NAME

Devel::FindRef - where is that reference to my scalar hiding?

SYNOPSIS

use Devel::FindRef;

DESCRIPTION

Tracking down reference problems (e.g. you expect some object to be destroyed, but there are still references to it that keep it alive) can be very hard. Fortunately, perl keeps track of all its values, so tracking references "backwards" is usually possible.

The track function can help track down some of those references back to the variables containing them.

For example, for this fragment:

package Test;           
                      
our $var = "hi\n";
my $x = \$var;      
our %hash = (ukukey => \$var);
our $hash2 = {ukukey2 => \$var};
                        
sub testsub {             
   my $local = $hash2;      
   print Devel::FindRef::track \$var;
}                             
                                
testsub;                        

The output is as follows (or similar to this, in case I forget to update the manpage after some changes):

SCALAR(0x7bd2d0) is
   in the global $Test::var.
   referenced by REF(0x7bd240), which is
      in the member 'ukukey2' of HASH(0x7bd228), which is
         referenced by REF(0x81dae8), which is
            in the lexical '$local' in CODE(0x81da88), which is
               in the global &Test::testsub.
         referenced by REF(0x81da40), which is
            in the global $Test::hash2.
   referenced by REF(0x79f3f8), which is
      in the lexical '$x' in CODE(0x79f518), which is
         the containing scope for CODE(0x81da88), which is
            in the global &Test::testsub.
   referenced by REF(0x79f2f0), which is
      not found anywhere I looked :(
   referenced by REF(0x79f140), which is
      in the member 'ukukey' of HASH(0x81d698), which is
         in the global %Test::hash.

It is a bit convoluted to read, but basically it says that the value stored in $var can be found:

- in some variable $x whose origin is not known (I frankly have no idea why, hints accepted).

- in the hash element with key ukukey in the hash stored in %Test::hash.

- in the global variable named $Test::var.

- in the hash element ukukey2, in the hash in the my variable $local in the sub Test::testsub and also in the hash referenced by $Test::hash2.

EXPORTS

None.

FUNCTIONS

$string = Devel::FindRef::track $ref[, $depth]

Track the perl value pointed to by $ref up to a depth of $depth and return a descriptive string. $ref can point at any perl value, be it anonymous sub, hash, array, scalar etc.

This is the function you most often use.

@references = Devel::FindRef::find $ref

Return arrayrefs that contain [$message, $ref] pairs. The message describes what kind of reference was found and the $ref is the reference itself, which can be omitted if find decided to end the search. The returned references are all weak references.

The track function uses this to find references to the value you are interested in and recurses on the returned references.

$ref = Devel::FindRef::ptr2ref $integer

Sometimes you know (from debugging output) the address of a perl scalar you are interested in (e.g. HASH(0x176ff70)). This function can be used to turn the address into a reference to that scalar. It is quite safe to call on valid addresses, but extremely dangerous to call on invalid ones.

# we know that HASH(0x176ff70) exists, so turn it into a hashref:
my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;

AUTHOR

Marc Lehmann <pcg@goof.com>.

BUGS

Only code values, arrays, hashes, scalars and magic are being looked at.

This is a quick hack only.

COPYRIGHT AND LICENSE

Copyright (C) 2007 by Marc Lehmann.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available.