[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 = '1.18';
$XS_VERSION = $VERSION;
$VERSION = eval $VERSION;

require Exporter;
require XSLoader;

@ISA = qw(Exporter);
@EXPORT = qw(Dump mstat DeadCode DumpArray DumpWithOP DumpProg
	     fill_mstats mstats_fillhash mstats2hash runops_debug debug_flags);
@EXPORT_OK = qw(SvREFCNT CvGV);
%EXPORT_TAGS = ('ALL' => [@EXPORT, @EXPORT_OK]);

XSLoader::load();

sub import {
  my $c = shift;
  my $ops_rx = qr/^:opd(=[stP]*)?\b/;
  my @db = grep m/$ops_rx/, @_;
  @_ = grep !m/$ops_rx/, @_;
  if (@db) {
    die "Too many :opd options" if @db > 1;
    runops_debug(1);
    my $flags = ($db[0] =~ m/$ops_rx/ and $1);
    $flags = 'st' unless defined $flags;
    my $f = 0;
    $f |= 2  if $flags =~ /s/;
    $f |= 8  if $flags =~ /t/;
    $f |= 64 if $flags =~ /P/;
    $^D |= $f if $f;
  }
  unshift @_, $c;
  goto &Exporter::import;
}

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

$D_flags = 'psltocPmfrxuLHXDSTR';

sub debug_flags (;$) {
  my $out = "";
  for my $i (0 .. length($D_flags)-1) {
    $out .= substr $D_flags, $i, 1 if $^D & (1<<$i);
  }
  my $arg = shift;
  my $num = $arg;
  if (defined $arg and $arg =~ /\D/) {
    die "unknown flags in debug_flags()" if $arg =~ /[^-$D_flags]/;
    my ($on,$off) = split /-/, "$arg-";
    $num = $^D;
    $num |=  (1<<index($D_flags, $_)) for split //, $on;
    $num &= ~(1<<index($D_flags, $_)) for split //, $off;
  }
  $^D = $num if defined $arg;
  $out
}

1;
__END__

=head1 NAME

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

=head1 SYNOPSIS

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

        use Devel::Peek ':opd=st';

=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()> which can query 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.

The C<Dump()> function takes one or two arguments: something to dump, and
an optional limit for recursion and array elements (default is 4).  The
first argument is evaluted in rvalue scalar context, with exceptions for
@array and %hash, which dump the array or hash itself.  So C<Dump @array>
works, as does C<Dump $foo>.  And C<Dump pos> will call C<pos> in rvalue
context, whereas C<Dump ${\pos}> will call it in lvalue context.

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

If C<use Devel::Peek> directive has a C<:opd=FLAGS> argument,
this switches on debugging of opcode dispatch.  C<FLAGS> should be a
combination of C<s>, C<t>, and C<P> (see B<-D> flags in L<perlrun>).
C<:opd> is a shortcut for C<:opd=st>.

=head2 Runtime debugging

C<CvGV($cv)> return one of the globs associated to a subroutine reference $cv.

debug_flags() returns a string representation of C<$^D> (similar to
what is allowed for B<-D> flag).  When called with a numeric argument,
sets $^D to the corresponding value.  When called with an argument of
the form C<"flags-flags">, set on/off bits of C<$^D> corresponding to
letters before/after C<->.  (The returned value is for C<$^D> before
the modification.)

runops_debug() returns true if the current I<opcode dispatcher> is the
debugging one.  When called with an argument, switches to debugging or
non-debugging dispatcher depending on the argument (active for
newly-entered subs/etc only).  (The returned value is for the dispatcher before the modification.)

=head2 Memory footprint debugging

When perl is compiled with support for memory footprint debugging
(default with Perl's malloc()), Devel::Peek provides an access to this API.

Use mstat() function to emit a memory state statistic to the terminal.
For more information on the format of output of mstat() see
L<perldebguts/Using $ENV{PERL_DEBUG_MSTATS}>.

Three additional functions allow access to this statistic from Perl.
First, use C<mstats_fillhash(%hash)> to get the information contained
in the output of mstat() into %hash. The field of this hash are

  minbucket nbuckets sbrk_good sbrk_slack sbrked_remains sbrks
  start_slack topbucket topbucket_ev topbucket_odd total total_chain
  total_sbrk totfree

Two additional fields C<free>, C<used> contain array references which
provide per-bucket count of free and used chunks.  Two other fields
C<mem_size>, C<available_size> contain array references which provide
the information about the allocated size and usable size of chunks in
each bucket.  Again, see L<perldebguts/Using $ENV{PERL_DEBUG_MSTATS}>
for details.


Keep in mind that only the first several "odd-numbered" buckets are
used, so the information on size of the "odd-numbered" buckets which are
not used is probably meaningless.

The information in

 mem_size available_size minbucket nbuckets

is the property of a particular build of perl, and does not depend on
the current process.  If you do not provide the optional argument to
the functions mstats_fillhash(), fill_mstats(), mstats2hash(), then
the information in fields C<mem_size>, C<available_size> is not
updated.

C<fill_mstats($buf)> is a much cheaper call (both speedwise and
memory-wise) which collects the statistic into $buf in
machine-readable form.  At a later moment you may need to call
C<mstats2hash($buf, %hash)> to use this information to fill %hash.

All three APIs C<fill_mstats($buf)>, C<mstats_fillhash(%hash)>, and
C<mstats2hash($buf, %hash)> are designed to allocate no memory if used
I<the second time> on the same $buf and/or %hash.

So, if you want to collect memory info in a cycle, you may call

  $#buf = 999;
  fill_mstats($_) for @buf;
  mstats_fillhash(%report, 1);		# Static info too

  foreach (@buf) {
    # Do something...
    fill_mstats $_;			# Collect statistic
  }
  foreach (@buf) {
    mstats2hash($_, %report);		# Preserve static info
    # Do something with %report
  }

=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 = 42; $a = "hello";
        Dump $a;

The output:

        SV = PVIV(0xbc288) at 0xbe9a8
          REFCNT = 1
          FLAGS = (POK,pPOK)
          IV = 42
          PV = 0xb2048 "hello"\0
          CUR = 5
          LEN = 8

This says C<$a> is an SV, a scalar.  The scalar type is a PVIV, which is
capable of holding an integer (IV) and/or a string (PV) value. The scalar's
head is allocated at address 0xbe9a8, while the body is at 0xbc288.
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.
Note that the IV field still contains its old numeric value, but because
FLAGS doesn't have IOK set, we must ignore the IV item.
CUR indicates the number of characters in the PV.  LEN indicates the
number of bytes allocated for the PV (at least one more than CUR, because
LEN includes an extra byte for the end-of-string marker, then usually
rounded up to some efficient allocation unit).

=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) at 0xbe9a8
          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) at 0xbe9a8
          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 = IV(0xf041c) at 0xbe9a0
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xbab08
          SV = IV(0xbe860) at 0xbe9a8
            REFCNT = 2
            FLAGS = (IOK,pIOK)
            IV = 42

Starting from the top, this says C<$b> is an SV.  The scalar is an IV,
which is capable of holding an integer or reference value.
It has the C<ROK> flag set, meaning it is a reference (rather than an
integer or string).  Notice that Dump
follows the reference and shows us what C<$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 IV() are addresses of
C<X***> structures which hold 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 = IV(0xc85998) at 0xc859a8
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xc70de8
          SV = PVAV(0xc71e10) at 0xc70de8
            REFCNT = 1
            FLAGS = ()
            ARRAY = 0xc7e820
            FILL = 0
            MAX = 0
            ARYLEN = 0x0
            FLAGS = (REAL)
            Elt No. 0
            SV = IV(0xc70f88) at 0xc70f98
              REFCNT = 1
              FLAGS = (IOK,pIOK)
              IV = 42

This says C<$a> is a reference (ROK), which points to
another SV which is a PVAV, an array.  The array has one element,
element zero, which is another SV. The field C<FILL> above indicates
the last element in the array, similar to C<$#$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 = IV(0x158c998) at 0x158c9a8
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0x1577de8
          SV = PVAV(0x1578e10) at 0x1577de8
            REFCNT = 1
            FLAGS = ()
            ARRAY = 0x1585820
            FILL = 1
            MAX = 1
            ARYLEN = 0x0
            FLAGS = (REAL)
            Elt No. 0
            SV = IV(0x1577f88) at 0x1577f98
              REFCNT = 1
              FLAGS = (IOK,pIOK)
              IV = 42
            Elt No. 1
            SV = IV(0x158be88) at 0x158be98
              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 = IV(0x8177858) at 0x816a618
	  REFCNT = 1
	  FLAGS = (ROK)
	  RV = 0x814fc10
	  SV = PVHV(0x8167768) at 0x814fc10
	    REFCNT = 1
	    FLAGS = (SHAREKEYS)
	    ARRAY = 0x816c5b8  (0:7, 1:1)
	    hash quality = 100.0%
	    KEYS = 1
	    FILL = 1
	    MAX = 7
	    RITER = -1
	    EITER = 0x0
	    Elt "hello" HASH = 0xc8fd181b
	    SV = IV(0x816c030) at 0x814fcf4
	      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<perlfunc/each>>.

The "quality" of a hash is defined as the total number of comparisons needed
to access every element once, relative to the expected number needed for a
random hash. The value can go over 100%.

The total number of comparisons is equal to the sum of the squares of the
number of entries in each bucket.  For a random hash of C<<n>> keys into
C<<k>> buckets, the expected value is:

		n + n(n-1)/2k

=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 = IV(0xf381c) at 0xc859a8
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xb8ad8
          SV = PVMG(0xbb3c8) at 0xc859a0
            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 a reference, which 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 = IV(0xf381c) at 0xc859a8
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0xb8ad8
          SV = PVMG(0xbb3c8) at 0xc859a0
            REFCNT = 1
            FLAGS = (IOK,pIOK)
            IV = 729160
            NV = 0
            PV = 0

=head2 A reference to a subroutine

Looks like this:

	SV = IV(0x24d2dd8) at 0x24d2de8
	  REFCNT = 1
	  FLAGS = (TEMP,ROK)
	  RV = 0x24e79d8
	  SV = PVCV(0x24e5798) at 0x24e79d8
	    REFCNT = 2
	    FLAGS = ()
	    COMP_STASH = 0x22c9c50	"main"
	    START = 0x22eed60 ===> 0
	    ROOT = 0x22ee490
	    GVGV::GV = 0x22de9d8	"MY" :: "top_targets"
	    FILE = "(eval 5)"
	    DEPTH = 0
	    FLAGS = 0x0
	    OUTSIDE_SEQ = 93
	    PADLIST = 0x22e9ed8
	    PADNAME = 0x22e9ec0(0x22eed00) PAD = 0x22e9ea8(0x22eecd0)
	    OUTSIDE = 0x22c9fb0 (MAIN)


This shows that 

=over 4

=item *

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

=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).

=back

=head1 EXPORTS

C<Dump>, C<mstat>, C<DeadCode>, C<DumpArray>, C<DumpWithOP> and
C<DumpProg>, C<fill_mstats>, C<mstats_fillhash>, C<mstats2hash> 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
1ed44841	6	$VERSION = '1.18';
105cd853 YST	7	$XS_VERSION = $VERSION;
105cd853 YST	8	$VERSION = eval $VERSION;
3967c732 JD	9
3967c732 JD	10	require Exporter;
da4061d3	11	require XSLoader;
3967c732	12
9426adcd	13	@ISA = qw(Exporter);
d1424c31	14	@EXPORT = qw(Dump mstat DeadCode DumpArray DumpWithOP DumpProg
bd16a5f0	15	fill_mstats mstats_fillhash mstats2hash runops_debug debug_flags);
da1929e7	16	@EXPORT_OK = qw(SvREFCNT CvGV);
3967c732 JD	17	%EXPORT_TAGS = ('ALL' => [@EXPORT, @EXPORT_OK]);
3967c732 JD	18
da4061d3	19	XSLoader::load();
3967c732	20
1045810a IZ	21	sub import {
	22	my $c = shift;
	23	my $ops_rx = qr/^:opd(=[stP]*)?\b/;
	24	my @db = grep m/$ops_rx/, @_;
	25	@_ = grep !m/$ops_rx/, @_;
	26	if (@db) {
	27	die "Too many :opd options" if @db > 1;
	28	runops_debug(1);
	29	my $flags = ($db[0] =~ m/$ops_rx/ and $1);
	30	$flags = 'st' unless defined $flags;
	31	my $f = 0;
	32	$f \|= 2 if $flags =~ /s/;
	33	$f \|= 8 if $flags =~ /t/;
	34	$f \|= 64 if $flags =~ /P/;
	35	$^D \|= $f if $f;
	36	}
	37	unshift @_, $c;
	38	goto &Exporter::import;
	39	}
	40
3967c732 JD	41	sub DumpWithOP ($;$) {
	42	local($Devel::Peek::dump_ops)=1;
	43	my $depth = @_ > 1 ? $_[1] : 4 ;
	44	Dump($_[0],$depth);
	45	}
	46
bd16a5f0 IZ	47	$D_flags = 'psltocPmfrxuLHXDSTR';
	48
	49	sub debug_flags (;$) {
	50	my $out = "";
	51	for my $i (0 .. length($D_flags)-1) {
	52	$out .= substr $D_flags, $i, 1 if $^D & (1<<$i);
	53	}
	54	my $arg = shift;
	55	my $num = $arg;
	56	if (defined $arg and $arg =~ /\D/) {
	57	die "unknown flags in debug_flags()" if $arg =~ /[^-$D_flags]/;
	58	my ($on,$off) = split /-/, "$arg-";
	59	$num = $^D;
	60	$num \|= (1<<index($D_flags, $_)) for split //, $on;
	61	$num &= ~(1<<index($D_flags, $_)) for split //, $off;
	62	}
	63	$^D = $num if defined $arg;
	64	$out
	65	}
	66
3967c732 JD	67	1;
	68	__END__
	69
	70	=head1 NAME
	71
	72	Devel::Peek - A data debugging tool for the XS programmer
	73
	74	=head1 SYNOPSIS
	75
	76	use Devel::Peek;
	77	Dump( $a );
	78	Dump( $a, 5 );
40091657 FC	79	Dump( @a );
40091657 FC	80	Dump( %h );
3967c732 JD	81	DumpArray( 5, $a, $b, ... );
	82	mstat "Point 5";
	83
1045810a IZ	84	use Devel::Peek ':opd=st';
1045810a IZ	85
3967c732 JD	86	=head1 DESCRIPTION
	87
	88	Devel::Peek contains functions which allows raw Perl datatypes to be
	89	manipulated from a Perl script. This is used by those who do XS programming
	90	to check that the data they are sending from C to Perl looks as they think
	91	it should look. The trick, then, is to know what the raw datatype is
	92	supposed to look like when it gets to Perl. This document offers some tips
	93	and hints to describe good and bad raw data.
	94
	95	It is very possible that this document will fall far short of being useful
	96	to the casual reader. The reader is expected to understand the material in
	97	the first few sections of L<perlguts>.
	98
	99	Devel::Peek supplies a C<Dump()> function which can dump a raw Perl
	100	datatype, and C<mstat("marker")> function to report on memory usage
	101	(if perl is compiled with corresponding option). The function
	102	DeadCode() provides statistics on the data "frozen" into inactive
da1929e7	103	C<CV>. Devel::Peek also supplies C<SvREFCNT()> which can query reference
3967c732 JD	104	counts on SVs. This document will take a passive, and safe, approach
3967c732 JD	105	to data debugging and for that it will describe only the C<Dump()>
d1424c31	106	function.
3967c732	107
40091657 FC	108	The C<Dump()> function takes one or two arguments: something to dump, and
	109	an optional limit for recursion and array elements (default is 4). The
	110	first argument is evaluted in rvalue scalar context, with exceptions for
	111	@array and %hash, which dump the array or hash itself. So C<Dump @array>
	112	works, as does C<Dump $foo>. And C<Dump pos> will call C<pos> in rvalue
	113	context, whereas C<Dump ${\pos}> will call it in lvalue context.
	114
3967c732	115	Function C<DumpArray()> allows dumping of multiple values (useful when you
076c2fc0	116	need to analyze returns of functions).
3967c732 JD	117
	118	The global variable $Devel::Peek::pv_limit can be set to limit the
	119	number of character printed in various string values. Setting it to 0
	120	means no limit.
	121
1045810a IZ	122	If C<use Devel::Peek> directive has a C<:opd=FLAGS> argument,
	123	this switches on debugging of opcode dispatch. C<FLAGS> should be a
	124	combination of C<s>, C<t>, and C<P> (see B<-D> flags in L<perlrun>).
	125	C<:opd> is a shortcut for C<:opd=st>.
	126
bd16a5f0 IZ	127	=head2 Runtime debugging
	128
	129	C<CvGV($cv)> return one of the globs associated to a subroutine reference $cv.
	130
	131	debug_flags() returns a string representation of C<$^D> (similar to
	132	what is allowed for B<-D> flag). When called with a numeric argument,
	133	sets $^D to the corresponding value. When called with an argument of
	134	the form C<"flags-flags">, set on/off bits of C<$^D> corresponding to
	135	letters before/after C<->. (The returned value is for C<$^D> before
	136	the modification.)
	137
	138	runops_debug() returns true if the current I<opcode dispatcher> is the
	139	debugging one. When called with an argument, switches to debugging or
	140	non-debugging dispatcher depending on the argument (active for
	141	newly-entered subs/etc only). (The returned value is for the dispatcher before the modification.)
	142
d1424c31 IZ	143	=head2 Memory footprint debugging
	144
	145	When perl is compiled with support for memory footprint debugging
	146	(default with Perl's malloc()), Devel::Peek provides an access to this API.
	147
	148	Use mstat() function to emit a memory state statistic to the terminal.
	149	For more information on the format of output of mstat() see
9704a6c6	150	L<perldebguts/Using $ENV{PERL_DEBUG_MSTATS}>.
d1424c31 IZ	151
	152	Three additional functions allow access to this statistic from Perl.
	153	First, use C<mstats_fillhash(%hash)> to get the information contained
	154	in the output of mstat() into %hash. The field of this hash are
	155
555bd962 BG	156	minbucket nbuckets sbrk_good sbrk_slack sbrked_remains sbrks
	157	start_slack topbucket topbucket_ev topbucket_odd total total_chain
	158	total_sbrk totfree
d1424c31 IZ	159
	160	Two additional fields C<free>, C<used> contain array references which
	161	provide per-bucket count of free and used chunks. Two other fields
	162	C<mem_size>, C<available_size> contain array references which provide
	163	the information about the allocated size and usable size of chunks in
9704a6c6	164	each bucket. Again, see L<perldebguts/Using $ENV{PERL_DEBUG_MSTATS}>
d1424c31 IZ	165	for details.
d1424c31 IZ	166
b1e4fe07	167
d1424c31 IZ	168	Keep in mind that only the first several "odd-numbered" buckets are
	169	used, so the information on size of the "odd-numbered" buckets which are
	170	not used is probably meaningless.
	171
	172	The information in
	173
	174	mem_size available_size minbucket nbuckets
	175
	176	is the property of a particular build of perl, and does not depend on
	177	the current process. If you do not provide the optional argument to
	178	the functions mstats_fillhash(), fill_mstats(), mstats2hash(), then
	179	the information in fields C<mem_size>, C<available_size> is not
	180	updated.
	181
	182	C<fill_mstats($buf)> is a much cheaper call (both speedwise and
	183	memory-wise) which collects the statistic into $buf in
	184	machine-readable form. At a later moment you may need to call
	185	C<mstats2hash($buf, %hash)> to use this information to fill %hash.
	186
	187	All three APIs C<fill_mstats($buf)>, C<mstats_fillhash(%hash)>, and
	188	C<mstats2hash($buf, %hash)> are designed to allocate no memory if used
	189	I<the second time> on the same $buf and/or %hash.
	190
	191	So, if you want to collect memory info in a cycle, you may call
	192
	193	$#buf = 999;
	194	fill_mstats($_) for @buf;
	195	mstats_fillhash(%report, 1); # Static info too
	196
	197	foreach (@buf) {
	198	# Do something...
	199	fill_mstats $_; # Collect statistic
	200	}
	201	foreach (@buf) {
	202	mstats2hash($_, %report); # Preserve static info
	203	# Do something with %report
	204	}
	205
3967c732 JD	206	=head1 EXAMPLES
	207
	208	The following examples don't attempt to show everything as that would be a
	209	monumental task, and, frankly, we don't want this manpage to be an internals
	210	document for Perl. The examples do demonstrate some basics of the raw Perl
	211	datatypes, and should suffice to get most determined people on their way.
	212	There are no guidewires or safety nets, nor blazed trails, so be prepared to
	213	travel alone from this point and on and, if at all possible, don't fall into
	214	the quicksand (it's bad for business).
	215
	216	Oh, one final bit of advice: take L<perlguts> with you. When you return we
	217	expect to see it well-thumbed.
	218
	219	=head2 A simple scalar string
	220
	221	Let's begin by looking a simple scalar which is holding a string.
	222
a423dfdd	223	use Devel::Peek;
f64eb7e3	224	$a = 42; $a = "hello";
3967c732 JD	225	Dump $a;
	226
	227	The output:
	228
f64eb7e3	229	SV = PVIV(0xbc288) at 0xbe9a8
3967c732 JD	230	REFCNT = 1
3967c732 JD	231	FLAGS = (POK,pPOK)
f64eb7e3	232	IV = 42
3967c732 JD	233	PV = 0xb2048 "hello"\0
3967c732 JD	234	CUR = 5
f64eb7e3	235	LEN = 8
3967c732	236
f64eb7e3 DM	237	This says C<$a> is an SV, a scalar. The scalar type is a PVIV, which is
	238	capable of holding an integer (IV) and/or a string (PV) value. The scalar's
	239	head is allocated at address 0xbe9a8, while the body is at 0xbc288.
3967c732 JD	240	Its reference count is 1. It has the C<POK> flag set, meaning its
	241	current PV field is valid. Because POK is set we look at the PV item
	242	to see what is in the scalar. The \0 at the end indicate that this
	243	PV is properly NUL-terminated.
f64eb7e3 DM	244	Note that the IV field still contains its old numeric value, but because
	245	FLAGS doesn't have IOK set, we must ignore the IV item.
	246	CUR indicates the number of characters in the PV. LEN indicates the
	247	number of bytes allocated for the PV (at least one more than CUR, because
	248	LEN includes an extra byte for the end-of-string marker, then usually
	249	rounded up to some efficient allocation unit).
3967c732 JD	250
	251	=head2 A simple scalar number
	252
	253	If the scalar contains a number the raw SV will be leaner.
	254
a423dfdd	255	use Devel::Peek;
3967c732 JD	256	$a = 42;
	257	Dump $a;
	258
	259	The output:
	260
f64eb7e3	261	SV = IV(0xbc818) at 0xbe9a8
3967c732 JD	262	REFCNT = 1
	263	FLAGS = (IOK,pIOK)
	264	IV = 42
	265
	266	This says C<$a> is an SV, a scalar. The scalar is an IV, a number. Its
	267	reference count is 1. It has the C<IOK> flag set, meaning it is currently
	268	being evaluated as a number. Because IOK is set we look at the IV item to
	269	see what is in the scalar.
	270
	271	=head2 A simple scalar with an extra reference
	272
	273	If the scalar from the previous example had an extra reference:
	274
a423dfdd	275	use Devel::Peek;
3967c732 JD	276	$a = 42;
	277	$b = \$a;
	278	Dump $a;
	279
	280	The output:
	281
f64eb7e3	282	SV = IV(0xbe860) at 0xbe9a8
3967c732 JD	283	REFCNT = 2
	284	FLAGS = (IOK,pIOK)
	285	IV = 42
	286
	287	Notice that this example differs from the previous example only in its
	288	reference count. Compare this to the next example, where we dump C<$b>
	289	instead of C<$a>.
	290
	291	=head2 A reference to a simple scalar
	292
	293	This shows what a reference looks like when it references a simple scalar.
	294
a423dfdd	295	use Devel::Peek;
3967c732 JD	296	$a = 42;
	297	$b = \$a;
	298	Dump $b;
	299
	300	The output:
	301
f64eb7e3	302	SV = IV(0xf041c) at 0xbe9a0
3967c732 JD	303	REFCNT = 1
	304	FLAGS = (ROK)
	305	RV = 0xbab08
f64eb7e3 DM	306	SV = IV(0xbe860) at 0xbe9a8
	307	REFCNT = 2
	308	FLAGS = (IOK,pIOK)
	309	IV = 42
	310
	311	Starting from the top, this says C<$b> is an SV. The scalar is an IV,
	312	which is capable of holding an integer or reference value.
	313	It has the C<ROK> flag set, meaning it is a reference (rather than an
	314	integer or string). Notice that Dump
3967c732 JD	315	follows the reference and shows us what C<$b> was referencing. We see the
	316	same C<$a> that we found in the previous example.
	317
	318	Note that the value of C<RV> coincides with the numbers we see when we
f64eb7e3 DM	319	stringify $b. The addresses inside IV() are addresses of
f64eb7e3 DM	320	C<X***> structures which hold the current state of an C<SV>. This
3967c732 JD	321	address may change during lifetime of an SV.
	322
	323	=head2 A reference to an array
	324
	325	This shows what a reference to an array looks like.
	326
a423dfdd	327	use Devel::Peek;
3967c732 JD	328	$a = [42];
	329	Dump $a;
	330
	331	The output:
	332
f64eb7e3	333	SV = IV(0xc85998) at 0xc859a8
3967c732 JD	334	REFCNT = 1
3967c732 JD	335	FLAGS = (ROK)
f64eb7e3 DM	336	RV = 0xc70de8
	337	SV = PVAV(0xc71e10) at 0xc70de8
	338	REFCNT = 1
	339	FLAGS = ()
	340	ARRAY = 0xc7e820
	341	FILL = 0
	342	MAX = 0
	343	ARYLEN = 0x0
	344	FLAGS = (REAL)
	345	Elt No. 0
	346	SV = IV(0xc70f88) at 0xc70f98
	347	REFCNT = 1
	348	FLAGS = (IOK,pIOK)
	349	IV = 42
	350
	351	This says C<$a> is a reference (ROK), which points to
3967c732 JD	352	another SV which is a PVAV, an array. The array has one element,
	353	element zero, which is another SV. The field C<FILL> above indicates
	354	the last element in the array, similar to C<$#$a>.
	355
	356	If C<$a> pointed to an array of two elements then we would see the
	357	following.
	358
	359	use Devel::Peek 'Dump';
	360	$a = [42,24];
	361	Dump $a;
	362
	363	The output:
	364
f64eb7e3	365	SV = IV(0x158c998) at 0x158c9a8
3967c732 JD	366	REFCNT = 1
3967c732 JD	367	FLAGS = (ROK)
f64eb7e3 DM	368	RV = 0x1577de8
	369	SV = PVAV(0x1578e10) at 0x1577de8
	370	REFCNT = 1
	371	FLAGS = ()
	372	ARRAY = 0x1585820
	373	FILL = 1
	374	MAX = 1
	375	ARYLEN = 0x0
	376	FLAGS = (REAL)
	377	Elt No. 0
	378	SV = IV(0x1577f88) at 0x1577f98
	379	REFCNT = 1
	380	FLAGS = (IOK,pIOK)
	381	IV = 42
	382	Elt No. 1
	383	SV = IV(0x158be88) at 0x158be98
	384	REFCNT = 1
	385	FLAGS = (IOK,pIOK)
	386	IV = 24
3967c732 JD	387
	388	Note that C<Dump> will not report I<all> the elements in the array,
	389	only several first (depending on how deep it already went into the
	390	report tree).
	391
	392	=head2 A reference to a hash
	393
	394	The following shows the raw form of a reference to a hash.
	395
a423dfdd	396	use Devel::Peek;
3967c732 JD	397	$a = {hello=>42};
	398	Dump $a;
	399
	400	The output:
	401
f64eb7e3	402	SV = IV(0x8177858) at 0x816a618
d5889220 T	403	REFCNT = 1
	404	FLAGS = (ROK)
	405	RV = 0x814fc10
	406	SV = PVHV(0x8167768) at 0x814fc10
	407	REFCNT = 1
	408	FLAGS = (SHAREKEYS)
d5889220 T	409	ARRAY = 0x816c5b8 (0:7, 1:1)
	410	hash quality = 100.0%
	411	KEYS = 1
	412	FILL = 1
	413	MAX = 7
	414	RITER = -1
	415	EITER = 0x0
	416	Elt "hello" HASH = 0xc8fd181b
	417	SV = IV(0x816c030) at 0x814fcf4
	418	REFCNT = 1
	419	FLAGS = (IOK,pIOK)
	420	IV = 42
3967c732 JD	421
3967c732 JD	422	This shows C<$a> is a reference pointing to an SV. That SV is a PVHV, a
b1e4fe07	423	hash. Fields RITER and EITER are used by C<L<perlfunc/each>>.
3967c732	424
d5889220 T	425	The "quality" of a hash is defined as the total number of comparisons needed
	426	to access every element once, relative to the expected number needed for a
	427	random hash. The value can go over 100%.
	428
	429	The total number of comparisons is equal to the sum of the squares of the
	430	number of entries in each bucket. For a random hash of C<<n>> keys into
	431	C<<k>> buckets, the expected value is:
	432
	433	n + n(n-1)/2k
	434
3967c732 JD	435	=head2 Dumping a large array or hash
	436
	437	The C<Dump()> function, by default, dumps up to 4 elements from a
	438	toplevel array or hash. This number can be increased by supplying a
	439	second argument to the function.
	440
a423dfdd	441	use Devel::Peek;
3967c732 JD	442	$a = [10,11,12,13,14];
	443	Dump $a;
	444
	445	Notice that C<Dump()> prints only elements 10 through 13 in the above code.
	446	The following code will print all of the elements.
	447
	448	use Devel::Peek 'Dump';
	449	$a = [10,11,12,13,14];
	450	Dump $a, 5;
	451
	452	=head2 A reference to an SV which holds a C pointer
	453
	454	This is what you really need to know as an XS programmer, of course. When
	455	an XSUB returns a pointer to a C structure that pointer is stored in an SV
	456	and a reference to that SV is placed on the XSUB stack. So the output from
	457	an XSUB which uses something like the T_PTROBJ map might look something like
	458	this:
	459
f64eb7e3	460	SV = IV(0xf381c) at 0xc859a8
3967c732 JD	461	REFCNT = 1
	462	FLAGS = (ROK)
	463	RV = 0xb8ad8
f64eb7e3 DM	464	SV = PVMG(0xbb3c8) at 0xc859a0
	465	REFCNT = 1
	466	FLAGS = (OBJECT,IOK,pIOK)
	467	IV = 729160
	468	NV = 0
	469	PV = 0
	470	STASH = 0xc1d10 "CookBookB::Opaque"
	471
	472	This shows that we have an SV which is a reference, which points at another
3967c732 JD	473	SV. In this case that second SV is a PVMG, a blessed scalar. Because it is
	474	blessed it has the C<OBJECT> flag set. Note that an SV which holds a C
	475	pointer also has the C<IOK> flag set. The C<STASH> is set to the package
	476	name which this SV was blessed into.
	477
	478	The output from an XSUB which uses something like the T_PTRREF map, which
	479	doesn't bless the object, might look something like this:
	480
f64eb7e3	481	SV = IV(0xf381c) at 0xc859a8
3967c732 JD	482	REFCNT = 1
	483	FLAGS = (ROK)
	484	RV = 0xb8ad8
f64eb7e3 DM	485	SV = PVMG(0xbb3c8) at 0xc859a0
	486	REFCNT = 1
	487	FLAGS = (IOK,pIOK)
	488	IV = 729160
	489	NV = 0
	490	PV = 0
3967c732 JD	491
	492	=head2 A reference to a subroutine
	493
	494	Looks like this:
	495
f64eb7e3	496	SV = IV(0x24d2dd8) at 0x24d2de8
3967c732 JD	497	REFCNT = 1
3967c732 JD	498	FLAGS = (TEMP,ROK)
f64eb7e3 DM	499	RV = 0x24e79d8
	500	SV = PVCV(0x24e5798) at 0x24e79d8
	501	REFCNT = 2
	502	FLAGS = ()
	503	COMP_STASH = 0x22c9c50 "main"
	504	START = 0x22eed60 ===> 0
	505	ROOT = 0x22ee490
	506	GVGV::GV = 0x22de9d8 "MY" :: "top_targets"
	507	FILE = "(eval 5)"
	508	DEPTH = 0
	509	FLAGS = 0x0
	510	OUTSIDE_SEQ = 93
	511	PADLIST = 0x22e9ed8
	512	PADNAME = 0x22e9ec0(0x22eed00) PAD = 0x22e9ea8(0x22eecd0)
	513	OUTSIDE = 0x22c9fb0 (MAIN)
	514
3967c732 JD	515
	516	This shows that
	517
bbc7dcd2	518	=over 4
3967c732	519
a45bd81d	520	=item *
3967c732 JD	521
3967c732 JD	522	the subroutine is not an XSUB (since C<START> and C<ROOT> are
f64eb7e3	523	non-zero, and C<XSUB> is not listed, and is thus null);
3967c732	524
a45bd81d	525	=item *
3967c732 JD	526
	527	that it was compiled in the package C<main>;
	528
a45bd81d	529	=item *
3967c732 JD	530
	531	under the name C<MY::top_targets>;
	532
a45bd81d	533	=item *
3967c732 JD	534
	535	inside a 5th eval in the program;
	536
a45bd81d	537	=item *
3967c732 JD	538
	539	it is not currently executed (see C<DEPTH>);
	540
a45bd81d	541	=item *
3967c732 JD	542
	543	it has no prototype (C<PROTOTYPE> field is missing).
	544
a45bd81d	545	=back
3967c732 JD	546
	547	=head1 EXPORTS
	548
	549	C<Dump>, C<mstat>, C<DeadCode>, C<DumpArray>, C<DumpWithOP> and
7c6ca602	550	C<DumpProg>, C<fill_mstats>, C<mstats_fillhash>, C<mstats2hash> by
d1424c31 IZ	551	default. Additionally available C<SvREFCNT>, C<SvREFCNT_inc> and
d1424c31 IZ	552	C<SvREFCNT_dec>.
3967c732 JD	553
	554	=head1 BUGS
	555
	556	Readers have been known to skip important parts of L<perlguts>, causing much
	557	frustration for all.
	558
	559	=head1 AUTHOR
	560
	561	Ilya Zakharevich ilya@math.ohio-state.edu
	562
	563	Copyright (c) 1995-98 Ilya Zakharevich. All rights reserved.
	564	This program is free software; you can redistribute it and/or
	565	modify it under the same terms as Perl itself.
	566
	567	Author of this software makes no claim whatsoever about suitability,
	568	reliability, edability, editability or usability of this product, and
	569	should not be kept liable for any damage resulting from the use of
	570	it. If you can use it, you are in luck, if not, I should not be kept
	571	responsible. Keep a handy copy of your backup tape at hand.
	572
	573	=head1 SEE ALSO
	574
	575	L<perlguts>, and L<perlguts>, again.
	576
	577	=cut