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[perl5.git] / ext / Devel-DProf / DProf.pm

use 5.006_001;

=head1 NAME

Devel::DProf - a Perl code profiler

=head1 SYNOPSIS

	perl -d:DProf test.pl

=head1 DESCRIPTION

The Devel::DProf package is a Perl code profiler.  This will collect
information on the execution time of a Perl script and of the subs in that
script.  This information can be used to determine which subroutines are
using the most time and which subroutines are being called most often.  This
information can also be used to create an execution graph of the script,
showing subroutine relationships.

To profile a Perl script run the perl interpreter with the B<-d> debugging
switch.  The profiler uses the debugging hooks.  So to profile script
F<test.pl> the following command should be used:

	perl -d:DProf test.pl

When the script terminates (or when the output buffer is filled) the
profiler will dump the profile information to a file called
F<tmon.out>.  A tool like I<dprofpp> can be used to interpret the
information which is in that profile.  The following command will
print the top 15 subroutines which used the most time:

	dprofpp

To print an execution graph of the subroutines in the script use the
following command:

	dprofpp -T

Consult L<dprofpp> for other options.

=head1 PROFILE FORMAT

The old profile is a text file which looks like this:

	#fOrTyTwO
	$hz=100;
	$XS_VERSION='DProf 19970606';
	# All values are given in HZ
	$rrun_utime=2; $rrun_stime=0; $rrun_rtime=7
	PART2
	+ 26 28 566822884 DynaLoader::import
	- 26 28 566822884 DynaLoader::import
	+ 27 28 566822885 main::bar
	- 27 28 566822886 main::bar
	+ 27 28 566822886 main::baz
	+ 27 28 566822887 main::bar
	- 27 28 566822888 main::bar
	[....]

The first line is the magic number.  The second line is the hertz value, or
clock ticks, of the machine where the profile was collected.  The third line
is the name and version identifier of the tool which created the profile.
The fourth line is a comment.  The fifth line contains three variables
holding the user time, system time, and realtime of the process while it was
being profiled.  The sixth line indicates the beginning of the sub
entry/exit profile section.

The columns in B<PART2> are:

	sub entry(+)/exit(-) mark
	app's user time at sub entry/exit mark, in ticks
	app's system time at sub entry/exit mark, in ticks
	app's realtime at sub entry/exit mark, in ticks
	fully-qualified sub name, when possible

With newer perls another format is used, which may look like this:

        #fOrTyTwO
        $hz=10000;
        $XS_VERSION='DProf 19971213';
        # All values are given in HZ
        $over_utime=5917; $over_stime=0; $over_rtime=5917;
        $over_tests=10000;
        $rrun_utime=1284; $rrun_stime=0; $rrun_rtime=1284;
        $total_marks=6;

        PART2
        @ 406 0 406
        & 2 main bar
        + 2
        @ 456 0 456
        - 2
        @ 1 0 1
        & 3 main baz
        + 3
        @ 141 0 141
        + 2
        @ 141 0 141
        - 2
        @ 1 0 1
        & 4 main foo
        + 4
        @ 142 0 142
        + & Devel::DProf::write
        @ 5 0 5
        - & Devel::DProf::write

(with high value of $ENV{PERL_DPROF_TICKS}).  

New C<$over_*> values show the measured overhead of making $over_tests
calls to the profiler These values are used by the profiler to
subtract the overhead from the runtimes.

Lines starting with C<@> mark the amount of time passed since the
previous C<@> line.  The numbers following the C<@> are integer tick
counts representing user, system, and real time.  Divide these numbers
by the $hz value in the header to get seconds.

Lines starting with C<&> map subroutine identifiers (an integer) to
subroutine packages and names.  These should only occur once per
subroutine.

Lines starting with C<+> or C<-> mark normal entering and exit of
subroutines.  The number following is a reference to a subroutine
identifier.

Lines starting with C<*> mark where subroutines are entered by C<goto
&subr>, but note that the return will still be marked as coming from
the original sub.  The sequence might look like this:

	+ 5
	* 6
	- 5

Lines starting with C</> is like C<-> but mark where subroutines are
exited by dying.  Example:

	+ 5
	+ 6
	/ 6
	/ 5

Finally you might find C<@> time stamp marks surrounded by C<+ &
Devel::DProf::write> and C<- & Devel::DProf::write> lines.  These 3
lines are outputted when printing of the mark above actually consumed
measurable time.

=head1 AUTOLOAD

When Devel::DProf finds a call to an C<&AUTOLOAD> subroutine it looks at the
C<$AUTOLOAD> variable to find the real name of the sub being called.  See
L<perlsub/"Autoloading">.

=head1 ENVIRONMENT

C<PERL_DPROF_BUFFER> sets size of output buffer in words.  Defaults to 2**14.

C<PERL_DPROF_TICKS> sets number of ticks per second on some systems where
a replacement for times() is used.  Defaults to the value of C<HZ> macro.

C<PERL_DPROF_OUT_FILE_NAME> sets the name of the output file.  If not set,
defaults to tmon.out.

=head1 BUGS

Builtin functions cannot be measured by Devel::DProf.

With a newer Perl DProf relies on the fact that the numeric slot of
$DB::sub contains an address of a subroutine.  Excessive manipulation
of this variable may overwrite this slot, as in

  $DB::sub = 'current_sub';
  ...
  $addr = $DB::sub + 0;

will set this numeric slot to numeric value of the string
C<current_sub>, i.e., to C<0>.  This will cause a segfault on the exit
from this subroutine.  Note that the first assignment above does not
change the numeric slot (it will I<mark> it as invalid, but will not
write over it).

Another problem is that if a subroutine exits using goto(LABEL),
last(LABEL) or next(LABEL) then perl may crash or Devel::DProf will die
with the error:

   panic: Devel::DProf inconsistent subroutine return

For example, this code will break under Devel::DProf:

   sub foo {
     last FOO;
   }
   FOO: {
     foo();
   }

A pattern like this is used by Test::More's skip() function, for
example.  See L<perldiag> for more details.

Mail bug reports and feature requests to the perl5-porters mailing list at
F<E<lt>perl5-porters@perl.orgE<gt>>.

=head1 SEE ALSO

L<perl>, L<dprofpp>, times(2)

=cut

# This sub is needed for calibration.
package Devel::DProf;

sub NONESUCH_noxs {
	return $Devel::DProf::VERSION;
}

package DB;

#
# As of perl5.003_20, &DB::sub stub is not needed (some versions
# even had problems if stub was redefined with XS version).
#

# disable DB single-stepping
BEGIN { $single = 0; }

# This sub is needed during startup.
sub DB { 
#	print "nonXS DBDB\n";
}

use XSLoader ();

$Devel::DProf::VERSION = '20080331.00';  # this version not authorized by
				         # Dean Roehrich. See "Changes" file.

XSLoader::load 'Devel::DProf', $Devel::DProf::VERSION;

1;