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1 | # Devel::Peek - A data debugging tool for the XS programmer |
2 | # The documentation is after the __END__ | |
3 | ||
4 | package Devel::Peek; | |
5 | ||
6 | $VERSION = '1.03'; | |
7 | $XS_VERSION = $VERSION; | |
8 | $VERSION = eval $VERSION; | |
9 | ||
10 | require Exporter; | |
11 | use XSLoader (); | |
12 | ||
13 | @ISA = qw(Exporter); | |
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]); | |
18 | ||
19 | XSLoader::load 'Devel::Peek'; | |
20 | ||
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 @_, $c; | |
38 | goto &Exporter::import; | |
39 | } | |
40 | ||
41 | sub DumpWithOP ($;$) { | |
42 | local($Devel::Peek::dump_ops)=1; | |
43 | my $depth = @_ > 1 ? $_[1] : 4 ; | |
44 | Dump($_[0],$depth); | |
45 | } | |
46 | ||
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 | ||
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 ); | |
79 | DumpArray( 5, $a, $b, ... ); | |
80 | mstat "Point 5"; | |
81 | ||
82 | use Devel::Peek ':opd=st'; | |
83 | ||
84 | =head1 DESCRIPTION | |
85 | ||
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. | |
92 | ||
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>. | |
96 | ||
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()> | |
105 | function. | |
106 | ||
107 | Function C<DumpArray()> allows dumping of multiple values (useful when you | |
108 | need to analyze returns of functions). | |
109 | ||
110 | The global variable $Devel::Peek::pv_limit can be set to limit the | |
111 | number of character printed in various string values. Setting it to 0 | |
112 | means no limit. | |
113 | ||
114 | If C<use Devel::Peek> directive has a C<:opd=FLAGS> argument, | |
115 | this switches on debugging of opcode dispatch. C<FLAGS> should be a | |
116 | combination of C<s>, C<t>, and C<P> (see B<-D> flags in L<perlrun>). | |
117 | C<:opd> is a shortcut for C<:opd=st>. | |
118 | ||
119 | =head2 Runtime debugging | |
120 | ||
121 | C<CvGV($cv)> return one of the globs associated to a subroutine reference $cv. | |
122 | ||
123 | debug_flags() returns a string representation of C<$^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<$^D> before | |
128 | the modification.) | |
129 | ||
130 | runops_debug() returns true if the current I<opcode dispatcher> is the | |
131 | debugging one. When called with an argument, switches to debugging or | |
132 | non-debugging dispatcher depending on the argument (active for | |
133 | newly-entered subs/etc only). (The returned value is for the dispatcher before the modification.) | |
134 | ||
135 | =head2 Memory footprint debugging | |
136 | ||
137 | When perl is compiled with support for memory footprint debugging | |
138 | (default with Perl's malloc()), Devel::Peek provides an access to this API. | |
139 | ||
140 | Use mstat() function to emit a memory state statistic to the terminal. | |
141 | For more information on the format of output of mstat() see | |
142 | L<perldebguts/Using C<$ENV{PERL_DEBUG_MSTATS}>>. | |
143 | ||
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 | |
147 | ||
148 | minbucket nbuckets sbrk_good sbrk_slack sbrked_remains sbrks start_slack | |
149 | topbucket topbucket_ev topbucket_odd total total_chain total_sbrk totfree | |
150 | ||
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<$ENV{PERL_DEBUG_MSTATS}>> | |
156 | for details. | |
157 | ||
158 | Keep in mind that only the first several "odd-numbered" buckets are | |
159 | used, so the information on size of the "odd-numbered" buckets which are | |
160 | not used is probably meaningless. | |
161 | ||
162 | The information in | |
163 | ||
164 | mem_size available_size minbucket nbuckets | |
165 | ||
166 | is the property of a particular build of perl, and does not depend on | |
167 | the current process. If you do not provide the optional argument to | |
168 | the functions mstats_fillhash(), fill_mstats(), mstats2hash(), then | |
169 | the information in fields C<mem_size>, C<available_size> is not | |
170 | updated. | |
171 | ||
172 | C<fill_mstats($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. | |
176 | ||
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. | |
180 | ||
181 | So, if you want to collect memory info in a cycle, you may call | |
182 | ||
183 | $#buf = 999; | |
184 | fill_mstats($_) for @buf; | |
185 | mstats_fillhash(%report, 1); # Static info too | |
186 | ||
187 | foreach (@buf) { | |
188 | # Do something... | |
189 | fill_mstats $_; # Collect statistic | |
190 | } | |
191 | foreach (@buf) { | |
192 | mstats2hash($_, %report); # Preserve static info | |
193 | # Do something with %report | |
194 | } | |
195 | ||
196 | =head1 EXAMPLES | |
197 | ||
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). | |
205 | ||
206 | Oh, one final bit of advice: take L<perlguts> with you. When you return we | |
207 | expect to see it well-thumbed. | |
208 | ||
209 | =head2 A simple scalar string | |
210 | ||
211 | Let's begin by looking a simple scalar which is holding a string. | |
212 | ||
213 | use Devel::Peek; | |
214 | $a = "hello"; | |
215 | Dump $a; | |
216 | ||
217 | The output: | |
218 | ||
219 | SV = PVIV(0xbc288) | |
220 | REFCNT = 1 | |
221 | FLAGS = (POK,pPOK) | |
222 | IV = 0 | |
223 | PV = 0xb2048 "hello"\0 | |
224 | CUR = 5 | |
225 | LEN = 6 | |
226 | ||
227 | This says C<$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). | |
237 | ||
238 | =head2 A simple scalar number | |
239 | ||
240 | If the scalar contains a number the raw SV will be leaner. | |
241 | ||
242 | use Devel::Peek; | |
243 | $a = 42; | |
244 | Dump $a; | |
245 | ||
246 | The output: | |
247 | ||
248 | SV = IV(0xbc818) | |
249 | REFCNT = 1 | |
250 | FLAGS = (IOK,pIOK) | |
251 | IV = 42 | |
252 | ||
253 | This says C<$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. | |
257 | ||
258 | =head2 A simple scalar with an extra reference | |
259 | ||
260 | If the scalar from the previous example had an extra reference: | |
261 | ||
262 | use Devel::Peek; | |
263 | $a = 42; | |
264 | $b = \$a; | |
265 | Dump $a; | |
266 | ||
267 | The output: | |
268 | ||
269 | SV = IV(0xbe860) | |
270 | REFCNT = 2 | |
271 | FLAGS = (IOK,pIOK) | |
272 | IV = 42 | |
273 | ||
274 | Notice that this example differs from the previous example only in its | |
275 | reference count. Compare this to the next example, where we dump C<$b> | |
276 | instead of C<$a>. | |
277 | ||
278 | =head2 A reference to a simple scalar | |
279 | ||
280 | This shows what a reference looks like when it references a simple scalar. | |
281 | ||
282 | use Devel::Peek; | |
283 | $a = 42; | |
284 | $b = \$a; | |
285 | Dump $b; | |
286 | ||
287 | The output: | |
288 | ||
289 | SV = RV(0xf041c) | |
290 | REFCNT = 1 | |
291 | FLAGS = (ROK) | |
292 | RV = 0xbab08 | |
293 | SV = IV(0xbe860) | |
294 | REFCNT = 2 | |
295 | FLAGS = (IOK,pIOK) | |
296 | IV = 42 | |
297 | ||
298 | Starting from the top, this says C<$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. | |
303 | ||
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. | |
308 | ||
309 | =head2 A reference to an array | |
310 | ||
311 | This shows what a reference to an array looks like. | |
312 | ||
313 | use Devel::Peek; | |
314 | $a = [42]; | |
315 | Dump $a; | |
316 | ||
317 | The output: | |
318 | ||
319 | SV = RV(0xf041c) | |
320 | REFCNT = 1 | |
321 | FLAGS = (ROK) | |
322 | RV = 0xb2850 | |
323 | SV = PVAV(0xbd448) | |
324 | REFCNT = 1 | |
325 | FLAGS = () | |
326 | IV = 0 | |
327 | NV = 0 | |
328 | ARRAY = 0xb2048 | |
329 | ALLOC = 0xb2048 | |
330 | FILL = 0 | |
331 | MAX = 0 | |
332 | ARYLEN = 0x0 | |
333 | FLAGS = (REAL) | |
334 | Elt No. 0 0xb5658 | |
335 | SV = IV(0xbe860) | |
336 | REFCNT = 1 | |
337 | FLAGS = (IOK,pIOK) | |
338 | IV = 42 | |
339 | ||
340 | This says C<$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>. | |
344 | ||
345 | If C<$a> pointed to an array of two elements then we would see the | |
346 | following. | |
347 | ||
348 | use Devel::Peek 'Dump'; | |
349 | $a = [42,24]; | |
350 | Dump $a; | |
351 | ||
352 | The output: | |
353 | ||
354 | SV = RV(0xf041c) | |
355 | REFCNT = 1 | |
356 | FLAGS = (ROK) | |
357 | RV = 0xb2850 | |
358 | SV = PVAV(0xbd448) | |
359 | REFCNT = 1 | |
360 | FLAGS = () | |
361 | IV = 0 | |
362 | NV = 0 | |
363 | ARRAY = 0xb2048 | |
364 | ALLOC = 0xb2048 | |
365 | FILL = 0 | |
366 | MAX = 0 | |
367 | ARYLEN = 0x0 | |
368 | FLAGS = (REAL) | |
369 | Elt No. 0 0xb5658 | |
370 | SV = IV(0xbe860) | |
371 | REFCNT = 1 | |
372 | FLAGS = (IOK,pIOK) | |
373 | IV = 42 | |
374 | Elt No. 1 0xb5680 | |
375 | SV = IV(0xbe818) | |
376 | REFCNT = 1 | |
377 | FLAGS = (IOK,pIOK) | |
378 | IV = 24 | |
379 | ||
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 | |
382 | report tree). | |
383 | ||
384 | =head2 A reference to a hash | |
385 | ||
386 | The following shows the raw form of a reference to a hash. | |
387 | ||
388 | use Devel::Peek; | |
389 | $a = {hello=>42}; | |
390 | Dump $a; | |
391 | ||
392 | The output: | |
393 | ||
394 | SV = RV(0x8177858) at 0x816a618 | |
395 | REFCNT = 1 | |
396 | FLAGS = (ROK) | |
397 | RV = 0x814fc10 | |
398 | SV = PVHV(0x8167768) at 0x814fc10 | |
399 | REFCNT = 1 | |
400 | FLAGS = (SHAREKEYS) | |
401 | IV = 1 | |
402 | NV = 0 | |
403 | ARRAY = 0x816c5b8 (0:7, 1:1) | |
404 | hash quality = 100.0% | |
405 | KEYS = 1 | |
406 | FILL = 1 | |
407 | MAX = 7 | |
408 | RITER = -1 | |
409 | EITER = 0x0 | |
410 | Elt "hello" HASH = 0xc8fd181b | |
411 | SV = IV(0x816c030) at 0x814fcf4 | |
412 | REFCNT = 1 | |
413 | FLAGS = (IOK,pIOK) | |
414 | IV = 42 | |
415 | ||
416 | This shows C<$a> is a reference pointing to an SV. That SV is a PVHV, a | |
417 | hash. Fields RITER and EITER are used by C<L<each>>. | |
418 | ||
419 | The "quality" of a hash is defined as the total number of comparisons needed | |
420 | to access every element once, relative to the expected number needed for a | |
421 | random hash. The value can go over 100%. | |
422 | ||
423 | The total number of comparisons is equal to the sum of the squares of the | |
424 | number of entries in each bucket. For a random hash of C<<n>> keys into | |
425 | C<<k>> buckets, the expected value is: | |
426 | ||
427 | n + n(n-1)/2k | |
428 | ||
429 | =head2 Dumping a large array or hash | |
430 | ||
431 | The C<Dump()> function, by default, dumps up to 4 elements from a | |
432 | toplevel array or hash. This number can be increased by supplying a | |
433 | second argument to the function. | |
434 | ||
435 | use Devel::Peek; | |
436 | $a = [10,11,12,13,14]; | |
437 | Dump $a; | |
438 | ||
439 | Notice that C<Dump()> prints only elements 10 through 13 in the above code. | |
440 | The following code will print all of the elements. | |
441 | ||
442 | use Devel::Peek 'Dump'; | |
443 | $a = [10,11,12,13,14]; | |
444 | Dump $a, 5; | |
445 | ||
446 | =head2 A reference to an SV which holds a C pointer | |
447 | ||
448 | This is what you really need to know as an XS programmer, of course. When | |
449 | an XSUB returns a pointer to a C structure that pointer is stored in an SV | |
450 | and a reference to that SV is placed on the XSUB stack. So the output from | |
451 | an XSUB which uses something like the T_PTROBJ map might look something like | |
452 | this: | |
453 | ||
454 | SV = RV(0xf381c) | |
455 | REFCNT = 1 | |
456 | FLAGS = (ROK) | |
457 | RV = 0xb8ad8 | |
458 | SV = PVMG(0xbb3c8) | |
459 | REFCNT = 1 | |
460 | FLAGS = (OBJECT,IOK,pIOK) | |
461 | IV = 729160 | |
462 | NV = 0 | |
463 | PV = 0 | |
464 | STASH = 0xc1d10 "CookBookB::Opaque" | |
465 | ||
466 | This shows that we have an SV which is an RV. That RV points at another | |
467 | SV. In this case that second SV is a PVMG, a blessed scalar. Because it is | |
468 | blessed it has the C<OBJECT> flag set. Note that an SV which holds a C | |
469 | pointer also has the C<IOK> flag set. The C<STASH> is set to the package | |
470 | name which this SV was blessed into. | |
471 | ||
472 | The output from an XSUB which uses something like the T_PTRREF map, which | |
473 | doesn't bless the object, might look something like this: | |
474 | ||
475 | SV = RV(0xf381c) | |
476 | REFCNT = 1 | |
477 | FLAGS = (ROK) | |
478 | RV = 0xb8ad8 | |
479 | SV = PVMG(0xbb3c8) | |
480 | REFCNT = 1 | |
481 | FLAGS = (IOK,pIOK) | |
482 | IV = 729160 | |
483 | NV = 0 | |
484 | PV = 0 | |
485 | ||
486 | =head2 A reference to a subroutine | |
487 | ||
488 | Looks like this: | |
489 | ||
490 | SV = RV(0x798ec) | |
491 | REFCNT = 1 | |
492 | FLAGS = (TEMP,ROK) | |
493 | RV = 0x1d453c | |
494 | SV = PVCV(0x1c768c) | |
495 | REFCNT = 2 | |
496 | FLAGS = () | |
497 | IV = 0 | |
498 | NV = 0 | |
499 | COMP_STASH = 0x31068 "main" | |
500 | START = 0xb20e0 | |
501 | ROOT = 0xbece0 | |
502 | XSUB = 0x0 | |
503 | XSUBANY = 0 | |
504 | GVGV::GV = 0x1d44e8 "MY" :: "top_targets" | |
505 | FILE = "(eval 5)" | |
506 | DEPTH = 0 | |
507 | PADLIST = 0x1c9338 | |
508 | ||
509 | This shows that | |
510 | ||
511 | =over 4 | |
512 | ||
513 | =item * | |
514 | ||
515 | the subroutine is not an XSUB (since C<START> and C<ROOT> are | |
516 | non-zero, and C<XSUB> is zero); | |
517 | ||
518 | =item * | |
519 | ||
520 | that it was compiled in the package C<main>; | |
521 | ||
522 | =item * | |
523 | ||
524 | under the name C<MY::top_targets>; | |
525 | ||
526 | =item * | |
527 | ||
528 | inside a 5th eval in the program; | |
529 | ||
530 | =item * | |
531 | ||
532 | it is not currently executed (see C<DEPTH>); | |
533 | ||
534 | =item * | |
535 | ||
536 | it has no prototype (C<PROTOTYPE> field is missing). | |
537 | ||
538 | =back | |
539 | ||
540 | =head1 EXPORTS | |
541 | ||
542 | C<Dump>, C<mstat>, C<DeadCode>, C<DumpArray>, C<DumpWithOP> and | |
543 | C<DumpProg>, C<fill_mstats>, C<mstats_fillhash>, C<mstats2hash> by | |
544 | default. Additionally available C<SvREFCNT>, C<SvREFCNT_inc> and | |
545 | C<SvREFCNT_dec>. | |
546 | ||
547 | =head1 BUGS | |
548 | ||
549 | Readers have been known to skip important parts of L<perlguts>, causing much | |
550 | frustration for all. | |
551 | ||
552 | =head1 AUTHOR | |
553 | ||
554 | Ilya Zakharevich ilya@math.ohio-state.edu | |
555 | ||
556 | Copyright (c) 1995-98 Ilya Zakharevich. All rights reserved. | |
557 | This program is free software; you can redistribute it and/or | |
558 | modify it under the same terms as Perl itself. | |
559 | ||
560 | Author of this software makes no claim whatsoever about suitability, | |
561 | reliability, edability, editability or usability of this product, and | |
562 | should not be kept liable for any damage resulting from the use of | |
563 | it. If you can use it, you are in luck, if not, I should not be kept | |
564 | responsible. Keep a handy copy of your backup tape at hand. | |
565 | ||
566 | =head1 SEE ALSO | |
567 | ||
568 | L<perlguts>, and L<perlguts>, again. | |
569 | ||
570 | =cut |