1 # Devel::Peek - A data debugging tool for the XS programmer
2 # The documentation is after the __END__
7 $XS_VERSION = $VERSION;
8 $VERSION = eval $VERSION;
14 @EXPORT = qw(Dump mstat DeadCode DumpArray DumpWithOP DumpProg
15 fill_mstats mstats_fillhash mstats2hash runops_debug debug_flags);
16 @EXPORT_OK = qw(SvREFCNT SvREFCNT_inc SvREFCNT_dec CvGV);
17 %EXPORT_TAGS = ('ALL' => [@EXPORT, @EXPORT_OK]);
19 XSLoader::load 'Devel::Peek';
23 my $ops_rx = qr/^:opd(=[stP]*)?\b/;
24 my @db = grep m/$ops_rx/, @_;
25 @_ = grep !m/$ops_rx/, @_;
27 die "Too many :opd options" if @db > 1;
29 my $flags = ($db[0] =~ m/$ops_rx/ and $1);
30 $flags = 'st' unless defined $flags;
32 $f |= 2 if $flags =~ /s/;
33 $f |= 8 if $flags =~ /t/;
34 $f |= 64 if $flags =~ /P/;
38 goto &Exporter::import;
41 sub DumpWithOP ($;$) {
42 local($Devel::Peek::dump_ops)=1;
43 my $depth = @_ > 1 ? $_[1] : 4 ;
47 $D_flags = 'psltocPmfrxuLHXDSTR';
49 sub debug_flags (;$) {
51 for my $i (0 .. length($D_flags)-1) {
52 $out .= substr $D_flags, $i, 1 if $^D & (1<<$i);
56 if (defined $arg and $arg =~ /\D/) {
57 die "unknown flags in debug_flags()" if $arg =~ /[^-$D_flags]/;
58 my ($on,$off) = split /-/, "$arg-";
60 $num |= (1<<index($D_flags, $_)) for split //, $on;
61 $num &= ~(1<<index($D_flags, $_)) for split //, $off;
63 $^D = $num if defined $arg;
72 Devel::Peek - A data debugging tool for the XS programmer
79 DumpArray( 5, $a, $b, ... );
82 use Devel::Peek ':opd=st';
86 Devel::Peek contains functions which allows raw Perl datatypes to be
87 manipulated from a Perl script. This is used by those who do XS programming
88 to check that the data they are sending from C to Perl looks as they think
89 it should look. The trick, then, is to know what the raw datatype is
90 supposed to look like when it gets to Perl. This document offers some tips
91 and hints to describe good and bad raw data.
93 It is very possible that this document will fall far short of being useful
94 to the casual reader. The reader is expected to understand the material in
95 the first few sections of L<perlguts>.
97 Devel::Peek supplies a C<Dump()> function which can dump a raw Perl
98 datatype, and C<mstat("marker")> function to report on memory usage
99 (if perl is compiled with corresponding option). The function
100 DeadCode() provides statistics on the data "frozen" into inactive
101 C<CV>. Devel::Peek also supplies C<SvREFCNT()>, C<SvREFCNT_inc()>, and
102 C<SvREFCNT_dec()> which can query, increment, and decrement reference
103 counts on SVs. This document will take a passive, and safe, approach
104 to data debugging and for that it will describe only the C<Dump()>
107 Function C<DumpArray()> allows dumping of multiple values (useful when you
108 need to analyze returns of functions).
110 The global variable $Devel::Peek::pv_limit can be set to limit the
111 number of character printed in various string values. Setting it to 0
114 If C<use Devel::Peek> directive has a C<:opd=FLAGS> argument,
115 this switches on debugging of opcode dispatch. C<FLAGS> should be a
116 combination of C<s>, C<t>, and C<P> (see B<-D> flags in L<perlrun>).
117 C<:opd> is a shortcut for C<:opd=st>.
119 =head2 Runtime debugging
121 C<CvGV($cv)> return one of the globs associated to a subroutine reference $cv.
123 debug_flags() returns a string representation of C<$^D> (similar to
124 what is allowed for B<-D> flag). When called with a numeric argument,
125 sets $^D to the corresponding value. When called with an argument of
126 the form C<"flags-flags">, set on/off bits of C<$^D> corresponding to
127 letters before/after C<->. (The returned value is for C<$^D> before
130 runops_debug() returns true if the current I<opcode dispatcher> is the
131 debugging one. When called with an argument, switches to debugging or
132 non-debugging dispatcher depending on the argument (active for
133 newly-entered subs/etc only). (The returned value is for the dispatcher before the modification.)
135 =head2 Memory footprint debugging
137 When perl is compiled with support for memory footprint debugging
138 (default with Perl's malloc()), Devel::Peek provides an access to this API.
140 Use mstat() function to emit a memory state statistic to the terminal.
141 For more information on the format of output of mstat() see
142 L<perldebguts/Using C<$ENV{PERL_DEBUG_MSTATS}>>.
144 Three additional functions allow access to this statistic from Perl.
145 First, use C<mstats_fillhash(%hash)> to get the information contained
146 in the output of mstat() into %hash. The field of this hash are
148 minbucket nbuckets sbrk_good sbrk_slack sbrked_remains sbrks start_slack
149 topbucket topbucket_ev topbucket_odd total total_chain total_sbrk totfree
151 Two additional fields C<free>, C<used> contain array references which
152 provide per-bucket count of free and used chunks. Two other fields
153 C<mem_size>, C<available_size> contain array references which provide
154 the information about the allocated size and usable size of chunks in
155 each bucket. Again, see L<perldebguts/Using C<$ENV{PERL_DEBUG_MSTATS}>>
158 Keep in mind that only the first several "odd-numbered" buckets are
159 used, so the information on size of the "odd-numbered" buckets which are
160 not used is probably meaningless.
164 mem_size available_size minbucket nbuckets
166 is the property of a particular build of perl, and does not depend on
167 the current process. If you do not provide the optional argument to
168 the functions mstats_fillhash(), fill_mstats(), mstats2hash(), then
169 the information in fields C<mem_size>, C<available_size> is not
172 C<fill_mstats($buf)> is a much cheaper call (both speedwise and
173 memory-wise) which collects the statistic into $buf in
174 machine-readable form. At a later moment you may need to call
175 C<mstats2hash($buf, %hash)> to use this information to fill %hash.
177 All three APIs C<fill_mstats($buf)>, C<mstats_fillhash(%hash)>, and
178 C<mstats2hash($buf, %hash)> are designed to allocate no memory if used
179 I<the second time> on the same $buf and/or %hash.
181 So, if you want to collect memory info in a cycle, you may call
184 fill_mstats($_) for @buf;
185 mstats_fillhash(%report, 1); # Static info too
189 fill_mstats $_; # Collect statistic
192 mstats2hash($_, %report); # Preserve static info
193 # Do something with %report
198 The following examples don't attempt to show everything as that would be a
199 monumental task, and, frankly, we don't want this manpage to be an internals
200 document for Perl. The examples do demonstrate some basics of the raw Perl
201 datatypes, and should suffice to get most determined people on their way.
202 There are no guidewires or safety nets, nor blazed trails, so be prepared to
203 travel alone from this point and on and, if at all possible, don't fall into
204 the quicksand (it's bad for business).
206 Oh, one final bit of advice: take L<perlguts> with you. When you return we
207 expect to see it well-thumbed.
209 =head2 A simple scalar string
211 Let's begin by looking a simple scalar which is holding a string.
223 PV = 0xb2048 "hello"\0
227 This says C<$a> is an SV, a scalar. The scalar is a PVIV, a string.
228 Its reference count is 1. It has the C<POK> flag set, meaning its
229 current PV field is valid. Because POK is set we look at the PV item
230 to see what is in the scalar. The \0 at the end indicate that this
231 PV is properly NUL-terminated.
232 If the FLAGS had been IOK we would look
233 at the IV item. CUR indicates the number of characters in the PV.
234 LEN indicates the number of bytes requested for the PV (one more than
235 CUR, in this case, because LEN includes an extra byte for the
236 end-of-string marker).
238 =head2 A simple scalar number
240 If the scalar contains a number the raw SV will be leaner.
253 This says C<$a> is an SV, a scalar. The scalar is an IV, a number. Its
254 reference count is 1. It has the C<IOK> flag set, meaning it is currently
255 being evaluated as a number. Because IOK is set we look at the IV item to
256 see what is in the scalar.
258 =head2 A simple scalar with an extra reference
260 If the scalar from the previous example had an extra reference:
274 Notice that this example differs from the previous example only in its
275 reference count. Compare this to the next example, where we dump C<$b>
278 =head2 A reference to a simple scalar
280 This shows what a reference looks like when it references a simple scalar.
298 Starting from the top, this says C<$b> is an SV. The scalar is an RV, a
299 reference. It has the C<ROK> flag set, meaning it is a reference. Because
300 ROK is set we have an RV item rather than an IV or PV. Notice that Dump
301 follows the reference and shows us what C<$b> was referencing. We see the
302 same C<$a> that we found in the previous example.
304 Note that the value of C<RV> coincides with the numbers we see when we
305 stringify $b. The addresses inside RV() and IV() are addresses of
306 C<X***> structure which holds the current state of an C<SV>. This
307 address may change during lifetime of an SV.
309 =head2 A reference to an array
311 This shows what a reference to an array looks like.
340 This says C<$a> is an SV and that it is an RV. That RV points to
341 another SV which is a PVAV, an array. The array has one element,
342 element zero, which is another SV. The field C<FILL> above indicates
343 the last element in the array, similar to C<$#$a>.
345 If C<$a> pointed to an array of two elements then we would see the
348 use Devel::Peek 'Dump';
380 Note that C<Dump> will not report I<all> the elements in the array,
381 only several first (depending on how deep it already went into the
384 =head2 A reference to a hash
386 The following shows the raw form of a reference to a hash.
408 Elt "hello" => 0xbaaf0
414 This shows C<$a> is a reference pointing to an SV. That SV is a PVHV, a
415 hash. Fields RITER and EITER are used by C<L<each>>.
417 =head2 Dumping a large array or hash
419 The C<Dump()> function, by default, dumps up to 4 elements from a
420 toplevel array or hash. This number can be increased by supplying a
421 second argument to the function.
424 $a = [10,11,12,13,14];
427 Notice that C<Dump()> prints only elements 10 through 13 in the above code.
428 The following code will print all of the elements.
430 use Devel::Peek 'Dump';
431 $a = [10,11,12,13,14];
434 =head2 A reference to an SV which holds a C pointer
436 This is what you really need to know as an XS programmer, of course. When
437 an XSUB returns a pointer to a C structure that pointer is stored in an SV
438 and a reference to that SV is placed on the XSUB stack. So the output from
439 an XSUB which uses something like the T_PTROBJ map might look something like
448 FLAGS = (OBJECT,IOK,pIOK)
452 STASH = 0xc1d10 "CookBookB::Opaque"
454 This shows that we have an SV which is an RV. That RV points at another
455 SV. In this case that second SV is a PVMG, a blessed scalar. Because it is
456 blessed it has the C<OBJECT> flag set. Note that an SV which holds a C
457 pointer also has the C<IOK> flag set. The C<STASH> is set to the package
458 name which this SV was blessed into.
460 The output from an XSUB which uses something like the T_PTRREF map, which
461 doesn't bless the object, might look something like this:
474 =head2 A reference to a subroutine
487 COMP_STASH = 0x31068 "main"
492 GVGV::GV = 0x1d44e8 "MY" :: "top_targets"
503 the subroutine is not an XSUB (since C<START> and C<ROOT> are
504 non-zero, and C<XSUB> is zero);
508 that it was compiled in the package C<main>;
512 under the name C<MY::top_targets>;
516 inside a 5th eval in the program;
520 it is not currently executed (see C<DEPTH>);
524 it has no prototype (C<PROTOTYPE> field is missing).
530 C<Dump>, C<mstat>, C<DeadCode>, C<DumpArray>, C<DumpWithOP> and
531 C<DumpProg>, C<fill_mstats>, C<mstats_fillhash>, C<mstats2hash> by
532 default. Additionally available C<SvREFCNT>, C<SvREFCNT_inc> and
537 Readers have been known to skip important parts of L<perlguts>, causing much
542 Ilya Zakharevich ilya@math.ohio-state.edu
544 Copyright (c) 1995-98 Ilya Zakharevich. All rights reserved.
545 This program is free software; you can redistribute it and/or
546 modify it under the same terms as Perl itself.
548 Author of this software makes no claim whatsoever about suitability,
549 reliability, edability, editability or usability of this product, and
550 should not be kept liable for any damage resulting from the use of
551 it. If you can use it, you are in luck, if not, I should not be kept
552 responsible. Keep a handy copy of your backup tape at hand.
556 L<perlguts>, and L<perlguts>, again.