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Stopwatch(3pm) User Contributed Perl Documentation Stopwatch(3pm)
NAME
Time::Stopwatch - Use tied scalars as timers
SYNOPSIS
use Time::Stopwatch;
tie my $timer, 'Time::Stopwatch';
do_something();
print "Did something in $timer seconds.\n";
my @times = map {
$timer = 0;
do_something_else();
$timer;
} 1 .. 5;
DESCRIPTION
The Time::Stopwatch module provides a convenient interface to timing functions through
tied scalars. From the point of view of the user, scalars tied to the module simply
increase their value by one every second.
Using the module should mostly be obvious from the synopsis. You can provide an initial
value for the timers either by assigning to them or by passing the value as a third
argument to tie().
If you have the module Time::HiRes installed, the timers created by Time::Stopwatch will
automatically count fractional seconds. Do not assume that the values of the timers are
always integers. You may test the constant "Time::Stopwatch::HIRES" to find out whether
high resolution timing is enabled.
A note on timing short intervals
Time::Stopwatch is primarily designed for timing moderately long intervals (i.e. several
seconds), where the overhead imposed by the tie() interface does not matter. With
Time::HiRes installed, it can nonetheless be used for even microsecond timing, provided
that appropriate care is taken.
o Explicitly initialize the timer by assignment. The first measurement taken before
resetting the timer will be a few microseconds longer due to the overhead of the tie()
call.
o Always subtract the overhead of the timing code. This is true in general even if
you're not using Time::Stopwatch. (High-level benchmarking tools like Benchmark.pm do
this automatically.) See the code example below.
o Take as many measurements as you can to minimize random errors. The
Statistics::Descriptive module may be useful for analyzing the data. This advice is
also true for all benchmarking.
o Remember that a benchmark measures the time take to run the benchmark. Any
generalizations to real applications may or may not be valid. If you want real world
data, profile the real code in real use.
The following sample code should give a relatively reasonable measurement of a the time
taken by a short operation:
use Time::HiRes; # high resolution timing required
use Time::Stopwatch;
use Statistics::Descriptive;
my $stat = Statistics::Descriptive::Sparse->new();
tie my $time, 'Time::Stopwatch'; # code timer
tie my $wait, 'Time::Stopwatch'; # loop timer
while ($wait < 60) { # run for one minute
my $diff = 0;
$time = 0; do_whatever(); $diff += $time;
$time = 0; $diff -= $time;
$stat->add_data($diff);
}
print("count: ", $stat->count(), " iterations\n",
"mean: ", $stat->mean(), " seconds\n",
"s.d.: ", $stat->standard_deviation(), " seconds\n");
Note that the above code includes the time of the subroutine call in the measurement.
BUGS
Since tied scalars do not (yet?) support atomic modification, use of operators like "$t++"
or "$t *= 2" on timers will cause them to lose the time it takes to fetch, modify and
store the value. I might be able to get around this by overloading the return value of
"FETCH", but I doubt if it's worth the trouble. Just don't do that.
There is no way to force low-resolution timing if Time::HiRes has been installed. I'm not
sure why anyone would want to, since int() will do just fine if you want whole seconds,
but still..
CHANGE LOG
1.00 (15 Mar 2001)
Explicitly localized $SIG{__DIE__} when testing for Time::HiRes availability. Added
"A note on timing short intervals" to the POD documentation. Bumped version to 1, no
longer beta.
0.03 (27 Feb 2001)
Modified tests to give more information, reduced subsecond accuracy test to 1/10
seconds to allow for inaccurate select() implementations. Tweaked synopsis and
README.
SEE ALSO
Time::HiRes, "tie" in perlfunc
For a higher-level approach to timing, try (among others) the modules Time::SoFar,
Devel::Timer, or Benchmark. Also see the profiling modules Devel::DProf, Devel::SmallProf
and Devel::OpProf.
AUTHORS
Copyright 2000-2001, Ilmari Karonen. All rights reserved.
This library is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
Address bug reports and comments to: perl AT itz.fi
perl v5.32.0 2021-01-06 Stopwatch(3pm)
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On Apache
Under GNU General Public License
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