Devel-FindRef/FindRef.pm

package Devel::FindRef;

no warnings; # I hate warning nazis
use strict;

use XSLoader;
use Scalar::Util;

BEGIN {
   our $VERSION = '1.4';
   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 - in the lexical C<$closure_var> (0x8abcc8), which is inside an instantiated
closure, which in turn is used quite a bit.

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

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

=item - in 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 - in 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) {
               $buf .= "$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:	1.19
Committed:	Mon Dec 1 13:47:09 2008 UTC (15 years, 5 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_4
Changes since 1.18:	+58 -31 lines
Log Message:	1.4
#	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	1.19	our $VERSION = '1.4';
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	1.19	=item - in the lexical C<$closure_var> (0x8abcc8), which is inside an instantiated
94			closure, which in turn is used quite a bit.
95	root	1.1
96	root	1.19	=item - in the package-level lexical C<$global_my>.
97	root	1.1
98	root	1.19	=item - in the global package variable named C<$Test::var>.
99	root	1.1
100			=item - in the hash element C<ukukey2>, in the hash in the my variable
101	root	1.19	C<$testsub_local> in the sub C<Test::testsub> and also in the hash
102			C<$referenced by Test::hash2>.
103
104			=item - in the hash element with key C<ukukey> in the hash stored in
105			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	1.19	$buf .= "$indent" . (@about > 1 ? "+- " : "") . $about->[0];
157	root	1.1	if (@$about > 1) {
158	root	1.14	if ($seen{ref2ptr $about->[1]}++) {
159	root	1.18	$buf .= " " . (_f $about->[1]) . ", which was seen before.\n";
160	root	1.11	} else {
161	root	1.18	$buf .= " " . (_f $about->[1]) . ", which is\n";
162	root	1.12	$track->(\$about->[1], $depth - 1, $about == $about[-1] ? "$indent " : "$indent\| ");
163	root	1.11	}
164	root	1.1	} else {
165			$buf .= ".\n";
166			}
167			}
168			} else {
169	root	1.12	$buf .= "$indent not found anywhere I looked :(\n";
170	root	1.1	}
171			} else {
172	root	1.12	$buf .= "$indent not referenced within the search depth.\n";
173	root	1.1	}
174			};
175
176	root	1.18	$buf .= (_f $ref) . " is\n";
177	root	1.12	$track->(\$ref, $depth \|\| $ENV{PERL_DEVEL_FINDREF_DEPTH} \|\| 10, "");
178	root	1.1	$buf
179			}
180
181			=item @references = Devel::FindRef::find $ref
182
183			Return arrayrefs that contain [$message, $ref] pairs. The message
184			describes what kind of reference was found and the C<$ref> is the
185	root	1.9	reference itself, which can be omitted if C<find> decided to end the
186			search. The returned references are all weak references.
187	root	1.1
188			The C<track> function uses this to find references to the value you are
189			interested in and recurses on the returned references.
190
191			=cut
192
193			sub find($) {
194			my ($about, $excl) = &find_;
195	root	1.6	my %excl = map +($_ => undef), @$excl;
196	root	1.14	grep !exists $excl{ref2ptr $_->[1]}, @$about
197	root	1.1	}
198
199	root	1.7	=item $ref = Devel::FindRef::ptr2ref $integer
200	root	1.1
201			Sometimes you know (from debugging output) the address of a perl scalar
202	root	1.7	you are interested in (e.g. C<HASH(0x176ff70)>). This function can be used
203			to turn the address into a reference to that scalar. It is quite safe to
204			call on valid addresses, but extremely dangerous to call on invalid ones.
205
206			# we know that HASH(0x176ff70) exists, so turn it into a hashref:
207			my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
208	root	1.1
209	root	1.14	=item $ref = Devel::FindRef::ref2ptr $reference
210
211			The opposite of C<ptr2ref>, above: returns the internal address of the
212			value pointed to by the passed reference. I<No checks whatsoever will be
213			done>, so don't use this.
214
215	root	1.1	=back
216
217	root	1.12	=head1 ENVIRONMENT VARIABLES
218
219			You can set the environment variable C<PERL_DEVEL_FINDREF_DEPTH> to an
220			integer to override the default depth in C<track>. If a call explicitly
221			specified a depth it is not overridden.
222
223	root	1.1	=head1 AUTHOR
224
225			Marc Lehmann <pcg@goof.com>.
226
227			=head1 COPYRIGHT AND LICENSE
228
229	root	1.17	Copyright (C) 2007, 2008 by Marc Lehmann.
230	root	1.1
231			This library is free software; you can redistribute it and/or modify
232			it under the same terms as Perl itself, either Perl version 5.8.8 or,
233			at your option, any later version of Perl 5 you may have available.
234
235			=cut
236
237			1
238