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

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:

    - in the lexical $closure_var (0x8abcc8), which is inside an
    instantiated closure, which in turn is used quite a bit.
    - in the package-level lexical $global_my.
    - in the global package variable named $Test::var.
    - in 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".
    - in 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.

Revision:	1.9
Committed:	Mon Dec 1 13:47:09 2008 UTC (15 years, 5 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_4
Changes since 1.8:	+55 -35 lines
Log Message:	1.4
#	User	Rev	Content
1	root	1.2	NAME
2	root	1.7	Devel::FindRef - where is that reference to my variable hiding?
3	root	1.2
4			SYNOPSIS
5			use Devel::FindRef;
6
7	root	1.9	print Devel::FindRef::track \$some_variable;
8
9	root	1.2	DESCRIPTION
10			Tracking down reference problems (e.g. you expect some object to be
11	root	1.3	destroyed, but there are still references to it that keep it alive) can
12			be very hard. Fortunately, perl keeps track of all its values, so
13			tracking references "backwards" is usually possible.
14	root	1.2
15	root	1.3	The "track" function can help track down some of those references back
16			to the variables containing them.
17	root	1.2
18			For example, for this fragment:
19
20			package Test;
21	root	1.9
22			use Devel::FindRef;
23			use Scalar::Util;
24	root	1.6
25			our $var = "hi\n";
26	root	1.9	my $global_my = \$var;
27			our %global_hash = (ukukey => \$var);
28			our $global_hashref = { ukukey2 => \$var };
29	root	1.6
30			sub testsub {
31	root	1.9	my $testsub_local = $global_hashref;
32	root	1.2	print Devel::FindRef::track \$var;
33			}
34	root	1.9
35
36			my $closure = sub {
37			my $closure_var = \$_[0];
38			Scalar::Util::weaken (my $weak_ref = \$var);
39			testsub;
40			};
41
42			$closure->($var);
43	root	1.2
44	root	1.3	The output is as follows (or similar to this, in case I forget to update
45			the manpage after some changes):
46	root	1.2
47	root	1.9	SCALAR(0x7cc888) [refcount 6] is
48			+- referenced by REF(0x8abcc8) [refcount 1], which is
49			\| in the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
50			\| +- the closure created at tst:18.
51			\| +- referenced by REF(0x7d3c58) [refcount 1], which is
52			\| \| in the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
53			\| \| +- the containing scope for CODE(0x8ab430) [refcount 3], which is
54			\| \| \| in the global &Test::testsub.
55			\| \| +- the main body of the program.
56			\| +- in the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
57			+- referenced by REF(0x7cc7c8) [refcount 1], which is
58			\| in the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
59	root	1.7	+- in the global $Test::var.
60	root	1.9	+- referenced by REF(0x7cc558) [refcount 1], which is
61			\| in the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
62			\| +- referenced by REF(0x8abad0) [refcount 1], which is
63			\| \| in the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
64			\| +- referenced by REF(0x8ab4f0) [refcount 1], which is
65			\| in the global $Test::global_hashref.
66			+- referenced by REF(0x7ae518) [refcount 1], which is
67			\| in the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
68			\| in the global %Test::global_hash.
69			+- referenced by REF(0x7ae2f0) [refcount 1], which is
70			a temporary on the stack.
71	root	1.2
72			It is a bit convoluted to read, but basically it says that the value
73	root	1.9	stored in $var is referenced by:
74	root	1.2
75	root	1.9	- in the lexical $closure_var (0x8abcc8), which is inside an
76			instantiated closure, which in turn is used quite a bit.
77			- in the package-level lexical $global_my.
78			- in the global package variable named $Test::var.
79			- in the hash element "ukukey2", in the hash in the my variable
80			$testsub_local in the sub "Test::testsub" and also in the hash
81			"$referenced by Test::hash2".
82	root	1.2	- in the hash element with key "ukukey" in the hash stored in
83			%Test::hash.
84	root	1.9	- some anonymous mortalised reference on the stack (which is caused by
85			calling "track" with the expression "\$var", which creates the
86			reference).
87
88			And all these account for six reference counts.
89	root	1.2
90			EXPORTS
91	root	1.4	None.
92	root	1.2
93			FUNCTIONS
94	root	1.4	$string = Devel::FindRef::track $ref[, $depth]
95			Track the perl value pointed to by $ref up to a depth of $depth and
96			return a descriptive string. $ref can point at any perl value, be it
97			anonymous sub, hash, array, scalar etc.
98
99			This is the function you most often use.
100
101			@references = Devel::FindRef::find $ref
102			Return arrayrefs that contain [$message, $ref] pairs. The message
103			describes what kind of reference was found and the $ref is the
104	root	1.5	reference itself, which can be omitted if "find" decided to end the
105			search. The returned references are all weak references.
106	root	1.4
107			The "track" function uses this to find references to the value you
108			are interested in and recurses on the returned references.
109
110			$ref = Devel::FindRef::ptr2ref $integer
111			Sometimes you know (from debugging output) the address of a perl
112			scalar you are interested in (e.g. "HASH(0x176ff70)"). This function
113			can be used to turn the address into a reference to that scalar. It
114			is quite safe to call on valid addresses, but extremely dangerous to
115			call on invalid ones.
116
117			# we know that HASH(0x176ff70) exists, so turn it into a hashref:
118			my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
119	root	1.2
120	root	1.8	$ref = Devel::FindRef::ref2ptr $reference
121			The opposite of "ptr2ref", above: returns the internal address of
122			the value pointed to by the passed reference. *No checks whatsoever
123			will be done*, so don't use this.
124
125	root	1.7	ENVIRONMENT VARIABLES
126			You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an
127			integer to override the default depth in "track". If a call explicitly
128			specified a depth it is not overridden.
129
130	root	1.2	AUTHOR
131	root	1.4	Marc Lehmann <pcg@goof.com>.
132	root	1.2
133			COPYRIGHT AND LICENSE
134	root	1.9	Copyright (C) 2007, 2008 by Marc Lehmann.
135	root	1.2
136	root	1.4	This library is free software; you can redistribute it and/or modify it
137			under the same terms as Perl itself, either Perl version 5.8.8 or, at
138			your option, any later version of Perl 5 you may have available.
139	root	1.2