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Revision: 1.12
Committed: Tue Jun 3 18:40:50 2014 UTC (10 years, 1 month ago) by root
Branch: MAIN
CVS Tags: rel-1_46, rel-1_44, rel-1_45, HEAD
Changes since 1.11: +1 -1 lines
Log Message:
1.44

File Contents

# Content
1 NAME
2 Devel::FindRef - where is that reference to my variable hiding?
3
4 SYNOPSIS
5 use Devel::FindRef;
6
7 print Devel::FindRef::track \$some_variable;
8
9 DESCRIPTION
10 Tracking down reference problems (e.g. you expect some object to be
11 destroyed, but there are still references to it that keep it alive) can
12 be very hard. Fortunately, perl keeps track of all its values, so
13 tracking references "backwards" is usually possible.
14
15 The "track" function can help track down some of those references back
16 to the variables containing them.
17
18 For example, for this fragment:
19
20 package Test;
21
22 use Devel::FindRef;
23 use Scalar::Util;
24
25 our $var = "hi\n";
26 my $global_my = \$var;
27 our %global_hash = (ukukey => \$var);
28 our $global_hashref = { ukukey2 => \$var };
29
30 sub testsub {
31 my $testsub_local = $global_hashref;
32 print Devel::FindRef::track \$var;
33 }
34
35 my $closure = sub {
36 my $closure_var = \$_[0];
37 Scalar::Util::weaken (my $weak_ref = \$var);
38 testsub;
39 };
40
41 $closure->($var);
42
43 The output is as follows (or similar to this, in case I forget to update
44 the manpage after some changes):
45
46 SCALAR(0x7cc888) [refcount 6] is
47 +- referenced by REF(0x8abcc8) [refcount 1], which is
48 | the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
49 | +- the closure created at tst:18.
50 | +- referenced by REF(0x7d3c58) [refcount 1], which is
51 | | the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
52 | | +- the containing scope for CODE(0x8ab430) [refcount 3], which is
53 | | | the global &Test::testsub.
54 | | +- the main body of the program.
55 | +- the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
56 +- referenced by REF(0x7cc7c8) [refcount 1], which is
57 | the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
58 +- the global $Test::var.
59 +- referenced by REF(0x7cc558) [refcount 1], which is
60 | the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
61 | +- referenced by REF(0x8abad0) [refcount 1], which is
62 | | the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
63 | +- referenced by REF(0x8ab4f0) [refcount 1], which is
64 | the global $Test::global_hashref.
65 +- referenced by REF(0x7ae518) [refcount 1], which is
66 | the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
67 | the global %Test::global_hash.
68 +- referenced by REF(0x7ae2f0) [refcount 1], which is
69 a temporary on the stack.
70
71 It is a bit convoluted to read, but basically it says that the value
72 stored in $var is referenced by:
73
74 - the lexical $closure_var (0x8abcc8), which is inside an instantiated
75 closure, which in turn is used quite a bit.
76 - the package-level lexical $global_my.
77 - the global package variable named $Test::var.
78 - the hash element "ukukey2", in the hash in the my variable
79 $testsub_local in the sub "Test::testsub" and also in the hash
80 "$referenced by Test::hash2".
81 - the hash element with key "ukukey" in the hash stored in %Test::hash.
82 - some anonymous mortalised reference on the stack (which is caused by
83 calling "track" with the expression "\$var", which creates the
84 reference).
85
86 And all these account for six reference counts.
87
88 EXPORTS
89 None.
90
91 FUNCTIONS
92 $string = Devel::FindRef::track $ref[, $depth]
93 Track the perl value pointed to by $ref up to a depth of $depth and
94 return a descriptive string. $ref can point at any perl value, be it
95 anonymous sub, hash, array, scalar etc.
96
97 This is the function you most likely want to use when tracking down
98 references.
99
100 @references = Devel::FindRef::find $ref
101 Return arrayrefs that contain [$message, $ref] pairs. The message
102 describes what kind of reference was found and the $ref is the
103 reference itself, which can be omitted if "find" decided to end the
104 search. The returned references are all weak references.
105
106 The "track" function uses this to find references to the value you
107 are interested in and recurses on the returned references.
108
109 $ref = Devel::FindRef::ptr2ref $integer
110 Sometimes you know (from debugging output) the address of a perl
111 value you are interested in (e.g. "HASH(0x176ff70)"). This function
112 can be used to turn the address into a reference to that value. It
113 is quite safe to call on valid addresses, but extremely dangerous to
114 call on invalid ones. *No checks whatsoever will be done*, so don't
115 use this unless you really know the value is the address of a valid
116 perl value.
117
118 # we know that HASH(0x176ff70) exists, so turn it into a hashref:
119 my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
120
121 $ptr = Devel::FindRef::ref2ptr $reference
122 The opposite of "ptr2ref", above: returns the internal address of
123 the value pointed to by the passed reference. This function is safe
124 to call on anything, and returns the same value that a normal
125 reference would if used in a numeric context.
126
127 ENVIRONMENT VARIABLES
128 You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an
129 integer to override the default depth in "track". If a call explicitly
130 specifies a depth, it is not overridden.
131
132 AUTHOR
133 Marc Lehmann <pcg@goof.com>.
134
135 COPYRIGHT AND LICENSE
136 Copyright (C) 2007, 2008, 2009, 2013 by Marc Lehmann.
137
138 This library is free software; you can redistribute it and/or modify it
139 under the same terms as Perl itself, either Perl version 5.8.8 or, at
140 your option, any later version of Perl 5 you may have available.
141