Devel-FindRef/FindRef.pm

package Devel::FindRef;

no warnings; # I hate warning nazis
use strict;

use XSLoader;
use Scalar::Util;

BEGIN {
   our $VERSION = '1.421';
   XSLoader::load __PACKAGE__, $VERSION;
}

=head1 NAME

Devel::FindRef - where is that reference to my variable hiding?

=head1 SYNOPSIS

  use Devel::FindRef;

  print Devel::FindRef::track \$some_variable;

=head1 DESCRIPTION

Tracking down reference problems (e.g. you expect some object to be
destroyed, but there are still references to it that keep it alive) can be
very hard. Fortunately, perl keeps track of all its values, so tracking
references "backwards" is usually possible.

The C<track> function can help track down some of those references back to
the variables containing them.

For example, for this fragment:

   package Test;           

   use Devel::FindRef;
   use Scalar::Util;
                         
   our $var = "hi\n";
   my $global_my = \$var;
   our %global_hash = (ukukey => \$var);
   our $global_hashref = { ukukey2 => \$var };
                           
   sub testsub {             
      my $testsub_local = $global_hashref;
      print Devel::FindRef::track \$var;
   }                             


   my $closure = sub {
      my $closure_var = \$_[0];
      Scalar::Util::weaken (my $weak_ref = \$var);
      testsub;
   };

   $closure->($var);

The output is as follows (or similar to this, in case I forget to update
the manpage after some changes):

   SCALAR(0x7cc888) [refcount 6] is
   +- referenced by REF(0x8abcc8) [refcount 1], which is
   |  in the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
   |     +- the closure created at tst:18.
   |     +- referenced by REF(0x7d3c58) [refcount 1], which is
   |     |  in the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
   |     |     +- the containing scope for CODE(0x8ab430) [refcount 3], which is
   |     |     |  in the global &Test::testsub.
   |     |     +- the main body of the program.
   |     +- in the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
   +- referenced by REF(0x7cc7c8) [refcount 1], which is
   |  in the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
   +- in the global $Test::var.
   +- referenced by REF(0x7cc558) [refcount 1], which is
   |  in the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
   |     +- referenced by REF(0x8abad0) [refcount 1], which is
   |     |  in the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
   |     +- referenced by REF(0x8ab4f0) [refcount 1], which is
   |        in the global $Test::global_hashref.
   +- referenced by REF(0x7ae518) [refcount 1], which is
   |  in the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
   |     in the global %Test::global_hash.
   +- referenced by REF(0x7ae2f0) [refcount 1], which is
      a temporary on the stack.

It is a bit convoluted to read, but basically it says that the value
stored in C<$var> is referenced by:

=over 4

=item - the lexical C<$closure_var> (0x8abcc8), which is inside an instantiated
closure, which in turn is used quite a bit.

=item - the package-level lexical C<$global_my>.

=item - the global package variable named C<$Test::var>.

=item - the hash element C<ukukey2>, in the hash in the my variable
C<$testsub_local> in the sub C<Test::testsub> and also in the hash
C<$referenced by Test::hash2>.

=item - the hash element with key C<ukukey> in the hash stored in
C<%Test::hash>.

=item - some anonymous mortalised reference on the stack (which is caused
by calling C<track> with the expression C<\$var>, which creates the
reference).

=back

And all these account for six reference counts.


=head1 EXPORTS

None.

=head1 FUNCTIONS

=over 4

=item $string = Devel::FindRef::track $ref[, $depth]

Track the perl value pointed to by C<$ref> up to a depth of C<$depth> and
return a descriptive string. C<$ref> can point at any perl value, be it
anonymous sub, hash, array, scalar etc.

This is the function you most often use.

=cut

sub find($);

sub _f($) {
   "$_[0] [refcount " . (_refcnt $_[0]) . "]"
}

sub track {
   my ($ref, $depth) = @_;
   @_ = ();

   my $buf = "";
   my %seen;

   Scalar::Util::weaken $ref;

   my $track; $track = sub {
      my ($refref, $depth, $indent) = @_;

      if ($depth) {
         my (@about) = find $$refref;
         if (@about) {
            for my $about (@about) {
               $about->[0] =~ s/([^\x20-\x7e])/sprintf "\\{%02x}", ord $1/ge;
               $buf .= "$indent" . (@about > 1 ? "+- " : "") . $about->[0];
               if (@$about > 1) {
                  if ($seen{ref2ptr $about->[1]}++) {
                     $buf .= " " . (_f $about->[1]) . ", which was seen before.\n";
                  } else {
                     $buf .= " " . (_f $about->[1]) . ", which is\n";
                     $track->(\$about->[1], $depth - 1, $about == $about[-1] ? "$indent   " : "$indent|  ");
                  }
               } else {
                  $buf .= ".\n";
               }
            }
         } else {
            $buf .= "$indent   not found anywhere I looked :(\n";
         }
      } else {
         $buf .= "$indent   not referenced within the search depth.\n";
      }
   };

   $buf .= (_f $ref) . " is\n";

   $track->(\$ref, $depth || $ENV{PERL_DEVEL_FINDREF_DEPTH} || 10, "");
   $buf
}

=item @references = Devel::FindRef::find $ref

Return arrayrefs that contain [$message, $ref] pairs. The message
describes what kind of reference was found and the C<$ref> is the
reference itself, which can be omitted if C<find> decided to end the
search. The returned references are all weak references.

The C<track> function uses this to find references to the value you are
interested in and recurses on the returned references.

=cut

sub find($) {
   my ($about, $excl) = &find_;
   my %excl = map +($_ => undef), @$excl;
   grep !($#$_ && exists $excl{ref2ptr $_->[1]}), @$about
}

=item $ref = Devel::FindRef::ptr2ref $integer

Sometimes you know (from debugging output) the address of a perl scalar
you are interested in (e.g. C<HASH(0x176ff70)>). This function can be used
to turn the address into a reference to that scalar. It is quite safe to
call on valid addresses, but extremely dangerous to call on invalid ones.

   # we know that HASH(0x176ff70) exists, so turn it into a hashref:
   my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;

=item $ref = Devel::FindRef::ref2ptr $reference

The opposite of C<ptr2ref>, above: returns the internal address of the
value pointed to by the passed reference. I<No checks whatsoever will be
done>, so don't use this.

=back

=head1 ENVIRONMENT VARIABLES

You can set the environment variable C<PERL_DEVEL_FINDREF_DEPTH> to an
integer to override the default depth in C<track>. If a call explicitly
specified a depth it is not overridden.

=head1 AUTHOR

Marc Lehmann <pcg@goof.com>.

=head1 COPYRIGHT AND LICENSE

Copyright (C) 2007, 2008 by Marc Lehmann.

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.8.8 or,
at your option, any later version of Perl 5 you may have available.

=cut

1

Revision:	1.24
Committed:	Fri Aug 28 20:30:07 2009 UTC (14 years, 8 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_421
Changes since 1.23:	+1 -1 lines
Log Message:	1.421
#	User	Rev	Content
1	root	1.1	package Devel::FindRef;
2
3	root	1.15	no warnings; # I hate warning nazis
4	root	1.1	use strict;
5
6			use XSLoader;
7	root	1.9	use Scalar::Util;
8	root	1.1
9			BEGIN {
10	root	1.24	our $VERSION = '1.421';
11	root	1.1	XSLoader::load __PACKAGE__, $VERSION;
12			}
13
14			=head1 NAME
15
16	root	1.13	Devel::FindRef - where is that reference to my variable hiding?
17	root	1.1
18			=head1 SYNOPSIS
19
20			use Devel::FindRef;
21
22	root	1.16	print Devel::FindRef::track \$some_variable;
23
24	root	1.1	=head1 DESCRIPTION
25
26			Tracking down reference problems (e.g. you expect some object to be
27	root	1.4	destroyed, but there are still references to it that keep it alive) can be
28			very hard. Fortunately, perl keeps track of all its values, so tracking
29			references "backwards" is usually possible.
30	root	1.1
31	root	1.4	The C<track> function can help track down some of those references back to
32	root	1.1	the variables containing them.
33
34			For example, for this fragment:
35
36			package Test;
37	root	1.19
38			use Devel::FindRef;
39			use Scalar::Util;
40	root	1.1
41			our $var = "hi\n";
42	root	1.19	my $global_my = \$var;
43			our %global_hash = (ukukey => \$var);
44			our $global_hashref = { ukukey2 => \$var };
45	root	1.1
46			sub testsub {
47	root	1.19	my $testsub_local = $global_hashref;
48	root	1.1	print Devel::FindRef::track \$var;
49			}
50	root	1.19
51
52			my $closure = sub {
53			my $closure_var = \$_[0];
54			Scalar::Util::weaken (my $weak_ref = \$var);
55			testsub;
56			};
57
58			$closure->($var);
59	root	1.1
60	root	1.4	The output is as follows (or similar to this, in case I forget to update
61	root	1.3	the manpage after some changes):
62	root	1.1
63	root	1.19	SCALAR(0x7cc888) [refcount 6] is
64			+- referenced by REF(0x8abcc8) [refcount 1], which is
65			\| in the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
66			\| +- the closure created at tst:18.
67			\| +- referenced by REF(0x7d3c58) [refcount 1], which is
68			\| \| in the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
69			\| \| +- the containing scope for CODE(0x8ab430) [refcount 3], which is
70			\| \| \| in the global &Test::testsub.
71			\| \| +- the main body of the program.
72			\| +- in the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
73			+- referenced by REF(0x7cc7c8) [refcount 1], which is
74			\| in the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
75	root	1.13	+- in the global $Test::var.
76	root	1.19	+- referenced by REF(0x7cc558) [refcount 1], which is
77			\| in the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
78			\| +- referenced by REF(0x8abad0) [refcount 1], which is
79			\| \| in the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
80			\| +- referenced by REF(0x8ab4f0) [refcount 1], which is
81			\| in the global $Test::global_hashref.
82			+- referenced by REF(0x7ae518) [refcount 1], which is
83			\| in the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
84			\| in the global %Test::global_hash.
85			+- referenced by REF(0x7ae2f0) [refcount 1], which is
86			a temporary on the stack.
87	root	1.1
88	root	1.4	It is a bit convoluted to read, but basically it says that the value
89	root	1.19	stored in C<$var> is referenced by:
90	root	1.1
91			=over 4
92
93	root	1.20	=item - the lexical C<$closure_var> (0x8abcc8), which is inside an instantiated
94	root	1.19	closure, which in turn is used quite a bit.
95	root	1.1
96	root	1.20	=item - the package-level lexical C<$global_my>.
97	root	1.1
98	root	1.20	=item - the global package variable named C<$Test::var>.
99	root	1.1
100	root	1.20	=item - the hash element C<ukukey2>, in the hash in the my variable
101	root	1.19	C<$testsub_local> in the sub C<Test::testsub> and also in the hash
102			C<$referenced by Test::hash2>.
103
104	root	1.20	=item - the hash element with key C<ukukey> in the hash stored in
105	root	1.19	C<%Test::hash>.
106
107			=item - some anonymous mortalised reference on the stack (which is caused
108			by calling C<track> with the expression C<\$var>, which creates the
109			reference).
110	root	1.1
111	root	1.6	=back
112
113	root	1.19	And all these account for six reference counts.
114
115
116	root	1.1	=head1 EXPORTS
117
118			None.
119
120			=head1 FUNCTIONS
121
122			=over 4
123
124			=item $string = Devel::FindRef::track $ref[, $depth]
125
126			Track the perl value pointed to by C<$ref> up to a depth of C<$depth> and
127			return a descriptive string. C<$ref> can point at any perl value, be it
128			anonymous sub, hash, array, scalar etc.
129
130			This is the function you most often use.
131
132			=cut
133
134			sub find($);
135
136	root	1.18	sub _f($) {
137			"$_[0] [refcount " . (_refcnt $_[0]) . "]"
138			}
139
140	root	1.1	sub track {
141	root	1.9	my ($ref, $depth) = @_;
142			@_ = ();
143
144	root	1.1	my $buf = "";
145	root	1.11	my %seen;
146	root	1.9
147			Scalar::Util::weaken $ref;
148	root	1.1
149			my $track; $track = sub {
150	root	1.9	my ($refref, $depth, $indent) = @_;
151	root	1.1
152			if ($depth) {
153	root	1.9	my (@about) = find $$refref;
154	root	1.1	if (@about) {
155			for my $about (@about) {
156	root	1.21	$about->[0] =~ s/([^\x20-\x7e])/sprintf "\\{%02x}", ord $1/ge;
157	root	1.19	$buf .= "$indent" . (@about > 1 ? "+- " : "") . $about->[0];
158	root	1.1	if (@$about > 1) {
159	root	1.14	if ($seen{ref2ptr $about->[1]}++) {
160	root	1.18	$buf .= " " . (_f $about->[1]) . ", which was seen before.\n";
161	root	1.11	} else {
162	root	1.18	$buf .= " " . (_f $about->[1]) . ", which is\n";
163	root	1.12	$track->(\$about->[1], $depth - 1, $about == $about[-1] ? "$indent " : "$indent\| ");
164	root	1.11	}
165	root	1.1	} else {
166			$buf .= ".\n";
167			}
168			}
169			} else {
170	root	1.12	$buf .= "$indent not found anywhere I looked :(\n";
171	root	1.1	}
172			} else {
173	root	1.12	$buf .= "$indent not referenced within the search depth.\n";
174	root	1.1	}
175			};
176
177	root	1.18	$buf .= (_f $ref) . " is\n";
178	root	1.21
179	root	1.12	$track->(\$ref, $depth \|\| $ENV{PERL_DEVEL_FINDREF_DEPTH} \|\| 10, "");
180	root	1.1	$buf
181			}
182
183			=item @references = Devel::FindRef::find $ref
184
185			Return arrayrefs that contain [$message, $ref] pairs. The message
186			describes what kind of reference was found and the C<$ref> is the
187	root	1.9	reference itself, which can be omitted if C<find> decided to end the
188			search. The returned references are all weak references.
189	root	1.1
190			The C<track> function uses this to find references to the value you are
191			interested in and recurses on the returned references.
192
193			=cut
194
195			sub find($) {
196			my ($about, $excl) = &find_;
197	root	1.6	my %excl = map +($_ => undef), @$excl;
198	root	1.21	grep !($#$_ && exists $excl{ref2ptr $_->[1]}), @$about
199	root	1.1	}
200
201	root	1.7	=item $ref = Devel::FindRef::ptr2ref $integer
202	root	1.1
203			Sometimes you know (from debugging output) the address of a perl scalar
204	root	1.7	you are interested in (e.g. C<HASH(0x176ff70)>). This function can be used
205			to turn the address into a reference to that scalar. It is quite safe to
206			call on valid addresses, but extremely dangerous to call on invalid ones.
207
208			# we know that HASH(0x176ff70) exists, so turn it into a hashref:
209			my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
210	root	1.1
211	root	1.14	=item $ref = Devel::FindRef::ref2ptr $reference
212
213			The opposite of C<ptr2ref>, above: returns the internal address of the
214			value pointed to by the passed reference. I<No checks whatsoever will be
215			done>, so don't use this.
216
217	root	1.1	=back
218
219	root	1.12	=head1 ENVIRONMENT VARIABLES
220
221			You can set the environment variable C<PERL_DEVEL_FINDREF_DEPTH> to an
222			integer to override the default depth in C<track>. If a call explicitly
223			specified a depth it is not overridden.
224
225	root	1.1	=head1 AUTHOR
226
227			Marc Lehmann <pcg@goof.com>.
228
229			=head1 COPYRIGHT AND LICENSE
230
231	root	1.17	Copyright (C) 2007, 2008 by Marc Lehmann.
232	root	1.1
233			This library is free software; you can redistribute it and/or modify
234			it under the same terms as Perl itself, either Perl version 5.8.8 or,
235			at your option, any later version of Perl 5 you may have available.
236
237			=cut
238
239			1
240