587 lines
18 KiB
Perl
587 lines
18 KiB
Perl
# Devel::Peek - A data debugging tool for the XS programmer
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# The documentation is after the __END__
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package Devel::Peek;
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$VERSION = '1.28';
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$XS_VERSION = $VERSION;
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$VERSION = eval $VERSION;
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require Exporter;
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require XSLoader;
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@ISA = qw(Exporter);
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@EXPORT = qw(Dump mstat DeadCode DumpArray DumpWithOP DumpProg
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fill_mstats mstats_fillhash mstats2hash runops_debug debug_flags);
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@EXPORT_OK = qw(SvREFCNT CvGV);
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%EXPORT_TAGS = ('ALL' => [@EXPORT, @EXPORT_OK]);
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XSLoader::load();
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sub import {
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my $c = shift;
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my $ops_rx = qr/^:opd(=[stP]*)?\b/;
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my @db = grep m/$ops_rx/, @_;
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@_ = grep !m/$ops_rx/, @_;
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if (@db) {
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die "Too many :opd options" if @db > 1;
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runops_debug(1);
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my $flags = ($db[0] =~ m/$ops_rx/ and $1);
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$flags = 'st' unless defined $flags;
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my $f = 0;
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$f |= 2 if $flags =~ /s/;
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$f |= 8 if $flags =~ /t/;
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$f |= 64 if $flags =~ /P/;
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$^D |= $f if $f;
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}
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unshift @_, $c;
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goto &Exporter::import;
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}
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sub DumpWithOP ($;$) {
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local($Devel::Peek::dump_ops)=1;
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my $depth = @_ > 1 ? $_[1] : 4 ;
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Dump($_[0],$depth);
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}
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$D_flags = 'psltocPmfrxuLHXDSTR';
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sub debug_flags (;$) {
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my $out = "";
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for my $i (0 .. length($D_flags)-1) {
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$out .= substr $D_flags, $i, 1 if $^D & (1<<$i);
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}
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my $arg = shift;
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my $num = $arg;
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if (defined $arg and $arg =~ /\D/) {
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die "unknown flags in debug_flags()" if $arg =~ /[^-$D_flags]/;
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my ($on,$off) = split /-/, "$arg-";
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$num = $^D;
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$num |= (1<<index($D_flags, $_)) for split //, $on;
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$num &= ~(1<<index($D_flags, $_)) for split //, $off;
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}
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$^D = $num if defined $arg;
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$out
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}
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sub B::Deparse::pp_Devel_Peek_Dump {
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my ($deparse,$op,$cx) = @_;
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my @kids = $deparse->deparse($op->first, 6);
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my $sib = $op->first->sibling;
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if (ref $sib ne 'B::NULL') {
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push @kids, $deparse->deparse($sib, 6);
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}
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return "Devel::Peek::Dump(" . join(", ", @kids) . ")";
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}
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1;
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__END__
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=head1 NAME
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Devel::Peek - A data debugging tool for the XS programmer
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=head1 SYNOPSIS
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use Devel::Peek;
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Dump( $a );
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Dump( $a, 5 );
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Dump( @a );
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Dump( %h );
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DumpArray( 5, $a, $b, ... );
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mstat "Point 5";
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use Devel::Peek ':opd=st';
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=head1 DESCRIPTION
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Devel::Peek contains functions which allows raw Perl datatypes to be
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manipulated from a Perl script. This is used by those who do XS programming
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to check that the data they are sending from C to Perl looks as they think
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it should look. The trick, then, is to know what the raw datatype is
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supposed to look like when it gets to Perl. This document offers some tips
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and hints to describe good and bad raw data.
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It is very possible that this document will fall far short of being useful
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to the casual reader. The reader is expected to understand the material in
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the first few sections of L<perlguts>.
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Devel::Peek supplies a C<Dump()> function which can dump a raw Perl
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datatype, and C<mstat("marker")> function to report on memory usage
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(if perl is compiled with corresponding option). The function
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DeadCode() provides statistics on the data "frozen" into inactive
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C<CV>. Devel::Peek also supplies C<SvREFCNT()> which can query reference
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counts on SVs. This document will take a passive, and safe, approach
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to data debugging and for that it will describe only the C<Dump()>
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function.
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All output is to STDERR.
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The C<Dump()> function takes one or two arguments: something to dump, and
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an optional limit for recursion and array elements (default is 4). The
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first argument is evaluted in rvalue scalar context, with exceptions for
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@array and %hash, which dump the array or hash itself. So C<Dump @array>
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works, as does C<Dump $foo>. And C<Dump pos> will call C<pos> in rvalue
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context, whereas C<Dump ${\pos}> will call it in lvalue context.
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Function C<DumpArray()> allows dumping of multiple values (useful when you
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need to analyze returns of functions).
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The global variable $Devel::Peek::pv_limit can be set to limit the
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number of character printed in various string values. Setting it to 0
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means no limit.
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If C<use Devel::Peek> directive has a C<:opd=FLAGS> argument,
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this switches on debugging of opcode dispatch. C<FLAGS> should be a
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combination of C<s>, C<t>, and C<P> (see
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L<< B<-D> flags in perlrun|perlrun/B<-D>I<letters> >>).
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C<:opd> is a shortcut for C<:opd=st>.
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=head2 Runtime debugging
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C<CvGV($cv)> return one of the globs associated to a subroutine reference $cv.
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debug_flags() returns a string representation of C<$^D> (similar to
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what is allowed for B<-D> flag). When called with a numeric argument,
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sets $^D to the corresponding value. When called with an argument of
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the form C<"flags-flags">, set on/off bits of C<$^D> corresponding to
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letters before/after C<->. (The returned value is for C<$^D> before
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the modification.)
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runops_debug() returns true if the current I<opcode dispatcher> is the
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debugging one. When called with an argument, switches to debugging or
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non-debugging dispatcher depending on the argument (active for
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newly-entered subs/etc only). (The returned value is for the dispatcher before the modification.)
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=head2 Memory footprint debugging
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When perl is compiled with support for memory footprint debugging
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(default with Perl's malloc()), Devel::Peek provides an access to this API.
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Use mstat() function to emit a memory state statistic to the terminal.
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For more information on the format of output of mstat() see
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L<perldebguts/Using $ENV{PERL_DEBUG_MSTATS}>.
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Three additional functions allow access to this statistic from Perl.
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First, use C<mstats_fillhash(%hash)> to get the information contained
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in the output of mstat() into %hash. The field of this hash are
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minbucket nbuckets sbrk_good sbrk_slack sbrked_remains sbrks
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start_slack topbucket topbucket_ev topbucket_odd total total_chain
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total_sbrk totfree
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Two additional fields C<free>, C<used> contain array references which
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provide per-bucket count of free and used chunks. Two other fields
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C<mem_size>, C<available_size> contain array references which provide
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the information about the allocated size and usable size of chunks in
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each bucket. Again, see L<perldebguts/Using $ENV{PERL_DEBUG_MSTATS}>
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for details.
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Keep in mind that only the first several "odd-numbered" buckets are
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used, so the information on size of the "odd-numbered" buckets which are
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not used is probably meaningless.
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The information in
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mem_size available_size minbucket nbuckets
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is the property of a particular build of perl, and does not depend on
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the current process. If you do not provide the optional argument to
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the functions mstats_fillhash(), fill_mstats(), mstats2hash(), then
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the information in fields C<mem_size>, C<available_size> is not
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updated.
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C<fill_mstats($buf)> is a much cheaper call (both speedwise and
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memory-wise) which collects the statistic into $buf in
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machine-readable form. At a later moment you may need to call
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C<mstats2hash($buf, %hash)> to use this information to fill %hash.
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All three APIs C<fill_mstats($buf)>, C<mstats_fillhash(%hash)>, and
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C<mstats2hash($buf, %hash)> are designed to allocate no memory if used
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I<the second time> on the same $buf and/or %hash.
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So, if you want to collect memory info in a cycle, you may call
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$#buf = 999;
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fill_mstats($_) for @buf;
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mstats_fillhash(%report, 1); # Static info too
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foreach (@buf) {
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# Do something...
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fill_mstats $_; # Collect statistic
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}
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foreach (@buf) {
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mstats2hash($_, %report); # Preserve static info
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# Do something with %report
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}
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=head1 EXAMPLES
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The following examples don't attempt to show everything as that would be a
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monumental task, and, frankly, we don't want this manpage to be an internals
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document for Perl. The examples do demonstrate some basics of the raw Perl
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datatypes, and should suffice to get most determined people on their way.
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There are no guidewires or safety nets, nor blazed trails, so be prepared to
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travel alone from this point and on and, if at all possible, don't fall into
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the quicksand (it's bad for business).
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Oh, one final bit of advice: take L<perlguts> with you. When you return we
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expect to see it well-thumbed.
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=head2 A simple scalar string
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Let's begin by looking a simple scalar which is holding a string.
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use Devel::Peek;
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$a = 42; $a = "hello";
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Dump $a;
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The output:
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SV = PVIV(0xbc288) at 0xbe9a8
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REFCNT = 1
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FLAGS = (POK,pPOK)
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IV = 42
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PV = 0xb2048 "hello"\0
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CUR = 5
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LEN = 8
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This says C<$a> is an SV, a scalar. The scalar type is a PVIV, which is
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capable of holding an integer (IV) and/or a string (PV) value. The scalar's
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head is allocated at address 0xbe9a8, while the body is at 0xbc288.
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Its reference count is 1. It has the C<POK> flag set, meaning its
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current PV field is valid. Because POK is set we look at the PV item
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to see what is in the scalar. The \0 at the end indicate that this
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PV is properly NUL-terminated.
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Note that the IV field still contains its old numeric value, but because
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FLAGS doesn't have IOK set, we must ignore the IV item.
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CUR indicates the number of characters in the PV. LEN indicates the
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number of bytes allocated for the PV (at least one more than CUR, because
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LEN includes an extra byte for the end-of-string marker, then usually
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rounded up to some efficient allocation unit).
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=head2 A simple scalar number
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If the scalar contains a number the raw SV will be leaner.
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use Devel::Peek;
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$a = 42;
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Dump $a;
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The output:
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SV = IV(0xbc818) at 0xbe9a8
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REFCNT = 1
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FLAGS = (IOK,pIOK)
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IV = 42
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This says C<$a> is an SV, a scalar. The scalar is an IV, a number. Its
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reference count is 1. It has the C<IOK> flag set, meaning it is currently
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being evaluated as a number. Because IOK is set we look at the IV item to
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see what is in the scalar.
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=head2 A simple scalar with an extra reference
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If the scalar from the previous example had an extra reference:
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use Devel::Peek;
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$a = 42;
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$b = \$a;
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Dump $a;
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The output:
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SV = IV(0xbe860) at 0xbe9a8
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REFCNT = 2
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FLAGS = (IOK,pIOK)
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IV = 42
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Notice that this example differs from the previous example only in its
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reference count. Compare this to the next example, where we dump C<$b>
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instead of C<$a>.
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=head2 A reference to a simple scalar
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This shows what a reference looks like when it references a simple scalar.
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use Devel::Peek;
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$a = 42;
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$b = \$a;
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Dump $b;
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The output:
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SV = IV(0xf041c) at 0xbe9a0
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REFCNT = 1
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FLAGS = (ROK)
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RV = 0xbab08
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SV = IV(0xbe860) at 0xbe9a8
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REFCNT = 2
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FLAGS = (IOK,pIOK)
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IV = 42
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Starting from the top, this says C<$b> is an SV. The scalar is an IV,
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which is capable of holding an integer or reference value.
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It has the C<ROK> flag set, meaning it is a reference (rather than an
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integer or string). Notice that Dump
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follows the reference and shows us what C<$b> was referencing. We see the
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same C<$a> that we found in the previous example.
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Note that the value of C<RV> coincides with the numbers we see when we
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stringify $b. The addresses inside IV() are addresses of
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C<X***> structures which hold the current state of an C<SV>. This
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address may change during lifetime of an SV.
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=head2 A reference to an array
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This shows what a reference to an array looks like.
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use Devel::Peek;
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$a = [42];
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Dump $a;
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The output:
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SV = IV(0xc85998) at 0xc859a8
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REFCNT = 1
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FLAGS = (ROK)
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RV = 0xc70de8
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SV = PVAV(0xc71e10) at 0xc70de8
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REFCNT = 1
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FLAGS = ()
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ARRAY = 0xc7e820
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FILL = 0
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MAX = 0
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FLAGS = (REAL)
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Elt No. 0
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SV = IV(0xc70f88) at 0xc70f98
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REFCNT = 1
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FLAGS = (IOK,pIOK)
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IV = 42
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This says C<$a> is a reference (ROK), which points to
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another SV which is a PVAV, an array. The array has one element,
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element zero, which is another SV. The field C<FILL> above indicates
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the last element in the array, similar to C<$#$a>.
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If C<$a> pointed to an array of two elements then we would see the
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following.
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use Devel::Peek 'Dump';
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$a = [42,24];
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Dump $a;
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The output:
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SV = IV(0x158c998) at 0x158c9a8
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REFCNT = 1
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FLAGS = (ROK)
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RV = 0x1577de8
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SV = PVAV(0x1578e10) at 0x1577de8
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REFCNT = 1
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FLAGS = ()
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ARRAY = 0x1585820
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FILL = 1
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MAX = 1
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FLAGS = (REAL)
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Elt No. 0
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SV = IV(0x1577f88) at 0x1577f98
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REFCNT = 1
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FLAGS = (IOK,pIOK)
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IV = 42
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Elt No. 1
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SV = IV(0x158be88) at 0x158be98
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REFCNT = 1
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FLAGS = (IOK,pIOK)
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IV = 24
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Note that C<Dump> will not report I<all> the elements in the array,
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only several first (depending on how deep it already went into the
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report tree).
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=head2 A reference to a hash
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The following shows the raw form of a reference to a hash.
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use Devel::Peek;
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$a = {hello=>42};
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Dump $a;
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The output:
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SV = IV(0x55cb50b50fb0) at 0x55cb50b50fc0
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REFCNT = 1
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FLAGS = (ROK)
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RV = 0x55cb50b2b758
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SV = PVHV(0x55cb50b319c0) at 0x55cb50b2b758
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REFCNT = 1
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FLAGS = (SHAREKEYS)
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ARRAY = 0x55cb50b941a0 (0:7, 1:1)
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hash quality = 100.0%
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KEYS = 1
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FILL = 1
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MAX = 7
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Elt "hello" HASH = 0x3128ece4
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SV = IV(0x55cb50b464f8) at 0x55cb50b46508
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REFCNT = 1
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FLAGS = (IOK,pIOK)
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IV = 42
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This shows C<$a> is a reference pointing to an SV. That SV is a PVHV, a hash.
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The "quality" of a hash is defined as the total number of comparisons needed
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to access every element once, relative to the expected number needed for a
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random hash. The value can go over 100%.
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The total number of comparisons is equal to the sum of the squares of the
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number of entries in each bucket. For a random hash of C<<n>> keys into
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C<<k>> buckets, the expected value is:
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n + n(n-1)/2k
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=head2 Dumping a large array or hash
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The C<Dump()> function, by default, dumps up to 4 elements from a
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toplevel array or hash. This number can be increased by supplying a
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second argument to the function.
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use Devel::Peek;
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$a = [10,11,12,13,14];
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Dump $a;
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Notice that C<Dump()> prints only elements 10 through 13 in the above code.
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The following code will print all of the elements.
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use Devel::Peek 'Dump';
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$a = [10,11,12,13,14];
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Dump $a, 5;
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=head2 A reference to an SV which holds a C pointer
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This is what you really need to know as an XS programmer, of course. When
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an XSUB returns a pointer to a C structure that pointer is stored in an SV
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and a reference to that SV is placed on the XSUB stack. So the output from
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an XSUB which uses something like the T_PTROBJ map might look something like
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this:
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SV = IV(0xf381c) at 0xc859a8
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REFCNT = 1
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FLAGS = (ROK)
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RV = 0xb8ad8
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SV = PVMG(0xbb3c8) at 0xc859a0
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REFCNT = 1
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FLAGS = (OBJECT,IOK,pIOK)
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IV = 729160
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NV = 0
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PV = 0
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STASH = 0xc1d10 "CookBookB::Opaque"
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This shows that we have an SV which is a reference, which points at another
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SV. In this case that second SV is a PVMG, a blessed scalar. Because it is
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blessed it has the C<OBJECT> flag set. Note that an SV which holds a C
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pointer also has the C<IOK> flag set. The C<STASH> is set to the package
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name which this SV was blessed into.
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The output from an XSUB which uses something like the T_PTRREF map, which
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doesn't bless the object, might look something like this:
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SV = IV(0xf381c) at 0xc859a8
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REFCNT = 1
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FLAGS = (ROK)
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RV = 0xb8ad8
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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 (because C<DEPTH> is 0);
|
|
|
|
=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
|