trusty (3) Devel::FindRef.3pm.gz

NAME

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

SYNOPSIS

         use Devel::FindRef;

         print Devel::FindRef::track \$some_variable;

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;

          use Devel::FindRef;
          use Scalar::Util;

          our $var = "hi\n";
          my $global_my = \$var;
          our %global_hash = (ukukey => \$var);
          our $global_hashref = { ukukey2 => \$var };

          sub testsub {
             my $testsub_local = $global_hashref;
             print Devel::FindRef::track \$var;
          }

          my $closure = sub {
             my $closure_var = \$_[0];
             Scalar::Util::weaken (my $weak_ref = \$var);
             testsub;
          };

          $closure->($var);

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

          SCALAR(0x7cc888) [refcount 6] is
          +- referenced by REF(0x8abcc8) [refcount 1], which is
          |  in the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
          |     +- the closure created at tst:18.
          |     +- referenced by REF(0x7d3c58) [refcount 1], which is
          |     |  in the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
          |     |     +- the containing scope for CODE(0x8ab430) [refcount 3], which is
          |     |     |  in the global &Test::testsub.
          |     |     +- the main body of the program.
          |     +- in the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
          +- referenced by REF(0x7cc7c8) [refcount 1], which is
          |  in the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
          +- in the global $Test::var.
          +- referenced by REF(0x7cc558) [refcount 1], which is
          |  in the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
          |     +- referenced by REF(0x8abad0) [refcount 1], which is
          |     |  in the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
          |     +- referenced by REF(0x8ab4f0) [refcount 1], which is
          |        in the global $Test::global_hashref.
          +- referenced by REF(0x7ae518) [refcount 1], which is
          |  in the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
          |     in the global %Test::global_hash.
          +- referenced by REF(0x7ae2f0) [refcount 1], which is
             a temporary on the stack.

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

       - the lexical $closure_var (0x8abcc8), which is inside an instantiated closure, which in turn is used
       quite a bit.
       - the package-level lexical $global_my.
       - the global package variable named $Test::var.
       - the hash element "ukukey2", in the hash in the my variable $testsub_local in the sub "Test::testsub"
       and also in the hash "$referenced by Test::hash2".
       - the hash element with key "ukukey" in the hash stored in %Test::hash.
       - some anonymous mortalised reference on the stack (which is caused by calling "track" with the
       expression "\$var", which creates the reference).

       And all these account for six reference counts.

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;

       $ref = Devel::FindRef::ref2ptr $reference
           The opposite of "ptr2ref", above: returns the internal address of the value pointed to by the passed
           reference. No checks whatsoever will be done, so don't use this.

ENVIRONMENT VARIABLES

       You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an integer to override the default
       depth in "track". If a call explicitly specified a depth it is not overridden.

AUTHOR

       Marc Lehmann <pcg@goof.com>.

COPYRIGHT AND LICENSE

       Copyright (C) 2007, 2008 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.