Devel-FindRef/FindRef.pm

package Devel::FindRef;

use common::sense;

use XSLoader;
use Scalar::Util;

BEGIN {
   our $VERSION = '1.422';
   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
   |  the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
   |     +- the closure created at tst:18.
   |     +- referenced by REF(0x7d3c58) [refcount 1], which is
   |     |  the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
   |     |     +- the containing scope for CODE(0x8ab430) [refcount 3], which is
   |     |     |  the global &Test::testsub.
   |     |     +- the main body of the program.
   |     +- the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
   +- referenced by REF(0x7cc7c8) [refcount 1], which is
   |  the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
   +- the global $Test::var.
   +- referenced by REF(0x7cc558) [refcount 1], which is
   |  the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
   |     +- referenced by REF(0x8abad0) [refcount 1], which is
   |     |  the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
   |     +- referenced by REF(0x8ab4f0) [refcount 1], which is
   |        the global $Test::global_hashref.
   +- referenced by REF(0x7ae518) [refcount 1], which is
   |  the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
   |     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 $ptr = 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:	1.27
Committed:	Thu Apr 5 05:11:14 2012 UTC (12 years, 1 month ago) by root
Branch:	MAIN
Changes since 1.26:	+1 -1 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	package Devel::FindRef;
2
3	root	1.25	use common::sense;
4	root	1.1
5			use XSLoader;
6	root	1.9	use Scalar::Util;
7	root	1.1
8			BEGIN {
9	root	1.25	our $VERSION = '1.422';
10	root	1.1	XSLoader::load __PACKAGE__, $VERSION;
11			}
12
13			=head1 NAME
14
15	root	1.13	Devel::FindRef - where is that reference to my variable hiding?
16	root	1.1
17			=head1 SYNOPSIS
18
19			use Devel::FindRef;
20
21	root	1.16	print Devel::FindRef::track \$some_variable;
22
23	root	1.1	=head1 DESCRIPTION
24
25			Tracking down reference problems (e.g. you expect some object to be
26	root	1.4	destroyed, but there are still references to it that keep it alive) can be
27			very hard. Fortunately, perl keeps track of all its values, so tracking
28			references "backwards" is usually possible.
29	root	1.1
30	root	1.4	The C<track> function can help track down some of those references back to
31	root	1.1	the variables containing them.
32
33			For example, for this fragment:
34
35			package Test;
36	root	1.19
37			use Devel::FindRef;
38			use Scalar::Util;
39	root	1.1
40			our $var = "hi\n";
41	root	1.19	my $global_my = \$var;
42			our %global_hash = (ukukey => \$var);
43			our $global_hashref = { ukukey2 => \$var };
44	root	1.1
45			sub testsub {
46	root	1.19	my $testsub_local = $global_hashref;
47	root	1.1	print Devel::FindRef::track \$var;
48			}
49	root	1.19
50
51			my $closure = sub {
52			my $closure_var = \$_[0];
53			Scalar::Util::weaken (my $weak_ref = \$var);
54			testsub;
55			};
56
57			$closure->($var);
58	root	1.1
59	root	1.4	The output is as follows (or similar to this, in case I forget to update
60	root	1.3	the manpage after some changes):
61	root	1.1
62	root	1.19	SCALAR(0x7cc888) [refcount 6] is
63			+- referenced by REF(0x8abcc8) [refcount 1], which is
64	root	1.26	\| the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
65	root	1.19	\| +- the closure created at tst:18.
66			\| +- referenced by REF(0x7d3c58) [refcount 1], which is
67	root	1.26	\| \| the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
68	root	1.19	\| \| +- the containing scope for CODE(0x8ab430) [refcount 3], which is
69	root	1.26	\| \| \| the global &Test::testsub.
70	root	1.19	\| \| +- the main body of the program.
71	root	1.26	\| +- the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
72	root	1.19	+- referenced by REF(0x7cc7c8) [refcount 1], which is
73	root	1.26	\| the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
74			+- the global $Test::var.
75	root	1.19	+- referenced by REF(0x7cc558) [refcount 1], which is
76	root	1.26	\| the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
77	root	1.19	\| +- referenced by REF(0x8abad0) [refcount 1], which is
78	root	1.26	\| \| the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
79	root	1.19	\| +- referenced by REF(0x8ab4f0) [refcount 1], which is
80	root	1.26	\| the global $Test::global_hashref.
81	root	1.19	+- referenced by REF(0x7ae518) [refcount 1], which is
82	root	1.26	\| the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
83			\| the global %Test::global_hash.
84	root	1.19	+- referenced by REF(0x7ae2f0) [refcount 1], which is
85			a temporary on the stack.
86	root	1.1
87	root	1.4	It is a bit convoluted to read, but basically it says that the value
88	root	1.19	stored in C<$var> is referenced by:
89	root	1.1
90			=over 4
91
92	root	1.20	=item - the lexical C<$closure_var> (0x8abcc8), which is inside an instantiated
93	root	1.19	closure, which in turn is used quite a bit.
94	root	1.1
95	root	1.20	=item - the package-level lexical C<$global_my>.
96	root	1.1
97	root	1.20	=item - the global package variable named C<$Test::var>.
98	root	1.1
99	root	1.20	=item - the hash element C<ukukey2>, in the hash in the my variable
100	root	1.19	C<$testsub_local> in the sub C<Test::testsub> and also in the hash
101			C<$referenced by Test::hash2>.
102
103	root	1.20	=item - the hash element with key C<ukukey> in the hash stored in
104	root	1.19	C<%Test::hash>.
105
106			=item - some anonymous mortalised reference on the stack (which is caused
107			by calling C<track> with the expression C<\$var>, which creates the
108			reference).
109	root	1.1
110	root	1.6	=back
111
112	root	1.19	And all these account for six reference counts.
113
114
115	root	1.1	=head1 EXPORTS
116
117			None.
118
119			=head1 FUNCTIONS
120
121			=over 4
122
123			=item $string = Devel::FindRef::track $ref[, $depth]
124
125			Track the perl value pointed to by C<$ref> up to a depth of C<$depth> and
126			return a descriptive string. C<$ref> can point at any perl value, be it
127			anonymous sub, hash, array, scalar etc.
128
129			This is the function you most often use.
130
131			=cut
132
133			sub find($);
134
135	root	1.18	sub _f($) {
136			"$_[0] [refcount " . (_refcnt $_[0]) . "]"
137			}
138
139	root	1.1	sub track {
140	root	1.9	my ($ref, $depth) = @_;
141			@_ = ();
142
143	root	1.1	my $buf = "";
144	root	1.11	my %seen;
145	root	1.9
146			Scalar::Util::weaken $ref;
147	root	1.1
148			my $track; $track = sub {
149	root	1.9	my ($refref, $depth, $indent) = @_;
150	root	1.1
151			if ($depth) {
152	root	1.9	my (@about) = find $$refref;
153	root	1.1	if (@about) {
154			for my $about (@about) {
155	root	1.21	$about->[0] =~ s/([^\x20-\x7e])/sprintf "\\{%02x}", ord $1/ge;
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	1.21
178	root	1.12	$track->(\$ref, $depth \|\| $ENV{PERL_DEVEL_FINDREF_DEPTH} \|\| 10, "");
179	root	1.1	$buf
180			}
181
182			=item @references = Devel::FindRef::find $ref
183
184			Return arrayrefs that contain [$message, $ref] pairs. The message
185			describes what kind of reference was found and the C<$ref> is the
186	root	1.9	reference itself, which can be omitted if C<find> decided to end the
187			search. The returned references are all weak references.
188	root	1.1
189			The C<track> function uses this to find references to the value you are
190			interested in and recurses on the returned references.
191
192			=cut
193
194			sub find($) {
195			my ($about, $excl) = &find_;
196	root	1.6	my %excl = map +($_ => undef), @$excl;
197	root	1.21	grep !($#$_ && exists $excl{ref2ptr $_->[1]}), @$about
198	root	1.1	}
199
200	root	1.7	=item $ref = Devel::FindRef::ptr2ref $integer
201	root	1.1
202			Sometimes you know (from debugging output) the address of a perl scalar
203	root	1.7	you are interested in (e.g. C<HASH(0x176ff70)>). This function can be used
204			to turn the address into a reference to that scalar. It is quite safe to
205			call on valid addresses, but extremely dangerous to call on invalid ones.
206
207			# we know that HASH(0x176ff70) exists, so turn it into a hashref:
208			my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
209	root	1.1
210	root	1.27	=item $ptr = Devel::FindRef::ref2ptr $reference
211	root	1.14
212			The opposite of C<ptr2ref>, above: returns the internal address of the
213			value pointed to by the passed reference. I<No checks whatsoever will be
214			done>, so don't use this.
215
216	root	1.1	=back
217
218	root	1.12	=head1 ENVIRONMENT VARIABLES
219
220			You can set the environment variable C<PERL_DEVEL_FINDREF_DEPTH> to an
221			integer to override the default depth in C<track>. If a call explicitly
222			specified a depth it is not overridden.
223
224	root	1.1	=head1 AUTHOR
225
226			Marc Lehmann <pcg@goof.com>.
227
228			=head1 COPYRIGHT AND LICENSE
229
230	root	1.17	Copyright (C) 2007, 2008 by Marc Lehmann.
231	root	1.1
232			This library is free software; you can redistribute it and/or modify
233			it under the same terms as Perl itself, either Perl version 5.8.8 or,
234			at your option, any later version of Perl 5 you may have available.
235
236			=cut
237
238			1
239