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
   |  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:	1.25
Committed:	Sun Aug 30 14:34:41 2009 UTC (14 years, 8 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_422
Changes since 1.24:	+2 -3 lines
Log Message:	1.422
#	Content
1	package Devel::FindRef;
2
3	use common::sense;
4
5	use XSLoader;
6	use Scalar::Util;
7
8	BEGIN {
9	our $VERSION = '1.422';
10	XSLoader::load __PACKAGE__, $VERSION;
11	}
12
13	=head1 NAME
14
15	Devel::FindRef - where is that reference to my variable hiding?
16
17	=head1 SYNOPSIS
18
19	use Devel::FindRef;
20
21	print Devel::FindRef::track \$some_variable;
22
23	=head1 DESCRIPTION
24
25	Tracking down reference problems (e.g. you expect some object to be
26	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
30	The C<track> function can help track down some of those references back to
31	the variables containing them.
32
33	For example, for this fragment:
34
35	package Test;
36
37	use Devel::FindRef;
38	use Scalar::Util;
39
40	our $var = "hi\n";
41	my $global_my = \$var;
42	our %global_hash = (ukukey => \$var);
43	our $global_hashref = { ukukey2 => \$var };
44
45	sub testsub {
46	my $testsub_local = $global_hashref;
47	print Devel::FindRef::track \$var;
48	}
49
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
59	The output is as follows (or similar to this, in case I forget to update
60	the manpage after some changes):
61
62	SCALAR(0x7cc888) [refcount 6] is
63	+- referenced by REF(0x8abcc8) [refcount 1], which is
64	\| in the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
65	\| +- the closure created at tst:18.
66	\| +- referenced by REF(0x7d3c58) [refcount 1], which is
67	\| \| in the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
68	\| \| +- the containing scope for CODE(0x8ab430) [refcount 3], which is
69	\| \| \| in the global &Test::testsub.
70	\| \| +- the main body of the program.
71	\| +- in the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
72	+- referenced by REF(0x7cc7c8) [refcount 1], which is
73	\| in the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
74	+- in the global $Test::var.
75	+- referenced by REF(0x7cc558) [refcount 1], which is
76	\| in the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
77	\| +- referenced by REF(0x8abad0) [refcount 1], which is
78	\| \| in the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
79	\| +- referenced by REF(0x8ab4f0) [refcount 1], which is
80	\| in the global $Test::global_hashref.
81	+- referenced by REF(0x7ae518) [refcount 1], which is
82	\| in the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
83	\| in the global %Test::global_hash.
84	+- referenced by REF(0x7ae2f0) [refcount 1], which is
85	a temporary on the stack.
86
87	It is a bit convoluted to read, but basically it says that the value
88	stored in C<$var> is referenced by:
89
90	=over 4
91
92	=item - the lexical C<$closure_var> (0x8abcc8), which is inside an instantiated
93	closure, which in turn is used quite a bit.
94
95	=item - the package-level lexical C<$global_my>.
96
97	=item - the global package variable named C<$Test::var>.
98
99	=item - the hash element C<ukukey2>, in the hash in the my variable
100	C<$testsub_local> in the sub C<Test::testsub> and also in the hash
101	C<$referenced by Test::hash2>.
102
103	=item - the hash element with key C<ukukey> in the hash stored in
104	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
110	=back
111
112	And all these account for six reference counts.
113
114
115	=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($);
134
135	sub _f($) {
136	"$_[0] [refcount " . (_refcnt $_[0]) . "]"
137	}
138
139	sub track {
140	my ($ref, $depth) = @_;
141	@_ = ();
142
143	my $buf = "";
144	my %seen;
145
146	Scalar::Util::weaken $ref;
147
148	my $track; $track = sub {
149	my ($refref, $depth, $indent) = @_;
150
151	if ($depth) {
152	my (@about) = find $$refref;
153	if (@about) {
154	for my $about (@about) {
155	$about->[0] =~ s/([^\x20-\x7e])/sprintf "\\{%02x}", ord $1/ge;
156	$buf .= "$indent" . (@about > 1 ? "+- " : "") . $about->[0];
157	if (@$about > 1) {
158	if ($seen{ref2ptr $about->[1]}++) {
159	$buf .= " " . (_f $about->[1]) . ", which was seen before.\n";
160	} else {
161	$buf .= " " . (_f $about->[1]) . ", which is\n";
162	$track->(\$about->[1], $depth - 1, $about == $about[-1] ? "$indent " : "$indent\| ");
163	}
164	} else {
165	$buf .= ".\n";
166	}
167	}
168	} else {
169	$buf .= "$indent not found anywhere I looked :(\n";
170	}
171	} else {
172	$buf .= "$indent not referenced within the search depth.\n";
173	}
174	};
175
176	$buf .= (_f $ref) . " is\n";
177
178	$track->(\$ref, $depth \|\| $ENV{PERL_DEVEL_FINDREF_DEPTH} \|\| 10, "");
179	$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	reference itself, which can be omitted if C<find> decided to end the
187	search. The returned references are all weak references.
188
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, $excl) = &find_;
196	my %excl = map +($_ => undef), @$excl;
197	grep !($#$_ && exists $excl{ref2ptr $_->[1]}), @$about
198	}
199
200	=item $ref = Devel::FindRef::ptr2ref $integer
201
202	Sometimes you know (from debugging output) the address of a perl scalar
203	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
210	=item $ref = Devel::FindRef::ref2ptr $reference
211
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	=back
217
218	=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	=head1 AUTHOR
225
226	Marc Lehmann <pcg@goof.com>.
227
228	=head1 COPYRIGHT AND LICENSE
229
230	Copyright (C) 2007, 2008 by Marc Lehmann.
231
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