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Revision 1.3 by root, Wed Feb 7 21:34:02 2007 UTC vs.
Revision 1.9 by root, Mon Dec 1 13:47:09 2008 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
7 print Devel::FindRef::track \$some_variable;
6 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. Fortunately, perl keeps track of all its values, so 12 be very hard. Fortunately, perl keeps track of all its values, so
… …
14 to the variables containing them. 16 to the variables containing them.
15 17
16 For example, for this fragment: 18 For example, for this fragment:
17 19
18 package Test; 20 package Test;
19 21
20 our $var = "hi\n"; 22 use Devel::FindRef;
21 my $x = \$var; 23 use Scalar::Util;
22 our %hash = (ukukey => \$var);
23 our $hash2 = {ukukey2 => \$var};
24 24
25 our $var = "hi\n";
26 my $global_my = \$var;
27 our %global_hash = (ukukey => \$var);
28 our $global_hashref = { ukukey2 => \$var };
29
25 sub testsub { 30 sub testsub {
26 my $local = $hash2; 31 my $testsub_local = $global_hashref;
27 print Devel::FindRef::track \$var; 32 print Devel::FindRef::track \$var;
28 } 33 }
29 34
30 testsub; 35
36 my $closure = sub {
37 my $closure_var = \$_[0];
38 Scalar::Util::weaken (my $weak_ref = \$var);
39 testsub;
40 };
41
42 $closure->($var);
31 43
32 The output is as follows (or similar to this, in case I forget to update 44 The output is as follows (or similar to this, in case I forget to update
33 the manpage after some changes): 45 the manpage after some changes):
34 46
35 SCALAR(0x676fa0) is 47 SCALAR(0x7cc888) [refcount 6] is
36 referenced by REF(0x676fb0), which is 48 +- referenced by REF(0x8abcc8) [refcount 1], which is
37 in the lexical '$x' in CODE(0x676370), which is 49 | in the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
38 not found anywhere I looked :( 50 | +- the closure created at tst:18.
39 referenced by REF(0x676360), which is 51 | +- referenced by REF(0x7d3c58) [refcount 1], which is
40 in the member 'ukukey' of HASH(0x756660), which is 52 | | in the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
41 in the global %Test::hash. 53 | | +- the containing scope for CODE(0x8ab430) [refcount 3], which is
54 | | | in the global &Test::testsub.
55 | | +- the main body of the program.
56 | +- in the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
57 +- referenced by REF(0x7cc7c8) [refcount 1], which is
58 | in the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
42 in the global $Test::var. 59 +- in the global $Test::var.
43 referenced by REF(0x6760e0), which is 60 +- referenced by REF(0x7cc558) [refcount 1], which is
44 in the member 'ukukey2' of HASH(0x676f30), which is 61 | in the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
45 referenced by REF(0x77bcf0), which is 62 | +- referenced by REF(0x8abad0) [refcount 1], which is
46 in the lexical '$local' in CODE(0x77bcb0), which is 63 | | in the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
47 in the global &Test::testsub. 64 | +- referenced by REF(0x8ab4f0) [refcount 1], which is
48 referenced by REF(0x77bc80), which is
49 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.
50 71
51 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
52 stored in $var can be found: 73 stored in $var is referenced by:
53 74
54 - in some variable $x whose origin is not known (I frankly have no idea 75 - in the lexical $closure_var (0x8abcc8), which is inside an
55 why, hints accepted). 76 instantiated closure, which in turn is used quite a bit.
77 - in the package-level lexical $global_my.
78 - in the global package variable named $Test::var.
79 - in the hash element "ukukey2", in the hash in the my variable
80 $testsub_local in the sub "Test::testsub" and also in the hash
81 "$referenced by Test::hash2".
56 - in the hash element with key "ukukey" in the hash stored in 82 - in the hash element with key "ukukey" in the hash stored in
57 %Test::hash. 83 %Test::hash.
58 - in the global variable named $Test::var. 84 - some anonymous mortalised reference on the stack (which is caused by
59 - in the hash element "ukukey2", in the hash in the my variable $local 85 calling "track" with the expression "\$var", which creates the
60 in the sub "Test::testsub" and also in the hash referenced by 86 reference).
61 $Test::hash2. 87
88 And all these account for six reference counts.
62 89
63EXPORTS 90EXPORTS
64 None. 91 None.
65 92
66FUNCTIONS 93FUNCTIONS
67 $string = Devel::FindRef::track $ref[, $depth] 94 $string = Devel::FindRef::track $ref[, $depth]
68 Track the perl value pointed to by $ref up to a depth of $depth 95 Track the perl value pointed to by $ref up to a depth of $depth and
69 and return a descriptive string. $ref can point at any perl 96 return a descriptive string. $ref can point at any perl value, be it
70 value, be it anonymous sub, hash, array, scalar etc. 97 anonymous sub, hash, array, scalar etc.
71 98
72 This is the function you most often use. 99 This is the function you most often use.
73 100
74 @references = Devel::FindRef::find $ref 101 @references = Devel::FindRef::find $ref
75 Return arrayrefs that contain [$message, $ref] pairs. The 102 Return arrayrefs that contain [$message, $ref] pairs. The message
76 message describes what kind of reference was found and the $ref 103 describes what kind of reference was found and the $ref is the
77 is the reference itself, which cna be omitted if "find" decided 104 reference itself, which can be omitted if "find" decided to end the
78 to end the search. 105 search. The returned references are all weak references.
79 106
80 The "track" function uses this to find references to the value 107 The "track" function uses this to find references to the value you
81 you are interested in and recurses on the returned references. 108 are interested in and recurses on the returned references.
82 109
83 $ref = Devel::FindRef::ref2ptr $ptr 110 $ref = Devel::FindRef::ptr2ref $integer
84 Sometimes you know (from debugging output) the address of a perl 111 Sometimes you know (from debugging output) the address of a perl
85 scalar you are interested in. This function can be used to turn 112 scalar you are interested in (e.g. "HASH(0x176ff70)"). This function
86 the address into a reference to that scalar. It is quite safe to 113 can be used to turn the address into a reference to that scalar. It
87 call on valid addresses, but extremely dangerous to call on 114 is quite safe to call on valid addresses, but extremely dangerous to
88 invalid ones. 115 call on invalid ones.
116
117 # we know that HASH(0x176ff70) exists, so turn it into a hashref:
118 my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
119
120 $ref = Devel::FindRef::ref2ptr $reference
121 The opposite of "ptr2ref", above: returns the internal address of
122 the value pointed to by the passed reference. *No checks whatsoever
123 will be done*, so don't use this.
124
125ENVIRONMENT VARIABLES
126 You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an
127 integer to override the default depth in "track". If a call explicitly
128 specified a depth it is not overridden.
89 129
90AUTHOR 130AUTHOR
91 Marc Lehmann <pcg@goof.com>. 131 Marc Lehmann <pcg@goof.com>.
92
93BUGS
94 Only code values, arrays, hashes, scalars and magic are being looked
95 at.
96
97 This is a quick hack only.
98 132
99COPYRIGHT AND LICENSE 133COPYRIGHT AND LICENSE
100 Copyright (C) 2007 by Marc Lehmann. 134 Copyright (C) 2007, 2008 by Marc Lehmann.
101 135
102 This library is free software; you can redistribute it and/or modify 136 This library is free software; you can redistribute it and/or modify it
103 it under the same terms as Perl itself, either Perl version 5.8.8 137 under the same terms as Perl itself, either Perl version 5.8.8 or, at
104 or, at your option, any later version of Perl 5 you may have 138 your option, any later version of Perl 5 you may have available.
105 available.
106 139

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