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Revision 1.12 by root, Tue Jun 3 18:40:50 2014 UTC

1NAME 1NAME
2 Devel::FindRef - where is that reference to my variable 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
… …
13 The "track" function can help track down some of those references back 15 The "track" function can help track down some of those references back
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;
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 };
19 29
20 our $var = "hi\n"; 30 sub testsub {
21 my $x = \$var; 31 my $testsub_local = $global_hashref;
22 our %hash = (ukukey => \$var);
23 our $hash2 = {ukukey2 => \$var};
24
25 sub testsub {
26 my $local = $hash2;
27 print Devel::FindRef::track \$var; 32 print Devel::FindRef::track \$var;
28 } 33 }
29 34
35 my $closure = sub {
36 my $closure_var = \$_[0];
37 Scalar::Util::weaken (my $weak_ref = \$var);
30 testsub; 38 testsub;
39 };
40
41 $closure->($var);
31 42
32 The output is as follows (or similar to this, in case I forget to update 43 The output is as follows (or similar to this, in case I forget to update
33 the manpage after some changes): 44 the manpage after some changes):
34 45
35 SCALAR(0x814ece8) is 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.
36 +- in the global $Test::var. 58 +- the global $Test::var.
37 +- referenced by REF(0x814f9e4), which is 59 +- referenced by REF(0x7cc558) [refcount 1], which is
38 | in the lexical '$x' in CODE(0x814ed78), which is 60 | the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
39 | the containing scope for CODE(0x820c4b0), which is 61 | +- referenced by REF(0x8abad0) [refcount 1], which is
40 | in the global &Test::testsub. 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 $Test::global_hashref.
41 +- referenced by REF(0x814ed6c), which is 65 +- referenced by REF(0x7ae518) [refcount 1], which is
42 | in the member 'ukukey' of HASH(0x81da20c), which is 66 | the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
43 | in the global %Test::hash. 67 | the global %Test::global_hash.
44 +- referenced by REF(0x814ec28), which is 68 +- referenced by REF(0x7ae2f0) [refcount 1], which is
45 | not found anywhere I looked :( 69 a temporary on the stack.
46 +- referenced by REF(0x814eb44), which is
47 in the member 'ukukey2' of HASH(0x814f99c), which is
48 +- referenced by REF(0x820c450), which is
49 | in the lexical '$local' in CODE(0x820c4b0), which was seen before.
50 +- referenced by REF(0x820c204), which is
51 in the global $Test::hash2.
52 70
53 It is a bit convoluted to read, but basically it says that the value 71 It is a bit convoluted to read, but basically it says that the value
54 stored in $var can be found: 72 stored in $var is referenced by:
55 73
56 - in some variable $x whose origin is not known (I frankly have no idea 74 - the lexical $closure_var (0x8abcc8), which is inside an instantiated
57 why, hints accepted). 75 closure, which in turn is used quite a bit.
58 - in the hash element with key "ukukey" in the hash stored in 76 - the package-level lexical $global_my.
59 %Test::hash.
60 - in the global variable named $Test::var. 77 - the global package variable named $Test::var.
61 - in the hash element "ukukey2", in the hash in the my variable $local 78 - the hash element "ukukey2", in the hash in the my variable
62 in the sub "Test::testsub" and also in the hash referenced by 79 $testsub_local in the sub "Test::testsub" and also in the hash
63 $Test::hash2. 80 "$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.
64 87
65EXPORTS 88EXPORTS
66 None. 89 None.
67 90
68FUNCTIONS 91FUNCTIONS
69 $string = Devel::FindRef::track $ref[, $depth] 92 $string = Devel::FindRef::track $ref[, $depth]
70 Track the perl value pointed to by $ref up to a depth of $depth and 93 Track the perl value pointed to by $ref up to a depth of $depth and
71 return a descriptive string. $ref can point at any perl value, be it 94 return a descriptive string. $ref can point at any perl value, be it
72 anonymous sub, hash, array, scalar etc. 95 anonymous sub, hash, array, scalar etc.
73 96
74 This is the function you most often use. 97 This is the function you most likely want to use when tracking down
98 references.
75 99
76 @references = Devel::FindRef::find $ref 100 @references = Devel::FindRef::find $ref
77 Return arrayrefs that contain [$message, $ref] pairs. The message 101 Return arrayrefs that contain [$message, $ref] pairs. The message
78 describes what kind of reference was found and the $ref is the 102 describes what kind of reference was found and the $ref is the
79 reference itself, which can be omitted if "find" decided to end the 103 reference itself, which can be omitted if "find" decided to end the
… …
82 The "track" function uses this to find references to the value you 106 The "track" function uses this to find references to the value you
83 are interested in and recurses on the returned references. 107 are interested in and recurses on the returned references.
84 108
85 $ref = Devel::FindRef::ptr2ref $integer 109 $ref = Devel::FindRef::ptr2ref $integer
86 Sometimes you know (from debugging output) the address of a perl 110 Sometimes you know (from debugging output) the address of a perl
87 scalar you are interested in (e.g. "HASH(0x176ff70)"). This function 111 value you are interested in (e.g. "HASH(0x176ff70)"). This function
88 can be used to turn the address into a reference to that scalar. It 112 can be used to turn the address into a reference to that value. It
89 is quite safe to call on valid addresses, but extremely dangerous to 113 is quite safe to call on valid addresses, but extremely dangerous to
90 call on invalid ones. 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.
91 117
92 # we know that HASH(0x176ff70) exists, so turn it into a hashref: 118 # we know that HASH(0x176ff70) exists, so turn it into a hashref:
93 my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70; 119 my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
94 120
95 $ref = Devel::FindRef::ref2ptr $reference 121 $ptr = Devel::FindRef::ref2ptr $reference
96 The opposite of "ptr2ref", above: returns the internal address of 122 The opposite of "ptr2ref", above: returns the internal address of
97 the value pointed to by the passed reference. *No checks whatsoever 123 the value pointed to by the passed reference. This function is safe
98 will be done*, so don't use this. 124 to call on anything, and returns the same value that a normal
125 reference would if used in a numeric context.
99 126
100ENVIRONMENT VARIABLES 127ENVIRONMENT VARIABLES
101 You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an 128 You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an
102 integer to override the default depth in "track". If a call explicitly 129 integer to override the default depth in "track". If a call explicitly
103 specified a depth it is not overridden. 130 specifies a depth, it is not overridden.
104 131
105AUTHOR 132AUTHOR
106 Marc Lehmann <pcg@goof.com>. 133 Marc Lehmann <pcg@goof.com>.
107 134
108BUGS
109 Only code values, arrays, hashes, scalars and magic are being looked at.
110
111 This is a quick hack only.
112
113COPYRIGHT AND LICENSE 135COPYRIGHT AND LICENSE
114 Copyright (C) 2007 by Marc Lehmann. 136 Copyright (C) 2007, 2008, 2009, 2013 by Marc Lehmann.
115 137
116 This library is free software; you can redistribute it and/or modify it 138 This library is free software; you can redistribute it and/or modify it
117 under the same terms as Perl itself, either Perl version 5.8.8 or, at 139 under the same terms as Perl itself, either Perl version 5.8.8 or, at
118 your option, any later version of Perl 5 you may have available. 140 your option, any later version of Perl 5 you may have available.
119 141

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