Devel-FindRef/FindRef.pm

package Devel::FindRef;

use common::sense;

use XSLoader;
use Scalar::Util;

BEGIN {
   our $VERSION = '1.43';
   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 likely want to use when tracking down
references.

=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 value you
are interested in (e.g. C<HASH(0x176ff70)>). This function can be used to
turn the address into a reference to that value. It is quite safe to call
on valid addresses, but extremely dangerous to call on invalid ones.  I<No
checks whatsoever will be done>, so don't use this unless you really know
the value is the address of a valid perl value.

   # 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. This function is safe to call on
anything, and returns the same value taht a normal reference would if used
in a numeric context.

=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
specifies a depth, it is not overridden.

=head1 AUTHOR

Marc Lehmann <pcg@goof.com>.

=head1 COPYRIGHT AND LICENSE

Copyright (C) 2007, 2008, 2009, 2013 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:	1.30
Committed:	Fri May 16 07:43:52 2014 UTC (10 years ago) by root
Branch:	MAIN
CVS Tags:	rel-1_43
Changes since 1.29:	+1 -1 lines
Log Message:	1.43
#	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	1.30	our $VERSION = '1.43';
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	root	1.29	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	root	1.29	sub testsub {
46	root	1.19	my $testsub_local = $global_hashref;
47	root	1.1	print Devel::FindRef::track \$var;
48	root	1.29	}
49	root	1.19
50			my $closure = sub {
51			my $closure_var = \$_[0];
52			Scalar::Util::weaken (my $weak_ref = \$var);
53			testsub;
54			};
55
56			$closure->($var);
57	root	1.1
58	root	1.4	The output is as follows (or similar to this, in case I forget to update
59	root	1.3	the manpage after some changes):
60	root	1.1
61	root	1.19	SCALAR(0x7cc888) [refcount 6] is
62			+- referenced by REF(0x8abcc8) [refcount 1], which is
63	root	1.26	\| the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
64	root	1.19	\| +- the closure created at tst:18.
65			\| +- referenced by REF(0x7d3c58) [refcount 1], which is
66	root	1.26	\| \| the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
67	root	1.19	\| \| +- the containing scope for CODE(0x8ab430) [refcount 3], which is
68	root	1.26	\| \| \| the global &Test::testsub.
69	root	1.19	\| \| +- the main body of the program.
70	root	1.26	\| +- the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
71	root	1.19	+- referenced by REF(0x7cc7c8) [refcount 1], which is
72	root	1.26	\| the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
73			+- the global $Test::var.
74	root	1.19	+- referenced by REF(0x7cc558) [refcount 1], which is
75	root	1.26	\| the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
76	root	1.19	\| +- referenced by REF(0x8abad0) [refcount 1], which is
77	root	1.26	\| \| the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
78	root	1.19	\| +- referenced by REF(0x8ab4f0) [refcount 1], which is
79	root	1.26	\| the global $Test::global_hashref.
80	root	1.19	+- referenced by REF(0x7ae518) [refcount 1], which is
81	root	1.26	\| the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
82			\| the global %Test::global_hash.
83	root	1.19	+- referenced by REF(0x7ae2f0) [refcount 1], which is
84			a temporary on the stack.
85	root	1.1
86	root	1.4	It is a bit convoluted to read, but basically it says that the value
87	root	1.19	stored in C<$var> is referenced by:
88	root	1.1
89			=over 4
90
91	root	1.20	=item - the lexical C<$closure_var> (0x8abcc8), which is inside an instantiated
92	root	1.19	closure, which in turn is used quite a bit.
93	root	1.1
94	root	1.20	=item - the package-level lexical C<$global_my>.
95	root	1.1
96	root	1.20	=item - the global package variable named C<$Test::var>.
97	root	1.1
98	root	1.20	=item - the hash element C<ukukey2>, in the hash in the my variable
99	root	1.19	C<$testsub_local> in the sub C<Test::testsub> and also in the hash
100			C<$referenced by Test::hash2>.
101
102	root	1.20	=item - the hash element with key C<ukukey> in the hash stored in
103	root	1.19	C<%Test::hash>.
104
105			=item - some anonymous mortalised reference on the stack (which is caused
106			by calling C<track> with the expression C<\$var>, which creates the
107			reference).
108	root	1.1
109	root	1.6	=back
110
111	root	1.19	And all these account for six reference counts.
112
113	root	1.1	=head1 EXPORTS
114
115			None.
116
117			=head1 FUNCTIONS
118
119			=over 4
120
121			=item $string = Devel::FindRef::track $ref[, $depth]
122
123			Track the perl value pointed to by C<$ref> up to a depth of C<$depth> and
124			return a descriptive string. C<$ref> can point at any perl value, be it
125			anonymous sub, hash, array, scalar etc.
126
127	root	1.29	This is the function you most likely want to use when tracking down
128			references.
129	root	1.1
130			=cut
131
132			sub find($);
133
134	root	1.18	sub _f($) {
135			"$_[0] [refcount " . (_refcnt $_[0]) . "]"
136			}
137
138	root	1.1	sub track {
139	root	1.9	my ($ref, $depth) = @_;
140			@_ = ();
141
142	root	1.1	my $buf = "";
143	root	1.11	my %seen;
144	root	1.9
145			Scalar::Util::weaken $ref;
146	root	1.1
147			my $track; $track = sub {
148	root	1.9	my ($refref, $depth, $indent) = @_;
149	root	1.1
150			if ($depth) {
151	root	1.9	my (@about) = find $$refref;
152	root	1.1	if (@about) {
153			for my $about (@about) {
154	root	1.21	$about->[0] =~ s/([^\x20-\x7e])/sprintf "\\{%02x}", ord $1/ge;
155	root	1.19	$buf .= "$indent" . (@about > 1 ? "+- " : "") . $about->[0];
156	root	1.1	if (@$about > 1) {
157	root	1.14	if ($seen{ref2ptr $about->[1]}++) {
158	root	1.18	$buf .= " " . (_f $about->[1]) . ", which was seen before.\n";
159	root	1.11	} else {
160	root	1.18	$buf .= " " . (_f $about->[1]) . ", which is\n";
161	root	1.12	$track->(\$about->[1], $depth - 1, $about == $about[-1] ? "$indent " : "$indent\| ");
162	root	1.11	}
163	root	1.1	} else {
164			$buf .= ".\n";
165			}
166			}
167			} else {
168	root	1.12	$buf .= "$indent not found anywhere I looked :(\n";
169	root	1.1	}
170			} else {
171	root	1.12	$buf .= "$indent not referenced within the search depth.\n";
172	root	1.1	}
173			};
174
175	root	1.18	$buf .= (_f $ref) . " is\n";
176	root	1.21
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), @$excl;
196	root	1.21	grep !($#$_ && 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	root	1.28	Sometimes you know (from debugging output) the address of a perl value you
202			are interested in (e.g. C<HASH(0x176ff70)>). This function can be used to
203			turn the address into a reference to that value. It is quite safe to call
204			on valid addresses, but extremely dangerous to call on invalid ones. I<No
205			checks whatsoever will be done>, so don't use this unless you really know
206			the value is the address of a valid perl value.
207	root	1.7
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	1.27	=item $ptr = Devel::FindRef::ref2ptr $reference
212	root	1.14
213			The opposite of C<ptr2ref>, above: returns the internal address of the
214	root	1.28	value pointed to by the passed reference. This function is safe to call on
215			anything, and returns the same value taht a normal reference would if used
216			in a numeric context.
217	root	1.14
218	root	1.1	=back
219
220	root	1.12	=head1 ENVIRONMENT VARIABLES
221
222			You can set the environment variable C<PERL_DEVEL_FINDREF_DEPTH> to an
223			integer to override the default depth in C<track>. If a call explicitly
224	root	1.29	specifies a depth, it is not overridden.
225	root	1.12
226	root	1.1	=head1 AUTHOR
227
228			Marc Lehmann <pcg@goof.com>.
229
230			=head1 COPYRIGHT AND LICENSE
231
232	root	1.29	Copyright (C) 2007, 2008, 2009, 2013 by Marc Lehmann.
233	root	1.1
234			This library is free software; you can redistribute it and/or modify
235			it under the same terms as Perl itself, either Perl version 5.8.8 or,
236			at your option, any later version of Perl 5 you may have available.
237
238			=cut
239
240			1
241