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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>
d3d47aac 528being C<SBOL>, C<MBOL>, or C<GPOS>. See the table below.
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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'$>.
055fd3a9 534
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535The optimizer-specific information is used to avoid entering (a slow) regex
536engine on strings that will not definitely match. If the C<isall> flag
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537is set, a call to the regex engine may be avoided even when the optimizer
538found an appropriate place for the match.
539
1c102323 540Above the optimizer section is the list of I<nodes> of the compiled
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541form of the regex. Each line has format
542
543C< >I<id>: I<TYPE> I<OPTIONAL-INFO> (I<next-id>)
544
7b406369 545=head2 Types of Nodes
055fd3a9 546
78465a4b 547Here are the current possible types, with short descriptions:
055fd3a9 548
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549=for comment
550This table is generated by regen/regcomp.pl. Any changes made here
551will be lost.
552
553=for regcomp.pl begin
554
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555 # TYPE arg-description [num-args] [longjump-len] DESCRIPTION
556
557 # Exit points
65aa4ca7 558
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559 END no End of program.
560 SUCCEED no Return from a subroutine, basically.
5da6b59a 561
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562 # Line Start Anchors:
563 SBOL no Match "" at beginning of line: /^/, /\A/
564 MBOL no Same, assuming multiline: /^/m
5da6b59a 565
d3d47aac
YO
566 # Line End Anchors:
567 SEOL no Match "" at end of line: /$/
568 MEOL no Same, assuming multiline: /$/m
569 EOS no Match "" at end of string: /\z/
570
571 # Match Start Anchors:
572 GPOS no Matches where last m//g left off.
573
574 # Word Boundary Opcodes:
7bc66b18 575 BOUND no Match "" at any word boundary using native
850b7ec9 576 charset rules for non-utf8
7bc66b18
KW
577 BOUNDL no Match "" at any locale word boundary
578 BOUNDU no Match "" at any word boundary using Unicode
850b7ec9 579 rules
7bc66b18 580 BOUNDA no Match "" at any word boundary using ASCII
850b7ec9 581 rules
7bc66b18 582 NBOUND no Match "" at any word non-boundary using
850b7ec9 583 native charset rules for non-utf8
7bc66b18
KW
584 NBOUNDL no Match "" at any locale word non-boundary
585 NBOUNDU no Match "" at any word non-boundary using
850b7ec9 586 Unicode rules
7bc66b18 587 NBOUNDA no Match "" at any word non-boundary using
850b7ec9 588 ASCII rules
5da6b59a
KW
589
590 # [Special] alternatives:
7bc66b18
KW
591 REG_ANY no Match any one character (except newline).
592 SANY no Match any one character.
593 CANY no Match any one byte.
975a06f7 594 ANYOF sv 1 Match character in (or not in) this class,
7bc66b18
KW
595 single char match only
596
d3d47aac 597 # POSIX Character Classes:
7bc66b18
KW
598 POSIXD none Some [[:class:]] under /d; the FLAGS field
599 gives which one
600 POSIXL none Some [[:class:]] under /l; the FLAGS field
601 gives which one
602 POSIXU none Some [[:class:]] under /u; the FLAGS field
603 gives which one
604 POSIXA none Some [[:class:]] under /a; the FLAGS field
605 gives which one
606 NPOSIXD none complement of POSIXD, [[:^class:]]
607 NPOSIXL none complement of POSIXL, [[:^class:]]
608 NPOSIXU none complement of POSIXU, [[:^class:]]
609 NPOSIXA none complement of POSIXA, [[:^class:]]
610
611 CLUMP no Match any extended grapheme cluster sequence
5da6b59a
KW
612
613 # Alternation
614
65aa4ca7
FC
615 # BRANCH The set of branches constituting a single choice are
616 # hooked together with their "next" pointers, since
617 # precedence prevents anything being concatenated to
618 # any individual branch. The "next" pointer of the last
619 # BRANCH in a choice points to the thing following the
620 # whole choice. This is also where the final "next"
621 # pointer of each individual branch points; each branch
622 # starts with the operand node of a BRANCH node.
5da6b59a 623 #
7bc66b18 624 BRANCH node Match this alternative, or the next...
5da6b59a 625
5da6b59a
KW
626 # Literals
627
7bc66b18
KW
628 EXACT str Match this string (preceded by length).
629 EXACTF str Match this non-UTF-8 string (not guaranteed
630 to be folded) using /id rules (w/len).
631 EXACTFL str Match this string (not guaranteed to be
632 folded) using /il rules (w/len).
633 EXACTFU str Match this string (folded iff in UTF-8,
634 length in folding doesn't change if not in
635 UTF-8) using /iu rules (w/len).
636 EXACTFA str Match this string (not guaranteed to be
637 folded) using /iaa rules (w/len).
638 EXACTFU_SS str Match this string (folded iff in UTF-8,
639 length in folding may change even if not in
640 UTF-8) using /iu rules (w/len).
641 EXACTFA_NO_TRIE str Match this string (which is not trie-able;
642 not guaranteed to be folded) using /iaa
643 rules (w/len).
5da6b59a
KW
644
645 # Do nothing types
646
7bc66b18 647 NOTHING no Match empty string.
5da6b59a 648 # A variant of above which delimits a group, thus stops optimizations
7bc66b18
KW
649 TAIL no Match empty string. Can jump here from
650 outside.
5da6b59a
KW
651
652 # Loops
653
65aa4ca7 654 # STAR,PLUS '?', and complex '*' and '+', are implemented as
62e6ef33 655 # circular BRANCH structures. Simple cases
65aa4ca7
FC
656 # (one character per match) are implemented with STAR
657 # and PLUS for speed and to minimize recursive plunges.
5da6b59a 658 #
7bc66b18
KW
659 STAR node Match this (simple) thing 0 or more times.
660 PLUS node Match this (simple) thing 1 or more times.
661
662 CURLY sv 2 Match this simple thing {n,m} times.
663 CURLYN no 2 Capture next-after-this simple thing
664 CURLYM no 2 Capture this medium-complex thing {n,m}
665 times.
666 CURLYX sv 2 Match this complex thing {n,m} times.
5da6b59a
KW
667
668 # This terminator creates a loop structure for CURLYX
7bc66b18 669 WHILEM no Do curly processing and see if rest matches.
5da6b59a
KW
670
671 # Buffer related
672
673 # OPEN,CLOSE,GROUPP ...are numbered at compile time.
7bc66b18
KW
674 OPEN num 1 Mark this point in input as start of #n.
675 CLOSE num 1 Analogous to OPEN.
676
677 REF num 1 Match some already matched string
678 REFF num 1 Match already matched string, folded using
850b7ec9 679 native charset rules for non-utf8
7bc66b18
KW
680 REFFL num 1 Match already matched string, folded in loc.
681 REFFU num 1 Match already matched string, folded using
850b7ec9 682 unicode rules for non-utf8
7bc66b18 683 REFFA num 1 Match already matched string, folded using
850b7ec9
KW
684 unicode rules for non-utf8, no mixing ASCII,
685 non-ASCII
65aa4ca7
FC
686
687 # Named references. Code in regcomp.c assumes that these all are after
688 # the numbered references
7bc66b18
KW
689 NREF no-sv 1 Match some already matched string
690 NREFF no-sv 1 Match already matched string, folded using
850b7ec9 691 native charset rules for non-utf8
7bc66b18
KW
692 NREFFL no-sv 1 Match already matched string, folded in loc.
693 NREFFU num 1 Match already matched string, folded using
850b7ec9 694 unicode rules for non-utf8
7bc66b18 695 NREFFA num 1 Match already matched string, folded using
850b7ec9
KW
696 unicode rules for non-utf8, no mixing ASCII,
697 non-ASCII
7bc66b18 698
d3d47aac
YO
699 # Support for long RE
700 LONGJMP off 1 1 Jump far away.
701 BRANCHJ off 1 1 BRANCH with long offset.
702
703 # Special Case Regops
7bc66b18
KW
704 IFMATCH off 1 2 Succeeds if the following matches.
705 UNLESSM off 1 2 Fails if the following matches.
706 SUSPEND off 1 1 "Independent" sub-RE.
707 IFTHEN off 1 1 Switch, should be preceded by switcher.
708 GROUPP num 1 Whether the group matched.
5da6b59a 709
5da6b59a
KW
710 # The heavy worker
711
13f27704
KW
712 EVAL evl/flags Execute some Perl code.
713 2L
5da6b59a
KW
714
715 # Modifiers
716
7bc66b18
KW
717 MINMOD no Next operator is not greedy.
718 LOGICAL no Next opcode should set the flag only.
5da6b59a
KW
719
720 # This is not used yet
7bc66b18 721 RENUM off 1 1 Group with independently numbered parens.
5da6b59a
KW
722
723 # Trie Related
724
65aa4ca7
FC
725 # Behave the same as A|LIST|OF|WORDS would. The '..C' variants
726 # have inline charclass data (ascii only), the 'C' store it in the
727 # structure.
5da6b59a 728
7bc66b18
KW
729 TRIE trie 1 Match many EXACT(F[ALU]?)? at once.
730 flags==type
731 TRIEC trie Same as TRIE, but with embedded charclass
732 charclass data
5da6b59a 733
7bc66b18
KW
734 AHOCORASICK trie 1 Aho Corasick stclass. flags==type
735 AHOCORASICKC trie Same as AHOCORASICK, but with embedded
736 charclass charclass data
5da6b59a
KW
737
738 # Regex Subroutines
7bc66b18
KW
739 GOSUB num/ofs 2L recurse to paren arg1 at (signed) ofs arg2
740 GOSTART no recurse to start of pattern
5da6b59a
KW
741
742 # Special conditionals
7bc66b18
KW
743 NGROUPP no-sv 1 Whether the group matched.
744 INSUBP num 1 Whether we are in a specific recurse.
745 DEFINEP none 1 Never execute directly.
5da6b59a
KW
746
747 # Backtracking Verbs
7bc66b18
KW
748 ENDLIKE none Used only for the type field of verbs
749 OPFAIL none Same as (?!)
750 ACCEPT parno 1 Accepts the current matched string.
5da6b59a
KW
751
752 # Verbs With Arguments
7bc66b18
KW
753 VERB no-sv 1 Used only for the type field of verbs
754 PRUNE no-sv 1 Pattern fails at this startpoint if no-
755 backtracking through this
756 MARKPOINT no-sv 1 Push the current location for rollback by
757 cut.
758 SKIP no-sv 1 On failure skip forward (to the mark) before
759 retrying
760 COMMIT no-sv 1 Pattern fails outright if backtracking
761 through this
762 CUTGROUP no-sv 1 On failure go to the next alternation in the
763 group
5da6b59a
KW
764
765 # Control what to keep in $&.
7bc66b18 766 KEEPS no $& begins here.
5da6b59a
KW
767
768 # New charclass like patterns
7bc66b18 769 LNBREAK none generic newline pattern
5da6b59a
KW
770
771 # SPECIAL REGOPS
772
65aa4ca7
FC
773 # This is not really a node, but an optimized away piece of a "long"
774 # node. To simplify debugging output, we mark it as if it were a node
7bc66b18 775 OPTIMIZED off Placeholder for dump.
5da6b59a
KW
776
777 # Special opcode with the property that no opcode in a compiled program
778 # will ever be of this type. Thus it can be used as a flag value that
779 # no other opcode has been seen. END is used similarly, in that an END
65aa4ca7
FC
780 # node cant be optimized. So END implies "unoptimizable" and PSEUDO
781 # mean "not seen anything to optimize yet".
7bc66b18 782 PSEUDO off Pseudo opcode for internal use.
65aa4ca7
FC
783
784=for regcomp.pl end
055fd3a9 785
1c102323
MJD
786=for unprinted-credits
787Next section M-J. Dominus (mjd-perl-patch+@plover.com) 20010421
788
789Following the optimizer information is a dump of the offset/length
790table, here split across several lines:
791
792 Offsets: [45]
793 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1]
794 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0]
795 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0]
796 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0]
797
798The first line here indicates that the offset/length table contains 45
799entries. Each entry is a pair of integers, denoted by C<offset[length]>.
17c338f3 800Entries are numbered starting with 1, so entry #1 here is C<1[4]> and
1c102323
MJD
801entry #12 is C<5[1]>. C<1[4]> indicates that the node labeled C<1:>
802(the C<1: ANYOF[bc]>) begins at character position 1 in the
803pre-compiled form of the regex, and has a length of 4 characters.
804C<5[1]> in position 12
805indicates that the node labeled C<12:>
806(the C<< 12: EXACT <d> >>) begins at character position 5 in the
807pre-compiled form of the regex, and has a length of 1 character.
808C<12[1]> in position 14
809indicates that the node labeled C<14:>
810(the C<< 14: CURLYX[0] {1,32767} >>) begins at character position 12 in the
811pre-compiled form of the regex, and has a length of 1 character---that
812is, it corresponds to the C<+> symbol in the precompiled regex.
813
814C<0[0]> items indicate that there is no corresponding node.
815
7b406369 816=head2 Run-time Output
055fd3a9
GS
817
818First of all, when doing a match, one may get no run-time output even
819if debugging is enabled. This means that the regex engine was never
820entered and that all of the job was therefore done by the optimizer.
821
822If the regex engine was entered, the output may look like this:
823
ccf3535a 824 Matching '[bc]d(ef*g)+h[ij]k$' against 'abcdefg__gh__'
055fd3a9
GS
825 Setting an EVAL scope, savestack=3
826 2 <ab> <cdefg__gh_> | 1: ANYOF
827 3 <abc> <defg__gh_> | 11: EXACT <d>
828 4 <abcd> <efg__gh_> | 13: CURLYX {1,32767}
829 4 <abcd> <efg__gh_> | 26: WHILEM
830 0 out of 1..32767 cc=effff31c
831 4 <abcd> <efg__gh_> | 15: OPEN1
832 4 <abcd> <efg__gh_> | 17: EXACT <e>
833 5 <abcde> <fg__gh_> | 19: STAR
834 EXACT <f> can match 1 times out of 32767...
835 Setting an EVAL scope, savestack=3
836 6 <bcdef> <g__gh__> | 22: EXACT <g>
837 7 <bcdefg> <__gh__> | 24: CLOSE1
838 7 <bcdefg> <__gh__> | 26: WHILEM
839 1 out of 1..32767 cc=effff31c
840 Setting an EVAL scope, savestack=12
841 7 <bcdefg> <__gh__> | 15: OPEN1
842 7 <bcdefg> <__gh__> | 17: EXACT <e>
843 restoring \1 to 4(4)..7
844 failed, try continuation...
845 7 <bcdefg> <__gh__> | 27: NOTHING
846 7 <bcdefg> <__gh__> | 28: EXACT <h>
847 failed...
848 failed...
849
850The most significant information in the output is about the particular I<node>
851of the compiled regex that is currently being tested against the target string.
852The format of these lines is
853
854C< >I<STRING-OFFSET> <I<PRE-STRING>> <I<POST-STRING>> |I<ID>: I<TYPE>
855
856The I<TYPE> info is indented with respect to the backtracking level.
857Other incidental information appears interspersed within.
858
7b406369 859=head1 Debugging Perl Memory Usage
055fd3a9
GS
860
861Perl is a profligate wastrel when it comes to memory use. There
862is a saying that to estimate memory usage of Perl, assume a reasonable
863algorithm for memory allocation, multiply that estimate by 10, and
864while you still may miss the mark, at least you won't be quite so
4375e838 865astonished. This is not absolutely true, but may provide a good
055fd3a9
GS
866grasp of what happens.
867
868Assume that an integer cannot take less than 20 bytes of memory, a
869float cannot take less than 24 bytes, a string cannot take less
870than 32 bytes (all these examples assume 32-bit architectures, the
871result are quite a bit worse on 64-bit architectures). If a variable
872is accessed in two of three different ways (which require an integer,
873a float, or a string), the memory footprint may increase yet another
b9449ee0 87420 bytes. A sloppy malloc(3) implementation can inflate these
055fd3a9
GS
875numbers dramatically.
876
877On the opposite end of the scale, a declaration like
878
879 sub foo;
880
881may take up to 500 bytes of memory, depending on which release of Perl
882you're running.
883
884Anecdotal estimates of source-to-compiled code bloat suggest an
885eightfold increase. This means that the compiled form of reasonable
886(normally commented, properly indented etc.) code will take
887about eight times more space in memory than the code took
888on disk.
889
b30f304a
JH
890The B<-DL> command-line switch is obsolete since circa Perl 5.6.0
891(it was available only if Perl was built with C<-DDEBUGGING>).
892The switch was used to track Perl's memory allocations and possible
893memory leaks. These days the use of malloc debugging tools like
5b6a3331 894F<Purify> or F<valgrind> is suggested instead. See also
7b406369 895L<perlhacktips/PERL_MEM_LOG>.
b30f304a
JH
896
897One way to find out how much memory is being used by Perl data
898structures is to install the Devel::Size module from CPAN: it gives
899you the minimum number of bytes required to store a particular data
900structure. Please be mindful of the difference between the size()
901and total_size().
902
903If Perl has been compiled using Perl's malloc you can analyze Perl
7b406369 904memory usage by setting $ENV{PERL_DEBUG_MSTATS}.
055fd3a9
GS
905
906=head2 Using C<$ENV{PERL_DEBUG_MSTATS}>
907
908If your perl is using Perl's malloc() and was compiled with the
909necessary switches (this is the default), then it will print memory
4375e838 910usage statistics after compiling your code when C<< $ENV{PERL_DEBUG_MSTATS}
055fd3a9
GS
911> 1 >>, and before termination of the program when C<<
912$ENV{PERL_DEBUG_MSTATS} >= 1 >>. The report format is similar to
913the following example:
914
915 $ PERL_DEBUG_MSTATS=2 perl -e "require Carp"
916 Memory allocation statistics after compilation: (buckets 4(4)..8188(8192)
917 14216 free: 130 117 28 7 9 0 2 2 1 0 0
918 437 61 36 0 5
919 60924 used: 125 137 161 55 7 8 6 16 2 0 1
920 74 109 304 84 20
921 Total sbrk(): 77824/21:119. Odd ends: pad+heads+chain+tail: 0+636+0+2048.
922 Memory allocation statistics after execution: (buckets 4(4)..8188(8192)
923 30888 free: 245 78 85 13 6 2 1 3 2 0 1
924 315 162 39 42 11
925 175816 used: 265 176 1112 111 26 22 11 27 2 1 1
926 196 178 1066 798 39
927 Total sbrk(): 215040/47:145. Odd ends: pad+heads+chain+tail: 0+2192+0+6144.
928
929It is possible to ask for such a statistic at arbitrary points in
b9449ee0 930your execution using the mstat() function out of the standard
055fd3a9
GS
931Devel::Peek module.
932
933Here is some explanation of that format:
934
13a2d996 935=over 4
055fd3a9
GS
936
937=item C<buckets SMALLEST(APPROX)..GREATEST(APPROX)>
938
939Perl's malloc() uses bucketed allocations. Every request is rounded
940up to the closest bucket size available, and a bucket is taken from
941the pool of buckets of that size.
942
943The line above describes the limits of buckets currently in use.
944Each bucket has two sizes: memory footprint and the maximal size
945of user data that can fit into this bucket. Suppose in the above
946example that the smallest bucket were size 4. The biggest bucket
947would have usable size 8188, and the memory footprint would be 8192.
948
949In a Perl built for debugging, some buckets may have negative usable
950size. This means that these buckets cannot (and will not) be used.
951For larger buckets, the memory footprint may be one page greater
7b406369 952than a power of 2. If so, the corresponding power of two is
055fd3a9
GS
953printed in the C<APPROX> field above.
954
955=item Free/Used
956
957The 1 or 2 rows of numbers following that correspond to the number
958of buckets of each size between C<SMALLEST> and C<GREATEST>. In
959the first row, the sizes (memory footprints) of buckets are powers
960of two--or possibly one page greater. In the second row, if present,
961the memory footprints of the buckets are between the memory footprints
962of two buckets "above".
963
4375e838 964For example, suppose under the previous example, the memory footprints
055fd3a9
GS
965were
966
967 free: 8 16 32 64 128 256 512 1024 2048 4096 8192
968 4 12 24 48 80
969
7b406369 970With a non-C<DEBUGGING> perl, the buckets starting from C<128> have
d1be9408 971a 4-byte overhead, and thus an 8192-long bucket may take up to
055fd3a9
GS
9728188-byte allocations.
973
974=item C<Total sbrk(): SBRKed/SBRKs:CONTINUOUS>
975
976The first two fields give the total amount of memory perl sbrk(2)ed
977(ess-broken? :-) and number of sbrk(2)s used. The third number is
978what perl thinks about continuity of returned chunks. So long as
979this number is positive, malloc() will assume that it is probable
980that sbrk(2) will provide continuous memory.
981
982Memory allocated by external libraries is not counted.
983
984=item C<pad: 0>
985
986The amount of sbrk(2)ed memory needed to keep buckets aligned.
987
988=item C<heads: 2192>
989
990Although memory overhead of bigger buckets is kept inside the bucket, for
991smaller buckets, it is kept in separate areas. This field gives the
992total size of these areas.
993
994=item C<chain: 0>
995
996malloc() may want to subdivide a bigger bucket into smaller buckets.
997If only a part of the deceased bucket is left unsubdivided, the rest
998is kept as an element of a linked list. This field gives the total
999size of these chunks.
1000
1001=item C<tail: 6144>
1002
1003To minimize the number of sbrk(2)s, malloc() asks for more memory. This
1004field gives the size of the yet unused part, which is sbrk(2)ed, but
1005never touched.
1006
1007=back
1008
055fd3a9
GS
1009=head1 SEE ALSO
1010
1011L<perldebug>,
1012L<perlguts>,
1013L<perlrun>
1014L<re>,
1015and
fe854a6f 1016L<Devel::DProf>.