[perl5.git] / ext / Devel / Peek / Peek.pm

# Devel::Peek - A data debugging tool for the XS programmer
# The documentation is after the __END__

package Devel::Peek;

$VERSION = 0.95;

require Exporter;
use XSLoader ();

@ISA = qw(Exporter);
@EXPORT = qw(Dump mstat DeadCode DumpArray DumpWithOP DumpProg);
@EXPORT_OK = qw(SvREFCNT SvREFCNT_inc SvREFCNT_dec);
%EXPORT_TAGS = ('ALL' => [@EXPORT, @EXPORT_OK]);

XSLoader::load 'Devel::Peek';

sub DumpWithOP ($;$) {
   local($Devel::Peek::dump_ops)=1;
   my $depth = @_ > 1 ? $_[1] : 4 ;
   Dump($_[0],$depth);
}

1;
__END__

=head1 NAME

Devel::Peek - A data debugging tool for the XS programmer

=head1 SYNOPSIS

        use Devel::Peek;
        Dump( $a );
        Dump( $a, 5 );
        DumpArray( 5, $a, $b, ... );
	mstat "Point 5";

=head1 DESCRIPTION

Devel::Peek contains functions which allows raw Perl datatypes to be
manipulated from a Perl script.  This is used by those who do XS programming
to check that the data they are sending from C to Perl looks as they think
it should look.  The trick, then, is to know what the raw datatype is
supposed to look like when it gets to Perl.  This document offers some tips
and hints to describe good and bad raw data.

It is very possible that this document will fall far short of being useful
to the casual reader.  The reader is expected to understand the material in
the first few sections of L<perlguts>.

Devel::Peek supplies a C<Dump()> function which can dump a raw Perl
datatype, and C<mstat("marker")> function to report on memory usage
(if perl is compiled with corresponding option).  The function
DeadCode() provides statistics on the data "frozen" into inactive
C<CV>.  Devel::Peek also supplies C<SvREFCNT()>, C<SvREFCNT_inc()>, and
C<SvREFCNT_dec()> which can query, increment, and decrement reference
counts on SVs.  This document will take a passive, and safe, approach
to data debugging and for that it will describe only the C<Dump()>
function.  For format of output of mstats() see
L<perldebug/Using C<$ENV{PERL_DEBUG_MSTATS}>>.

Function C<DumpArray()> allows dumping of multiple values (useful when you
need to analize returns of functions).

The global variable $Devel::Peek::pv_limit can be set to limit the
number of character printed in various string values.  Setting it to 0
means no limit.

=head1 EXAMPLES

The following examples don't attempt to show everything as that would be a
monumental task, and, frankly, we don't want this manpage to be an internals
document for Perl.  The examples do demonstrate some basics of the raw Perl
datatypes, and should suffice to get most determined people on their way.
There are no guidewires or safety nets, nor blazed trails, so be prepared to
travel alone from this point and on and, if at all possible, don't fall into
the quicksand (it's bad for business).

Oh, one final bit of advice: take L<perlguts> with you.  When you return we
expect to see it well-thumbed.

=head2 A simple scalar string

Let's begin by looking a simple scalar which is holding a string.

        use Devel::Peek;
        $a = "hello";
        Dump $a;

The output:

        SV = PVIV(0xbc288)
          REFCNT = 1
          FLAGS = (POK,pPOK)
          IV = 0
          PV = 0xb2048 "hello"\0
          CUR = 5
          LEN = 6

This says C<$a> is an SV, a scalar.  The scalar is a PVIV, a string.
Its reference count is 1.  It has the C<POK> flag set, meaning its
current PV field is valid.  Because POK is set we look at the PV item
to see what is in the scalar.  The \0 at the end indicate that this
PV is properly NUL-terminated.
If the FLAGS had been IOK we would look
at the IV item.  CUR indicates the number of characters in the PV.
LEN indicates the number of bytes requested for the PV (one more than
CUR, in this case, because LEN includes an extra byte for the
end-of-string marker).

=head2 A simple scalar number

If the scalar contains a number the raw SV will be leaner.

        use Devel::Peek;
        $a = 42;
        Dump $a;

The output:

        SV = IV(0xbc818)
          REFCNT = 1
          FLAGS = (IOK,pIOK)
          IV = 42

This says C<$a> is an SV, a scalar.  The scalar is an IV, a number.  Its
reference count is 1.  It has the C<IOK> flag set, meaning it is currently
being evaluated as a number.  Because IOK is set we look at the IV item to
see what is in the scalar.

=head2 A simple scalar with an extra reference

If the scalar from the previous example had an extra reference:

        use Devel::Peek;
        $a = 42;
        $b = \$a;
        Dump $a;

The output:

        SV = IV(0xbe860)
          REFCNT = 2
          FLAGS = (IOK,pIOK)
          IV = 42

Notice that this example differs from the previous example only in its
reference count.  Compare this to the next example, where we dump C<$b>
instead of C<$a>.

=head2 A reference to a simple scalar

This shows what a reference looks like when it references a simple scalar.

        use Devel::Peek;
        $a = 42;
        $b = \$a;
        Dump $b;

The output:

        SV = RV(0xf041c)
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xbab08
        SV = IV(0xbe860)
          REFCNT = 2
          FLAGS = (IOK,pIOK)
          IV = 42

Starting from the top, this says C<$b> is an SV.  The scalar is an RV, a
reference.  It has the C<ROK> flag set, meaning it is a reference.  Because
ROK is set we have an RV item rather than an IV or PV.  Notice that Dump
follows the reference and shows us what C<$b> was referencing.  We see the
same C<$a> that we found in the previous example.

Note that the value of C<RV> coincides with the numbers we see when we
stringify $b. The addresses inside RV() and IV() are addresses of
C<X***> structure which holds the current state of an C<SV>. This
address may change during lifetime of an SV.

=head2 A reference to an array

This shows what a reference to an array looks like.

        use Devel::Peek;
        $a = [42];
        Dump $a;

The output:

        SV = RV(0xf041c)
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xb2850
        SV = PVAV(0xbd448)
          REFCNT = 1
          FLAGS = ()
          IV = 0
          NV = 0
          ARRAY = 0xb2048
          ALLOC = 0xb2048
          FILL = 0
          MAX = 0
          ARYLEN = 0x0
          FLAGS = (REAL)
        Elt No. 0 0xb5658
        SV = IV(0xbe860)
          REFCNT = 1
          FLAGS = (IOK,pIOK)
          IV = 42

This says C<$a> is an SV and that it is an RV.  That RV points to
another SV which is a PVAV, an array.  The array has one element,
element zero, which is another SV. The field C<FILL> above indicates
the last element in the array, similar to C<$#$a>.

If C<$a> pointed to an array of two elements then we would see the
following.

        use Devel::Peek 'Dump';
        $a = [42,24];
        Dump $a;

The output:

        SV = RV(0xf041c)
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xb2850
        SV = PVAV(0xbd448)
          REFCNT = 1
          FLAGS = ()
          IV = 0
          NV = 0
          ARRAY = 0xb2048
          ALLOC = 0xb2048
          FILL = 0
          MAX = 0
          ARYLEN = 0x0
          FLAGS = (REAL)
        Elt No. 0  0xb5658
        SV = IV(0xbe860)
          REFCNT = 1
          FLAGS = (IOK,pIOK)
          IV = 42
        Elt No. 1  0xb5680
        SV = IV(0xbe818)
          REFCNT = 1
          FLAGS = (IOK,pIOK)
          IV = 24

Note that C<Dump> will not report I<all> the elements in the array,
only several first (depending on how deep it already went into the
report tree).

=head2 A reference to a hash

The following shows the raw form of a reference to a hash.

        use Devel::Peek;
        $a = {hello=>42};
        Dump $a;

The output:

        SV = RV(0xf041c)
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xb2850
        SV = PVHV(0xbd448)
          REFCNT = 1
          FLAGS = ()
          NV = 0
          ARRAY = 0xbd748
          KEYS = 1
          FILL = 1
          MAX = 7
          RITER = -1
          EITER = 0x0
        Elt "hello" => 0xbaaf0
        SV = IV(0xbe860)
          REFCNT = 1
          FLAGS = (IOK,pIOK)
          IV = 42

This shows C<$a> is a reference pointing to an SV.  That SV is a PVHV, a
hash. Fields RITER and EITER are used by C<L<each>>.

=head2 Dumping a large array or hash

The C<Dump()> function, by default, dumps up to 4 elements from a
toplevel array or hash.  This number can be increased by supplying a
second argument to the function.

        use Devel::Peek;
        $a = [10,11,12,13,14];
        Dump $a;

Notice that C<Dump()> prints only elements 10 through 13 in the above code.
The following code will print all of the elements.

        use Devel::Peek 'Dump';
        $a = [10,11,12,13,14];
        Dump $a, 5;

=head2 A reference to an SV which holds a C pointer

This is what you really need to know as an XS programmer, of course.  When
an XSUB returns a pointer to a C structure that pointer is stored in an SV
and a reference to that SV is placed on the XSUB stack.  So the output from
an XSUB which uses something like the T_PTROBJ map might look something like
this:

        SV = RV(0xf381c)
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xb8ad8
        SV = PVMG(0xbb3c8)
          REFCNT = 1
          FLAGS = (OBJECT,IOK,pIOK)
          IV = 729160
          NV = 0
          PV = 0
          STASH = 0xc1d10       "CookBookB::Opaque"

This shows that we have an SV which is an RV.  That RV points at another
SV.  In this case that second SV is a PVMG, a blessed scalar.  Because it is
blessed it has the C<OBJECT> flag set.  Note that an SV which holds a C
pointer also has the C<IOK> flag set.  The C<STASH> is set to the package
name which this SV was blessed into.

The output from an XSUB which uses something like the T_PTRREF map, which
doesn't bless the object, might look something like this:

        SV = RV(0xf381c)
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xb8ad8
        SV = PVMG(0xbb3c8)
          REFCNT = 1
          FLAGS = (IOK,pIOK)
          IV = 729160
          NV = 0
          PV = 0

=head2 A reference to a subroutine

Looks like this:

	SV = RV(0x798ec)
	  REFCNT = 1
	  FLAGS = (TEMP,ROK)
	  RV = 0x1d453c
	SV = PVCV(0x1c768c)
	  REFCNT = 2
	  FLAGS = ()
	  IV = 0
	  NV = 0
	  COMP_STASH = 0x31068  "main"
	  START = 0xb20e0
	  ROOT = 0xbece0
	  XSUB = 0x0
	  XSUBANY = 0
	  GVGV::GV = 0x1d44e8   "MY" :: "top_targets"
	  FILE = "(eval 5)"
	  DEPTH = 0
	  PADLIST = 0x1c9338

This shows that 

=over

=item

the subroutine is not an XSUB (since C<START> and C<ROOT> are
non-zero, and C<XSUB> is zero);

=item

that it was compiled in the package C<main>;

=item

under the name C<MY::top_targets>; 

=item

inside a 5th eval in the program;

=item

it is not currently executed (see C<DEPTH>);

=item

it has no prototype (C<PROTOTYPE> field is missing).

=over

=head1 EXPORTS

C<Dump>, C<mstat>, C<DeadCode>, C<DumpArray>, C<DumpWithOP> and
C<DumpProg> by default. Additionally available C<SvREFCNT>,
C<SvREFCNT_inc> and C<SvREFCNT_dec>.

=head1 BUGS

Readers have been known to skip important parts of L<perlguts>, causing much
frustration for all.

=head1 AUTHOR

Ilya Zakharevich	ilya@math.ohio-state.edu

Copyright (c) 1995-98 Ilya Zakharevich. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

Author of this software makes no claim whatsoever about suitability,
reliability, edability, editability or usability of this product, and
should not be kept liable for any damage resulting from the use of
it. If you can use it, you are in luck, if not, I should not be kept
responsible. Keep a handy copy of your backup tape at hand.

=head1 SEE ALSO

L<perlguts>, and L<perlguts>, again.

=cut
Commit	Line	Data
3967c732 JD	1	# Devel::Peek - A data debugging tool for the XS programmer
	2	# The documentation is after the __END__
	3
	4	package Devel::Peek;
	5
9426adcd	6	$VERSION = 0.95;
3967c732 JD	7
3967c732 JD	8	require Exporter;
9426adcd	9	use XSLoader ();
3967c732	10
9426adcd	11	@ISA = qw(Exporter);
3967c732 JD	12	@EXPORT = qw(Dump mstat DeadCode DumpArray DumpWithOP DumpProg);
	13	@EXPORT_OK = qw(SvREFCNT SvREFCNT_inc SvREFCNT_dec);
	14	%EXPORT_TAGS = ('ALL' => [@EXPORT, @EXPORT_OK]);
	15
9426adcd	16	XSLoader::load 'Devel::Peek';
3967c732 JD	17
	18	sub DumpWithOP ($;$) {
	19	local($Devel::Peek::dump_ops)=1;
	20	my $depth = @_ > 1 ? $_[1] : 4 ;
	21	Dump($_[0],$depth);
	22	}
	23
	24	1;
	25	__END__
	26
	27	=head1 NAME
	28
	29	Devel::Peek - A data debugging tool for the XS programmer
	30
	31	=head1 SYNOPSIS
	32
	33	use Devel::Peek;
	34	Dump( $a );
	35	Dump( $a, 5 );
	36	DumpArray( 5, $a, $b, ... );
	37	mstat "Point 5";
	38
	39	=head1 DESCRIPTION
	40
	41	Devel::Peek contains functions which allows raw Perl datatypes to be
	42	manipulated from a Perl script. This is used by those who do XS programming
	43	to check that the data they are sending from C to Perl looks as they think
	44	it should look. The trick, then, is to know what the raw datatype is
	45	supposed to look like when it gets to Perl. This document offers some tips
	46	and hints to describe good and bad raw data.
	47
	48	It is very possible that this document will fall far short of being useful
	49	to the casual reader. The reader is expected to understand the material in
	50	the first few sections of L<perlguts>.
	51
	52	Devel::Peek supplies a C<Dump()> function which can dump a raw Perl
	53	datatype, and C<mstat("marker")> function to report on memory usage
	54	(if perl is compiled with corresponding option). The function
	55	DeadCode() provides statistics on the data "frozen" into inactive
	56	C<CV>. Devel::Peek also supplies C<SvREFCNT()>, C<SvREFCNT_inc()>, and
	57	C<SvREFCNT_dec()> which can query, increment, and decrement reference
	58	counts on SVs. This document will take a passive, and safe, approach
	59	to data debugging and for that it will describe only the C<Dump()>
a423dfdd IZ	60	function. For format of output of mstats() see
a423dfdd IZ	61	L<perldebug/Using C<$ENV{PERL_DEBUG_MSTATS}>>.
3967c732 JD	62
	63	Function C<DumpArray()> allows dumping of multiple values (useful when you
	64	need to analize returns of functions).
	65
	66	The global variable $Devel::Peek::pv_limit can be set to limit the
	67	number of character printed in various string values. Setting it to 0
	68	means no limit.
	69
	70	=head1 EXAMPLES
	71
	72	The following examples don't attempt to show everything as that would be a
	73	monumental task, and, frankly, we don't want this manpage to be an internals
	74	document for Perl. The examples do demonstrate some basics of the raw Perl
	75	datatypes, and should suffice to get most determined people on their way.
	76	There are no guidewires or safety nets, nor blazed trails, so be prepared to
	77	travel alone from this point and on and, if at all possible, don't fall into
	78	the quicksand (it's bad for business).
	79
	80	Oh, one final bit of advice: take L<perlguts> with you. When you return we
	81	expect to see it well-thumbed.
	82
	83	=head2 A simple scalar string
	84
	85	Let's begin by looking a simple scalar which is holding a string.
	86
a423dfdd	87	use Devel::Peek;
3967c732 JD	88	$a = "hello";
	89	Dump $a;
	90
	91	The output:
	92
	93	SV = PVIV(0xbc288)
	94	REFCNT = 1
	95	FLAGS = (POK,pPOK)
	96	IV = 0
	97	PV = 0xb2048 "hello"\0
	98	CUR = 5
	99	LEN = 6
	100
	101	This says C<$a> is an SV, a scalar. The scalar is a PVIV, a string.
	102	Its reference count is 1. It has the C<POK> flag set, meaning its
	103	current PV field is valid. Because POK is set we look at the PV item
	104	to see what is in the scalar. The \0 at the end indicate that this
	105	PV is properly NUL-terminated.
	106	If the FLAGS had been IOK we would look
	107	at the IV item. CUR indicates the number of characters in the PV.
	108	LEN indicates the number of bytes requested for the PV (one more than
	109	CUR, in this case, because LEN includes an extra byte for the
	110	end-of-string marker).
	111
	112	=head2 A simple scalar number
	113
	114	If the scalar contains a number the raw SV will be leaner.
	115
a423dfdd	116	use Devel::Peek;
3967c732 JD	117	$a = 42;
	118	Dump $a;
	119
	120	The output:
	121
	122	SV = IV(0xbc818)
	123	REFCNT = 1
	124	FLAGS = (IOK,pIOK)
	125	IV = 42
	126
	127	This says C<$a> is an SV, a scalar. The scalar is an IV, a number. Its
	128	reference count is 1. It has the C<IOK> flag set, meaning it is currently
	129	being evaluated as a number. Because IOK is set we look at the IV item to
	130	see what is in the scalar.
	131
	132	=head2 A simple scalar with an extra reference
	133
	134	If the scalar from the previous example had an extra reference:
	135
a423dfdd	136	use Devel::Peek;
3967c732 JD	137	$a = 42;
	138	$b = \$a;
	139	Dump $a;
	140
	141	The output:
	142
	143	SV = IV(0xbe860)
	144	REFCNT = 2
	145	FLAGS = (IOK,pIOK)
	146	IV = 42
	147
	148	Notice that this example differs from the previous example only in its
	149	reference count. Compare this to the next example, where we dump C<$b>
	150	instead of C<$a>.
	151
	152	=head2 A reference to a simple scalar
	153
	154	This shows what a reference looks like when it references a simple scalar.
	155
a423dfdd	156	use Devel::Peek;
3967c732 JD	157	$a = 42;
	158	$b = \$a;
	159	Dump $b;
	160
	161	The output:
	162
	163	SV = RV(0xf041c)
	164	REFCNT = 1
	165	FLAGS = (ROK)
	166	RV = 0xbab08
	167	SV = IV(0xbe860)
	168	REFCNT = 2
	169	FLAGS = (IOK,pIOK)
	170	IV = 42
	171
	172	Starting from the top, this says C<$b> is an SV. The scalar is an RV, a
	173	reference. It has the C<ROK> flag set, meaning it is a reference. Because
	174	ROK is set we have an RV item rather than an IV or PV. Notice that Dump
	175	follows the reference and shows us what C<$b> was referencing. We see the
	176	same C<$a> that we found in the previous example.
	177
	178	Note that the value of C<RV> coincides with the numbers we see when we
	179	stringify $b. The addresses inside RV() and IV() are addresses of
	180	C<X***> structure which holds the current state of an C<SV>. This
	181	address may change during lifetime of an SV.
	182
	183	=head2 A reference to an array
	184
	185	This shows what a reference to an array looks like.
	186
a423dfdd	187	use Devel::Peek;
3967c732 JD	188	$a = [42];
	189	Dump $a;
	190
	191	The output:
	192
	193	SV = RV(0xf041c)
	194	REFCNT = 1
	195	FLAGS = (ROK)
	196	RV = 0xb2850
	197	SV = PVAV(0xbd448)
	198	REFCNT = 1
	199	FLAGS = ()
	200	IV = 0
	201	NV = 0
	202	ARRAY = 0xb2048
	203	ALLOC = 0xb2048
	204	FILL = 0
	205	MAX = 0
	206	ARYLEN = 0x0
	207	FLAGS = (REAL)
	208	Elt No. 0 0xb5658
	209	SV = IV(0xbe860)
	210	REFCNT = 1
	211	FLAGS = (IOK,pIOK)
	212	IV = 42
	213
	214	This says C<$a> is an SV and that it is an RV. That RV points to
	215	another SV which is a PVAV, an array. The array has one element,
	216	element zero, which is another SV. The field C<FILL> above indicates
	217	the last element in the array, similar to C<$#$a>.
	218
	219	If C<$a> pointed to an array of two elements then we would see the
	220	following.
	221
	222	use Devel::Peek 'Dump';
	223	$a = [42,24];
	224	Dump $a;
	225
	226	The output:
	227
	228	SV = RV(0xf041c)
	229	REFCNT = 1
	230	FLAGS = (ROK)
	231	RV = 0xb2850
	232	SV = PVAV(0xbd448)
	233	REFCNT = 1
	234	FLAGS = ()
	235	IV = 0
	236	NV = 0
	237	ARRAY = 0xb2048
	238	ALLOC = 0xb2048
	239	FILL = 0
	240	MAX = 0
	241	ARYLEN = 0x0
	242	FLAGS = (REAL)
	243	Elt No. 0 0xb5658
	244	SV = IV(0xbe860)
	245	REFCNT = 1
	246	FLAGS = (IOK,pIOK)
	247	IV = 42
	248	Elt No. 1 0xb5680
	249	SV = IV(0xbe818)
	250	REFCNT = 1
	251	FLAGS = (IOK,pIOK)
252	IV = 24
253
254	Note that C<Dump> will not report I<all> the elements in the array,
255	only several first (depending on how deep it already went into the
256	report tree).
257
258	=head2 A reference to a hash
259
260	The following shows the raw form of a reference to a hash.
261
a423dfdd	262	use Devel::Peek;
3967c732 JD	263	$a = {hello=>42};
	264	Dump $a;
	265
	266	The output:
	267
	268	SV = RV(0xf041c)
	269	REFCNT = 1
	270	FLAGS = (ROK)
	271	RV = 0xb2850
	272	SV = PVHV(0xbd448)
	273	REFCNT = 1
	274	FLAGS = ()
	275	NV = 0
	276	ARRAY = 0xbd748
	277	KEYS = 1
	278	FILL = 1
	279	MAX = 7
	280	RITER = -1
	281	EITER = 0x0
	282	Elt "hello" => 0xbaaf0
	283	SV = IV(0xbe860)
	284	REFCNT = 1
	285	FLAGS = (IOK,pIOK)
	286	IV = 42
	287
	288	This shows C<$a> is a reference pointing to an SV. That SV is a PVHV, a
	289	hash. Fields RITER and EITER are used by C<L<each>>.
	290
	291	=head2 Dumping a large array or hash
	292
	293	The C<Dump()> function, by default, dumps up to 4 elements from a
	294	toplevel array or hash. This number can be increased by supplying a
	295	second argument to the function.
	296
a423dfdd	297	use Devel::Peek;
3967c732 JD	298	$a = [10,11,12,13,14];
	299	Dump $a;
	300
	301	Notice that C<Dump()> prints only elements 10 through 13 in the above code.
	302	The following code will print all of the elements.
	303
	304	use Devel::Peek 'Dump';
	305	$a = [10,11,12,13,14];
	306	Dump $a, 5;
	307
	308	=head2 A reference to an SV which holds a C pointer
	309
	310	This is what you really need to know as an XS programmer, of course. When
	311	an XSUB returns a pointer to a C structure that pointer is stored in an SV
	312	and a reference to that SV is placed on the XSUB stack. So the output from
	313	an XSUB which uses something like the T_PTROBJ map might look something like
	314	this:
	315
	316	SV = RV(0xf381c)
	317	REFCNT = 1
	318	FLAGS = (ROK)
	319	RV = 0xb8ad8
	320	SV = PVMG(0xbb3c8)
	321	REFCNT = 1
	322	FLAGS = (OBJECT,IOK,pIOK)
	323	IV = 729160
	324	NV = 0
	325	PV = 0
	326	STASH = 0xc1d10 "CookBookB::Opaque"
	327
	328	This shows that we have an SV which is an RV. That RV points at another
	329	SV. In this case that second SV is a PVMG, a blessed scalar. Because it is
	330	blessed it has the C<OBJECT> flag set. Note that an SV which holds a C
	331	pointer also has the C<IOK> flag set. The C<STASH> is set to the package
	332	name which this SV was blessed into.
	333
	334	The output from an XSUB which uses something like the T_PTRREF map, which
	335	doesn't bless the object, might look something like this:
	336
	337	SV = RV(0xf381c)
	338	REFCNT = 1
	339	FLAGS = (ROK)
	340	RV = 0xb8ad8
	341	SV = PVMG(0xbb3c8)
	342	REFCNT = 1
	343	FLAGS = (IOK,pIOK)
	344	IV = 729160
	345	NV = 0
	346	PV = 0
	347
	348	=head2 A reference to a subroutine
	349
	350	Looks like this:
	351
	352	SV = RV(0x798ec)
	353	REFCNT = 1
	354	FLAGS = (TEMP,ROK)
	355	RV = 0x1d453c
	356	SV = PVCV(0x1c768c)
	357	REFCNT = 2
	358	FLAGS = ()
	359	IV = 0
	360	NV = 0
	361	COMP_STASH = 0x31068 "main"
362	START = 0xb20e0
363	ROOT = 0xbece0
364	XSUB = 0x0
365	XSUBANY = 0
366	GVGV::GV = 0x1d44e8 "MY" :: "top_targets"
57843af0	367	FILE = "(eval 5)"
3967c732 JD	368	DEPTH = 0
	369	PADLIST = 0x1c9338
	370
	371	This shows that
	372
	373	=over
	374
	375	=item
	376
	377	the subroutine is not an XSUB (since C<START> and C<ROOT> are
	378	non-zero, and C<XSUB> is zero);
	379
	380	=item
	381
	382	that it was compiled in the package C<main>;
	383
	384	=item
	385
	386	under the name C<MY::top_targets>;
	387
	388	=item
	389
	390	inside a 5th eval in the program;
	391
	392	=item
	393
	394	it is not currently executed (see C<DEPTH>);
	395
	396	=item
	397
	398	it has no prototype (C<PROTOTYPE> field is missing).
	399
	400	=over
	401
	402	=head1 EXPORTS
	403
	404	C<Dump>, C<mstat>, C<DeadCode>, C<DumpArray>, C<DumpWithOP> and
	405	C<DumpProg> by default. Additionally available C<SvREFCNT>,
	406	C<SvREFCNT_inc> and C<SvREFCNT_dec>.
	407
	408	=head1 BUGS
	409
	410	Readers have been known to skip important parts of L<perlguts>, causing much
	411	frustration for all.
	412
	413	=head1 AUTHOR
	414
	415	Ilya Zakharevich ilya@math.ohio-state.edu
	416
	417	Copyright (c) 1995-98 Ilya Zakharevich. All rights reserved.
	418	This program is free software; you can redistribute it and/or
	419	modify it under the same terms as Perl itself.
	420
	421	Author of this software makes no claim whatsoever about suitability,
	422	reliability, edability, editability or usability of this product, and
	423	should not be kept liable for any damage resulting from the use of
	424	it. If you can use it, you are in luck, if not, I should not be kept
	425	responsible. Keep a handy copy of your backup tape at hand.
	426
	427	=head1 SEE ALSO
	428
	429	L<perlguts>, and L<perlguts>, again.
	430
	431	=cut