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       Benchmark - benchmark running times of Perl code


           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... },
           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';


       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

       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:

                     $t = timeit(10, ' 5 ** $Global ');

       iters     Returns the number of iterations.

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

       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

                 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().

       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.


       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:



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


       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%   --


           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%   --


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


       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

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


       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.


       Devel::DProf - a Perl code profiler


       Jarkko Hietaniemi <>, Tim Bunce <>


       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

       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.