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Benchmark(3pm)	       Perl Programmers Reference Guide		Benchmark(3pm)

NAME
       Benchmark - benchmark running times of Perl code

SYNOPSIS
	   use Benchmark qw(:all) ;

	   timethis ($count, "code");

	   # Use Perl code in strings...
	   timethese($count, {
	       'Name1' => '...code1...',
	       'Name2' => '...code2...',
	   });

	   # ... or use subroutine references.
	   timethese($count, {
	       'Name1' => sub { ...code1... },
	       'Name2' => sub { ...code2... },
	   });

	   # cmpthese can be used both ways as well
	   cmpthese($count, {
	       'Name1' => '...code1...',
	       'Name2' => '...code2...',
	   });

	   cmpthese($count, {
	       'Name1' => sub { ...code1... },
	       'Name2' => sub { ...code2... },
	   });

	   # ...or in two stages
	   $results = timethese($count,
	       {
		   'Name1' => sub { ...code1... },
		   'Name2' => sub { ...code2... },
	       },
	       'none'
	   );
	   cmpthese( $results ) ;

	   $t = timeit($count, '...other code...')
	   print "$count loops of other code took:",timestr($t),"\n";

	   $t = countit($time, '...other code...')
	   $count = $t->iters ;
	   print "$count loops of other code took:",timestr($t),"\n";

	   # enable hires wallclock timing if possible
	   use Benchmark ':hireswallclock';

DESCRIPTION
       The Benchmark module encapsulates a number of routines to help you
       figure out how long it takes to execute some code.

       timethis - run a chunk of code several times

       timethese - run several chunks of code several times

       cmpthese - print results of timethese as a comparison chart

       timeit - run a chunk of code and see how long it goes

       countit - see how many times a chunk of code runs in a given time

   Methods
       new	 Returns the current time.   Example:

		     use Benchmark;
		     $t0 = Benchmark->new;
		     # ... your code here ...
		     $t1 = Benchmark->new;
		     $td = timediff($t1, $t0);
		     print "the code took:",timestr($td),"\n";

       debug	 Enables or disable debugging by setting the $Benchmark::Debug
		 flag:

		     Benchmark->debug(1);
		     $t = timeit(10, ' 5 ** $Global ');
		     Benchmark->debug(0);

       iters	 Returns the number of iterations.

   Standard Exports
       The following routines will be exported into your namespace if you use
       the Benchmark module:

       timeit(COUNT, CODE)
		 Arguments: COUNT is the number of times to run the loop, and
		 CODE is the code to run.  CODE may be either a code reference
		 or a string to be eval'd; either way it will be run in the
		 caller's package.

		 Returns: a Benchmark object.

       timethis ( COUNT, CODE, [ TITLE, [ STYLE ]] )
		 Time COUNT iterations of CODE. CODE may be a string to eval
		 or a code reference; either way the CODE will run in the
		 caller's package.  Results will be printed to STDOUT as TITLE
		 followed by the times.	 TITLE defaults to "timethis COUNT" if
		 none is provided. STYLE determines the format of the output,
		 as described for timestr() below.

		 The COUNT can be zero or negative: this means the minimum
		 number of CPU seconds to run.	A zero signifies the default
		 of 3 seconds.	For example to run at least for 10 seconds:

			 timethis(-10, $code)

		 or to run two pieces of code tests for at least 3 seconds:

			 timethese(0, { test1 => '...', test2 => '...'})

		 CPU seconds is, in UNIX terms, the user time plus the system
		 time of the process itself, as opposed to the real
		 (wallclock) time and the time spent by the child processes.
		 Less than 0.1 seconds is not accepted (-0.01 as the count,
		 for example, will cause a fatal runtime exception).

		 Note that the CPU seconds is the minimum time: CPU scheduling
		 and other operating system factors may complicate the attempt
		 so that a little bit more time is spent.  The benchmark
		 output will, however, also tell the number of $code
		 runs/second, which should be a more interesting number than
		 the actually spent seconds.

		 Returns a Benchmark object.

       timethese ( COUNT, CODEHASHREF, [ STYLE ] )
		 The CODEHASHREF is a reference to a hash containing names as
		 keys and either a string to eval or a code reference for each
		 value.	 For each (KEY, VALUE) pair in the CODEHASHREF, this
		 routine will call

			 timethis(COUNT, VALUE, KEY, STYLE)

		 The routines are called in string comparison order of KEY.

		 The COUNT can be zero or negative, see timethis().

		 Returns a hash reference of Benchmark objects, keyed by name.

       timediff ( T1, T2 )
		 Returns the difference between two Benchmark times as a
		 Benchmark object suitable for passing to timestr().

       timestr ( TIMEDIFF, [ STYLE, [ FORMAT ] ] )
		 Returns a string that formats the times in the TIMEDIFF
		 object in the requested STYLE. TIMEDIFF is expected to be a
		 Benchmark object similar to that returned by timediff().

		 STYLE can be any of 'all', 'none', 'noc', 'nop' or 'auto'.
		 'all' shows each of the 5 times available ('wallclock' time,
		 user time, system time, user time of children, and system
		 time of children). 'noc' shows all except the two children
		 times. 'nop' shows only wallclock and the two children times.
		 'auto' (the default) will act as 'all' unless the children
		 times are both zero, in which case it acts as 'noc'.  'none'
		 prevents output.

		 FORMAT is the printf(3)-style format specifier (without the
		 leading '%') to use to print the times. It defaults to
		 '5.2f'.

   Optional Exports
       The following routines will be exported into your namespace if you
       specifically ask that they be imported:

       clearcache ( COUNT )
		 Clear the cached time for COUNT rounds of the null loop.

       clearallcache ( )
		 Clear all cached times.

       cmpthese ( COUNT, CODEHASHREF, [ STYLE ] )
       cmpthese ( RESULTSHASHREF, [ STYLE ] )
		 Optionally calls timethese(), then outputs comparison chart.
		 This:

		     cmpthese( -1, { a => "++\$i", b => "\$i *= 2" } ) ;

		 outputs a chart like:

			    Rate    b	 a
		     b 2831802/s   -- -61%
		     a 7208959/s 155%	--

		 This chart is sorted from slowest to fastest, and shows the
		 percent speed difference between each pair of tests.

		 "cmpthese" can also be passed the data structure that
		 timethese() returns:

		     $results = timethese( -1, { a => "++\$i", b => "\$i *= 2" } ) ;
		     cmpthese( $results );

		 in case you want to see both sets of results.	If the first
		 argument is an unblessed hash reference, that is
		 RESULTSHASHREF; otherwise that is COUNT.

		 Returns a reference to an ARRAY of rows, each row is an ARRAY
		 of cells from the above chart, including labels. This:

		     my $rows = cmpthese( -1, { a => '++$i', b => '$i *= 2' }, "none" );

		 returns a data structure like:

		     [
			 [ '',	     'Rate',   'b',    'a' ],
			 [ 'b', '2885232/s',  '--', '-59%' ],
			 [ 'a', '7099126/s', '146%',  '--' ],
		     ]

		 NOTE: This result value differs from previous versions, which
		 returned the "timethese()" result structure.  If you want
		 that, just use the two statement "timethese"..."cmpthese"
		 idiom shown above.

		 Incidentally, note the variance in the result values between
		 the two examples; this is typical of benchmarking.  If this
		 were a real benchmark, you would probably want to run a lot
		 more iterations.

       countit(TIME, CODE)
		 Arguments: TIME is the minimum length of time to run CODE
		 for, and CODE is the code to run.  CODE may be either a code
		 reference or a string to be eval'd; either way it will be run
		 in the caller's package.

		 TIME is not negative.	countit() will run the loop many times
		 to calculate the speed of CODE before running it for TIME.
		 The actual time run for will usually be greater than TIME due
		 to system clock resolution, so it's best to look at the
		 number of iterations divided by the times that you are
		 concerned with, not just the iterations.

		 Returns: a Benchmark object.

       disablecache ( )
		 Disable caching of timings for the null loop. This will force
		 Benchmark to recalculate these timings for each new piece of
		 code timed.

       enablecache ( )
		 Enable caching of timings for the null loop. The time taken
		 for COUNT rounds of the null loop will be calculated only
		 once for each different COUNT used.

       timesum ( T1, T2 )
		 Returns the sum of two Benchmark times as a Benchmark object
		 suitable for passing to timestr().

   :hireswallclock
       If the Time::HiRes module has been installed, you can specify the
       special tag ":hireswallclock" for Benchmark (if Time::HiRes is not
       available, the tag will be silently ignored).  This tag will cause the
       wallclock time to be measured in microseconds, instead of integer
       seconds.	 Note though that the speed computations are still conducted
       in CPU time, not wallclock time.

NOTES
       The data is stored as a list of values from the time and times
       functions:

	     ($real, $user, $system, $children_user, $children_system, $iters)

       in seconds for the whole loop (not divided by the number of rounds).

       The timing is done using time(3) and times(3).

       Code is executed in the caller's package.

       The time of the null loop (a loop with the same number of rounds but
       empty loop body) is subtracted from the time of the real loop.

       The null loop times can be cached, the key being the number of rounds.
       The caching can be controlled using calls like these:

	   clearcache($key);
	   clearallcache();

	   disablecache();
	   enablecache();

       Caching is off by default, as it can (usually slightly) decrease
       accuracy and does not usually noticeably affect runtimes.

EXAMPLES
       For example,

	   use Benchmark qw( cmpthese ) ;
	   $x = 3;
	   cmpthese( -5, {
	       a => sub{$x*$x},
	       b => sub{$x**2},
	   } );

       outputs something like this:

	  Benchmark: running a, b, each for at least 5 CPU seconds...
		 Rate	 b    a
	  b 1559428/s	-- -62%
	  a 4152037/s 166%   --

       while

	   use Benchmark qw( timethese cmpthese ) ;
	   $x = 3;
	   $r = timethese( -5, {
	       a => sub{$x*$x},
	       b => sub{$x**2},
	   } );
	   cmpthese $r;

       outputs something like this:

	   Benchmark: running a, b, each for at least 5 CPU seconds...
		    a: 10 wallclock secs ( 5.14 usr +  0.13 sys =  5.27 CPU) @ 3835055.60/s (n=20210743)
		    b:	5 wallclock secs ( 5.41 usr +  0.00 sys =  5.41 CPU) @ 1574944.92/s (n=8520452)
		  Rate	  b    a
	   b 1574945/s	 -- -59%
	   a 3835056/s 144%   --

INHERITANCE
       Benchmark inherits from no other class, except of course for Exporter.

CAVEATS
       Comparing eval'd strings with code references will give you inaccurate
       results: a code reference will show a slightly slower execution time
       than the equivalent eval'd string.

       The real time timing is done using time(2) and the granularity is
       therefore only one second.

       Short tests may produce negative figures because perl can appear to
       take longer to execute the empty loop than a short test; try:

	   timethis(100,'1');

       The system time of the null loop might be slightly more than the system
       time of the loop with the actual code and therefore the difference
       might end up being < 0.

SEE ALSO
       Devel::NYTProf - a Perl code profiler

AUTHORS
       Jarkko Hietaniemi <jhi@iki.fi>, Tim Bunce <Tim.Bunce@ig.co.uk>

MODIFICATION HISTORY
       September 8th, 1994; by Tim Bunce.

       March 28th, 1997; by Hugo van der Sanden: added support for code
       references and the already documented 'debug' method; revamped
       documentation.

       April 04-07th, 1997: by Jarkko Hietaniemi, added the run-for-some-time
       functionality.

       September, 1999; by Barrie Slaymaker: math fixes and accuracy and
       efficiency tweaks.  Added cmpthese().  A result is now returned from
       timethese().  Exposed countit() (was runfor()).

       December, 2001; by Nicholas Clark: make timestr() recognise the style
       'none' and return an empty string. If cmpthese is calling timethese,
       make it pass the style in. (so that 'none' will suppress output). Make
       sub new dump its debugging output to STDERR, to be consistent with
       everything else.	 All bugs found while writing a regression test.

       September, 2002; by Jarkko Hietaniemi: add ':hireswallclock' special
       tag.

       February, 2004; by Chia-liang Kao: make cmpthese and timestr use time
       statistics for children instead of parent when the style is 'nop'.

       November, 2007; by Christophe Grosjean: make cmpthese and timestr
       compute time consistently with style argument, default is 'all' not
       'noc' any more.

perl v5.16.2			  2012-10-11			Benchmark(3pm)
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