating
seconds like "Time::HiRes::time()" (see below).
usleep ( $useconds )
Sleeps for the number of microseconds specified. Returns the number of
microseconds actually slept. Can sleep for more than one second,
unlike the "usleep" system call. See also "Time::HiRes::sleep()" below.
ualarm ( $useconds [, $interval_useconds ] )
Issues a "ualarm" call; the $interval_useconds is optional and will be
zero if unspecified, resulting in "alarm"-like behaviour.
tv_interval
tv_interval ( $ref_to_gettimeofday [, $ref_to_later_gettimeofday] )
Returns the floating seconds between the two times, which should have
been returned by "gettimeofday()". If the second argument is omitted,
then the current time is used.
time ()
Returns a floating seconds since the epoch. This function can be
imported, resulting in a nice drop-in replacement for the "time"
provided with core Perl; see the "EXAMPLES" below.
NOTE 1: This higher resolution timer can return values either less or
more than the core "time()", depending on whether your platform rounds
the higher resolution timer values up, down, or to the nearest second
to get the core "time()", but naturally the difference should be never
more than half a second.
NOTE 2: Since Sunday, September 9th, 2001 at 01:46:40 AM GMT, when the
"time()" 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
"Time::HiRes::time()" 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 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 "printf"/"sprintf" with "%.6f", or the "gettimeofday()"
function in list context, which will give you the seconds and
microseconds as two separate values.
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 "sleep"
provided with perl, see the "EXAMPLES" below.
alarm ( $floating_seconds [, $interval_floating_seconds ] )
The "SIGALRM" signal is sent after the specified number of seconds.
Implemented using "ualarm()". The $interval_floating_seconds argument
is optional and will be zero if unspecified, resulting in
"alarm()"-like behaviour. This function can be imported, resulting in
a nice drop-in replacement for the "alarm" provided with perl, see the
"EXAMPLES" below.
NOTE 1: With some operating system and Perl release combinations
"SIGALRM" restarts "select()", instead of interuping it. This means
that an "alarm()" followed by a "select()" may together take the sum of
the times specified for the the "alarm()" and the "select()", not just
the time of the "alarm()".
setitimer ( $which, $floating_seconds [, $interval_floating_seconds ] )
Start up an interval timer: after a certain time, a signal arrives, and
more signals may keep arriving at certain intervals. To disable a
timer, use $floating_seconds of zero. If the
$interval_floating_seconds is set to zero (or unspecified), the timer
is disabled after the next delivered signal.
Use of interval timers may interfere with "alarm()", "sleep()", and
"usleep()". In standard-speak the "interaction is unspecified", which
means that anything may happen: it may work, it may not.
In scalar context, the remaining time in the timer is returned.
In list context, both the remaining time and the interval are returned.
There are usually three or four interval timers available: the $which
can be "ITIMER_REAL", "ITIMER_VIRTUAL", "ITIMER_PROF", or
"ITIMER_REALPROF". Note that which ones are available depends: true
UNIX platforms usually have the first three, but (for example) Win32
and Cygwin have only "ITIMER_REAL", and only Solaris seems to have
"ITIMER_REALPROF" (which is used to profile multithreaded programs).
"ITIMER_REAL" results in "alarm()"-like behavior. Time is counted in
real time; that is, wallclock time. "SIGALRM" is delivered when the
timer expires.
"ITIMER_VIRTUAL" counts time in (process) virtual time; that is, only
when the process is running. In multiprocessor/user/CPU systems this
may be more or less than real or wallclock time. (This time is also
known as the user time.) "SIGVTALRM" is delivered when the timer
expires.
"ITIMER_PROF" counts time when either the process virtual time or when
the operating system is running on behalf of the process (such as I/O).
(This time is also known as the system time.) (The sum of user time
and system time is known as the CPU time.) "SIGPROF" is delivered when
the timer expires. "SIGPROF" can interrupt system calls.
The semantics of interval timers for multithreaded programs are
system-specific, and some systems may support additional interval
timers. See your "setitimer()" documentation.
getitimer ( $which )
Return the remaining time in the interval timer specified by $which.
In scalar context, the remaining time is returned.
In list context, both the remaining time and the interval are returned.
The interval is always what you put in using "setitimer()".
EXAMPLES
use Time::HiRes qw(usleep ualarm gettimeofday tv_interval);
$microseconds = 750_000;
usleep $microseconds;
# signal alarm in 2.5s & every .1s thereafter
ualarm 2_500_000, 100_000;
# get seconds and microseconds since the epoch
($s, $usec) = gettimeofday;
# measure elapsed time
# (could also do by subtracting 2 gettimeofday return values)
$t0 = [gettimeofday];
# do bunch of stuff here
$t1 = [gettimeofday];
# do more stuff here
$t0_t1 = tv_interval $t0, $t1;
$elapsed = tv_interval ($t0, [gettimeofday]);
$elapsed = tv_interval ($t0); # equivalent code
#
# replacements for time, alarm and sleep that know about
# floating seconds
#
use Time::HiRes;
$now_fractions = Time::HiRes::time;
Time::HiRes::sleep (2.5);
Time::HiRes::alarm (10.6666666);
use Time::HiRes qw ( time alarm sleep );
$now_fractions = time;
sleep (2.5);
alarm (10.6666666);
# Arm an interval timer to go off first at 10 seconds and
# after that every 2.5 seconds, in process virtual time
use Time::HiRes qw ( setitimer ITIMER_VIRTUAL time );
$SIG{VTALRM} = sub { print time, "\n" };
setitimer(ITIMER_VIRTUAL, 10, 2.5);
C API
In addition to the perl API described above, a C API is available for
extension writers. The following C functions are available in the
modglobal hash:
name C prototype
--------------- ----------------------
Time::NVtime double (*)()
Time::U2time void (*)(UV ret[2])
Both functions return equivalent information (like "gettimeofday") but with
different representations. The names "NVtime" and "U2time" were selected
mainly because they are operating system independent. ("gettimeofday" is
Unix-centric, though some platforms like VMS have emulations for it.)
Here is an example of using "NVtime" from C:
double (*myNVtime)();
SV **svp = hv_fetch(PL_modglobal, "Time::NVtime", 12, 0);
if (!svp) croak("Time::HiRes is required");
if (!SvIOK(*svp)) croak("Time::NVtime isn't a function pointer");
myNVtime = INT2PTR(double(*)(), SvIV(*svp));
printf("The current time is: %f\n", (*myNVtime)());
DIAGNOSTICS
negative time not invented yet
You tried to use a negative time argument.
internal error: useconds < 0 (unsigned ... signed ...)
Something went horribly wrong-- the number of microseconds that cannot
become negative just became negative. Maybe your compiler is broken?
CAVEATS
Notice that the core "time()" maybe rounding rather than truncating. What
this means is that the core "time()" may be reporting the time as one
second later than "gettimeofday()" and "Time::HiRes::time()".
AUTHORS
D. Wegscheid <wegscd@whirlpool.com> R. Schertler <roderick@argon.org> J.
Hietaniemi <jhi@iki.fi> G. Aas <gisle@aas.no>
COPYRIGHT AND LICENSE
Copyright (c) 1996-2002 Douglas E. Wegscheid. All rights reserved.
Copyright (c) 2002,2003 Jarkko Hietaniemi. All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
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