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 - 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:	1.21
Committed:	Fri Jun 26 14:47:03 2009 UTC (14 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.20:	+3 -1 lines
Log Message:	* empty log message *
#	Content
1	package Devel::FindRef;
2
3	no warnings; # I hate warning nazis
4	use strict;
5
6	use XSLoader;
7	use Scalar::Util;
8
9	BEGIN {
10	our $VERSION = '1.4';
11	XSLoader::load __PACKAGE__, $VERSION;
12	}
13
14	=head1 NAME
15
16	Devel::FindRef - where is that reference to my variable hiding?
17
18	=head1 SYNOPSIS
19
20	use Devel::FindRef;
21
22	print Devel::FindRef::track \$some_variable;
23
24	=head1 DESCRIPTION
25
26	Tracking down reference problems (e.g. you expect some object to be
27	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
31	The C<track> function can help track down some of those references back to
32	the variables containing them.
33
34	For example, for this fragment:
35
36	package Test;
37
38	use Devel::FindRef;
39	use Scalar::Util;
40
41	our $var = "hi\n";
42	my $global_my = \$var;
43	our %global_hash = (ukukey => \$var);
44	our $global_hashref = { ukukey2 => \$var };
45
46	sub testsub {
47	my $testsub_local = $global_hashref;
48	print Devel::FindRef::track \$var;
49	}
50
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
60	The output is as follows (or similar to this, in case I forget to update
61	the manpage after some changes):
62
63	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	+- in the global $Test::var.
76	+- referenced by REF(0x7cc558) [refcount 1], which is
77	\| in the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
78	\| +- referenced by REF(0x8abad0) [refcount 1], which is
79	\| \| in the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
80	\| +- referenced by REF(0x8ab4f0) [refcount 1], which is
81	\| in the global $Test::global_hashref.
82	+- referenced by REF(0x7ae518) [refcount 1], which is
83	\| in the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
84	\| in the global %Test::global_hash.
85	+- referenced by REF(0x7ae2f0) [refcount 1], which is
86	a temporary on the stack.
87
88	It is a bit convoluted to read, but basically it says that the value
89	stored in C<$var> is referenced by:
90
91	=over 4
92
93	=item - the lexical C<$closure_var> (0x8abcc8), which is inside an instantiated
94	closure, which in turn is used quite a bit.
95
96	=item - the package-level lexical C<$global_my>.
97
98	=item - the global package variable named C<$Test::var>.
99
100	=item - the hash element C<ukukey2>, in the hash in the my variable
101	C<$testsub_local> in the sub C<Test::testsub> and also in the hash
102	C<$referenced by Test::hash2>.
103
104	=item - 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
111	=back
112
113	And all these account for six reference counts.
114
115
116	=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($);
135
136	sub _f($) {
137	"$_[0] [refcount " . (_refcnt $_[0]) . "]"
138	}
139
140	sub track {
141	my ($ref, $depth) = @_;
142	@_ = ();
143
144	my $buf = "";
145	my %seen;
146
147	Scalar::Util::weaken $ref;
148
149	my $track; $track = sub {
150	my ($refref, $depth, $indent) = @_;
151
152	if ($depth) {
153	my (@about) = find $$refref;
154	if (@about) {
155	for my $about (@about) {
156	$about->[0] =~ s/([^\x20-\x7e])/sprintf "\\{%02x}", ord $1/ge;
157	$buf .= "$indent" . (@about > 1 ? "+- " : "") . $about->[0];
158	if (@$about > 1) {
159	if ($seen{ref2ptr $about->[1]}++) {
160	$buf .= " " . (_f $about->[1]) . ", which was seen before.\n";
161	} else {
162	$buf .= " " . (_f $about->[1]) . ", which is\n";
163	$track->(\$about->[1], $depth - 1, $about == $about[-1] ? "$indent " : "$indent\| ");
164	}
165	} else {
166	$buf .= ".\n";
167	}
168	}
169	} else {
170	$buf .= "$indent not found anywhere I looked :(\n";
171	}
172	} else {
173	$buf .= "$indent not referenced within the search depth.\n";
174	}
175	};
176
177	$buf .= (_f $ref) . " is\n";
178
179	$track->(\$ref, $depth \|\| $ENV{PERL_DEVEL_FINDREF_DEPTH} \|\| 10, "");
180	$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	reference itself, which can be omitted if C<find> decided to end the
188	search. The returned references are all weak references.
189
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, $excl) = &find_;
197	my %excl = map +($_ => undef), @$excl;
198	grep !($#$_ && exists $excl{ref2ptr $_->[1]}), @$about
199	}
200
201	=item $ref = Devel::FindRef::ptr2ref $integer
202
203	Sometimes you know (from debugging output) the address of a perl scalar
204	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
211	=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	=back
218
219	=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	=head1 AUTHOR
226
227	Marc Lehmann <pcg@goof.com>.
228
229	=head1 COPYRIGHT AND LICENSE
230
231	Copyright (C) 2007, 2008 by Marc Lehmann.
232
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