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Revision 1.2 by root, Thu Jan 11 23:08:03 2007 UTC vs.
Revision 1.10 by root, Fri Jun 26 14:49:33 2009 UTC

1NAME 1NAME
2 Devel::FindRef - where is that reference to my scalar hiding? 2 Devel::FindRef - where is that reference to my variable hiding?
3 3
4SYNOPSIS 4SYNOPSIS
5 use Devel::FindRef; 5 use Devel::FindRef;
6 6
7 print Devel::FindRef::track \$some_variable;
8
7DESCRIPTION 9DESCRIPTION
8 Tracking down reference problems (e.g. you expect some object to be 10 Tracking down reference problems (e.g. you expect some object to be
9 destroyed, but there are still references to it that keep it alive). can 11 destroyed, but there are still references to it that keep it alive) can
10 be very hard, although perl keeps track of all values. 12 be very hard. Fortunately, perl keeps track of all its values, so
13 tracking references "backwards" is usually possible.
11 14
12 The "track" function can hlep track down some of those refernces back to 15 The "track" function can help track down some of those references back
13 the variables containing them. 16 to the variables containing them.
14 17
15 For example, for this fragment: 18 For example, for this fragment:
16 19
17 package Test; 20 package Test;
21
22 use Devel::FindRef;
23 use Scalar::Util;
18 24
19 our $var = "hi\n"; 25 our $var = "hi\n";
20 my $x = \$var; 26 my $global_my = \$var;
21 our %hash = (ukukey => \$var); 27 our %global_hash = (ukukey => \$var);
22 our $hash2 = {ukukey2 => \$var}; 28 our $global_hashref = { ukukey2 => \$var };
23 29
24 sub testsub { 30 sub testsub {
25 my $local = $hash2; 31 my $testsub_local = $global_hashref;
26 print Devel::FindRef::track \$var; 32 print Devel::FindRef::track \$var;
27 } 33 }
28
29 testsub;
30 34
31 The output is as follows (or similar to htis, in case I forget to update
32 the manpage afetr some changes):
33 35
34 SCALAR(0x676fa0) is 36 my $closure = sub {
35 referenced by REF(0x676fb0), which is 37 my $closure_var = \$_[0];
36 in the lexical '$x' in CODE(0x676370), which is 38 Scalar::Util::weaken (my $weak_ref = \$var);
37 not found anywhere I looked :( 39 testsub;
38 referenced by REF(0x676360), which is 40 };
39 in the member 'ukukey' of HASH(0x756660), which is 41
40 in the global %Test::hash. 42 $closure->($var);
43
44 The output is as follows (or similar to this, in case I forget to update
45 the manpage after some changes):
46
47 SCALAR(0x7cc888) [refcount 6] is
48 +- referenced by REF(0x8abcc8) [refcount 1], which is
49 | in the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
50 | +- the closure created at tst:18.
51 | +- referenced by REF(0x7d3c58) [refcount 1], which is
52 | | in the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
53 | | +- the containing scope for CODE(0x8ab430) [refcount 3], which is
54 | | | in the global &Test::testsub.
55 | | +- the main body of the program.
56 | +- in the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
57 +- referenced by REF(0x7cc7c8) [refcount 1], which is
58 | in the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
41 in the global $Test::var. 59 +- in the global $Test::var.
42 referenced by REF(0x6760e0), which is 60 +- referenced by REF(0x7cc558) [refcount 1], which is
43 in the member 'ukukey2' of HASH(0x676f30), which is 61 | in the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
44 referenced by REF(0x77bcf0), which is 62 | +- referenced by REF(0x8abad0) [refcount 1], which is
45 in the lexical '$local' in CODE(0x77bcb0), which is 63 | | in the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
46 in the global &Test::testsub. 64 | +- referenced by REF(0x8ab4f0) [refcount 1], which is
47 referenced by REF(0x77bc80), which is
48 in the global $Test::hash2. 65 | in the global $Test::global_hashref.
66 +- referenced by REF(0x7ae518) [refcount 1], which is
67 | in the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
68 | in the global %Test::global_hash.
69 +- referenced by REF(0x7ae2f0) [refcount 1], which is
70 a temporary on the stack.
49 71
50 It is a bit convoluted to read, but basically it says that the value 72 It is a bit convoluted to read, but basically it says that the value
51 stored in $var can be found: 73 stored in $var is referenced by:
52 74
53 - in some variable $x whose origin is not known (I frankly have no idea 75 - the lexical $closure_var (0x8abcc8), which is inside an instantiated
54 why, hints accepted). 76 closure, which in turn is used quite a bit.
55 - in the hash element with key "ukukey" in the hash stored in 77 - the package-level lexical $global_my.
56 %Test::hash.
57 - in the global variable named $Test::var. 78 - the global package variable named $Test::var.
58 - in the hash element "ukukey2", in the hash in the my variable $local 79 - the hash element "ukukey2", in the hash in the my variable
59 in the sub "Test::testsub" and also in the hash referenced by 80 $testsub_local in the sub "Test::testsub" and also in the hash
60 $Test::hash2. 81 "$referenced by Test::hash2".
82 - the hash element with key "ukukey" in the hash stored in %Test::hash.
83 - some anonymous mortalised reference on the stack (which is caused by
84 calling "track" with the expression "\$var", which creates the
85 reference).
86
87 And all these account for six reference counts.
61 88
62EXPORTS 89EXPORTS
63 None. 90 None.
64 91
65FUNCTIONS 92FUNCTIONS
66 $string = Devel::FindRef::track $ref[, $depth] 93 $string = Devel::FindRef::track $ref[, $depth]
67 Track the perl value pointed to by $ref up to a depth of $depth 94 Track the perl value pointed to by $ref up to a depth of $depth and
68 and return a descriptive string. $ref can point at any perl 95 return a descriptive string. $ref can point at any perl value, be it
69 value, be it anonymous sub, hash, array, scalar etc. 96 anonymous sub, hash, array, scalar etc.
70 97
71 This is the function you most often use. 98 This is the function you most often use.
72 99
73 @references = Devel::FindRef::find $ref 100 @references = Devel::FindRef::find $ref
74 Return arrayrefs that contain [$message, $ref] pairs. The 101 Return arrayrefs that contain [$message, $ref] pairs. The message
75 message describes what kind of reference was found and the $ref 102 describes what kind of reference was found and the $ref is the
76 is the reference itself, which cna be omitted if "find" decided 103 reference itself, which can be omitted if "find" decided to end the
77 to end the search. 104 search. The returned references are all weak references.
78 105
79 The "track" function uses this to find references to the value 106 The "track" function uses this to find references to the value you
80 you are interested in and recurses on the returned references. 107 are interested in and recurses on the returned references.
81 108
82 $ref = Devel::FindRef::ref2ptr $ptr 109 $ref = Devel::FindRef::ptr2ref $integer
83 Sometimes you know (from debugging output) the address of a perl 110 Sometimes you know (from debugging output) the address of a perl
84 scalar you are interested in. This function can be used to turn 111 scalar you are interested in (e.g. "HASH(0x176ff70)"). This function
85 the address into a reference to that scalar. It is quite safe to 112 can be used to turn the address into a reference to that scalar. It
86 call on valid addresses, but extremely dangerous to call on 113 is quite safe to call on valid addresses, but extremely dangerous to
87 invalid ones. 114 call on invalid ones.
115
116 # we know that HASH(0x176ff70) exists, so turn it into a hashref:
117 my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
118
119 $ref = Devel::FindRef::ref2ptr $reference
120 The opposite of "ptr2ref", above: returns the internal address of
121 the value pointed to by the passed reference. *No checks whatsoever
122 will be done*, so don't use this.
123
124ENVIRONMENT VARIABLES
125 You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an
126 integer to override the default depth in "track". If a call explicitly
127 specified a depth it is not overridden.
88 128
89AUTHOR 129AUTHOR
90 Marc Lehmann <pcg@goof.com>. 130 Marc Lehmann <pcg@goof.com>.
91
92BUGS
93 Only code values, arrays, hashes, scalars and magic are being looked
94 at.
95 131
96COPYRIGHT AND LICENSE 132COPYRIGHT AND LICENSE
97 Copyright (C) 2007 by Marc Lehmann. 133 Copyright (C) 2007, 2008 by Marc Lehmann.
98 134
99 This library is free software; you can redistribute it and/or modify 135 This library is free software; you can redistribute it and/or modify it
100 it under the same terms as Perl itself, either Perl version 5.8.8 136 under the same terms as Perl itself, either Perl version 5.8.8 or, at
101 or, at your option, any later version of Perl 5 you may have 137 your option, any later version of Perl 5 you may have available.
102 available.
103 138

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