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1=head1 NAME
2
3perldebguts - Guts of Perl debugging
4
5=head1 DESCRIPTION
6
ba555bf5 7This is not L<perldebug>, which tells you how to use
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8the debugger. This manpage describes low-level details concerning
9the debugger's internals, which range from difficult to impossible
10to understand for anyone who isn't incredibly intimate with Perl's guts.
11Caveat lector.
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12
13=head1 Debugger Internals
14
15Perl has special debugging hooks at compile-time and run-time used
16to create debugging environments. These hooks are not to be confused
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17with the I<perl -Dxxx> command described in L<perlrun>, which is
18usable only if a special Perl is built per the instructions in the
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19F<INSTALL> podpage in the Perl source tree.
20
21For example, whenever you call Perl's built-in C<caller> function
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22from the package C<DB>, the arguments that the corresponding stack
23frame was called with are copied to the C<@DB::args> array. These
24mechanisms are enabled by calling Perl with the B<-d> switch.
25Specifically, the following additional features are enabled
26(cf. L<perlvar/$^P>):
055fd3a9 27
13a2d996 28=over 4
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29
30=item *
31
32Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require
33'perl5db.pl'}> if not present) before the first line of your program.
34
35=item *
36
aa0b556f 37Each array C<@{"_<$filename"}> holds the lines of $filename for a
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38file compiled by Perl. The same is also true for C<eval>ed strings
39that contain subroutines, or which are currently being executed.
40The $filename for C<eval>ed strings looks like C<(eval 34)>.
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41
42Values in this array are magical in numeric context: they compare
43equal to zero only if the line is not breakable.
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44
45=item *
46
aa0b556f 47Each hash C<%{"_<$filename"}> contains breakpoints and actions keyed
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48by line number. Individual entries (as opposed to the whole hash)
49are settable. Perl only cares about Boolean true here, although
50the values used by F<perl5db.pl> have the form
8894c26d 51C<"$break_condition\0$action">.
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52
53The same holds for evaluated strings that contain subroutines, or
54which are currently being executed. The $filename for C<eval>ed strings
d24ca0c5 55looks like C<(eval 34)>.
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56
57=item *
58
aa0b556f 59Each scalar C<${"_<$filename"}> contains C<"_<$filename">. This is
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60also the case for evaluated strings that contain subroutines, or
61which are currently being executed. The $filename for C<eval>ed
d24ca0c5 62strings looks like C<(eval 34)>.
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63
64=item *
65
66After each C<require>d file is compiled, but before it is executed,
67C<DB::postponed(*{"_<$filename"})> is called if the subroutine
68C<DB::postponed> exists. Here, the $filename is the expanded name of
69the C<require>d file, as found in the values of %INC.
70
71=item *
72
73After each subroutine C<subname> is compiled, the existence of
74C<$DB::postponed{subname}> is checked. If this key exists,
75C<DB::postponed(subname)> is called if the C<DB::postponed> subroutine
76also exists.
77
78=item *
79
80A hash C<%DB::sub> is maintained, whose keys are subroutine names
81and whose values have the form C<filename:startline-endline>.
82C<filename> has the form C<(eval 34)> for subroutines defined inside
d24ca0c5 83C<eval>s.
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84
85=item *
86
87When the execution of your program reaches a point that can hold a
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88breakpoint, the C<DB::DB()> subroutine is called if any of the variables
89C<$DB::trace>, C<$DB::single>, or C<$DB::signal> is true. These variables
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90are not C<local>izable. This feature is disabled when executing
91inside C<DB::DB()>, including functions called from it
92unless C<< $^D & (1<<30) >> is true.
93
94=item *
95
96When execution of the program reaches a subroutine call, a call to
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97C<&DB::sub>(I<args>) is made instead, with C<$DB::sub> set to identify
98the called subroutine. (This doesn't happen if the calling subroutine
99was compiled in the C<DB> package.) C<$DB::sub> normally holds the name
100of the called subroutine, if it has a name by which it can be looked up.
101Failing that, C<$DB::sub> will hold a reference to the called subroutine.
102Either way, the C<&DB::sub> subroutine can use C<$DB::sub> as a reference
103by which to call the called subroutine, which it will normally want to do.
055fd3a9 104
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105X<&DB::lsub>If the call is to an lvalue subroutine, and C<&DB::lsub>
106is defined C<&DB::lsub>(I<args>) is called instead, otherwise falling
107back to C<&DB::sub>(I<args>).
108
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109=item *
110
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111When execution of the program uses C<goto> to enter a non-XS subroutine
112and the 0x80 bit is set in C<$^P>, a call to C<&DB::goto> is made, with
113C<$DB::sub> set to identify the subroutine being entered. The call to
114C<&DB::goto> does not replace the C<goto>; the requested subroutine will
115still be entered once C<&DB::goto> has returned. C<$DB::sub> normally
116holds the name of the subroutine being entered, if it has one. Failing
117that, C<$DB::sub> will hold a reference to the subroutine being entered.
118Unlike when C<&DB::sub> is called, it is not guaranteed that C<$DB::sub>
119can be used as a reference to operate on the subroutine being entered.
261cbad1 120
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121=back
122
123Note that if C<&DB::sub> needs external data for it to work, no
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124subroutine call is possible without it. As an example, the standard
125debugger's C<&DB::sub> depends on the C<$DB::deep> variable
126(it defines how many levels of recursion deep into the debugger you can go
127before a mandatory break). If C<$DB::deep> is not defined, subroutine
128calls are not possible, even though C<&DB::sub> exists.
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129
130=head2 Writing Your Own Debugger
131
74410c12 132=head3 Environment Variables
666f95b9 133
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134The C<PERL5DB> environment variable can be used to define a debugger.
135For example, the minimal "working" debugger (it actually doesn't do anything)
136consists of one line:
666f95b9 137
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138 sub DB::DB {}
139
74410c12 140It can easily be defined like this:
666f95b9 141
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142 $ PERL5DB="sub DB::DB {}" perl -d your-script
143
74410c12 144Another brief debugger, slightly more useful, can be created
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145with only the line:
146
147 sub DB::DB {print ++$i; scalar <STDIN>}
148
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149This debugger prints a number which increments for each statement
150encountered and waits for you to hit a newline before continuing
151to the next statement.
666f95b9 152
74410c12 153The following debugger is actually useful:
666f95b9 154
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155 {
156 package DB;
157 sub DB {}
158 sub sub {print ++$i, " $sub\n"; &$sub}
159 }
160
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161It prints the sequence number of each subroutine call and the name of the
162called subroutine. Note that C<&DB::sub> is being compiled into the
163package C<DB> through the use of the C<package> directive.
055fd3a9 164
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165When it starts, the debugger reads your rc file (F<./.perldb> or
166F<~/.perldb> under Unix), which can set important options.
167(A subroutine (C<&afterinit>) can be defined here as well; it is executed
168after the debugger completes its own initialization.)
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169
170After the rc file is read, the debugger reads the PERLDB_OPTS
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171environment variable and uses it to set debugger options. The
172contents of this variable are treated as if they were the argument
96090e4f 173of an C<o ...> debugger command (q.v. in L<perldebug/"Configurable Options">).
74410c12 174
7b406369 175=head3 Debugger Internal Variables
25cf7dea 176
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177In addition to the file and subroutine-related variables mentioned above,
178the debugger also maintains various magical internal variables.
179
180=over 4
181
182=item *
055fd3a9 183
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184C<@DB::dbline> is an alias for C<@{"::_<current_file"}>, which
185holds the lines of the currently-selected file (compiled by Perl), either
186explicitly chosen with the debugger's C<f> command, or implicitly by flow
187of execution.
188
189Values in this array are magical in numeric context: they compare
190equal to zero only if the line is not breakable.
191
192=item *
193
7b406369 194C<%DB::dbline> is an alias for C<%{"::_<current_file"}>, which
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195contains breakpoints and actions keyed by line number in
196the currently-selected file, either explicitly chosen with the
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197debugger's C<f> command, or implicitly by flow of execution.
198
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199As previously noted, individual entries (as opposed to the whole hash)
200are settable. Perl only cares about Boolean true here, although
201the values used by F<perl5db.pl> have the form
202C<"$break_condition\0$action">.
203
204=back
205
7b406369 206=head3 Debugger Customization Functions
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207
208Some functions are provided to simplify customization.
209
210=over 4
211
212=item *
213
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214See L<perldebug/"Configurable Options"> for a description of options parsed by
215C<DB::parse_options(string)>.
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216
217=item *
218
219C<DB::dump_trace(skip[,count])> skips the specified number of frames
220and returns a list containing information about the calling frames (all
221of them, if C<count> is missing). Each entry is reference to a hash
222with keys C<context> (either C<.>, C<$>, or C<@>), C<sub> (subroutine
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223name, or info about C<eval>), C<args> (C<undef> or a reference to
224an array), C<file>, and C<line>.
225
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226=item *
227
228C<DB::print_trace(FH, skip[, count[, short]])> prints
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229formatted info about caller frames. The last two functions may be
230convenient as arguments to C<< < >>, C<< << >> commands.
231
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232=back
233
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234Note that any variables and functions that are not documented in
235this manpages (or in L<perldebug>) are considered for internal
236use only, and as such are subject to change without notice.
237
238=head1 Frame Listing Output Examples
239
240The C<frame> option can be used to control the output of frame
241information. For example, contrast this expression trace:
242
243 $ perl -de 42
244 Stack dump during die enabled outside of evals.
245
246 Loading DB routines from perl5db.pl patch level 0.94
247 Emacs support available.
248
ccf3535a 249 Enter h or 'h h' for help.
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250
251 main::(-e:1): 0
252 DB<1> sub foo { 14 }
253
254 DB<2> sub bar { 3 }
255
256 DB<3> t print foo() * bar()
257 main::((eval 172):3): print foo() + bar();
258 main::foo((eval 168):2):
259 main::bar((eval 170):2):
260 42
261
492652be 262with this one, once the C<o>ption C<frame=2> has been set:
055fd3a9 263
492652be 264 DB<4> o f=2
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265 frame = '2'
266 DB<5> t print foo() * bar()
267 3: foo() * bar()
268 entering main::foo
269 2: sub foo { 14 };
270 exited main::foo
271 entering main::bar
272 2: sub bar { 3 };
273 exited main::bar
274 42
275
276By way of demonstration, we present below a laborious listing
277resulting from setting your C<PERLDB_OPTS> environment variable to
278the value C<f=n N>, and running I<perl -d -V> from the command line.
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279Examples using various values of C<n> are shown to give you a feel
280for the difference between settings. Long though it may be, this
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281is not a complete listing, but only excerpts.
282
283=over 4
284
285=item 1
286
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287 entering main::BEGIN
288 entering Config::BEGIN
289 Package lib/Exporter.pm.
290 Package lib/Carp.pm.
291 Package lib/Config.pm.
292 entering Config::TIEHASH
293 entering Exporter::import
294 entering Exporter::export
295 entering Config::myconfig
296 entering Config::FETCH
297 entering Config::FETCH
298 entering Config::FETCH
299 entering Config::FETCH
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300
301=item 2
302
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303 entering main::BEGIN
304 entering Config::BEGIN
305 Package lib/Exporter.pm.
306 Package lib/Carp.pm.
307 exited Config::BEGIN
308 Package lib/Config.pm.
309 entering Config::TIEHASH
310 exited Config::TIEHASH
311 entering Exporter::import
312 entering Exporter::export
313 exited Exporter::export
314 exited Exporter::import
315 exited main::BEGIN
316 entering Config::myconfig
317 entering Config::FETCH
318 exited Config::FETCH
319 entering Config::FETCH
320 exited Config::FETCH
321 entering Config::FETCH
055fd3a9 322
d5e42f17 323=item 3
055fd3a9 324
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325 in $=main::BEGIN() from /dev/null:0
326 in $=Config::BEGIN() from lib/Config.pm:2
327 Package lib/Exporter.pm.
328 Package lib/Carp.pm.
329 Package lib/Config.pm.
330 in $=Config::TIEHASH('Config') from lib/Config.pm:644
331 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
332 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li
333 in @=Config::myconfig() from /dev/null:0
334 in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
335 in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
336 in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
337 in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574
338 in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574
339 in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574
055fd3a9 340
d5e42f17 341=item 4
055fd3a9 342
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343 in $=main::BEGIN() from /dev/null:0
344 in $=Config::BEGIN() from lib/Config.pm:2
345 Package lib/Exporter.pm.
346 Package lib/Carp.pm.
347 out $=Config::BEGIN() from lib/Config.pm:0
348 Package lib/Config.pm.
349 in $=Config::TIEHASH('Config') from lib/Config.pm:644
350 out $=Config::TIEHASH('Config') from lib/Config.pm:644
351 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
352 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
353 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
354 out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
355 out $=main::BEGIN() from /dev/null:0
356 in @=Config::myconfig() from /dev/null:0
357 in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
358 out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
359 in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
360 out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
361 in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
362 out $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
363 in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574
055fd3a9 364
d5e42f17 365=item 5
055fd3a9 366
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367 in $=main::BEGIN() from /dev/null:0
368 in $=Config::BEGIN() from lib/Config.pm:2
369 Package lib/Exporter.pm.
370 Package lib/Carp.pm.
371 out $=Config::BEGIN() from lib/Config.pm:0
372 Package lib/Config.pm.
373 in $=Config::TIEHASH('Config') from lib/Config.pm:644
374 out $=Config::TIEHASH('Config') from lib/Config.pm:644
375 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
376 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
377 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
378 out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
379 out $=main::BEGIN() from /dev/null:0
380 in @=Config::myconfig() from /dev/null:0
381 in $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
382 out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
383 in $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
384 out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
055fd3a9 385
d5e42f17 386=item 6
055fd3a9 387
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388 in $=CODE(0x15eca4)() from /dev/null:0
389 in $=CODE(0x182528)() from lib/Config.pm:2
390 Package lib/Exporter.pm.
391 out $=CODE(0x182528)() from lib/Config.pm:0
392 scalar context return from CODE(0x182528): undef
393 Package lib/Config.pm.
394 in $=Config::TIEHASH('Config') from lib/Config.pm:628
395 out $=Config::TIEHASH('Config') from lib/Config.pm:628
396 scalar context return from Config::TIEHASH: empty hash
397 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
398 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
399 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
400 scalar context return from Exporter::export: ''
401 out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
402 scalar context return from Exporter::import: ''
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403
404=back
405
406In all cases shown above, the line indentation shows the call tree.
407If bit 2 of C<frame> is set, a line is printed on exit from a
408subroutine as well. If bit 4 is set, the arguments are printed
409along with the caller info. If bit 8 is set, the arguments are
410printed even if they are tied or references. If bit 16 is set, the
411return value is printed, too.
412
413When a package is compiled, a line like this
414
415 Package lib/Carp.pm.
416
417is printed with proper indentation.
418
7b406369 419=head1 Debugging Regular Expressions
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420
421There are two ways to enable debugging output for regular expressions.
422
423If your perl is compiled with C<-DDEBUGGING>, you may use the
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424B<-Dr> flag on the command line, and C<-Drv> for more verbose
425information.
055fd3a9 426
dafb2544 427Otherwise, one can C<use re 'debug'>, which has effects at both
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428compile time and run time. Since Perl 5.9.5, this pragma is lexically
429scoped.
055fd3a9 430
7b406369 431=head2 Compile-time Output
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432
433The debugging output at compile time looks like this:
434
ccf3535a 435 Compiling REx '[bc]d(ef*g)+h[ij]k$'
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436 size 45 Got 364 bytes for offset annotations.
437 first at 1
438 rarest char g at 0
439 rarest char d at 0
440 1: ANYOF[bc](12)
441 12: EXACT <d>(14)
442 14: CURLYX[0] {1,32767}(28)
443 16: OPEN1(18)
444 18: EXACT <e>(20)
445 20: STAR(23)
446 21: EXACT <f>(0)
447 23: EXACT <g>(25)
448 25: CLOSE1(27)
449 27: WHILEM[1/1](0)
450 28: NOTHING(29)
451 29: EXACT <h>(31)
452 31: ANYOF[ij](42)
453 42: EXACT <k>(44)
454 44: EOL(45)
455 45: END(0)
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456 anchored 'de' at 1 floating 'gh' at 3..2147483647 (checking floating)
457 stclass 'ANYOF[bc]' minlen 7
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458 Offsets: [45]
459 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1]
460 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0]
461 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0]
462 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0]
463 Omitting $` $& $' support.
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464
465The first line shows the pre-compiled form of the regex. The second
466shows the size of the compiled form (in arbitrary units, usually
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4674-byte words) and the total number of bytes allocated for the
468offset/length table, usually 4+C<size>*8. The next line shows the
469label I<id> of the first node that does a match.
055fd3a9 470
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471The
472
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473 anchored 'de' at 1 floating 'gh' at 3..2147483647 (checking floating)
474 stclass 'ANYOF[bc]' minlen 7
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475
476line (split into two lines above) contains optimizer
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477information. In the example shown, the optimizer found that the match
478should contain a substring C<de> at offset 1, plus substring C<gh>
479at some offset between 3 and infinity. Moreover, when checking for
480these substrings (to abandon impossible matches quickly), Perl will check
481for the substring C<gh> before checking for the substring C<de>. The
482optimizer may also use the knowledge that the match starts (at the
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483C<first> I<id>) with a character class, and no string
484shorter than 7 characters can possibly match.
055fd3a9 485
1c102323 486The fields of interest which may appear in this line are
055fd3a9 487
13a2d996 488=over 4
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489
490=item C<anchored> I<STRING> C<at> I<POS>
491
492=item C<floating> I<STRING> C<at> I<POS1..POS2>
493
494See above.
495
496=item C<matching floating/anchored>
497
498Which substring to check first.
499
500=item C<minlen>
501
502The minimal length of the match.
503
504=item C<stclass> I<TYPE>
505
506Type of first matching node.
507
508=item C<noscan>
509
510Don't scan for the found substrings.
511
512=item C<isall>
513
1c102323 514Means that the optimizer information is all that the regular
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515expression contains, and thus one does not need to enter the regex engine at
516all.
517
518=item C<GPOS>
519
520Set if the pattern contains C<\G>.
521
522=item C<plus>
523
524Set if the pattern starts with a repeated char (as in C<x+y>).
525
526=item C<implicit>
527
528Set if the pattern starts with C<.*>.
529
530=item C<with eval>
531
532Set if the pattern contain eval-groups, such as C<(?{ code })> and
533C<(??{ code })>.
534
535=item C<anchored(TYPE)>
536
7b406369 537If the pattern may match only at a handful of places, with C<TYPE>
d3d47aac 538being C<SBOL>, C<MBOL>, or C<GPOS>. See the table below.
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539
540=back
541
542If a substring is known to match at end-of-line only, it may be
ccf3535a 543followed by C<$>, as in C<floating 'k'$>.
055fd3a9 544
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545The optimizer-specific information is used to avoid entering (a slow) regex
546engine on strings that will not definitely match. If the C<isall> flag
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547is set, a call to the regex engine may be avoided even when the optimizer
548found an appropriate place for the match.
549
1c102323 550Above the optimizer section is the list of I<nodes> of the compiled
055fd3a9
GS
551form of the regex. Each line has format
552
553C< >I<id>: I<TYPE> I<OPTIONAL-INFO> (I<next-id>)
554
7b406369 555=head2 Types of Nodes
055fd3a9 556
78465a4b 557Here are the current possible types, with short descriptions:
055fd3a9 558
65aa4ca7
FC
559=for comment
560This table is generated by regen/regcomp.pl. Any changes made here
561will be lost.
562
563=for regcomp.pl begin
564
5da6b59a
KW
565 # TYPE arg-description [num-args] [longjump-len] DESCRIPTION
566
567 # Exit points
65aa4ca7 568
89829bb5
KW
569 END no End of program.
570 SUCCEED no Return from a subroutine, basically.
5da6b59a 571
d3d47aac 572 # Line Start Anchors:
89829bb5
KW
573 SBOL no Match "" at beginning of line: /^/, /\A/
574 MBOL no Same, assuming multiline: /^/m
5da6b59a 575
d3d47aac 576 # Line End Anchors:
89829bb5
KW
577 SEOL no Match "" at end of line: /$/
578 MEOL no Same, assuming multiline: /$/m
579 EOS no Match "" at end of string: /\z/
d3d47aac
YO
580
581 # Match Start Anchors:
89829bb5 582 GPOS no Matches where last m//g left off.
d3d47aac
YO
583
584 # Word Boundary Opcodes:
89829bb5
KW
585 BOUND no Like BOUNDA for non-utf8, otherwise match
586 "" between any Unicode \w\W or \W\w
587 BOUNDL no Like BOUND/BOUNDU, but \w and \W are
588 defined by current locale
589 BOUNDU no Match "" at any boundary of a given type
590 using Unicode rules
591 BOUNDA no Match "" at any boundary between \w\W or
592 \W\w, where \w is [_a-zA-Z0-9]
593 NBOUND no Like NBOUNDA for non-utf8, otherwise match
594 "" between any Unicode \w\w or \W\W
595 NBOUNDL no Like NBOUND/NBOUNDU, but \w and \W are
596 defined by current locale
597 NBOUNDU no Match "" at any non-boundary of a given
598 type using using Unicode rules
599 NBOUNDA no Match "" betweeen any \w\w or \W\W, where
600 \w is [_a-zA-Z0-9]
5da6b59a
KW
601
602 # [Special] alternatives:
89829bb5
KW
603 REG_ANY no Match any one character (except newline).
604 SANY no Match any one character.
46fc0c43
KW
605 ANYOF sv Match character in (or not in) this class,
606 charclass single char match only
607 ANYOFD sv Like ANYOF, but /d is in effect
608 charclass
609 ANYOFL sv Like ANYOF, but /l is in effect
610 charclass
611 ANYOFPOSIXL sv Like ANYOFL, but matches [[:posix:]]
612 charclass_ classes
613 posixl
89829bb5
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614 ANYOFM byte 1 Like ANYOF, but matches an invariant byte
615 as determined by the mask and arg
3db0bccc 616 NANYOFM byte 1 complement of ANYOFM
7bc66b18 617
d3d47aac 618 # POSIX Character Classes:
89829bb5
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619 POSIXD none Some [[:class:]] under /d; the FLAGS field
620 gives which one
621 POSIXL none Some [[:class:]] under /l; the FLAGS field
622 gives which one
623 POSIXU none Some [[:class:]] under /u; the FLAGS field
624 gives which one
625 POSIXA none Some [[:class:]] under /a; the FLAGS field
626 gives which one
627 NPOSIXD none complement of POSIXD, [[:^class:]]
628 NPOSIXL none complement of POSIXL, [[:^class:]]
629 NPOSIXU none complement of POSIXU, [[:^class:]]
630 NPOSIXA none complement of POSIXA, [[:^class:]]
631
632 ASCII none [[:ascii:]]
633 NASCII none [[:^ascii:]]
634
635 CLUMP no Match any extended grapheme cluster
636 sequence
5da6b59a
KW
637
638 # Alternation
639
65aa4ca7
FC
640 # BRANCH The set of branches constituting a single choice are
641 # hooked together with their "next" pointers, since
642 # precedence prevents anything being concatenated to
643 # any individual branch. The "next" pointer of the last
644 # BRANCH in a choice points to the thing following the
645 # whole choice. This is also where the final "next"
646 # pointer of each individual branch points; each branch
647 # starts with the operand node of a BRANCH node.
5da6b59a 648 #
89829bb5 649 BRANCH node Match this alternative, or the next...
5da6b59a 650
5da6b59a
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651 # Literals
652
89829bb5
KW
653 EXACT str Match this string (preceded by length).
654 EXACTL str Like EXACT, but /l is in effect (used so
655 locale-related warnings can be checked
656 for).
4f4c2c24
KW
657 EXACTF str Match this string using /id rules (w/len);
658 (string not UTF-8, not guaranteed to be
659 folded).
660 EXACTFL str Match this string using /il rules (w/len);
661 (string not guaranteed to be folded).
662 EXACTFU str Match this string using /iu rules (w/len);
663 (string folded iff in UTF-8; non-UTF8
664 folded length <= unfolded).
665 EXACTFAA str Match this string using /iaa rules (w/len)
666 (string folded iff in UTF-8; non-UTF8
667 folded length <= unfolded).
668
669 EXACTFU_SS str Match this string using /iu rules (w/len);
670 (string folded iff in UTF-8; non-UTF8
671 folded length > unfolded).
672 EXACTFLU8 str Like EXACTFU, but use /il, UTF-8, folded,
673 and everything in it is above 255.
674 EXACTFAA_NO_TRIE str Match this string using /iaa rules (w/len)
675 (string not UTF-8, not guaranteed to be
676 folded, not currently trie-able).
677
678 EXACT_ONLY8 str Like EXACT, but only UTF-8 encoded targets
679 can match
680 EXACTFU_ONLY8 str Like EXACTFU, but only UTF-8 encoded
681 targets can match
f6b4b99d 682
8a100c91
KW
683 EXACTFS_B_U str EXACTFU but begins with [Ss]; (string not
684 UTF-8; compile-time only).
685 EXACTFS_E_U str EXACTFU but ends with [Ss]; (string not UTF-
686 8; compile-time only).
687 EXACTFS_BE_U str EXACTFU but begins and ends with [Ss];
688 (string not UTF-8; compile-time only).
689
5da6b59a
KW
690 # Do nothing types
691
89829bb5 692 NOTHING no Match empty string.
5da6b59a 693 # A variant of above which delimits a group, thus stops optimizations
89829bb5
KW
694 TAIL no Match empty string. Can jump here from
695 outside.
5da6b59a
KW
696
697 # Loops
698
65aa4ca7 699 # STAR,PLUS '?', and complex '*' and '+', are implemented as
62e6ef33 700 # circular BRANCH structures. Simple cases
65aa4ca7
FC
701 # (one character per match) are implemented with STAR
702 # and PLUS for speed and to minimize recursive plunges.
5da6b59a 703 #
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704 STAR node Match this (simple) thing 0 or more times.
705 PLUS node Match this (simple) thing 1 or more times.
7bc66b18 706
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707 CURLY sv 2 Match this simple thing {n,m} times.
708 CURLYN no 2 Capture next-after-this simple thing
709 CURLYM no 2 Capture this medium-complex thing {n,m}
710 times.
711 CURLYX sv 2 Match this complex thing {n,m} times.
5da6b59a
KW
712
713 # This terminator creates a loop structure for CURLYX
89829bb5
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714 WHILEM no Do curly processing and see if rest
715 matches.
5da6b59a
KW
716
717 # Buffer related
718
719 # OPEN,CLOSE,GROUPP ...are numbered at compile time.
89829bb5
KW
720 OPEN num 1 Mark this point in input as start of #n.
721 CLOSE num 1 Close corresponding OPEN of #n.
722 SROPEN none Same as OPEN, but for script run
723 SRCLOSE none Close preceding SROPEN
724
725 REF num 1 Match some already matched string
726 REFF num 1 Match already matched string, folded using
727 native charset rules for non-utf8
728 REFFL num 1 Match already matched string, folded in
729 loc.
730 REFFU num 1 Match already matched string, folded using
731 unicode rules for non-utf8
732 REFFA num 1 Match already matched string, folded using
733 unicode rules for non-utf8, no mixing
734 ASCII, non-ASCII
65aa4ca7
FC
735
736 # Named references. Code in regcomp.c assumes that these all are after
737 # the numbered references
89829bb5
KW
738 NREF no-sv 1 Match some already matched string
739 NREFF no-sv 1 Match already matched string, folded using
740 native charset rules for non-utf8
741 NREFFL no-sv 1 Match already matched string, folded in
742 loc.
743 NREFFU num 1 Match already matched string, folded using
744 unicode rules for non-utf8
745 NREFFA num 1 Match already matched string, folded using
746 unicode rules for non-utf8, no mixing
747 ASCII, non-ASCII
7bc66b18 748
d3d47aac 749 # Support for long RE
89829bb5
KW
750 LONGJMP off 1 1 Jump far away.
751 BRANCHJ off 1 1 BRANCH with long offset.
d3d47aac
YO
752
753 # Special Case Regops
46167d76
KW
754 IFMATCH off 1 1 Succeeds if the following matches.
755 UNLESSM off 1 1 Fails if the following matches.
89829bb5
KW
756 SUSPEND off 1 1 "Independent" sub-RE.
757 IFTHEN off 1 1 Switch, should be preceded by switcher.
758 GROUPP num 1 Whether the group matched.
5da6b59a 759
5da6b59a
KW
760 # The heavy worker
761
89829bb5
KW
762 EVAL evl/flags Execute some Perl code.
763 2L
5da6b59a
KW
764
765 # Modifiers
766
89829bb5
KW
767 MINMOD no Next operator is not greedy.
768 LOGICAL no Next opcode should set the flag only.
5da6b59a
KW
769
770 # This is not used yet
89829bb5 771 RENUM off 1 1 Group with independently numbered parens.
5da6b59a
KW
772
773 # Trie Related
774
65aa4ca7
FC
775 # Behave the same as A|LIST|OF|WORDS would. The '..C' variants
776 # have inline charclass data (ascii only), the 'C' store it in the
777 # structure.
5da6b59a 778
89829bb5
KW
779 TRIE trie 1 Match many EXACT(F[ALU]?)? at once.
780 flags==type
781 TRIEC trie Same as TRIE, but with embedded charclass
782 charclass data
5da6b59a 783
89829bb5
KW
784 AHOCORASICK trie 1 Aho Corasick stclass. flags==type
785 AHOCORASICKC trie Same as AHOCORASICK, but with embedded
786 charclass charclass data
5da6b59a
KW
787
788 # Regex Subroutines
89829bb5 789 GOSUB num/ofs 2L recurse to paren arg1 at (signed) ofs arg2
5da6b59a
KW
790
791 # Special conditionals
89829bb5
KW
792 NGROUPP no-sv 1 Whether the group matched.
793 INSUBP num 1 Whether we are in a specific recurse.
794 DEFINEP none 1 Never execute directly.
5da6b59a
KW
795
796 # Backtracking Verbs
89829bb5
KW
797 ENDLIKE none Used only for the type field of verbs
798 OPFAIL no-sv 1 Same as (?!), but with verb arg
799 ACCEPT no-sv/num Accepts the current matched string, with
800 2L verbar
5da6b59a
KW
801
802 # Verbs With Arguments
89829bb5
KW
803 VERB no-sv 1 Used only for the type field of verbs
804 PRUNE no-sv 1 Pattern fails at this startpoint if no-
805 backtracking through this
806 MARKPOINT no-sv 1 Push the current location for rollback by
807 cut.
808 SKIP no-sv 1 On failure skip forward (to the mark)
809 before retrying
810 COMMIT no-sv 1 Pattern fails outright if backtracking
811 through this
812 CUTGROUP no-sv 1 On failure go to the next alternation in
813 the group
5da6b59a
KW
814
815 # Control what to keep in $&.
89829bb5 816 KEEPS no $& begins here.
5da6b59a
KW
817
818 # New charclass like patterns
89829bb5 819 LNBREAK none generic newline pattern
5da6b59a
KW
820
821 # SPECIAL REGOPS
822
65aa4ca7
FC
823 # This is not really a node, but an optimized away piece of a "long"
824 # node. To simplify debugging output, we mark it as if it were a node
89829bb5 825 OPTIMIZED off Placeholder for dump.
5da6b59a
KW
826
827 # Special opcode with the property that no opcode in a compiled program
828 # will ever be of this type. Thus it can be used as a flag value that
829 # no other opcode has been seen. END is used similarly, in that an END
65aa4ca7
FC
830 # node cant be optimized. So END implies "unoptimizable" and PSEUDO
831 # mean "not seen anything to optimize yet".
89829bb5 832 PSEUDO off Pseudo opcode for internal use.
65aa4ca7
FC
833
834=for regcomp.pl end
055fd3a9 835
1c102323
MJD
836=for unprinted-credits
837Next section M-J. Dominus (mjd-perl-patch+@plover.com) 20010421
838
839Following the optimizer information is a dump of the offset/length
840table, here split across several lines:
841
842 Offsets: [45]
843 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1]
844 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0]
845 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0]
846 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0]
847
848The first line here indicates that the offset/length table contains 45
849entries. Each entry is a pair of integers, denoted by C<offset[length]>.
17c338f3 850Entries are numbered starting with 1, so entry #1 here is C<1[4]> and
1c102323
MJD
851entry #12 is C<5[1]>. C<1[4]> indicates that the node labeled C<1:>
852(the C<1: ANYOF[bc]>) begins at character position 1 in the
853pre-compiled form of the regex, and has a length of 4 characters.
854C<5[1]> in position 12
855indicates that the node labeled C<12:>
856(the C<< 12: EXACT <d> >>) begins at character position 5 in the
857pre-compiled form of the regex, and has a length of 1 character.
858C<12[1]> in position 14
859indicates that the node labeled C<14:>
860(the C<< 14: CURLYX[0] {1,32767} >>) begins at character position 12 in the
861pre-compiled form of the regex, and has a length of 1 character---that
862is, it corresponds to the C<+> symbol in the precompiled regex.
863
864C<0[0]> items indicate that there is no corresponding node.
865
7b406369 866=head2 Run-time Output
055fd3a9
GS
867
868First of all, when doing a match, one may get no run-time output even
869if debugging is enabled. This means that the regex engine was never
870entered and that all of the job was therefore done by the optimizer.
871
872If the regex engine was entered, the output may look like this:
873
ccf3535a 874 Matching '[bc]d(ef*g)+h[ij]k$' against 'abcdefg__gh__'
055fd3a9
GS
875 Setting an EVAL scope, savestack=3
876 2 <ab> <cdefg__gh_> | 1: ANYOF
877 3 <abc> <defg__gh_> | 11: EXACT <d>
878 4 <abcd> <efg__gh_> | 13: CURLYX {1,32767}
879 4 <abcd> <efg__gh_> | 26: WHILEM
880 0 out of 1..32767 cc=effff31c
881 4 <abcd> <efg__gh_> | 15: OPEN1
882 4 <abcd> <efg__gh_> | 17: EXACT <e>
883 5 <abcde> <fg__gh_> | 19: STAR
884 EXACT <f> can match 1 times out of 32767...
885 Setting an EVAL scope, savestack=3
886 6 <bcdef> <g__gh__> | 22: EXACT <g>
887 7 <bcdefg> <__gh__> | 24: CLOSE1
888 7 <bcdefg> <__gh__> | 26: WHILEM
889 1 out of 1..32767 cc=effff31c
890 Setting an EVAL scope, savestack=12
891 7 <bcdefg> <__gh__> | 15: OPEN1
892 7 <bcdefg> <__gh__> | 17: EXACT <e>
893 restoring \1 to 4(4)..7
894 failed, try continuation...
895 7 <bcdefg> <__gh__> | 27: NOTHING
896 7 <bcdefg> <__gh__> | 28: EXACT <h>
897 failed...
898 failed...
899
900The most significant information in the output is about the particular I<node>
901of the compiled regex that is currently being tested against the target string.
902The format of these lines is
903
904C< >I<STRING-OFFSET> <I<PRE-STRING>> <I<POST-STRING>> |I<ID>: I<TYPE>
905
906The I<TYPE> info is indented with respect to the backtracking level.
907Other incidental information appears interspersed within.
908
7b406369 909=head1 Debugging Perl Memory Usage
055fd3a9
GS
910
911Perl is a profligate wastrel when it comes to memory use. There
912is a saying that to estimate memory usage of Perl, assume a reasonable
913algorithm for memory allocation, multiply that estimate by 10, and
914while you still may miss the mark, at least you won't be quite so
4375e838 915astonished. This is not absolutely true, but may provide a good
055fd3a9
GS
916grasp of what happens.
917
918Assume that an integer cannot take less than 20 bytes of memory, a
919float cannot take less than 24 bytes, a string cannot take less
920than 32 bytes (all these examples assume 32-bit architectures, the
921result are quite a bit worse on 64-bit architectures). If a variable
922is accessed in two of three different ways (which require an integer,
923a float, or a string), the memory footprint may increase yet another
b9449ee0 92420 bytes. A sloppy malloc(3) implementation can inflate these
055fd3a9
GS
925numbers dramatically.
926
927On the opposite end of the scale, a declaration like
928
929 sub foo;
930
931may take up to 500 bytes of memory, depending on which release of Perl
932you're running.
933
934Anecdotal estimates of source-to-compiled code bloat suggest an
935eightfold increase. This means that the compiled form of reasonable
936(normally commented, properly indented etc.) code will take
937about eight times more space in memory than the code took
938on disk.
939
b30f304a
JH
940The B<-DL> command-line switch is obsolete since circa Perl 5.6.0
941(it was available only if Perl was built with C<-DDEBUGGING>).
942The switch was used to track Perl's memory allocations and possible
943memory leaks. These days the use of malloc debugging tools like
5b6a3331 944F<Purify> or F<valgrind> is suggested instead. See also
7b406369 945L<perlhacktips/PERL_MEM_LOG>.
b30f304a
JH
946
947One way to find out how much memory is being used by Perl data
948structures is to install the Devel::Size module from CPAN: it gives
949you the minimum number of bytes required to store a particular data
950structure. Please be mindful of the difference between the size()
951and total_size().
952
953If Perl has been compiled using Perl's malloc you can analyze Perl
7b406369 954memory usage by setting $ENV{PERL_DEBUG_MSTATS}.
055fd3a9
GS
955
956=head2 Using C<$ENV{PERL_DEBUG_MSTATS}>
957
958If your perl is using Perl's malloc() and was compiled with the
959necessary switches (this is the default), then it will print memory
4375e838 960usage statistics after compiling your code when C<< $ENV{PERL_DEBUG_MSTATS}
055fd3a9
GS
961> 1 >>, and before termination of the program when C<<
962$ENV{PERL_DEBUG_MSTATS} >= 1 >>. The report format is similar to
963the following example:
964
f185f654
KW
965 $ PERL_DEBUG_MSTATS=2 perl -e "require Carp"
966 Memory allocation statistics after compilation: (buckets 4(4)..8188(8192)
967 14216 free: 130 117 28 7 9 0 2 2 1 0 0
055fd3a9 968 437 61 36 0 5
f185f654 969 60924 used: 125 137 161 55 7 8 6 16 2 0 1
055fd3a9 970 74 109 304 84 20
f185f654
KW
971 Total sbrk(): 77824/21:119. Odd ends: pad+heads+chain+tail: 0+636+0+2048.
972 Memory allocation statistics after execution: (buckets 4(4)..8188(8192)
973 30888 free: 245 78 85 13 6 2 1 3 2 0 1
055fd3a9 974 315 162 39 42 11
f185f654 975 175816 used: 265 176 1112 111 26 22 11 27 2 1 1
055fd3a9 976 196 178 1066 798 39
f185f654 977 Total sbrk(): 215040/47:145. Odd ends: pad+heads+chain+tail: 0+2192+0+6144.
055fd3a9
GS
978
979It is possible to ask for such a statistic at arbitrary points in
b9449ee0 980your execution using the mstat() function out of the standard
055fd3a9
GS
981Devel::Peek module.
982
983Here is some explanation of that format:
984
13a2d996 985=over 4
055fd3a9
GS
986
987=item C<buckets SMALLEST(APPROX)..GREATEST(APPROX)>
988
989Perl's malloc() uses bucketed allocations. Every request is rounded
990up to the closest bucket size available, and a bucket is taken from
991the pool of buckets of that size.
992
993The line above describes the limits of buckets currently in use.
994Each bucket has two sizes: memory footprint and the maximal size
995of user data that can fit into this bucket. Suppose in the above
996example that the smallest bucket were size 4. The biggest bucket
997would have usable size 8188, and the memory footprint would be 8192.
998
999In a Perl built for debugging, some buckets may have negative usable
1000size. This means that these buckets cannot (and will not) be used.
1001For larger buckets, the memory footprint may be one page greater
7b406369 1002than a power of 2. If so, the corresponding power of two is
055fd3a9
GS
1003printed in the C<APPROX> field above.
1004
1005=item Free/Used
1006
1007The 1 or 2 rows of numbers following that correspond to the number
1008of buckets of each size between C<SMALLEST> and C<GREATEST>. In
1009the first row, the sizes (memory footprints) of buckets are powers
1010of two--or possibly one page greater. In the second row, if present,
1011the memory footprints of the buckets are between the memory footprints
1012of two buckets "above".
1013
4375e838 1014For example, suppose under the previous example, the memory footprints
055fd3a9
GS
1015were
1016
f185f654 1017 free: 8 16 32 64 128 256 512 1024 2048 4096 8192
055fd3a9
GS
1018 4 12 24 48 80
1019
7b406369 1020With a non-C<DEBUGGING> perl, the buckets starting from C<128> have
d1be9408 1021a 4-byte overhead, and thus an 8192-long bucket may take up to
055fd3a9
GS
10228188-byte allocations.
1023
1024=item C<Total sbrk(): SBRKed/SBRKs:CONTINUOUS>
1025
1026The first two fields give the total amount of memory perl sbrk(2)ed
1027(ess-broken? :-) and number of sbrk(2)s used. The third number is
1028what perl thinks about continuity of returned chunks. So long as
1029this number is positive, malloc() will assume that it is probable
1030that sbrk(2) will provide continuous memory.
1031
1032Memory allocated by external libraries is not counted.
1033
1034=item C<pad: 0>
1035
1036The amount of sbrk(2)ed memory needed to keep buckets aligned.
1037
1038=item C<heads: 2192>
1039
1040Although memory overhead of bigger buckets is kept inside the bucket, for
1041smaller buckets, it is kept in separate areas. This field gives the
1042total size of these areas.
1043
1044=item C<chain: 0>
1045
1046malloc() may want to subdivide a bigger bucket into smaller buckets.
1047If only a part of the deceased bucket is left unsubdivided, the rest
1048is kept as an element of a linked list. This field gives the total
1049size of these chunks.
1050
1051=item C<tail: 6144>
1052
1053To minimize the number of sbrk(2)s, malloc() asks for more memory. This
1054field gives the size of the yet unused part, which is sbrk(2)ed, but
1055never touched.
1056
1057=back
1058
055fd3a9
GS
1059=head1 SEE ALSO
1060
1061L<perldebug>,
1062L<perlguts>,
1063L<perlrun>
1064L<re>,
1065and
fe854a6f 1066L<Devel::DProf>.