[ViewVC] Annotation of: cvs/Devel-FindRef/README

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(0x676fa0) is
          referenced by REF(0x676fb0), which is
             in the lexical '$x' in CODE(0x676370), which is
                not found anywhere I looked :(
          referenced by REF(0x676360), which is
             in the member 'ukukey' of HASH(0x756660), which is
                in the global %Test::hash.
          in the global $Test::var.
          referenced by REF(0x6760e0), which is
             in the member 'ukukey2' of HASH(0x676f30), which is
                referenced by REF(0x77bcf0), which is
                   in the lexical '$local' in CODE(0x77bcb0), which is
                      in the global &Test::testsub.
                referenced by REF(0x77bc80), which is
                   in the global $Test::hash2.

    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 cna be omitted if "find" decided to end the
        search.

        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.

Revision:	1.4
Committed:	Wed Nov 28 12:20:33 2007 UTC (18 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_0
Changes since 1.3:	+33 -32 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.2	NAME
2			Devel::FindRef - where is that reference to my scalar hiding?
3
4			SYNOPSIS
5			use Devel::FindRef;
6
7			DESCRIPTION
8			Tracking down reference problems (e.g. you expect some object to be
9	root	1.3	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
11			tracking references "backwards" is usually possible.
12	root	1.2
13	root	1.3	The "track" function can help track down some of those references back
14			to the variables containing them.
15	root	1.2
16			For example, for this fragment:
17
18			package Test;
19
20			our $var = "hi\n";
21			my $x = \$var;
22			our %hash = (ukukey => \$var);
23			our $hash2 = {ukukey2 => \$var};
24
25			sub testsub {
26			my $local = $hash2;
27			print Devel::FindRef::track \$var;
28			}
29
30			testsub;
31
32	root	1.3	The output is as follows (or similar to this, in case I forget to update
33			the manpage after some changes):
34	root	1.2
35			SCALAR(0x676fa0) is
36			referenced by REF(0x676fb0), which is
37			in the lexical '$x' in CODE(0x676370), which is
38			not found anywhere I looked :(
39			referenced by REF(0x676360), which is
40			in the member 'ukukey' of HASH(0x756660), which is
41			in the global %Test::hash.
42			in the global $Test::var.
43			referenced by REF(0x6760e0), which is
44			in the member 'ukukey2' of HASH(0x676f30), which is
45			referenced by REF(0x77bcf0), which is
46			in the lexical '$local' in CODE(0x77bcb0), which is
47			in the global &Test::testsub.
48			referenced by REF(0x77bc80), which is
49			in the global $Test::hash2.
50
51			It is a bit convoluted to read, but basically it says that the value
52			stored in $var can be found:
53
54			- in some variable $x whose origin is not known (I frankly have no idea
55			why, hints accepted).
56			- in the hash element with key "ukukey" in the hash stored in
57			%Test::hash.
58			- in the global variable named $Test::var.
59			- in the hash element "ukukey2", in the hash in the my variable $local
60			in the sub "Test::testsub" and also in the hash referenced by
61			$Test::hash2.
62
63			EXPORTS
64	root	1.4	None.
65	root	1.2
66			FUNCTIONS
67	root	1.4	$string = Devel::FindRef::track $ref[, $depth]
68			Track the perl value pointed to by $ref up to a depth of $depth and
69			return a descriptive string. $ref can point at any perl value, be it
70			anonymous sub, hash, array, scalar etc.
71
72			This is the function you most often use.
73
74			@references = Devel::FindRef::find $ref
75			Return arrayrefs that contain [$message, $ref] pairs. The message
76			describes what kind of reference was found and the $ref is the
77			reference itself, which cna be omitted if "find" decided to end the
78			search.
79
80			The "track" function uses this to find references to the value you
81			are interested in and recurses on the returned references.
82
83			$ref = Devel::FindRef::ptr2ref $integer
84			Sometimes you know (from debugging output) the address of a perl
85			scalar you are interested in (e.g. "HASH(0x176ff70)"). This function
86			can be used to turn the address into a reference to that scalar. It
87			is quite safe to call on valid addresses, but extremely dangerous to
88			call on invalid ones.
89
90			# we know that HASH(0x176ff70) exists, so turn it into a hashref:
91			my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
92	root	1.2
93			AUTHOR
94	root	1.4	Marc Lehmann <pcg@goof.com>.
95	root	1.2
96			BUGS
97	root	1.4	Only code values, arrays, hashes, scalars and magic are being looked at.
98	root	1.2
99	root	1.4	This is a quick hack only.
100	root	1.3
101	root	1.2	COPYRIGHT AND LICENSE
102	root	1.4	Copyright (C) 2007 by Marc Lehmann.
103	root	1.2
104	root	1.4	This library is free software; you can redistribute it and/or modify it
105			under the same terms as Perl itself, either Perl version 5.8.8 or, at
106			your option, any later version of Perl 5 you may have available.
107	root	1.2