[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
       |  the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
       |     +- the closure created at tst:18.
       |     +- referenced by REF(0x7d3c58) [refcount 1], which is
       |     |  the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
       |     |     +- the containing scope for CODE(0x8ab430) [refcount 3], which is
       |     |     |  the global &Test::testsub.
       |     |     +- the main body of the program.
       |     +- the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
       +- referenced by REF(0x7cc7c8) [refcount 1], which is
       |  the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
       +- the global $Test::var.
       +- referenced by REF(0x7cc558) [refcount 1], which is
       |  the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
       |     +- referenced by REF(0x8abad0) [refcount 1], which is
       |     |  the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
       |     +- referenced by REF(0x8ab4f0) [refcount 1], which is
       |        the global $Test::global_hashref.
       +- referenced by REF(0x7ae518) [refcount 1], which is
       |  the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
       |     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 likely want to use when tracking down
        references.

    @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
        value you are interested in (e.g. "HASH(0x176ff70)"). This function
        can be used to turn the address into a reference to that value. It
        is quite safe to call on valid addresses, but extremely dangerous to
        call on invalid ones. *No checks whatsoever will be done*, so don't
        use this unless you really know the value is the address of a valid
        perl value.

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

    $ptr = Devel::FindRef::ref2ptr $reference
        The opposite of "ptr2ref", above: returns the internal address of
        the value pointed to by the passed reference. This function is safe
        to call on anything, and returns the same value that a normal
        reference would if used in a numeric context.

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
    specifies a depth, it is not overridden.

AUTHOR
    Marc Lehmann <pcg@goof.com>.

COPYRIGHT AND LICENSE
    Copyright (C) 2007, 2008, 2009, 2013 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:	1.12
Committed:	Tue Jun 3 18:40:50 2014 UTC (9 years, 11 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_46, rel-1_44, rel-1_45, HEAD
Changes since 1.11:	+1 -1 lines
Log Message:	1.44
#	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	root	1.11	package Test;
21	root	1.9
22			use Devel::FindRef;
23			use Scalar::Util;
24	root	1.10
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	1.10
30	root	1.11	sub testsub {
31	root	1.9	my $testsub_local = $global_hashref;
32	root	1.2	print Devel::FindRef::track \$var;
33	root	1.11	}
34	root	1.9
35			my $closure = sub {
36			my $closure_var = \$_[0];
37			Scalar::Util::weaken (my $weak_ref = \$var);
38			testsub;
39			};
40
41			$closure->($var);
42	root	1.2
43	root	1.3	The output is as follows (or similar to this, in case I forget to update
44			the manpage after some changes):
45	root	1.2
46	root	1.9	SCALAR(0x7cc888) [refcount 6] is
47			+- referenced by REF(0x8abcc8) [refcount 1], which is
48	root	1.11	\| the lexical '$closure_var' in CODE(0x8abc50) [refcount 4], which is
49	root	1.9	\| +- the closure created at tst:18.
50			\| +- referenced by REF(0x7d3c58) [refcount 1], which is
51	root	1.11	\| \| the lexical '$closure' in CODE(0x7ae530) [refcount 2], which is
52	root	1.9	\| \| +- the containing scope for CODE(0x8ab430) [refcount 3], which is
53	root	1.11	\| \| \| the global &Test::testsub.
54	root	1.9	\| \| +- the main body of the program.
55	root	1.11	\| +- the lexical '&' in CODE(0x7ae530) [refcount 2], which was seen before.
56	root	1.9	+- referenced by REF(0x7cc7c8) [refcount 1], which is
57	root	1.11	\| the lexical '$global_my' in CODE(0x7ae530) [refcount 2], which was seen before.
58			+- the global $Test::var.
59	root	1.9	+- referenced by REF(0x7cc558) [refcount 1], which is
60	root	1.11	\| the member 'ukukey2' of HASH(0x7ae140) [refcount 2], which is
61	root	1.9	\| +- referenced by REF(0x8abad0) [refcount 1], which is
62	root	1.11	\| \| the lexical '$testsub_local' in CODE(0x8ab430) [refcount 3], which was seen before.
63	root	1.9	\| +- referenced by REF(0x8ab4f0) [refcount 1], which is
64	root	1.11	\| the global $Test::global_hashref.
65	root	1.9	+- referenced by REF(0x7ae518) [refcount 1], which is
66	root	1.11	\| the member 'ukukey' of HASH(0x7d3bb0) [refcount 1], which is
67			\| the global %Test::global_hash.
68	root	1.9	+- referenced by REF(0x7ae2f0) [refcount 1], which is
69			a temporary on the stack.
70	root	1.2
71			It is a bit convoluted to read, but basically it says that the value
72	root	1.9	stored in $var is referenced by:
73	root	1.2
74	root	1.10	- the lexical $closure_var (0x8abcc8), which is inside an instantiated
75			closure, which in turn is used quite a bit.
76			- the package-level lexical $global_my.
77			- the global package variable named $Test::var.
78			- the hash element "ukukey2", in the hash in the my variable
79	root	1.9	$testsub_local in the sub "Test::testsub" and also in the hash
80			"$referenced by Test::hash2".
81	root	1.10	- the hash element with key "ukukey" in the hash stored in %Test::hash.
82	root	1.9	- some anonymous mortalised reference on the stack (which is caused by
83			calling "track" with the expression "\$var", which creates the
84			reference).
85
86			And all these account for six reference counts.
87	root	1.2
88			EXPORTS
89	root	1.4	None.
90	root	1.2
91			FUNCTIONS
92	root	1.4	$string = Devel::FindRef::track $ref[, $depth]
93			Track the perl value pointed to by $ref up to a depth of $depth and
94			return a descriptive string. $ref can point at any perl value, be it
95			anonymous sub, hash, array, scalar etc.
96
97	root	1.11	This is the function you most likely want to use when tracking down
98			references.
99	root	1.4
100			@references = Devel::FindRef::find $ref
101			Return arrayrefs that contain [$message, $ref] pairs. The message
102			describes what kind of reference was found and the $ref is the
103	root	1.5	reference itself, which can be omitted if "find" decided to end the
104			search. The returned references are all weak references.
105	root	1.4
106			The "track" function uses this to find references to the value you
107			are interested in and recurses on the returned references.
108
109			$ref = Devel::FindRef::ptr2ref $integer
110			Sometimes you know (from debugging output) the address of a perl
111	root	1.11	value you are interested in (e.g. "HASH(0x176ff70)"). This function
112			can be used to turn the address into a reference to that value. It
113	root	1.4	is quite safe to call on valid addresses, but extremely dangerous to
114	root	1.11	call on invalid ones. No checks whatsoever will be done, so don't
115			use this unless you really know the value is the address of a valid
116			perl value.
117	root	1.4
118			# we know that HASH(0x176ff70) exists, so turn it into a hashref:
119			my $ref_to_hash = Devel::FindRef::ptr2ref 0x176ff70;
120	root	1.2
121	root	1.11	$ptr = Devel::FindRef::ref2ptr $reference
122	root	1.8	The opposite of "ptr2ref", above: returns the internal address of
123	root	1.11	the value pointed to by the passed reference. This function is safe
124	root	1.12	to call on anything, and returns the same value that a normal
125	root	1.11	reference would if used in a numeric context.
126	root	1.8
127	root	1.7	ENVIRONMENT VARIABLES
128			You can set the environment variable "PERL_DEVEL_FINDREF_DEPTH" to an
129			integer to override the default depth in "track". If a call explicitly
130	root	1.11	specifies a depth, it is not overridden.
131	root	1.7
132	root	1.2	AUTHOR
133	root	1.4	Marc Lehmann <pcg@goof.com>.
134	root	1.2
135			COPYRIGHT AND LICENSE
136	root	1.11	Copyright (C) 2007, 2008, 2009, 2013 by Marc Lehmann.
137	root	1.2
138	root	1.4	This library is free software; you can redistribute it and/or modify it
139			under the same terms as Perl itself, either Perl version 5.8.8 or, at
140			your option, any later version of Perl 5 you may have available.
141	root	1.2