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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<< $^D & (1<<30) >> is true.
93
94=item *
95
96When execution of the program reaches a subroutine call, a call to
97C<&DB::sub>(I<args>) is made instead, with C<$DB::sub> holding the
74410c12 98name of the called subroutine. (This doesn't happen if the subroutine
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99was compiled in the C<DB> package.)
100
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101X<&DB::lsub>If the call is to an lvalue subroutine, and C<&DB::lsub>
102is defined C<&DB::lsub>(I<args>) is called instead, otherwise falling
103back to C<&DB::sub>(I<args>).
104
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105=item *
106
107When execution of the program uses C<goto> to enter a non-XS
108subroutine and the 0x80 bit is set in C<$^P>, a call to C<&DB::goto>
109is made, with C<$DB::sub> holding the name of the subroutine being
110entered.
111
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112=back
113
114Note that if C<&DB::sub> needs external data for it to work, no
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115subroutine call is possible without it. As an example, the standard
116debugger's C<&DB::sub> depends on the C<$DB::deep> variable
117(it defines how many levels of recursion deep into the debugger you can go
118before a mandatory break). If C<$DB::deep> is not defined, subroutine
119calls are not possible, even though C<&DB::sub> exists.
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120
121=head2 Writing Your Own Debugger
122
74410c12 123=head3 Environment Variables
666f95b9 124
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125The C<PERL5DB> environment variable can be used to define a debugger.
126For example, the minimal "working" debugger (it actually doesn't do anything)
127consists of one line:
666f95b9 128
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129 sub DB::DB {}
130
74410c12 131It can easily be defined like this:
666f95b9 132
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133 $ PERL5DB="sub DB::DB {}" perl -d your-script
134
74410c12 135Another brief debugger, slightly more useful, can be created
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136with only the line:
137
138 sub DB::DB {print ++$i; scalar <STDIN>}
139
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140This debugger prints a number which increments for each statement
141encountered and waits for you to hit a newline before continuing
142to the next statement.
666f95b9 143
74410c12 144The following debugger is actually useful:
666f95b9 145
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146 {
147 package DB;
148 sub DB {}
149 sub sub {print ++$i, " $sub\n"; &$sub}
150 }
151
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152It prints the sequence number of each subroutine call and the name of the
153called subroutine. Note that C<&DB::sub> is being compiled into the
154package C<DB> through the use of the C<package> directive.
055fd3a9 155
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156When it starts, the debugger reads your rc file (F<./.perldb> or
157F<~/.perldb> under Unix), which can set important options.
158(A subroutine (C<&afterinit>) can be defined here as well; it is executed
159after the debugger completes its own initialization.)
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160
161After the rc file is read, the debugger reads the PERLDB_OPTS
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162environment variable and uses it to set debugger options. The
163contents of this variable are treated as if they were the argument
96090e4f 164of an C<o ...> debugger command (q.v. in L<perldebug/"Configurable Options">).
74410c12 165
7b406369 166=head3 Debugger Internal Variables
25cf7dea 167
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168In addition to the file and subroutine-related variables mentioned above,
169the debugger also maintains various magical internal variables.
170
171=over 4
172
173=item *
055fd3a9 174
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175C<@DB::dbline> is an alias for C<@{"::_<current_file"}>, which
176holds the lines of the currently-selected file (compiled by Perl), either
177explicitly chosen with the debugger's C<f> command, or implicitly by flow
178of execution.
179
180Values in this array are magical in numeric context: they compare
181equal to zero only if the line is not breakable.
182
183=item *
184
7b406369 185C<%DB::dbline> is an alias for C<%{"::_<current_file"}>, which
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186contains breakpoints and actions keyed by line number in
187the currently-selected file, either explicitly chosen with the
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188debugger's C<f> command, or implicitly by flow of execution.
189
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190As previously noted, individual entries (as opposed to the whole hash)
191are settable. Perl only cares about Boolean true here, although
192the values used by F<perl5db.pl> have the form
193C<"$break_condition\0$action">.
194
195=back
196
7b406369 197=head3 Debugger Customization Functions
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198
199Some functions are provided to simplify customization.
200
201=over 4
202
203=item *
204
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205See L<perldebug/"Configurable Options"> for a description of options parsed by
206C<DB::parse_options(string)>.
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207
208=item *
209
210C<DB::dump_trace(skip[,count])> skips the specified number of frames
211and returns a list containing information about the calling frames (all
212of them, if C<count> is missing). Each entry is reference to a hash
213with keys C<context> (either C<.>, C<$>, or C<@>), C<sub> (subroutine
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214name, or info about C<eval>), C<args> (C<undef> or a reference to
215an array), C<file>, and C<line>.
216
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217=item *
218
219C<DB::print_trace(FH, skip[, count[, short]])> prints
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220formatted info about caller frames. The last two functions may be
221convenient as arguments to C<< < >>, C<< << >> commands.
222
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223=back
224
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225Note that any variables and functions that are not documented in
226this manpages (or in L<perldebug>) are considered for internal
227use only, and as such are subject to change without notice.
228
229=head1 Frame Listing Output Examples
230
231The C<frame> option can be used to control the output of frame
232information. For example, contrast this expression trace:
233
234 $ perl -de 42
235 Stack dump during die enabled outside of evals.
236
237 Loading DB routines from perl5db.pl patch level 0.94
238 Emacs support available.
239
ccf3535a 240 Enter h or 'h h' for help.
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241
242 main::(-e:1): 0
243 DB<1> sub foo { 14 }
244
245 DB<2> sub bar { 3 }
246
247 DB<3> t print foo() * bar()
248 main::((eval 172):3): print foo() + bar();
249 main::foo((eval 168):2):
250 main::bar((eval 170):2):
251 42
252
492652be 253with this one, once the C<o>ption C<frame=2> has been set:
055fd3a9 254
492652be 255 DB<4> o f=2
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256 frame = '2'
257 DB<5> t print foo() * bar()
258 3: foo() * bar()
259 entering main::foo
260 2: sub foo { 14 };
261 exited main::foo
262 entering main::bar
263 2: sub bar { 3 };
264 exited main::bar
265 42
266
267By way of demonstration, we present below a laborious listing
268resulting from setting your C<PERLDB_OPTS> environment variable to
269the value C<f=n N>, and running I<perl -d -V> from the command line.
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270Examples using various values of C<n> are shown to give you a feel
271for the difference between settings. Long though it may be, this
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272is not a complete listing, but only excerpts.
273
274=over 4
275
276=item 1
277
278 entering main::BEGIN
279 entering Config::BEGIN
280 Package lib/Exporter.pm.
281 Package lib/Carp.pm.
282 Package lib/Config.pm.
283 entering Config::TIEHASH
284 entering Exporter::import
285 entering Exporter::export
286 entering Config::myconfig
287 entering Config::FETCH
288 entering Config::FETCH
289 entering Config::FETCH
290 entering Config::FETCH
291
292=item 2
293
294 entering main::BEGIN
295 entering Config::BEGIN
296 Package lib/Exporter.pm.
297 Package lib/Carp.pm.
298 exited Config::BEGIN
299 Package lib/Config.pm.
300 entering Config::TIEHASH
301 exited Config::TIEHASH
302 entering Exporter::import
303 entering Exporter::export
304 exited Exporter::export
305 exited Exporter::import
306 exited main::BEGIN
307 entering Config::myconfig
308 entering Config::FETCH
309 exited Config::FETCH
310 entering Config::FETCH
311 exited Config::FETCH
312 entering Config::FETCH
313
d5e42f17 314=item 3
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315
316 in $=main::BEGIN() from /dev/null:0
317 in $=Config::BEGIN() from lib/Config.pm:2
318 Package lib/Exporter.pm.
319 Package lib/Carp.pm.
320 Package lib/Config.pm.
321 in $=Config::TIEHASH('Config') from lib/Config.pm:644
322 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
323 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li
324 in @=Config::myconfig() from /dev/null:0
325 in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
326 in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
327 in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
328 in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574
329 in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574
330 in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574
331
d5e42f17 332=item 4
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333
334 in $=main::BEGIN() from /dev/null:0
335 in $=Config::BEGIN() from lib/Config.pm:2
336 Package lib/Exporter.pm.
337 Package lib/Carp.pm.
338 out $=Config::BEGIN() from lib/Config.pm:0
339 Package lib/Config.pm.
340 in $=Config::TIEHASH('Config') from lib/Config.pm:644
341 out $=Config::TIEHASH('Config') from lib/Config.pm:644
342 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
343 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
344 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
345 out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
346 out $=main::BEGIN() from /dev/null:0
347 in @=Config::myconfig() from /dev/null:0
348 in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
349 out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
350 in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
351 out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
352 in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
353 out $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
354 in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574
355
d5e42f17 356=item 5
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357
358 in $=main::BEGIN() from /dev/null:0
359 in $=Config::BEGIN() from lib/Config.pm:2
360 Package lib/Exporter.pm.
361 Package lib/Carp.pm.
362 out $=Config::BEGIN() from lib/Config.pm:0
363 Package lib/Config.pm.
364 in $=Config::TIEHASH('Config') from lib/Config.pm:644
365 out $=Config::TIEHASH('Config') from lib/Config.pm:644
366 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
367 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
368 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
369 out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
370 out $=main::BEGIN() from /dev/null:0
371 in @=Config::myconfig() from /dev/null:0
372 in $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
373 out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
374 in $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
375 out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
376
d5e42f17 377=item 6
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378
379 in $=CODE(0x15eca4)() from /dev/null:0
380 in $=CODE(0x182528)() from lib/Config.pm:2
381 Package lib/Exporter.pm.
382 out $=CODE(0x182528)() from lib/Config.pm:0
383 scalar context return from CODE(0x182528): undef
384 Package lib/Config.pm.
385 in $=Config::TIEHASH('Config') from lib/Config.pm:628
386 out $=Config::TIEHASH('Config') from lib/Config.pm:628
387 scalar context return from Config::TIEHASH: empty hash
388 in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
389 in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
390 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
391 scalar context return from Exporter::export: ''
392 out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
393 scalar context return from Exporter::import: ''
394
395=back
396
397In all cases shown above, the line indentation shows the call tree.
398If bit 2 of C<frame> is set, a line is printed on exit from a
399subroutine as well. If bit 4 is set, the arguments are printed
400along with the caller info. If bit 8 is set, the arguments are
401printed even if they are tied or references. If bit 16 is set, the
402return value is printed, too.
403
404When a package is compiled, a line like this
405
406 Package lib/Carp.pm.
407
408is printed with proper indentation.
409
7b406369 410=head1 Debugging Regular Expressions
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411
412There are two ways to enable debugging output for regular expressions.
413
414If your perl is compiled with C<-DDEBUGGING>, you may use the
415B<-Dr> flag on the command line.
416
417Otherwise, one can C<use re 'debug'>, which has effects at
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418compile time and run time. Since Perl 5.9.5, this pragma is lexically
419scoped.
055fd3a9 420
7b406369 421=head2 Compile-time Output
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422
423The debugging output at compile time looks like this:
424
ccf3535a 425 Compiling REx '[bc]d(ef*g)+h[ij]k$'
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426 size 45 Got 364 bytes for offset annotations.
427 first at 1
428 rarest char g at 0
429 rarest char d at 0
430 1: ANYOF[bc](12)
431 12: EXACT <d>(14)
432 14: CURLYX[0] {1,32767}(28)
433 16: OPEN1(18)
434 18: EXACT <e>(20)
435 20: STAR(23)
436 21: EXACT <f>(0)
437 23: EXACT <g>(25)
438 25: CLOSE1(27)
439 27: WHILEM[1/1](0)
440 28: NOTHING(29)
441 29: EXACT <h>(31)
442 31: ANYOF[ij](42)
443 42: EXACT <k>(44)
444 44: EOL(45)
445 45: END(0)
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446 anchored 'de' at 1 floating 'gh' at 3..2147483647 (checking floating)
447 stclass 'ANYOF[bc]' minlen 7
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448 Offsets: [45]
449 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1]
450 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0]
451 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0]
452 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0]
453 Omitting $` $& $' support.
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454
455The first line shows the pre-compiled form of the regex. The second
456shows the size of the compiled form (in arbitrary units, usually
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4574-byte words) and the total number of bytes allocated for the
458offset/length table, usually 4+C<size>*8. The next line shows the
459label I<id> of the first node that does a match.
055fd3a9 460
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461The
462
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463 anchored 'de' at 1 floating 'gh' at 3..2147483647 (checking floating)
464 stclass 'ANYOF[bc]' minlen 7
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465
466line (split into two lines above) contains optimizer
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467information. In the example shown, the optimizer found that the match
468should contain a substring C<de> at offset 1, plus substring C<gh>
469at some offset between 3 and infinity. Moreover, when checking for
470these substrings (to abandon impossible matches quickly), Perl will check
471for the substring C<gh> before checking for the substring C<de>. The
472optimizer may also use the knowledge that the match starts (at the
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473C<first> I<id>) with a character class, and no string
474shorter than 7 characters can possibly match.
055fd3a9 475
1c102323 476The fields of interest which may appear in this line are
055fd3a9 477
13a2d996 478=over 4
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479
480=item C<anchored> I<STRING> C<at> I<POS>
481
482=item C<floating> I<STRING> C<at> I<POS1..POS2>
483
484See above.
485
486=item C<matching floating/anchored>
487
488Which substring to check first.
489
490=item C<minlen>
491
492The minimal length of the match.
493
494=item C<stclass> I<TYPE>
495
496Type of first matching node.
497
498=item C<noscan>
499
500Don't scan for the found substrings.
501
502=item C<isall>
503
1c102323 504Means that the optimizer information is all that the regular
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505expression contains, and thus one does not need to enter the regex engine at
506all.
507
508=item C<GPOS>
509
510Set if the pattern contains C<\G>.
511
512=item C<plus>
513
514Set if the pattern starts with a repeated char (as in C<x+y>).
515
516=item C<implicit>
517
518Set if the pattern starts with C<.*>.
519
520=item C<with eval>
521
522Set if the pattern contain eval-groups, such as C<(?{ code })> and
523C<(??{ code })>.
524
525=item C<anchored(TYPE)>
526
7b406369 527If the pattern may match only at a handful of places, with C<TYPE>
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528being C<BOL>, C<MBOL>, or C<GPOS>. See the table below.
529
530=back
531
532If a substring is known to match at end-of-line only, it may be
ccf3535a 533followed by C<$>, as in C<floating 'k'$>.
055fd3a9 534
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535The optimizer-specific information is used to avoid entering (a slow) regex
536engine on strings that will not definitely match. If the C<isall> flag
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537is set, a call to the regex engine may be avoided even when the optimizer
538found an appropriate place for the match.
539
1c102323 540Above the optimizer section is the list of I<nodes> of the compiled
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541form of the regex. Each line has format
542
543C< >I<id>: I<TYPE> I<OPTIONAL-INFO> (I<next-id>)
544
7b406369 545=head2 Types of Nodes
055fd3a9 546
78465a4b 547Here are the current possible types, with short descriptions:
055fd3a9 548
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549=for comment
550This table is generated by regen/regcomp.pl. Any changes made here
551will be lost.
552
553=for regcomp.pl begin
554
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555 # TYPE arg-description [num-args] [longjump-len] DESCRIPTION
556
557 # Exit points
65aa4ca7 558
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559 END no End of program.
560 SUCCEED no Return from a subroutine,
561 basically.
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562
563 # Anchors:
564
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565 BOL no Match "" at beginning of line.
566 MBOL no Same, assuming multiline.
567 SBOL no Same, assuming singleline.
568 EOS no Match "" at end of string.
569 EOL no Match "" at end of line.
570 MEOL no Same, assuming multiline.
571 SEOL no Same, assuming singleline.
572 BOUND no Match "" at any word boundary
573 using native charset semantics
574 for non-utf8
575 BOUNDL no Match "" at any locale word
576 boundary
577 BOUNDU no Match "" at any word boundary
578 using Unicode semantics
579 BOUNDA no Match "" at any word boundary
580 using ASCII semantics
581 NBOUND no Match "" at any word non-
582 boundary using native charset
583 semantics for non-utf8
584 NBOUNDL no Match "" at any locale word non-
585 boundary
586 NBOUNDU no Match "" at any word non-
587 boundary using Unicode
588 semantics
589 NBOUNDA no Match "" at any word non-
590 boundary using ASCII semantics
591 GPOS no Matches where last m//g left
592 off.
5da6b59a
KW
593
594 # [Special] alternatives:
595
34fdef84
KW
596 REG_ANY no Match any one character (except
597 newline).
598 SANY no Match any one character.
599 CANY no Match any one byte.
600 ANYOF sv Match character in (or not in)
601 this class, single char match
602 only
603 ANYOF_NON_UTF8_NON_ASCII_ALL sv like ANYOF, also matches any
604 U+80 - U+FF when not in UTF-8
605
606 POSIXD none Some [[:class:]] under /d; the
607 FLAGS field gives which one
608 POSIXL none Some [[:class:]] under /l; the
609 FLAGS field gives which one
610 POSIXU none Some [[:class:]] under /u; the
611 FLAGS field gives which one
612 POSIXA none Some [[:class:]] under /a; the
613 FLAGS field gives which one
614 NPOSIXD none complement of POSIXD,
615 [[:^class:]]
616 NPOSIXL none complement of POSIXL,
617 [[:^class:]]
618 NPOSIXU none complement of POSIXU,
619 [[:^class:]]
620 NPOSIXA none complement of POSIXA,
621 [[:^class:]]
622
623 CLUMP no Match any extended grapheme
624 cluster sequence
5da6b59a
KW
625
626 # Alternation
627
65aa4ca7
FC
628 # BRANCH The set of branches constituting a single choice are
629 # hooked together with their "next" pointers, since
630 # precedence prevents anything being concatenated to
631 # any individual branch. The "next" pointer of the last
632 # BRANCH in a choice points to the thing following the
633 # whole choice. This is also where the final "next"
634 # pointer of each individual branch points; each branch
635 # starts with the operand node of a BRANCH node.
5da6b59a 636 #
34fdef84
KW
637 BRANCH node Match this alternative, or the
638 next...
5da6b59a
KW
639
640 # Back pointer
641
65aa4ca7
FC
642 # BACK Normal "next" pointers all implicitly point forward;
643 # BACK exists to make loop structures possible.
5da6b59a 644 # not used
34fdef84
KW
645 BACK no Match "", "next" ptr points
646 backward.
5da6b59a
KW
647
648 # Literals
649
34fdef84
KW
650 EXACT str Match this string (preceded by
651 length).
652 EXACTF str Match this non-UTF-8 string
653 (not guaranteed to be folded)
654 using /id rules (w/len).
655 EXACTFL str Match this string (not
656 guaranteed to be folded) using
657 /il rules (w/len).
658 EXACTFU str Match this string (folded iff
659 in UTF-8, length in folding
660 doesn't change if not in UTF-8)
661 using /iu rules (w/len).
662 EXACTFA str Match this string (not
663 guaranteed to be folded) using
664 /iaa rules (w/len).
665 EXACTFU_SS str Match this string (folded iff
666 in UTF-8, length in folding may
667 change even if not in UTF-8)
668 using /iu rules (w/len).
669 EXACTFA_NO_TRIE str Match this string (which is not
670 trie-able; not guaranteed to be
671 folded) using /iaa rules
672 (w/len).
5da6b59a
KW
673
674 # Do nothing types
675
34fdef84 676 NOTHING no Match empty string.
5da6b59a 677 # A variant of above which delimits a group, thus stops optimizations
34fdef84
KW
678 TAIL no Match empty string. Can jump
679 here from outside.
5da6b59a
KW
680
681 # Loops
682
65aa4ca7
FC
683 # STAR,PLUS '?', and complex '*' and '+', are implemented as
684 # circular BRANCH structures using BACK. Simple cases
685 # (one character per match) are implemented with STAR
686 # and PLUS for speed and to minimize recursive plunges.
5da6b59a 687 #
34fdef84
KW
688 STAR node Match this (simple) thing 0 or
689 more times.
690 PLUS node Match this (simple) thing 1 or
691 more times.
692
693 CURLY sv 2 Match this simple thing {n,m}
694 times.
695 CURLYN no 2 Capture next-after-this simple
696 thing
697 CURLYM no 2 Capture this medium-complex
698 thing {n,m} times.
699 CURLYX sv 2 Match this complex thing {n,m}
700 times.
5da6b59a
KW
701
702 # This terminator creates a loop structure for CURLYX
34fdef84
KW
703 WHILEM no Do curly processing and see if
704 rest matches.
5da6b59a
KW
705
706 # Buffer related
707
708 # OPEN,CLOSE,GROUPP ...are numbered at compile time.
34fdef84
KW
709 OPEN num 1 Mark this point in input as
710 start of #n.
711 CLOSE num 1 Analogous to OPEN.
712
713 REF num 1 Match some already matched
714 string
715 REFF num 1 Match already matched string,
716 folded using native charset
717 semantics for non-utf8
718 REFFL num 1 Match already matched string,
719 folded in loc.
720 REFFU num 1 Match already matched string,
721 folded using unicode semantics
722 for non-utf8
723 REFFA num 1 Match already matched string,
724 folded using unicode semantics
725 for non-utf8, no mixing ASCII,
726 non-ASCII
65aa4ca7
FC
727
728 # Named references. Code in regcomp.c assumes that these all are after
729 # the numbered references
34fdef84
KW
730 NREF no-sv 1 Match some already matched
731 string
732 NREFF no-sv 1 Match already matched string,
733 folded using native charset
734 semantics for non-utf8
735 NREFFL no-sv 1 Match already matched string,
736 folded in loc.
737 NREFFU num 1 Match already matched string,
738 folded using unicode semantics
739 for non-utf8
740 NREFFA num 1 Match already matched string,
741 folded using unicode semantics
742 for non-utf8, no mixing ASCII,
743 non-ASCII
744
745 IFMATCH off 1 2 Succeeds if the following
746 matches.
747 UNLESSM off 1 2 Fails if the following matches.
748 SUSPEND off 1 1 "Independent" sub-RE.
749 IFTHEN off 1 1 Switch, should be preceded by
750 switcher.
751 GROUPP num 1 Whether the group matched.
5da6b59a
KW
752
753 # Support for long RE
754
34fdef84
KW
755 LONGJMP off 1 1 Jump far away.
756 BRANCHJ off 1 1 BRANCH with long offset.
5da6b59a
KW
757
758 # The heavy worker
759
34fdef84 760 EVAL evl 1 Execute some Perl code.
5da6b59a
KW
761
762 # Modifiers
763
34fdef84
KW
764 MINMOD no Next operator is not greedy.
765 LOGICAL no Next opcode should set the flag
766 only.
5da6b59a
KW
767
768 # This is not used yet
34fdef84
KW
769 RENUM off 1 1 Group with independently
770 numbered parens.
5da6b59a
KW
771
772 # Trie Related
773
65aa4ca7
FC
774 # Behave the same as A|LIST|OF|WORDS would. The '..C' variants
775 # have inline charclass data (ascii only), the 'C' store it in the
776 # structure.
5da6b59a 777
34fdef84
KW
778 TRIE trie 1 Match many EXACT(F[ALU]?)? at
779 once. flags==type
780 TRIEC trie Same as TRIE, but with embedded
781 charclass charclass data
5da6b59a 782
34fdef84
KW
783 AHOCORASICK trie 1 Aho Corasick stclass.
784 flags==type
785 AHOCORASICKC trie Same as AHOCORASICK, but with
786 charclass embedded charclass data
5da6b59a
KW
787
788 # Regex Subroutines
34fdef84
KW
789 GOSUB num/ofs 2L recurse to paren arg1 at
790 (signed) ofs arg2
791 GOSTART no recurse to start of pattern
5da6b59a
KW
792
793 # Special conditionals
34fdef84
KW
794 NGROUPP no-sv 1 Whether the group matched.
795 INSUBP num 1 Whether we are in a specific
796 recurse.
797 DEFINEP none 1 Never execute directly.
5da6b59a
KW
798
799 # Backtracking Verbs
34fdef84
KW
800 ENDLIKE none Used only for the type field of
801 verbs
802 OPFAIL none Same as (?!)
803 ACCEPT parno 1 Accepts the current matched
804 string.
5da6b59a
KW
805
806 # Verbs With Arguments
34fdef84
KW
807 VERB no-sv 1 Used only for the type field of
808 verbs
809 PRUNE no-sv 1 Pattern fails at this
810 startpoint if no-backtracking
811 through this
812 MARKPOINT no-sv 1 Push the current location for
813 rollback by cut.
814 SKIP no-sv 1 On failure skip forward (to the
815 mark) before retrying
816 COMMIT no-sv 1 Pattern fails outright if
817 backtracking through this
818 CUTGROUP no-sv 1 On failure go to the next
819 alternation in the group
5da6b59a
KW
820
821 # Control what to keep in $&.
34fdef84 822 KEEPS no $& begins here.
5da6b59a
KW
823
824 # New charclass like patterns
34fdef84 825 LNBREAK none generic newline pattern
5da6b59a
KW
826
827 # SPECIAL REGOPS
828
65aa4ca7
FC
829 # This is not really a node, but an optimized away piece of a "long"
830 # node. To simplify debugging output, we mark it as if it were a node
34fdef84 831 OPTIMIZED off Placeholder for dump.
5da6b59a
KW
832
833 # Special opcode with the property that no opcode in a compiled program
834 # will ever be of this type. Thus it can be used as a flag value that
835 # no other opcode has been seen. END is used similarly, in that an END
65aa4ca7
FC
836 # node cant be optimized. So END implies "unoptimizable" and PSEUDO
837 # mean "not seen anything to optimize yet".
34fdef84 838 PSEUDO off Pseudo opcode for internal use.
65aa4ca7
FC
839
840=for regcomp.pl end
055fd3a9 841
1c102323
MJD
842=for unprinted-credits
843Next section M-J. Dominus (mjd-perl-patch+@plover.com) 20010421
844
845Following the optimizer information is a dump of the offset/length
846table, here split across several lines:
847
848 Offsets: [45]
849 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1]
850 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0]
851 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0]
852 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0]
853
854The first line here indicates that the offset/length table contains 45
855entries. Each entry is a pair of integers, denoted by C<offset[length]>.
17c338f3 856Entries are numbered starting with 1, so entry #1 here is C<1[4]> and
1c102323
MJD
857entry #12 is C<5[1]>. C<1[4]> indicates that the node labeled C<1:>
858(the C<1: ANYOF[bc]>) begins at character position 1 in the
859pre-compiled form of the regex, and has a length of 4 characters.
860C<5[1]> in position 12
861indicates that the node labeled C<12:>
862(the C<< 12: EXACT <d> >>) begins at character position 5 in the
863pre-compiled form of the regex, and has a length of 1 character.
864C<12[1]> in position 14
865indicates that the node labeled C<14:>
866(the C<< 14: CURLYX[0] {1,32767} >>) begins at character position 12 in the
867pre-compiled form of the regex, and has a length of 1 character---that
868is, it corresponds to the C<+> symbol in the precompiled regex.
869
870C<0[0]> items indicate that there is no corresponding node.
871
7b406369 872=head2 Run-time Output
055fd3a9
GS
873
874First of all, when doing a match, one may get no run-time output even
875if debugging is enabled. This means that the regex engine was never
876entered and that all of the job was therefore done by the optimizer.
877
878If the regex engine was entered, the output may look like this:
879
ccf3535a 880 Matching '[bc]d(ef*g)+h[ij]k$' against 'abcdefg__gh__'
055fd3a9
GS
881 Setting an EVAL scope, savestack=3
882 2 <ab> <cdefg__gh_> | 1: ANYOF
883 3 <abc> <defg__gh_> | 11: EXACT <d>
884 4 <abcd> <efg__gh_> | 13: CURLYX {1,32767}
885 4 <abcd> <efg__gh_> | 26: WHILEM
886 0 out of 1..32767 cc=effff31c
887 4 <abcd> <efg__gh_> | 15: OPEN1
888 4 <abcd> <efg__gh_> | 17: EXACT <e>
889 5 <abcde> <fg__gh_> | 19: STAR
890 EXACT <f> can match 1 times out of 32767...
891 Setting an EVAL scope, savestack=3
892 6 <bcdef> <g__gh__> | 22: EXACT <g>
893 7 <bcdefg> <__gh__> | 24: CLOSE1
894 7 <bcdefg> <__gh__> | 26: WHILEM
895 1 out of 1..32767 cc=effff31c
896 Setting an EVAL scope, savestack=12
897 7 <bcdefg> <__gh__> | 15: OPEN1
898 7 <bcdefg> <__gh__> | 17: EXACT <e>
899 restoring \1 to 4(4)..7
900 failed, try continuation...
901 7 <bcdefg> <__gh__> | 27: NOTHING
902 7 <bcdefg> <__gh__> | 28: EXACT <h>
903 failed...
904 failed...
905
906The most significant information in the output is about the particular I<node>
907of the compiled regex that is currently being tested against the target string.
908The format of these lines is
909
910C< >I<STRING-OFFSET> <I<PRE-STRING>> <I<POST-STRING>> |I<ID>: I<TYPE>
911
912The I<TYPE> info is indented with respect to the backtracking level.
913Other incidental information appears interspersed within.
914
7b406369 915=head1 Debugging Perl Memory Usage
055fd3a9
GS
916
917Perl is a profligate wastrel when it comes to memory use. There
918is a saying that to estimate memory usage of Perl, assume a reasonable
919algorithm for memory allocation, multiply that estimate by 10, and
920while you still may miss the mark, at least you won't be quite so
4375e838 921astonished. This is not absolutely true, but may provide a good
055fd3a9
GS
922grasp of what happens.
923
924Assume that an integer cannot take less than 20 bytes of memory, a
925float cannot take less than 24 bytes, a string cannot take less
926than 32 bytes (all these examples assume 32-bit architectures, the
927result are quite a bit worse on 64-bit architectures). If a variable
928is accessed in two of three different ways (which require an integer,
929a float, or a string), the memory footprint may increase yet another
b9449ee0 93020 bytes. A sloppy malloc(3) implementation can inflate these
055fd3a9
GS
931numbers dramatically.
932
933On the opposite end of the scale, a declaration like
934
935 sub foo;
936
937may take up to 500 bytes of memory, depending on which release of Perl
938you're running.
939
940Anecdotal estimates of source-to-compiled code bloat suggest an
941eightfold increase. This means that the compiled form of reasonable
942(normally commented, properly indented etc.) code will take
943about eight times more space in memory than the code took
944on disk.
945
b30f304a
JH
946The B<-DL> command-line switch is obsolete since circa Perl 5.6.0
947(it was available only if Perl was built with C<-DDEBUGGING>).
948The switch was used to track Perl's memory allocations and possible
949memory leaks. These days the use of malloc debugging tools like
5b6a3331 950F<Purify> or F<valgrind> is suggested instead. See also
7b406369 951L<perlhacktips/PERL_MEM_LOG>.
b30f304a
JH
952
953One way to find out how much memory is being used by Perl data
954structures is to install the Devel::Size module from CPAN: it gives
955you the minimum number of bytes required to store a particular data
956structure. Please be mindful of the difference between the size()
957and total_size().
958
959If Perl has been compiled using Perl's malloc you can analyze Perl
7b406369 960memory usage by setting $ENV{PERL_DEBUG_MSTATS}.
055fd3a9
GS
961
962=head2 Using C<$ENV{PERL_DEBUG_MSTATS}>
963
964If your perl is using Perl's malloc() and was compiled with the
965necessary switches (this is the default), then it will print memory
4375e838 966usage statistics after compiling your code when C<< $ENV{PERL_DEBUG_MSTATS}
055fd3a9
GS
967> 1 >>, and before termination of the program when C<<
968$ENV{PERL_DEBUG_MSTATS} >= 1 >>. The report format is similar to
969the following example:
970
971 $ PERL_DEBUG_MSTATS=2 perl -e "require Carp"
972 Memory allocation statistics after compilation: (buckets 4(4)..8188(8192)
973 14216 free: 130 117 28 7 9 0 2 2 1 0 0
974 437 61 36 0 5
975 60924 used: 125 137 161 55 7 8 6 16 2 0 1
976 74 109 304 84 20
977 Total sbrk(): 77824/21:119. Odd ends: pad+heads+chain+tail: 0+636+0+2048.
978 Memory allocation statistics after execution: (buckets 4(4)..8188(8192)
979 30888 free: 245 78 85 13 6 2 1 3 2 0 1
980 315 162 39 42 11
981 175816 used: 265 176 1112 111 26 22 11 27 2 1 1
982 196 178 1066 798 39
983 Total sbrk(): 215040/47:145. Odd ends: pad+heads+chain+tail: 0+2192+0+6144.
984
985It is possible to ask for such a statistic at arbitrary points in
b9449ee0 986your execution using the mstat() function out of the standard
055fd3a9
GS
987Devel::Peek module.
988
989Here is some explanation of that format:
990
13a2d996 991=over 4
055fd3a9
GS
992
993=item C<buckets SMALLEST(APPROX)..GREATEST(APPROX)>
994
995Perl's malloc() uses bucketed allocations. Every request is rounded
996up to the closest bucket size available, and a bucket is taken from
997the pool of buckets of that size.
998
999The line above describes the limits of buckets currently in use.
1000Each bucket has two sizes: memory footprint and the maximal size
1001of user data that can fit into this bucket. Suppose in the above
1002example that the smallest bucket were size 4. The biggest bucket
1003would have usable size 8188, and the memory footprint would be 8192.
1004
1005In a Perl built for debugging, some buckets may have negative usable
1006size. This means that these buckets cannot (and will not) be used.
1007For larger buckets, the memory footprint may be one page greater
7b406369 1008than a power of 2. If so, the corresponding power of two is
055fd3a9
GS
1009printed in the C<APPROX> field above.
1010
1011=item Free/Used
1012
1013The 1 or 2 rows of numbers following that correspond to the number
1014of buckets of each size between C<SMALLEST> and C<GREATEST>. In
1015the first row, the sizes (memory footprints) of buckets are powers
1016of two--or possibly one page greater. In the second row, if present,
1017the memory footprints of the buckets are between the memory footprints
1018of two buckets "above".
1019
4375e838 1020For example, suppose under the previous example, the memory footprints
055fd3a9
GS
1021were
1022
1023 free: 8 16 32 64 128 256 512 1024 2048 4096 8192
1024 4 12 24 48 80
1025
7b406369 1026With a non-C<DEBUGGING> perl, the buckets starting from C<128> have
d1be9408 1027a 4-byte overhead, and thus an 8192-long bucket may take up to
055fd3a9
GS
10288188-byte allocations.
1029
1030=item C<Total sbrk(): SBRKed/SBRKs:CONTINUOUS>
1031
1032The first two fields give the total amount of memory perl sbrk(2)ed
1033(ess-broken? :-) and number of sbrk(2)s used. The third number is
1034what perl thinks about continuity of returned chunks. So long as
1035this number is positive, malloc() will assume that it is probable
1036that sbrk(2) will provide continuous memory.
1037
1038Memory allocated by external libraries is not counted.
1039
1040=item C<pad: 0>
1041
1042The amount of sbrk(2)ed memory needed to keep buckets aligned.
1043
1044=item C<heads: 2192>
1045
1046Although memory overhead of bigger buckets is kept inside the bucket, for
1047smaller buckets, it is kept in separate areas. This field gives the
1048total size of these areas.
1049
1050=item C<chain: 0>
1051
1052malloc() may want to subdivide a bigger bucket into smaller buckets.
1053If only a part of the deceased bucket is left unsubdivided, the rest
1054is kept as an element of a linked list. This field gives the total
1055size of these chunks.
1056
1057=item C<tail: 6144>
1058
1059To minimize the number of sbrk(2)s, malloc() asks for more memory. This
1060field gives the size of the yet unused part, which is sbrk(2)ed, but
1061never touched.
1062
1063=back
1064
055fd3a9
GS
1065=head1 SEE ALSO
1066
1067L<perldebug>,
1068L<perlguts>,
1069L<perlrun>
1070L<re>,
1071and
fe854a6f 1072L<Devel::DProf>.