Benchmark

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



NAME
       Benchmark - benchmark running times of code

       timethis - run a chunk of code several times

       timethese - run several chunks of code several times

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

SYNOPSIS
           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... },
           });

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


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

       Methods

       new       Returns the current time.   Example:

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


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

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


       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().

       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', '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'.

                 FORMAT is the the printf(3) manpage-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.

       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.

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

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

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

           clearcache($key);
           clearallcache();

           disablecache();
           enablecache();


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 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.

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.



























3rd Berkeley Distribution    perl 5.005, patch 02                 Benchmark(3)