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.
";

	   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
",
		 "mean:  ", $stat->mean(), " seconds
",
		 "s.d.:  ", $stat->standard_deviation(), " seconds
");

       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

perl v5.12.3							    2001-04-15							    Stopwatch(3pm)