[perl5.git] / pod / modpods / Benchmark.pod

=head1 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

=head1 SYNOPSIS

    timethis ($count, "code");

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

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

=head1 DESCRIPTION

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

=head2 Methods

=over 10

=item new

Returns the current time.   Example:

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

=item debug

Enables or disable debugging by setting the C<$Benchmark::Debug> flag:

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

=back

=head2 Standard Exports

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

=over 10

=item timeit(COUNT, CODE)

Arguments: COUNT is the number of time to run the loop, and 
the second is the code to run.  CODE may be a string containing the code,
a reference to the function to run, or a reference to a hash containing 
keys which are names and values which are more CODE specs.

Side-effects: prints out noise to standard out.

Returns: a Benchmark object.  

=item timethis

=item timethese

=item timediff

=item timestr

=back

=head2 Optional Exports

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

=over 10

clearcache

clearallcache

disablecache

enablecache

=back

=head1 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.

Enable debugging by:  

    $Benchmark::debug = 1;

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();

=head1 INHERITANCE

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

=head1 CAVEATS

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.

More documentation is needed :-( especially for styles and formats.

=head1 AUTHORS

Jarkko Hietaniemi <Jarkko.Hietaniemi@hut.fi>,
Tim Bunce <Tim.Bunce@ig.co.uk>

=head1 MODIFICATION HISTORY

September 8th, 1994; by Tim Bunce.
Commit	Line	Data
a0d0e21e LW	1	=head1 NAME
	2
	3	Benchmark - benchmark running times of code
	4
	5	timethis - run a chunk of code several times
	6
	7	timethese - run several chunks of code several times
	8
	9	timeit - run a chunk of code and see how long it goes
	10
748a9306	11	=head1 SYNOPSIS
a0d0e21e LW	12
	13	timethis ($count, "code");
	14
	15	timethese($count, {
	16	'Name1' => '...code1...',
	17	'Name2' => '...code2...',
	18	});
	19
	20	$t = timeit($count, '...other code...')
	21	print "$count loops of other code took:",timestr($t),"\n";
	22
	23	=head1 DESCRIPTION
	24
	25	The Benchmark module encapsulates a number of routines to help you
	26	figure out how long it takes to execute some code.
	27
	28	=head2 Methods
	29
	30	=over 10
	31
	32	=item new
	33
	34	Returns the current time. Example:
	35
	36	use Benchmark;
	37	$t0 = new Benchmark;
	38	# ... your code here ...
	39	$t1 = new Benchmark;
	40	$td = timediff($t1, $t0);
	41	print "the code took:",timestr($dt),"\n";
	42
	43	=item debug
	44
	45	Enables or disable debugging by setting the C<$Benchmark::Debug> flag:
	46
	47	debug Benchmark 1;
	48	$t = timeit(10, ' 5 ** $Global ');
	49	debug Benchmark 0;
	50
	51	=back
	52
	53	=head2 Standard Exports
	54
	55	The following routines will be exported into your namespace
	56	if you use the Benchmark module:
	57
	58	=over 10
	59
	60	=item timeit(COUNT, CODE)
	61
	62	Arguments: COUNT is the number of time to run the loop, and
	63	the second is the code to run. CODE may be a string containing the code,
	64	a reference to the function to run, or a reference to a hash containing
	65	keys which are names and values which are more CODE specs.
	66
	67	Side-effects: prints out noise to standard out.
	68
	69	Returns: a Benchmark object.
	70
	71	=item timethis
	72
	73	=item timethese
	74
	75	=item timediff
76
77	=item timestr
78
79	=back
80
81	=head2 Optional Exports
82
83	The following routines will be exported into your namespace
84	if you specifically ask that they be imported:
85
86	=over 10
87
88	clearcache
89
90	clearallcache
91
92	disablecache
93
94	enablecache
95
96	=back
97
98	=head1 NOTES
99
100	The data is stored as a list of values from the time and times
101	functions:
102
103	($real, $user, $system, $children_user, $children_system)
104
105	in seconds for the whole loop (not divided by the number of rounds).
106
107	The timing is done using time(3) and times(3).
108
109	Code is executed in the caller's package.
110
111	Enable debugging by:
112
113	$Benchmark::debug = 1;
114
115	The time of the null loop (a loop with the same
116	number of rounds but empty loop body) is subtracted
117	from the time of the real loop.
118
119	The null loop times are cached, the key being the
120	number of rounds. The caching can be controlled using
121	calls like these:
122
123	clearcache($key);
124	clearallcache();
125
126	disablecache();
127	enablecache();
128
129	=head1 INHERITANCE
130
131	Benchmark inherits from no other class, except of course
132	for Exporter.
133
134	=head1 CAVEATS
135
136	The real time timing is done using time(2) and
137	the granularity is therefore only one second.
138
139	Short tests may produce negative figures because perl
140	can appear to take longer to execute the empty loop
141	than a short test; try:
142
143	timethis(100,'1');
144
145	The system time of the null loop might be slightly
146	more than the system time of the loop with the actual
147	code and therefore the difference might end up being < 0.
148
149	More documentation is needed :-( especially for styles and formats.
150
151	=head1 AUTHORS
152
153	Jarkko Hietaniemi <Jarkko.Hietaniemi@hut.fi>,
154	Tim Bunce <Tim.Bunce@ig.co.uk>
155
156	=head1 MODIFICATION HISTORY
157
158	September 8th, 1994; by Tim Bunce.
159