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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 | |
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6 | # Underscore to allow older Perls to access older version from CPAN |
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7 | $VERSION = '1.00_01'; |
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8 | |
9 | require Exporter; |
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10 | use XSLoader (); |
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11 | |
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12 | @ISA = qw(Exporter); |
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13 | @EXPORT = qw(Dump mstat DeadCode DumpArray DumpWithOP DumpProg |
14 | fill_mstats mstats_fillhash mstats2hash); |
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15 | @EXPORT_OK = qw(SvREFCNT SvREFCNT_inc SvREFCNT_dec CvGV); |
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16 | %EXPORT_TAGS = ('ALL' => [@EXPORT, @EXPORT_OK]); |
17 | |
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18 | XSLoader::load 'Devel::Peek'; |
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19 | |
20 | sub DumpWithOP ($;$) { |
21 | local($Devel::Peek::dump_ops)=1; |
22 | my $depth = @_ > 1 ? $_[1] : 4 ; |
23 | Dump($_[0],$depth); |
24 | } |
25 | |
26 | 1; |
27 | __END__ |
28 | |
29 | =head1 NAME |
30 | |
31 | Devel::Peek - A data debugging tool for the XS programmer |
32 | |
33 | =head1 SYNOPSIS |
34 | |
35 | use Devel::Peek; |
36 | Dump( $a ); |
37 | Dump( $a, 5 ); |
38 | DumpArray( 5, $a, $b, ... ); |
39 | mstat "Point 5"; |
40 | |
41 | =head1 DESCRIPTION |
42 | |
43 | Devel::Peek contains functions which allows raw Perl datatypes to be |
44 | manipulated from a Perl script. This is used by those who do XS programming |
45 | to check that the data they are sending from C to Perl looks as they think |
46 | it should look. The trick, then, is to know what the raw datatype is |
47 | supposed to look like when it gets to Perl. This document offers some tips |
48 | and hints to describe good and bad raw data. |
49 | |
50 | It is very possible that this document will fall far short of being useful |
51 | to the casual reader. The reader is expected to understand the material in |
52 | the first few sections of L<perlguts>. |
53 | |
54 | Devel::Peek supplies a C<Dump()> function which can dump a raw Perl |
55 | datatype, and C<mstat("marker")> function to report on memory usage |
56 | (if perl is compiled with corresponding option). The function |
57 | DeadCode() provides statistics on the data "frozen" into inactive |
58 | C<CV>. Devel::Peek also supplies C<SvREFCNT()>, C<SvREFCNT_inc()>, and |
59 | C<SvREFCNT_dec()> which can query, increment, and decrement reference |
60 | counts on SVs. This document will take a passive, and safe, approach |
61 | to data debugging and for that it will describe only the C<Dump()> |
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62 | function. |
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63 | |
64 | Function C<DumpArray()> allows dumping of multiple values (useful when you |
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65 | need to analyze returns of functions). |
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66 | |
67 | The global variable $Devel::Peek::pv_limit can be set to limit the |
68 | number of character printed in various string values. Setting it to 0 |
69 | means no limit. |
70 | |
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71 | =head2 Memory footprint debugging |
72 | |
73 | When perl is compiled with support for memory footprint debugging |
74 | (default with Perl's malloc()), Devel::Peek provides an access to this API. |
75 | |
76 | Use mstat() function to emit a memory state statistic to the terminal. |
77 | For more information on the format of output of mstat() see |
78 | L<perldebug/Using C<$ENV{PERL_DEBUG_MSTATS}>>. |
79 | |
80 | Three additional functions allow access to this statistic from Perl. |
81 | First, use C<mstats_fillhash(%hash)> to get the information contained |
82 | in the output of mstat() into %hash. The field of this hash are |
83 | |
84 | minbucket nbuckets sbrk_good sbrk_slack sbrked_remains sbrks start_slack |
85 | topbucket topbucket_ev topbucket_odd total total_chain total_sbrk totfree |
86 | |
87 | Two additional fields C<free>, C<used> contain array references which |
88 | provide per-bucket count of free and used chunks. Two other fields |
89 | C<mem_size>, C<available_size> contain array references which provide |
90 | the information about the allocated size and usable size of chunks in |
91 | each bucket. Again, see L<perldebug/Using C<$ENV{PERL_DEBUG_MSTATS}>> |
92 | for details. |
93 | |
94 | Keep in mind that only the first several "odd-numbered" buckets are |
95 | used, so the information on size of the "odd-numbered" buckets which are |
96 | not used is probably meaningless. |
97 | |
98 | The information in |
99 | |
100 | mem_size available_size minbucket nbuckets |
101 | |
102 | is the property of a particular build of perl, and does not depend on |
103 | the current process. If you do not provide the optional argument to |
104 | the functions mstats_fillhash(), fill_mstats(), mstats2hash(), then |
105 | the information in fields C<mem_size>, C<available_size> is not |
106 | updated. |
107 | |
108 | C<fill_mstats($buf)> is a much cheaper call (both speedwise and |
109 | memory-wise) which collects the statistic into $buf in |
110 | machine-readable form. At a later moment you may need to call |
111 | C<mstats2hash($buf, %hash)> to use this information to fill %hash. |
112 | |
113 | All three APIs C<fill_mstats($buf)>, C<mstats_fillhash(%hash)>, and |
114 | C<mstats2hash($buf, %hash)> are designed to allocate no memory if used |
115 | I<the second time> on the same $buf and/or %hash. |
116 | |
117 | So, if you want to collect memory info in a cycle, you may call |
118 | |
119 | $#buf = 999; |
120 | fill_mstats($_) for @buf; |
121 | mstats_fillhash(%report, 1); # Static info too |
122 | |
123 | foreach (@buf) { |
124 | # Do something... |
125 | fill_mstats $_; # Collect statistic |
126 | } |
127 | foreach (@buf) { |
128 | mstats2hash($_, %report); # Preserve static info |
129 | # Do something with %report |
130 | } |
131 | |
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132 | =head1 EXAMPLES |
133 | |
134 | The following examples don't attempt to show everything as that would be a |
135 | monumental task, and, frankly, we don't want this manpage to be an internals |
136 | document for Perl. The examples do demonstrate some basics of the raw Perl |
137 | datatypes, and should suffice to get most determined people on their way. |
138 | There are no guidewires or safety nets, nor blazed trails, so be prepared to |
139 | travel alone from this point and on and, if at all possible, don't fall into |
140 | the quicksand (it's bad for business). |
141 | |
142 | Oh, one final bit of advice: take L<perlguts> with you. When you return we |
143 | expect to see it well-thumbed. |
144 | |
145 | =head2 A simple scalar string |
146 | |
147 | Let's begin by looking a simple scalar which is holding a string. |
148 | |
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149 | use Devel::Peek; |
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150 | $a = "hello"; |
151 | Dump $a; |
152 | |
153 | The output: |
154 | |
155 | SV = PVIV(0xbc288) |
156 | REFCNT = 1 |
157 | FLAGS = (POK,pPOK) |
158 | IV = 0 |
159 | PV = 0xb2048 "hello"\0 |
160 | CUR = 5 |
161 | LEN = 6 |
162 | |
163 | This says C<$a> is an SV, a scalar. The scalar is a PVIV, a string. |
164 | Its reference count is 1. It has the C<POK> flag set, meaning its |
165 | current PV field is valid. Because POK is set we look at the PV item |
166 | to see what is in the scalar. The \0 at the end indicate that this |
167 | PV is properly NUL-terminated. |
168 | If the FLAGS had been IOK we would look |
169 | at the IV item. CUR indicates the number of characters in the PV. |
170 | LEN indicates the number of bytes requested for the PV (one more than |
171 | CUR, in this case, because LEN includes an extra byte for the |
172 | end-of-string marker). |
173 | |
174 | =head2 A simple scalar number |
175 | |
176 | If the scalar contains a number the raw SV will be leaner. |
177 | |
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178 | use Devel::Peek; |
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179 | $a = 42; |
180 | Dump $a; |
181 | |
182 | The output: |
183 | |
184 | SV = IV(0xbc818) |
185 | REFCNT = 1 |
186 | FLAGS = (IOK,pIOK) |
187 | IV = 42 |
188 | |
189 | This says C<$a> is an SV, a scalar. The scalar is an IV, a number. Its |
190 | reference count is 1. It has the C<IOK> flag set, meaning it is currently |
191 | being evaluated as a number. Because IOK is set we look at the IV item to |
192 | see what is in the scalar. |
193 | |
194 | =head2 A simple scalar with an extra reference |
195 | |
196 | If the scalar from the previous example had an extra reference: |
197 | |
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198 | use Devel::Peek; |
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199 | $a = 42; |
200 | $b = \$a; |
201 | Dump $a; |
202 | |
203 | The output: |
204 | |
205 | SV = IV(0xbe860) |
206 | REFCNT = 2 |
207 | FLAGS = (IOK,pIOK) |
208 | IV = 42 |
209 | |
210 | Notice that this example differs from the previous example only in its |
211 | reference count. Compare this to the next example, where we dump C<$b> |
212 | instead of C<$a>. |
213 | |
214 | =head2 A reference to a simple scalar |
215 | |
216 | This shows what a reference looks like when it references a simple scalar. |
217 | |
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218 | use Devel::Peek; |
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219 | $a = 42; |
220 | $b = \$a; |
221 | Dump $b; |
222 | |
223 | The output: |
224 | |
225 | SV = RV(0xf041c) |
226 | REFCNT = 1 |
227 | FLAGS = (ROK) |
228 | RV = 0xbab08 |
229 | SV = IV(0xbe860) |
230 | REFCNT = 2 |
231 | FLAGS = (IOK,pIOK) |
232 | IV = 42 |
233 | |
234 | Starting from the top, this says C<$b> is an SV. The scalar is an RV, a |
235 | reference. It has the C<ROK> flag set, meaning it is a reference. Because |
236 | ROK is set we have an RV item rather than an IV or PV. Notice that Dump |
237 | follows the reference and shows us what C<$b> was referencing. We see the |
238 | same C<$a> that we found in the previous example. |
239 | |
240 | Note that the value of C<RV> coincides with the numbers we see when we |
241 | stringify $b. The addresses inside RV() and IV() are addresses of |
242 | C<X***> structure which holds the current state of an C<SV>. This |
243 | address may change during lifetime of an SV. |
244 | |
245 | =head2 A reference to an array |
246 | |
247 | This shows what a reference to an array looks like. |
248 | |
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249 | use Devel::Peek; |
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250 | $a = [42]; |
251 | Dump $a; |
252 | |
253 | The output: |
254 | |
255 | SV = RV(0xf041c) |
256 | REFCNT = 1 |
257 | FLAGS = (ROK) |
258 | RV = 0xb2850 |
259 | SV = PVAV(0xbd448) |
260 | REFCNT = 1 |
261 | FLAGS = () |
262 | IV = 0 |
263 | NV = 0 |
264 | ARRAY = 0xb2048 |
265 | ALLOC = 0xb2048 |
266 | FILL = 0 |
267 | MAX = 0 |
268 | ARYLEN = 0x0 |
269 | FLAGS = (REAL) |
270 | Elt No. 0 0xb5658 |
271 | SV = IV(0xbe860) |
272 | REFCNT = 1 |
273 | FLAGS = (IOK,pIOK) |
274 | IV = 42 |
275 | |
276 | This says C<$a> is an SV and that it is an RV. That RV points to |
277 | another SV which is a PVAV, an array. The array has one element, |
278 | element zero, which is another SV. The field C<FILL> above indicates |
279 | the last element in the array, similar to C<$#$a>. |
280 | |
281 | If C<$a> pointed to an array of two elements then we would see the |
282 | following. |
283 | |
284 | use Devel::Peek 'Dump'; |
285 | $a = [42,24]; |
286 | Dump $a; |
287 | |
288 | The output: |
289 | |
290 | SV = RV(0xf041c) |
291 | REFCNT = 1 |
292 | FLAGS = (ROK) |
293 | RV = 0xb2850 |
294 | SV = PVAV(0xbd448) |
295 | REFCNT = 1 |
296 | FLAGS = () |
297 | IV = 0 |
298 | NV = 0 |
299 | ARRAY = 0xb2048 |
300 | ALLOC = 0xb2048 |
301 | FILL = 0 |
302 | MAX = 0 |
303 | ARYLEN = 0x0 |
304 | FLAGS = (REAL) |
305 | Elt No. 0 0xb5658 |
306 | SV = IV(0xbe860) |
307 | REFCNT = 1 |
308 | FLAGS = (IOK,pIOK) |
309 | IV = 42 |
310 | Elt No. 1 0xb5680 |
311 | SV = IV(0xbe818) |
312 | REFCNT = 1 |
313 | FLAGS = (IOK,pIOK) |
314 | IV = 24 |
315 | |
316 | Note that C<Dump> will not report I<all> the elements in the array, |
317 | only several first (depending on how deep it already went into the |
318 | report tree). |
319 | |
320 | =head2 A reference to a hash |
321 | |
322 | The following shows the raw form of a reference to a hash. |
323 | |
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324 | use Devel::Peek; |
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325 | $a = {hello=>42}; |
326 | Dump $a; |
327 | |
328 | The output: |
329 | |
330 | SV = RV(0xf041c) |
331 | REFCNT = 1 |
332 | FLAGS = (ROK) |
333 | RV = 0xb2850 |
334 | SV = PVHV(0xbd448) |
335 | REFCNT = 1 |
336 | FLAGS = () |
337 | NV = 0 |
338 | ARRAY = 0xbd748 |
339 | KEYS = 1 |
340 | FILL = 1 |
341 | MAX = 7 |
342 | RITER = -1 |
343 | EITER = 0x0 |
344 | Elt "hello" => 0xbaaf0 |
345 | SV = IV(0xbe860) |
346 | REFCNT = 1 |
347 | FLAGS = (IOK,pIOK) |
348 | IV = 42 |
349 | |
350 | This shows C<$a> is a reference pointing to an SV. That SV is a PVHV, a |
351 | hash. Fields RITER and EITER are used by C<L<each>>. |
352 | |
353 | =head2 Dumping a large array or hash |
354 | |
355 | The C<Dump()> function, by default, dumps up to 4 elements from a |
356 | toplevel array or hash. This number can be increased by supplying a |
357 | second argument to the function. |
358 | |
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359 | use Devel::Peek; |
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360 | $a = [10,11,12,13,14]; |
361 | Dump $a; |
362 | |
363 | Notice that C<Dump()> prints only elements 10 through 13 in the above code. |
364 | The following code will print all of the elements. |
365 | |
366 | use Devel::Peek 'Dump'; |
367 | $a = [10,11,12,13,14]; |
368 | Dump $a, 5; |
369 | |
370 | =head2 A reference to an SV which holds a C pointer |
371 | |
372 | This is what you really need to know as an XS programmer, of course. When |
373 | an XSUB returns a pointer to a C structure that pointer is stored in an SV |
374 | and a reference to that SV is placed on the XSUB stack. So the output from |
375 | an XSUB which uses something like the T_PTROBJ map might look something like |
376 | this: |
377 | |
378 | SV = RV(0xf381c) |
379 | REFCNT = 1 |
380 | FLAGS = (ROK) |
381 | RV = 0xb8ad8 |
382 | SV = PVMG(0xbb3c8) |
383 | REFCNT = 1 |
384 | FLAGS = (OBJECT,IOK,pIOK) |
385 | IV = 729160 |
386 | NV = 0 |
387 | PV = 0 |
388 | STASH = 0xc1d10 "CookBookB::Opaque" |
389 | |
390 | This shows that we have an SV which is an RV. That RV points at another |
391 | SV. In this case that second SV is a PVMG, a blessed scalar. Because it is |
392 | blessed it has the C<OBJECT> flag set. Note that an SV which holds a C |
393 | pointer also has the C<IOK> flag set. The C<STASH> is set to the package |
394 | name which this SV was blessed into. |
395 | |
396 | The output from an XSUB which uses something like the T_PTRREF map, which |
397 | doesn't bless the object, might look something like this: |
398 | |
399 | SV = RV(0xf381c) |
400 | REFCNT = 1 |
401 | FLAGS = (ROK) |
402 | RV = 0xb8ad8 |
403 | SV = PVMG(0xbb3c8) |
404 | REFCNT = 1 |
405 | FLAGS = (IOK,pIOK) |
406 | IV = 729160 |
407 | NV = 0 |
408 | PV = 0 |
409 | |
410 | =head2 A reference to a subroutine |
411 | |
412 | Looks like this: |
413 | |
414 | SV = RV(0x798ec) |
415 | REFCNT = 1 |
416 | FLAGS = (TEMP,ROK) |
417 | RV = 0x1d453c |
418 | SV = PVCV(0x1c768c) |
419 | REFCNT = 2 |
420 | FLAGS = () |
421 | IV = 0 |
422 | NV = 0 |
423 | COMP_STASH = 0x31068 "main" |
424 | START = 0xb20e0 |
425 | ROOT = 0xbece0 |
426 | XSUB = 0x0 |
427 | XSUBANY = 0 |
428 | GVGV::GV = 0x1d44e8 "MY" :: "top_targets" |
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429 | FILE = "(eval 5)" |
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430 | DEPTH = 0 |
431 | PADLIST = 0x1c9338 |
432 | |
433 | This shows that |
434 | |
435 | =over |
436 | |
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437 | =item * |
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438 | |
439 | the subroutine is not an XSUB (since C<START> and C<ROOT> are |
440 | non-zero, and C<XSUB> is zero); |
441 | |
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442 | =item * |
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443 | |
444 | that it was compiled in the package C<main>; |
445 | |
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446 | =item * |
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447 | |
448 | under the name C<MY::top_targets>; |
449 | |
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450 | =item * |
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451 | |
452 | inside a 5th eval in the program; |
453 | |
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454 | =item * |
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455 | |
456 | it is not currently executed (see C<DEPTH>); |
457 | |
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458 | =item * |
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459 | |
460 | it has no prototype (C<PROTOTYPE> field is missing). |
461 | |
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462 | =back |
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463 | |
464 | =head1 EXPORTS |
465 | |
466 | C<Dump>, C<mstat>, C<DeadCode>, C<DumpArray>, C<DumpWithOP> and |
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467 | C<DumpProg>, C<fill_mstats>, C<mstats_fillhash>, C<mstats2hash> by |
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468 | default. Additionally available C<SvREFCNT>, C<SvREFCNT_inc> and |
469 | C<SvREFCNT_dec>. |
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470 | |
471 | =head1 BUGS |
472 | |
473 | Readers have been known to skip important parts of L<perlguts>, causing much |
474 | frustration for all. |
475 | |
476 | =head1 AUTHOR |
477 | |
478 | Ilya Zakharevich ilya@math.ohio-state.edu |
479 | |
480 | Copyright (c) 1995-98 Ilya Zakharevich. All rights reserved. |
481 | This program is free software; you can redistribute it and/or |
482 | modify it under the same terms as Perl itself. |
483 | |
484 | Author of this software makes no claim whatsoever about suitability, |
485 | reliability, edability, editability or usability of this product, and |
486 | should not be kept liable for any damage resulting from the use of |
487 | it. If you can use it, you are in luck, if not, I should not be kept |
488 | responsible. Keep a handy copy of your backup tape at hand. |
489 | |
490 | =head1 SEE ALSO |
491 | |
492 | L<perlguts>, and L<perlguts>, again. |
493 | |
494 | =cut |