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NAME |
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Devel::FindRef - where is that reference to my variable hiding? |
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SYNOPSIS |
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use Devel::FindRef; |
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print Devel::FindRef::track \$some_variable; |
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DESCRIPTION |
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Tracking down reference problems (e.g. you expect some object to be |
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destroyed, but there are still references to it that keep it alive) can |
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be very hard. Fortunately, perl keeps track of all its values, so |
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tracking references "backwards" is usually possible. |
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The "track" function can help track down some of those references back |
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to the variables containing them. |
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For example, for this fragment: |
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package Test; |
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use Devel::FindRef; |
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use Scalar::Util; |
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our $var = "hi\n"; |
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my $global_my = \$var; |
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our %global_hash = (ukukey => \$var); |
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our $global_hashref = { ukukey2 => \$var }; |
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sub testsub { |
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my $testsub_local = $global_hashref; |
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print Devel::FindRef::track \$var; |
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} |
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my $closure = sub { |
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my $closure_var = \$_[0]; |
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Scalar::Util::weaken (my $weak_ref = \$var); |
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testsub; |
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}; |
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$closure->($var); |
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The output is as follows (or similar to this, in case I forget to update |
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the manpage after some changes): |
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SCALAR(0x7cc888) [refcount 6] is |
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+- referenced by REF(0x8abcc8) [refcount 1], which is |
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| the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is |
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| +- the closure created at tst:18. |
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| +- referenced by REF(0x7d3c58) [refcount 1], which is |
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| | the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is |
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| | +- the containing scope for CODE(0x8ab430) [refcount 3], which is |
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| | | the global &Test::testsub. |
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| | +- the main body of the program. |
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| +- the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before. |
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+- referenced by REF(0x7cc7c8) [refcount 1], which is |
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| the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before. |
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+- the global $Test::var. |
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+- referenced by REF(0x7cc558) [refcount 1], which is |
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| the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is |
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| +- referenced by REF(0x8abad0) [refcount 1], which is |
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| | the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before. |
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| +- referenced by REF(0x8ab4f0) [refcount 1], which is |
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| the global $Test::global_hashref. |
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+- referenced by REF(0x7ae518) [refcount 1], which is |
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| the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is |
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| the global %Test::global_hash. |
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+- referenced by REF(0x7ae2f0) [refcount 1], which is |
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a temporary on the stack. |
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It is a bit convoluted to read, but basically it says that the value |
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stored in $var is referenced by: |
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- the lexical $closure_var (0x8abcc8), which is inside an instantiated |
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closure, which in turn is used quite a bit. |
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- the package-level lexical $global_my. |
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- the global package variable named $Test::var. |
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- the hash element "ukukey2", in the hash in the my variable |
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$testsub_local in the sub "Test::testsub" and also in the hash |
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"$referenced by Test::hash2". |
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- the hash element with key "ukukey" in the hash stored in %Test::hash. |
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- some anonymous mortalised reference on the stack (which is caused by |
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calling "track" with the expression "\$var", which creates the |
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reference). |
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And all these account for six reference counts. |
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EXPORTS |
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None. |
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FUNCTIONS |
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$string = Devel::FindRef::track $ref[, $depth] |
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Track the perl value pointed to by $ref up to a depth of $depth and |
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return a descriptive string. $ref can point at any perl value, be it |
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anonymous sub, hash, array, scalar etc. |
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This is the function you most likely want to use when tracking down |
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references. |
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@references = Devel::FindRef::find $ref |
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Return arrayrefs that contain [$message, $ref] pairs. The message |
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describes what kind of reference was found and the $ref is the |
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reference itself, which can be omitted if "find" decided to end the |
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search. The returned references are all weak references. |
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The "track" function uses this to find references to the value you |
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are interested in and recurses on the returned references. |
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$ref = Devel::FindRef::ptr2ref $integer |
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Sometimes you know (from debugging output) the address of a perl |
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value you are interested in (e.g. "HASH(0x176ff70)"). This function |
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can be used to turn the address into a reference to that value. It |
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is quite safe to call on valid addresses, but extremely dangerous to |
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call on invalid ones. *No checks whatsoever will be done*, so don't |
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use this unless you really know the value is the address of a valid |
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perl value. |
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# we know that HASH(0x176ff70) exists, so turn it into a hashref: |
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my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70; |
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|
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$ptr = Devel::FindRef::ref2ptr $reference |
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The opposite of "ptr2ref", above: returns the internal address of |
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the value pointed to by the passed reference. This function is safe |
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to call on anything, and returns the same value taht a normal |
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reference would if used in a numeric context. |
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ENVIRONMENT VARIABLES |
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You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an |
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integer to override the default depth in "track". If a call explicitly |
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specifies a depth, it is not overridden. |
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AUTHOR |
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Marc Lehmann <pcg@goof.com>. |
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COPYRIGHT AND LICENSE |
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Copyright (C) 2007, 2008, 2009, 2013 by Marc Lehmann. |
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This library is free software; you can redistribute it and/or modify it |
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under the same terms as Perl itself, either Perl version 5.8.8 or, at |
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your option, any later version of Perl 5 you may have available. |
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