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.
- •
- 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.
- •
- 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.
- •
- 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.
- •
- 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@itz.pp.sci.fi