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