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| 128 | .rm #[ #] #H #V #F C |
| 129 | .\" ======================================================================== |
| 130 | .\" |
| 131 | .IX Title "PERLDEBGUTS 1" |
| 132 | .TH PERLDEBGUTS 1 "2002-06-08" "perl v5.8.0" "Perl Programmers Reference Guide" |
| 133 | .SH "NAME" |
| 134 | perldebguts \- Guts of Perl debugging |
| 135 | .SH "DESCRIPTION" |
| 136 | .IX Header "DESCRIPTION" |
| 137 | This is not the \fIperldebug\fR\|(1) manpage, which tells you how to use |
| 138 | the debugger. This manpage describes low-level details concerning |
| 139 | the debugger's internals, which range from difficult to impossible |
| 140 | to understand for anyone who isn't incredibly intimate with Perl's guts. |
| 141 | Caveat lector. |
| 142 | .SH "Debugger Internals" |
| 143 | .IX Header "Debugger Internals" |
| 144 | Perl has special debugging hooks at compile-time and run-time used |
| 145 | to create debugging environments. These hooks are not to be confused |
| 146 | with the \fIperl \-Dxxx\fR command described in perlrun, which is |
| 147 | usable only if a special Perl is built per the instructions in the |
| 148 | \&\fI\s-1INSTALL\s0\fR podpage in the Perl source tree. |
| 149 | .PP |
| 150 | For example, whenever you call Perl's built-in \f(CW\*(C`caller\*(C'\fR function |
| 151 | from the package \f(CW\*(C`DB\*(C'\fR, the arguments that the corresponding stack |
| 152 | frame was called with are copied to the \f(CW@DB::args\fR array. These |
| 153 | mechanisms are enabled by calling Perl with the \fB\-d\fR switch. |
| 154 | Specifically, the following additional features are enabled |
| 155 | (cf. \*(L"$^P\*(R" in perlvar): |
| 156 | .IP "\(bu" 4 |
| 157 | Perl inserts the contents of \f(CW$ENV{PERL5DB}\fR (or \f(CW\*(C`BEGIN {require |
| 158 | \&'perl5db.pl'}\*(C'\fR if not present) before the first line of your program. |
| 159 | .IP "\(bu" 4 |
| 160 | Each array \f(CW\*(C`@{"_<$filename"}\*(C'\fR holds the lines of \f(CW$filename\fR for a |
| 161 | file compiled by Perl. The same is also true for \f(CW\*(C`eval\*(C'\fRed strings |
| 162 | that contain subroutines, or which are currently being executed. |
| 163 | The \f(CW$filename\fR for \f(CW\*(C`eval\*(C'\fRed strings looks like \f(CW\*(C`(eval 34)\*(C'\fR. |
| 164 | Code assertions in regexes look like \f(CW\*(C`(re_eval 19)\*(C'\fR. |
| 165 | .Sp |
| 166 | Values in this array are magical in numeric context: they compare |
| 167 | equal to zero only if the line is not breakable. |
| 168 | .IP "\(bu" 4 |
| 169 | Each hash \f(CW\*(C`%{"_<$filename"}\*(C'\fR contains breakpoints and actions keyed |
| 170 | by line number. Individual entries (as opposed to the whole hash) |
| 171 | are settable. Perl only cares about Boolean true here, although |
| 172 | the values used by \fIperl5db.pl\fR have the form |
| 173 | \&\f(CW"$break_condition\e0$action"\fR. |
| 174 | .Sp |
| 175 | The same holds for evaluated strings that contain subroutines, or |
| 176 | which are currently being executed. The \f(CW$filename\fR for \f(CW\*(C`eval\*(C'\fRed strings |
| 177 | looks like \f(CW\*(C`(eval 34)\*(C'\fR or \f(CW\*(C`(re_eval 19)\*(C'\fR. |
| 178 | .IP "\(bu" 4 |
| 179 | Each scalar \f(CW\*(C`${"_<$filename"}\*(C'\fR contains \f(CW"_<$filename"\fR. This is |
| 180 | also the case for evaluated strings that contain subroutines, or |
| 181 | which are currently being executed. The \f(CW$filename\fR for \f(CW\*(C`eval\*(C'\fRed |
| 182 | strings looks like \f(CW\*(C`(eval 34)\*(C'\fR or \f(CW\*(C`(re_eval 19)\*(C'\fR. |
| 183 | .IP "\(bu" 4 |
| 184 | After each \f(CW\*(C`require\*(C'\fRd file is compiled, but before it is executed, |
| 185 | \&\f(CW\*(C`DB::postponed(*{"_<$filename"})\*(C'\fR is called if the subroutine |
| 186 | \&\f(CW\*(C`DB::postponed\*(C'\fR exists. Here, the \f(CW$filename\fR is the expanded name of |
| 187 | the \f(CW\*(C`require\*(C'\fRd file, as found in the values of \f(CW%INC\fR. |
| 188 | .IP "\(bu" 4 |
| 189 | After each subroutine \f(CW\*(C`subname\*(C'\fR is compiled, the existence of |
| 190 | \&\f(CW$DB::postponed{subname}\fR is checked. If this key exists, |
| 191 | \&\f(CW\*(C`DB::postponed(subname)\*(C'\fR is called if the \f(CW\*(C`DB::postponed\*(C'\fR subroutine |
| 192 | also exists. |
| 193 | .IP "\(bu" 4 |
| 194 | A hash \f(CW%DB::sub\fR is maintained, whose keys are subroutine names |
| 195 | and whose values have the form \f(CW\*(C`filename:startline\-endline\*(C'\fR. |
| 196 | \&\f(CW\*(C`filename\*(C'\fR has the form \f(CW\*(C`(eval 34)\*(C'\fR for subroutines defined inside |
| 197 | \&\f(CW\*(C`eval\*(C'\fRs, or \f(CW\*(C`(re_eval 19)\*(C'\fR for those within regex code assertions. |
| 198 | .IP "\(bu" 4 |
| 199 | When the execution of your program reaches a point that can hold a |
| 200 | breakpoint, the \f(CW\*(C`DB::DB()\*(C'\fR subroutine is called if any of the variables |
| 201 | \&\f(CW$DB::trace\fR, \f(CW$DB::single\fR, or \f(CW$DB::signal\fR is true. These variables |
| 202 | are not \f(CW\*(C`local\*(C'\fRizable. This feature is disabled when executing |
| 203 | inside \f(CW\*(C`DB::DB()\*(C'\fR, including functions called from it |
| 204 | unless \f(CW\*(C`$^D & (1<<30)\*(C'\fR is true. |
| 205 | .IP "\(bu" 4 |
| 206 | When execution of the program reaches a subroutine call, a call to |
| 207 | \&\f(CW&DB::sub\fR(\fIargs\fR) is made instead, with \f(CW$DB::sub\fR holding the |
| 208 | name of the called subroutine. (This doesn't happen if the subroutine |
| 209 | was compiled in the \f(CW\*(C`DB\*(C'\fR package.) |
| 210 | .PP |
| 211 | Note that if \f(CW&DB::sub\fR needs external data for it to work, no |
| 212 | subroutine call is possible without it. As an example, the standard |
| 213 | debugger's \f(CW&DB::sub\fR depends on the \f(CW$DB::deep\fR variable |
| 214 | (it defines how many levels of recursion deep into the debugger you can go |
| 215 | before a mandatory break). If \f(CW$DB::deep\fR is not defined, subroutine |
| 216 | calls are not possible, even though \f(CW&DB::sub\fR exists. |
| 217 | .Sh "Writing Your Own Debugger" |
| 218 | .IX Subsection "Writing Your Own Debugger" |
| 219 | \fIEnvironment Variables\fR |
| 220 | .IX Subsection "Environment Variables" |
| 221 | .PP |
| 222 | The \f(CW\*(C`PERL5DB\*(C'\fR environment variable can be used to define a debugger. |
| 223 | For example, the minimal \*(L"working\*(R" debugger (it actually doesn't do anything) |
| 224 | consists of one line: |
| 225 | .PP |
| 226 | .Vb 1 |
| 227 | \& sub DB::DB {} |
| 228 | .Ve |
| 229 | .PP |
| 230 | It can easily be defined like this: |
| 231 | .PP |
| 232 | .Vb 1 |
| 233 | \& $ PERL5DB="sub DB::DB {}" perl -d your-script |
| 234 | .Ve |
| 235 | .PP |
| 236 | Another brief debugger, slightly more useful, can be created |
| 237 | with only the line: |
| 238 | .PP |
| 239 | .Vb 1 |
| 240 | \& sub DB::DB {print ++$i; scalar <STDIN>} |
| 241 | .Ve |
| 242 | .PP |
| 243 | This debugger prints a number which increments for each statement |
| 244 | encountered and waits for you to hit a newline before continuing |
| 245 | to the next statement. |
| 246 | .PP |
| 247 | The following debugger is actually useful: |
| 248 | .PP |
| 249 | .Vb 5 |
| 250 | \& { |
| 251 | \& package DB; |
| 252 | \& sub DB {} |
| 253 | \& sub sub {print ++$i, " $sub\en"; &$sub} |
| 254 | \& } |
| 255 | .Ve |
| 256 | .PP |
| 257 | It prints the sequence number of each subroutine call and the name of the |
| 258 | called subroutine. Note that \f(CW&DB::sub\fR is being compiled into the |
| 259 | package \f(CW\*(C`DB\*(C'\fR through the use of the \f(CW\*(C`package\*(C'\fR directive. |
| 260 | .PP |
| 261 | When it starts, the debugger reads your rc file (\fI./.perldb\fR or |
| 262 | \&\fI~/.perldb\fR under Unix), which can set important options. |
| 263 | (A subroutine (\f(CW&afterinit\fR) can be defined here as well; it is executed |
| 264 | after the debugger completes its own initialization.) |
| 265 | .PP |
| 266 | After the rc file is read, the debugger reads the \s-1PERLDB_OPTS\s0 |
| 267 | environment variable and uses it to set debugger options. The |
| 268 | contents of this variable are treated as if they were the argument |
| 269 | of an \f(CW\*(C`o ...\*(C'\fR debugger command (q.v. in \*(L"Options\*(R" in perldebug). |
| 270 | .PP |
| 271 | \fIDebugger internal variables In addition to the file and subroutine-related variables mentioned above, the debugger also maintains various magical internal variables.\fR |
| 272 | .IX Subsection "Debugger internal variables In addition to the file and subroutine-related variables mentioned above, the debugger also maintains various magical internal variables." |
| 273 | .IP "\(bu" 4 |
| 274 | \&\f(CW@DB::dbline\fR is an alias for \f(CW\*(C`@{"::_<current_file"}\*(C'\fR, which |
| 275 | holds the lines of the currently-selected file (compiled by Perl), either |
| 276 | explicitly chosen with the debugger's \f(CW\*(C`f\*(C'\fR command, or implicitly by flow |
| 277 | of execution. |
| 278 | .Sp |
| 279 | Values in this array are magical in numeric context: they compare |
| 280 | equal to zero only if the line is not breakable. |
| 281 | .IP "\(bu" 4 |
| 282 | \&\f(CW%DB::dbline\fR, is an alias for \f(CW\*(C`%{"::_<current_file"}\*(C'\fR, which |
| 283 | contains breakpoints and actions keyed by line number in |
| 284 | the currently-selected file, either explicitly chosen with the |
| 285 | debugger's \f(CW\*(C`f\*(C'\fR command, or implicitly by flow of execution. |
| 286 | .Sp |
| 287 | As previously noted, individual entries (as opposed to the whole hash) |
| 288 | are settable. Perl only cares about Boolean true here, although |
| 289 | the values used by \fIperl5db.pl\fR have the form |
| 290 | \&\f(CW"$break_condition\e0$action"\fR. |
| 291 | .PP |
| 292 | \fIDebugger customization functions\fR |
| 293 | .IX Subsection "Debugger customization functions" |
| 294 | .PP |
| 295 | Some functions are provided to simplify customization. |
| 296 | .IP "\(bu" 4 |
| 297 | See \*(L"Options\*(R" in perldebug for description of options parsed by |
| 298 | \&\f(CW\*(C`DB::parse_options(string)\*(C'\fR parses debugger options; see |
| 299 | \&\*(L"Options\*(R" in pperldebug for a description of options recognized. |
| 300 | .IP "\(bu" 4 |
| 301 | \&\f(CW\*(C`DB::dump_trace(skip[,count])\*(C'\fR skips the specified number of frames |
| 302 | and returns a list containing information about the calling frames (all |
| 303 | of them, if \f(CW\*(C`count\*(C'\fR is missing). Each entry is reference to a hash |
| 304 | with keys \f(CW\*(C`context\*(C'\fR (either \f(CW\*(C`.\*(C'\fR, \f(CW\*(C`$\*(C'\fR, or \f(CW\*(C`@\*(C'\fR), \f(CW\*(C`sub\*(C'\fR (subroutine |
| 305 | name, or info about \f(CW\*(C`eval\*(C'\fR), \f(CW\*(C`args\*(C'\fR (\f(CW\*(C`undef\*(C'\fR or a reference to |
| 306 | an array), \f(CW\*(C`file\*(C'\fR, and \f(CW\*(C`line\*(C'\fR. |
| 307 | .IP "\(bu" 4 |
| 308 | \&\f(CW\*(C`DB::print_trace(FH, skip[, count[, short]])\*(C'\fR prints |
| 309 | formatted info about caller frames. The last two functions may be |
| 310 | convenient as arguments to \f(CW\*(C`<\*(C'\fR, \f(CW\*(C`<<\*(C'\fR commands. |
| 311 | .PP |
| 312 | Note that any variables and functions that are not documented in |
| 313 | this manpages (or in perldebug) are considered for internal |
| 314 | use only, and as such are subject to change without notice. |
| 315 | .SH "Frame Listing Output Examples" |
| 316 | .IX Header "Frame Listing Output Examples" |
| 317 | The \f(CW\*(C`frame\*(C'\fR option can be used to control the output of frame |
| 318 | information. For example, contrast this expression trace: |
| 319 | .PP |
| 320 | .Vb 2 |
| 321 | \& $ perl -de 42 |
| 322 | \& Stack dump during die enabled outside of evals. |
| 323 | .Ve |
| 324 | .PP |
| 325 | .Vb 2 |
| 326 | \& Loading DB routines from perl5db.pl patch level 0.94 |
| 327 | \& Emacs support available. |
| 328 | .Ve |
| 329 | .PP |
| 330 | .Vb 1 |
| 331 | \& Enter h or `h h' for help. |
| 332 | .Ve |
| 333 | .PP |
| 334 | .Vb 2 |
| 335 | \& main::(-e:1): 0 |
| 336 | \& DB<1> sub foo { 14 } |
| 337 | .Ve |
| 338 | .PP |
| 339 | .Vb 1 |
| 340 | \& DB<2> sub bar { 3 } |
| 341 | .Ve |
| 342 | .PP |
| 343 | .Vb 5 |
| 344 | \& DB<3> t print foo() * bar() |
| 345 | \& main::((eval 172):3): print foo() + bar(); |
| 346 | \& main::foo((eval 168):2): |
| 347 | \& main::bar((eval 170):2): |
| 348 | \& 42 |
| 349 | .Ve |
| 350 | .PP |
| 351 | with this one, once the \f(CW\*(C`o\*(C'\fRption \f(CW\*(C`frame=2\*(C'\fR has been set: |
| 352 | .PP |
| 353 | .Vb 11 |
| 354 | \& DB<4> o f=2 |
| 355 | \& frame = '2' |
| 356 | \& DB<5> t print foo() * bar() |
| 357 | \& 3: foo() * bar() |
| 358 | \& entering main::foo |
| 359 | \& 2: sub foo { 14 }; |
| 360 | \& exited main::foo |
| 361 | \& entering main::bar |
| 362 | \& 2: sub bar { 3 }; |
| 363 | \& exited main::bar |
| 364 | \& 42 |
| 365 | .Ve |
| 366 | .PP |
| 367 | By way of demonstration, we present below a laborious listing |
| 368 | resulting from setting your \f(CW\*(C`PERLDB_OPTS\*(C'\fR environment variable to |
| 369 | the value \f(CW\*(C`f=n N\*(C'\fR, and running \fIperl \-d \-V\fR from the command line. |
| 370 | Examples use various values of \f(CW\*(C`n\*(C'\fR are shown to give you a feel |
| 371 | for the difference between settings. Long those it may be, this |
| 372 | is not a complete listing, but only excerpts. |
| 373 | .IP "1" 4 |
| 374 | .IX Item "1" |
| 375 | .Vb 13 |
| 376 | \& entering main::BEGIN |
| 377 | \& entering Config::BEGIN |
| 378 | \& Package lib/Exporter.pm. |
| 379 | \& Package lib/Carp.pm. |
| 380 | \& Package lib/Config.pm. |
| 381 | \& entering Config::TIEHASH |
| 382 | \& entering Exporter::import |
| 383 | \& entering Exporter::export |
| 384 | \& entering Config::myconfig |
| 385 | \& entering Config::FETCH |
| 386 | \& entering Config::FETCH |
| 387 | \& entering Config::FETCH |
| 388 | \& entering Config::FETCH |
| 389 | .Ve |
| 390 | .IP "2" 4 |
| 391 | .IX Item "2" |
| 392 | .Vb 19 |
| 393 | \& entering main::BEGIN |
| 394 | \& entering Config::BEGIN |
| 395 | \& Package lib/Exporter.pm. |
| 396 | \& Package lib/Carp.pm. |
| 397 | \& exited Config::BEGIN |
| 398 | \& Package lib/Config.pm. |
| 399 | \& entering Config::TIEHASH |
| 400 | \& exited Config::TIEHASH |
| 401 | \& entering Exporter::import |
| 402 | \& entering Exporter::export |
| 403 | \& exited Exporter::export |
| 404 | \& exited Exporter::import |
| 405 | \& exited main::BEGIN |
| 406 | \& entering Config::myconfig |
| 407 | \& entering Config::FETCH |
| 408 | \& exited Config::FETCH |
| 409 | \& entering Config::FETCH |
| 410 | \& exited Config::FETCH |
| 411 | \& entering Config::FETCH |
| 412 | .Ve |
| 413 | .IP "4" 4 |
| 414 | .IX Item "4" |
| 415 | .Vb 15 |
| 416 | \& in $=main::BEGIN() from /dev/null:0 |
| 417 | \& in $=Config::BEGIN() from lib/Config.pm:2 |
| 418 | \& Package lib/Exporter.pm. |
| 419 | \& Package lib/Carp.pm. |
| 420 | \& Package lib/Config.pm. |
| 421 | \& in $=Config::TIEHASH('Config') from lib/Config.pm:644 |
| 422 | \& in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
| 423 | \& in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li |
| 424 | \& in @=Config::myconfig() from /dev/null:0 |
| 425 | \& in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 |
| 426 | \& in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 |
| 427 | \& in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 |
| 428 | \& in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574 |
| 429 | \& in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574 |
| 430 | \& in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574 |
| 431 | .Ve |
| 432 | .IP "6" 4 |
| 433 | .IX Item "6" |
| 434 | .Vb 21 |
| 435 | \& in $=main::BEGIN() from /dev/null:0 |
| 436 | \& in $=Config::BEGIN() from lib/Config.pm:2 |
| 437 | \& Package lib/Exporter.pm. |
| 438 | \& Package lib/Carp.pm. |
| 439 | \& out $=Config::BEGIN() from lib/Config.pm:0 |
| 440 | \& Package lib/Config.pm. |
| 441 | \& in $=Config::TIEHASH('Config') from lib/Config.pm:644 |
| 442 | \& out $=Config::TIEHASH('Config') from lib/Config.pm:644 |
| 443 | \& in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
| 444 | \& in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/ |
| 445 | \& out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/ |
| 446 | \& out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
| 447 | \& out $=main::BEGIN() from /dev/null:0 |
| 448 | \& in @=Config::myconfig() from /dev/null:0 |
| 449 | \& in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 |
| 450 | \& out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 |
| 451 | \& in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 |
| 452 | \& out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 |
| 453 | \& in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 |
| 454 | \& out $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 |
| 455 | \& in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574 |
| 456 | .Ve |
| 457 | .IP "14" 4 |
| 458 | .IX Item "14" |
| 459 | .Vb 18 |
| 460 | \& in $=main::BEGIN() from /dev/null:0 |
| 461 | \& in $=Config::BEGIN() from lib/Config.pm:2 |
| 462 | \& Package lib/Exporter.pm. |
| 463 | \& Package lib/Carp.pm. |
| 464 | \& out $=Config::BEGIN() from lib/Config.pm:0 |
| 465 | \& Package lib/Config.pm. |
| 466 | \& in $=Config::TIEHASH('Config') from lib/Config.pm:644 |
| 467 | \& out $=Config::TIEHASH('Config') from lib/Config.pm:644 |
| 468 | \& in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
| 469 | \& in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E |
| 470 | \& out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E |
| 471 | \& out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
| 472 | \& out $=main::BEGIN() from /dev/null:0 |
| 473 | \& in @=Config::myconfig() from /dev/null:0 |
| 474 | \& in $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574 |
| 475 | \& out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574 |
| 476 | \& in $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574 |
| 477 | \& out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574 |
| 478 | .Ve |
| 479 | .IP "30" 4 |
| 480 | .IX Item "30" |
| 481 | .Vb 15 |
| 482 | \& in $=CODE(0x15eca4)() from /dev/null:0 |
| 483 | \& in $=CODE(0x182528)() from lib/Config.pm:2 |
| 484 | \& Package lib/Exporter.pm. |
| 485 | \& out $=CODE(0x182528)() from lib/Config.pm:0 |
| 486 | \& scalar context return from CODE(0x182528): undef |
| 487 | \& Package lib/Config.pm. |
| 488 | \& in $=Config::TIEHASH('Config') from lib/Config.pm:628 |
| 489 | \& out $=Config::TIEHASH('Config') from lib/Config.pm:628 |
| 490 | \& scalar context return from Config::TIEHASH: empty hash |
| 491 | \& in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
| 492 | \& in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171 |
| 493 | \& out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171 |
| 494 | \& scalar context return from Exporter::export: '' |
| 495 | \& out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 |
| 496 | \& scalar context return from Exporter::import: '' |
| 497 | .Ve |
| 498 | .PP |
| 499 | In all cases shown above, the line indentation shows the call tree. |
| 500 | If bit 2 of \f(CW\*(C`frame\*(C'\fR is set, a line is printed on exit from a |
| 501 | subroutine as well. If bit 4 is set, the arguments are printed |
| 502 | along with the caller info. If bit 8 is set, the arguments are |
| 503 | printed even if they are tied or references. If bit 16 is set, the |
| 504 | return value is printed, too. |
| 505 | .PP |
| 506 | When a package is compiled, a line like this |
| 507 | .PP |
| 508 | .Vb 1 |
| 509 | \& Package lib/Carp.pm. |
| 510 | .Ve |
| 511 | .PP |
| 512 | is printed with proper indentation. |
| 513 | .SH "Debugging regular expressions" |
| 514 | .IX Header "Debugging regular expressions" |
| 515 | There are two ways to enable debugging output for regular expressions. |
| 516 | .PP |
| 517 | If your perl is compiled with \f(CW\*(C`\-DDEBUGGING\*(C'\fR, you may use the |
| 518 | \&\fB\-Dr\fR flag on the command line. |
| 519 | .PP |
| 520 | Otherwise, one can \f(CW\*(C`use re 'debug'\*(C'\fR, which has effects at |
| 521 | compile time and run time. It is not lexically scoped. |
| 522 | .Sh "Compile-time output" |
| 523 | .IX Subsection "Compile-time output" |
| 524 | The debugging output at compile time looks like this: |
| 525 | .PP |
| 526 | .Vb 29 |
| 527 | \& Compiling REx `[bc]d(ef*g)+h[ij]k$' |
| 528 | \& size 45 Got 364 bytes for offset annotations. |
| 529 | \& first at 1 |
| 530 | \& rarest char g at 0 |
| 531 | \& rarest char d at 0 |
| 532 | \& 1: ANYOF[bc](12) |
| 533 | \& 12: EXACT <d>(14) |
| 534 | \& 14: CURLYX[0] {1,32767}(28) |
| 535 | \& 16: OPEN1(18) |
| 536 | \& 18: EXACT <e>(20) |
| 537 | \& 20: STAR(23) |
| 538 | \& 21: EXACT <f>(0) |
| 539 | \& 23: EXACT <g>(25) |
| 540 | \& 25: CLOSE1(27) |
| 541 | \& 27: WHILEM[1/1](0) |
| 542 | \& 28: NOTHING(29) |
| 543 | \& 29: EXACT <h>(31) |
| 544 | \& 31: ANYOF[ij](42) |
| 545 | \& 42: EXACT <k>(44) |
| 546 | \& 44: EOL(45) |
| 547 | \& 45: END(0) |
| 548 | \& anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating) |
| 549 | \& stclass `ANYOF[bc]' minlen 7 |
| 550 | \& Offsets: [45] |
| 551 | \& 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1] |
| 552 | \& 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0] |
| 553 | \& 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0] |
| 554 | \& 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0] |
| 555 | \& Omitting $` $& $' support. |
| 556 | .Ve |
| 557 | .PP |
| 558 | The first line shows the pre-compiled form of the regex. The second |
| 559 | shows the size of the compiled form (in arbitrary units, usually |
| 560 | 4\-byte words) and the total number of bytes allocated for the |
| 561 | offset/length table, usually 4+\f(CW\*(C`size\*(C'\fR*8. The next line shows the |
| 562 | label \fIid\fR of the first node that does a match. |
| 563 | .PP |
| 564 | The |
| 565 | .PP |
| 566 | .Vb 2 |
| 567 | \& anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating) |
| 568 | \& stclass `ANYOF[bc]' minlen 7 |
| 569 | .Ve |
| 570 | .PP |
| 571 | line (split into two lines above) contains optimizer |
| 572 | information. In the example shown, the optimizer found that the match |
| 573 | should contain a substring \f(CW\*(C`de\*(C'\fR at offset 1, plus substring \f(CW\*(C`gh\*(C'\fR |
| 574 | at some offset between 3 and infinity. Moreover, when checking for |
| 575 | these substrings (to abandon impossible matches quickly), Perl will check |
| 576 | for the substring \f(CW\*(C`gh\*(C'\fR before checking for the substring \f(CW\*(C`de\*(C'\fR. The |
| 577 | optimizer may also use the knowledge that the match starts (at the |
| 578 | \&\f(CW\*(C`first\*(C'\fR \fIid\fR) with a character class, and no string |
| 579 | shorter than 7 characters can possibly match. |
| 580 | .PP |
| 581 | The fields of interest which may appear in this line are |
| 582 | .ie n .IP """anchored""\fR \fI\s-1STRING\s0\fR \f(CW""at""\fR \fI\s-1POS\s0" 4 |
| 583 | .el .IP "\f(CWanchored\fR \fI\s-1STRING\s0\fR \f(CWat\fR \fI\s-1POS\s0\fR" 4 |
| 584 | .IX Item "anchored STRING at POS" |
| 585 | .PD 0 |
| 586 | .ie n .IP """floating""\fR \fI\s-1STRING\s0\fR \f(CW""at""\fR \fI\s-1POS1\s0..POS2" 4 |
| 587 | .el .IP "\f(CWfloating\fR \fI\s-1STRING\s0\fR \f(CWat\fR \fI\s-1POS1\s0..POS2\fR" 4 |
| 588 | .IX Item "floating STRING at POS1..POS2" |
| 589 | .PD |
| 590 | See above. |
| 591 | .ie n .IP """matching floating/anchored""" 4 |
| 592 | .el .IP "\f(CWmatching floating/anchored\fR" 4 |
| 593 | .IX Item "matching floating/anchored" |
| 594 | Which substring to check first. |
| 595 | .ie n .IP """minlen""" 4 |
| 596 | .el .IP "\f(CWminlen\fR" 4 |
| 597 | .IX Item "minlen" |
| 598 | The minimal length of the match. |
| 599 | .ie n .IP """stclass""\fR \fI\s-1TYPE\s0" 4 |
| 600 | .el .IP "\f(CWstclass\fR \fI\s-1TYPE\s0\fR" 4 |
| 601 | .IX Item "stclass TYPE" |
| 602 | Type of first matching node. |
| 603 | .ie n .IP """noscan""" 4 |
| 604 | .el .IP "\f(CWnoscan\fR" 4 |
| 605 | .IX Item "noscan" |
| 606 | Don't scan for the found substrings. |
| 607 | .ie n .IP """isall""" 4 |
| 608 | .el .IP "\f(CWisall\fR" 4 |
| 609 | .IX Item "isall" |
| 610 | Means that the optimizer information is all that the regular |
| 611 | expression contains, and thus one does not need to enter the regex engine at |
| 612 | all. |
| 613 | .ie n .IP """GPOS""" 4 |
| 614 | .el .IP "\f(CWGPOS\fR" 4 |
| 615 | .IX Item "GPOS" |
| 616 | Set if the pattern contains \f(CW\*(C`\eG\*(C'\fR. |
| 617 | .ie n .IP """plus""" 4 |
| 618 | .el .IP "\f(CWplus\fR" 4 |
| 619 | .IX Item "plus" |
| 620 | Set if the pattern starts with a repeated char (as in \f(CW\*(C`x+y\*(C'\fR). |
| 621 | .ie n .IP """implicit""" 4 |
| 622 | .el .IP "\f(CWimplicit\fR" 4 |
| 623 | .IX Item "implicit" |
| 624 | Set if the pattern starts with \f(CW\*(C`.*\*(C'\fR. |
| 625 | .ie n .IP """with eval""" 4 |
| 626 | .el .IP "\f(CWwith eval\fR" 4 |
| 627 | .IX Item "with eval" |
| 628 | Set if the pattern contain eval\-groups, such as \f(CW\*(C`(?{ code })\*(C'\fR and |
| 629 | \&\f(CW\*(C`(??{ code })\*(C'\fR. |
| 630 | .ie n .IP """anchored(TYPE)""" 4 |
| 631 | .el .IP "\f(CWanchored(TYPE)\fR" 4 |
| 632 | .IX Item "anchored(TYPE)" |
| 633 | If the pattern may match only at a handful of places, (with \f(CW\*(C`TYPE\*(C'\fR |
| 634 | being \f(CW\*(C`BOL\*(C'\fR, \f(CW\*(C`MBOL\*(C'\fR, or \f(CW\*(C`GPOS\*(C'\fR. See the table below. |
| 635 | .PP |
| 636 | If a substring is known to match at end-of-line only, it may be |
| 637 | followed by \f(CW\*(C`$\*(C'\fR, as in \f(CW\*(C`floating `k'$\*(C'\fR. |
| 638 | .PP |
| 639 | The optimizer-specific information is used to avoid entering (a slow) regex |
| 640 | engine on strings that will not definitely match. If the \f(CW\*(C`isall\*(C'\fR flag |
| 641 | is set, a call to the regex engine may be avoided even when the optimizer |
| 642 | found an appropriate place for the match. |
| 643 | .PP |
| 644 | Above the optimizer section is the list of \fInodes\fR of the compiled |
| 645 | form of the regex. Each line has format |
| 646 | .PP |
| 647 | \&\f(CW\*(C` \*(C'\fR\fIid\fR: \fI\s-1TYPE\s0\fR \fIOPTIONAL-INFO\fR (\fInext-id\fR) |
| 648 | .Sh "Types of nodes" |
| 649 | .IX Subsection "Types of nodes" |
| 650 | Here are the possible types, with short descriptions: |
| 651 | .PP |
| 652 | .Vb 1 |
| 653 | \& # TYPE arg-description [num-args] [longjump-len] DESCRIPTION |
| 654 | .Ve |
| 655 | .PP |
| 656 | .Vb 3 |
| 657 | \& # Exit points |
| 658 | \& END no End of program. |
| 659 | \& SUCCEED no Return from a subroutine, basically. |
| 660 | .Ve |
| 661 | .PP |
| 662 | .Vb 13 |
| 663 | \& # Anchors: |
| 664 | \& BOL no Match "" at beginning of line. |
| 665 | \& MBOL no Same, assuming multiline. |
| 666 | \& SBOL no Same, assuming singleline. |
| 667 | \& EOS no Match "" at end of string. |
| 668 | \& EOL no Match "" at end of line. |
| 669 | \& MEOL no Same, assuming multiline. |
| 670 | \& SEOL no Same, assuming singleline. |
| 671 | \& BOUND no Match "" at any word boundary |
| 672 | \& BOUNDL no Match "" at any word boundary |
| 673 | \& NBOUND no Match "" at any word non-boundary |
| 674 | \& NBOUNDL no Match "" at any word non-boundary |
| 675 | \& GPOS no Matches where last m//g left off. |
| 676 | .Ve |
| 677 | .PP |
| 678 | .Vb 14 |
| 679 | \& # [Special] alternatives |
| 680 | \& ANY no Match any one character (except newline). |
| 681 | \& SANY no Match any one character. |
| 682 | \& ANYOF sv Match character in (or not in) this class. |
| 683 | \& ALNUM no Match any alphanumeric character |
| 684 | \& ALNUML no Match any alphanumeric char in locale |
| 685 | \& NALNUM no Match any non-alphanumeric character |
| 686 | \& NALNUML no Match any non-alphanumeric char in locale |
| 687 | \& SPACE no Match any whitespace character |
| 688 | \& SPACEL no Match any whitespace char in locale |
| 689 | \& NSPACE no Match any non-whitespace character |
| 690 | \& NSPACEL no Match any non-whitespace char in locale |
| 691 | \& DIGIT no Match any numeric character |
| 692 | \& NDIGIT no Match any non-numeric character |
| 693 | .Ve |
| 694 | .PP |
| 695 | .Vb 9 |
| 696 | \& # BRANCH The set of branches constituting a single choice are hooked |
| 697 | \& # together with their "next" pointers, since precedence prevents |
| 698 | \& # anything being concatenated to any individual branch. The |
| 699 | \& # "next" pointer of the last BRANCH in a choice points to the |
| 700 | \& # thing following the whole choice. This is also where the |
| 701 | \& # final "next" pointer of each individual branch points; each |
| 702 | \& # branch starts with the operand node of a BRANCH node. |
| 703 | \& # |
| 704 | \& BRANCH node Match this alternative, or the next... |
| 705 | .Ve |
| 706 | .PP |
| 707 | .Vb 4 |
| 708 | \& # BACK Normal "next" pointers all implicitly point forward; BACK |
| 709 | \& # exists to make loop structures possible. |
| 710 | \& # not used |
| 711 | \& BACK no Match "", "next" ptr points backward. |
| 712 | .Ve |
| 713 | .PP |
| 714 | .Vb 4 |
| 715 | \& # Literals |
| 716 | \& EXACT sv Match this string (preceded by length). |
| 717 | \& EXACTF sv Match this string, folded (prec. by length). |
| 718 | \& EXACTFL sv Match this string, folded in locale (w/len). |
| 719 | .Ve |
| 720 | .PP |
| 721 | .Vb 4 |
| 722 | \& # Do nothing |
| 723 | \& NOTHING no Match empty string. |
| 724 | \& # A variant of above which delimits a group, thus stops optimizations |
| 725 | \& TAIL no Match empty string. Can jump here from outside. |
| 726 | .Ve |
| 727 | .PP |
| 728 | .Vb 7 |
| 729 | \& # STAR,PLUS '?', and complex '*' and '+', are implemented as circular |
| 730 | \& # BRANCH structures using BACK. Simple cases (one character |
| 731 | \& # per match) are implemented with STAR and PLUS for speed |
| 732 | \& # and to minimize recursive plunges. |
| 733 | \& # |
| 734 | \& STAR node Match this (simple) thing 0 or more times. |
| 735 | \& PLUS node Match this (simple) thing 1 or more times. |
| 736 | .Ve |
| 737 | .PP |
| 738 | .Vb 5 |
| 739 | \& CURLY sv 2 Match this simple thing {n,m} times. |
| 740 | \& CURLYN no 2 Match next-after-this simple thing |
| 741 | \& # {n,m} times, set parens. |
| 742 | \& CURLYM no 2 Match this medium-complex thing {n,m} times. |
| 743 | \& CURLYX sv 2 Match this complex thing {n,m} times. |
| 744 | .Ve |
| 745 | .PP |
| 746 | .Vb 2 |
| 747 | \& # This terminator creates a loop structure for CURLYX |
| 748 | \& WHILEM no Do curly processing and see if rest matches. |
| 749 | .Ve |
| 750 | .PP |
| 751 | .Vb 3 |
| 752 | \& # OPEN,CLOSE,GROUPP ...are numbered at compile time. |
| 753 | \& OPEN num 1 Mark this point in input as start of #n. |
| 754 | \& CLOSE num 1 Analogous to OPEN. |
| 755 | .Ve |
| 756 | .PP |
| 757 | .Vb 3 |
| 758 | \& REF num 1 Match some already matched string |
| 759 | \& REFF num 1 Match already matched string, folded |
| 760 | \& REFFL num 1 Match already matched string, folded in loc. |
| 761 | .Ve |
| 762 | .PP |
| 763 | .Vb 6 |
| 764 | \& # grouping assertions |
| 765 | \& IFMATCH off 1 2 Succeeds if the following matches. |
| 766 | \& UNLESSM off 1 2 Fails if the following matches. |
| 767 | \& SUSPEND off 1 1 "Independent" sub-regex. |
| 768 | \& IFTHEN off 1 1 Switch, should be preceded by switcher . |
| 769 | \& GROUPP num 1 Whether the group matched. |
| 770 | .Ve |
| 771 | .PP |
| 772 | .Vb 3 |
| 773 | \& # Support for long regex |
| 774 | \& LONGJMP off 1 1 Jump far away. |
| 775 | \& BRANCHJ off 1 1 BRANCH with long offset. |
| 776 | .Ve |
| 777 | .PP |
| 778 | .Vb 2 |
| 779 | \& # The heavy worker |
| 780 | \& EVAL evl 1 Execute some Perl code. |
| 781 | .Ve |
| 782 | .PP |
| 783 | .Vb 3 |
| 784 | \& # Modifiers |
| 785 | \& MINMOD no Next operator is not greedy. |
| 786 | \& LOGICAL no Next opcode should set the flag only. |
| 787 | .Ve |
| 788 | .PP |
| 789 | .Vb 2 |
| 790 | \& # This is not used yet |
| 791 | \& RENUM off 1 1 Group with independently numbered parens. |
| 792 | .Ve |
| 793 | .PP |
| 794 | .Vb 3 |
| 795 | \& # This is not really a node, but an optimized away piece of a "long" node. |
| 796 | \& # To simplify debugging output, we mark it as if it were a node |
| 797 | \& OPTIMIZED off Placeholder for dump. |
| 798 | .Ve |
| 799 | .PP |
| 800 | Following the optimizer information is a dump of the offset/length |
| 801 | table, here split across several lines: |
| 802 | .PP |
| 803 | .Vb 5 |
| 804 | \& Offsets: [45] |
| 805 | \& 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1] |
| 806 | \& 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0] |
| 807 | \& 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0] |
| 808 | \& 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0] |
| 809 | .Ve |
| 810 | .PP |
| 811 | The first line here indicates that the offset/length table contains 45 |
| 812 | entries. Each entry is a pair of integers, denoted by \f(CW\*(C`offset[length]\*(C'\fR. |
| 813 | Entries are numbered starting with 1, so entry #1 here is \f(CW\*(C`1[4]\*(C'\fR and |
| 814 | entry #12 is \f(CW\*(C`5[1]\*(C'\fR. \f(CW\*(C`1[4]\*(C'\fR indicates that the node labeled \f(CW\*(C`1:\*(C'\fR |
| 815 | (the \f(CW\*(C`1: ANYOF[bc]\*(C'\fR) begins at character position 1 in the |
| 816 | pre-compiled form of the regex, and has a length of 4 characters. |
| 817 | \&\f(CW\*(C`5[1]\*(C'\fR in position 12 |
| 818 | indicates that the node labeled \f(CW\*(C`12:\*(C'\fR |
| 819 | (the \f(CW\*(C`12: EXACT <d>\*(C'\fR) begins at character position 5 in the |
| 820 | pre-compiled form of the regex, and has a length of 1 character. |
| 821 | \&\f(CW\*(C`12[1]\*(C'\fR in position 14 |
| 822 | indicates that the node labeled \f(CW\*(C`14:\*(C'\fR |
| 823 | (the \f(CW\*(C`14: CURLYX[0] {1,32767}\*(C'\fR) begins at character position 12 in the |
| 824 | pre-compiled form of the regex, and has a length of 1 character\-\-\-that |
| 825 | is, it corresponds to the \f(CW\*(C`+\*(C'\fR symbol in the precompiled regex. |
| 826 | .PP |
| 827 | \&\f(CW\*(C`0[0]\*(C'\fR items indicate that there is no corresponding node. |
| 828 | .Sh "Run-time output" |
| 829 | .IX Subsection "Run-time output" |
| 830 | First of all, when doing a match, one may get no run-time output even |
| 831 | if debugging is enabled. This means that the regex engine was never |
| 832 | entered and that all of the job was therefore done by the optimizer. |
| 833 | .PP |
| 834 | If the regex engine was entered, the output may look like this: |
| 835 | .PP |
| 836 | .Vb 25 |
| 837 | \& Matching `[bc]d(ef*g)+h[ij]k$' against `abcdefg__gh__' |
| 838 | \& Setting an EVAL scope, savestack=3 |
| 839 | \& 2 <ab> <cdefg__gh_> | 1: ANYOF |
| 840 | \& 3 <abc> <defg__gh_> | 11: EXACT <d> |
| 841 | \& 4 <abcd> <efg__gh_> | 13: CURLYX {1,32767} |
| 842 | \& 4 <abcd> <efg__gh_> | 26: WHILEM |
| 843 | \& 0 out of 1..32767 cc=effff31c |
| 844 | \& 4 <abcd> <efg__gh_> | 15: OPEN1 |
| 845 | \& 4 <abcd> <efg__gh_> | 17: EXACT <e> |
| 846 | \& 5 <abcde> <fg__gh_> | 19: STAR |
| 847 | \& EXACT <f> can match 1 times out of 32767... |
| 848 | \& Setting an EVAL scope, savestack=3 |
| 849 | \& 6 <bcdef> <g__gh__> | 22: EXACT <g> |
| 850 | \& 7 <bcdefg> <__gh__> | 24: CLOSE1 |
| 851 | \& 7 <bcdefg> <__gh__> | 26: WHILEM |
| 852 | \& 1 out of 1..32767 cc=effff31c |
| 853 | \& Setting an EVAL scope, savestack=12 |
| 854 | \& 7 <bcdefg> <__gh__> | 15: OPEN1 |
| 855 | \& 7 <bcdefg> <__gh__> | 17: EXACT <e> |
| 856 | \& restoring \e1 to 4(4)..7 |
| 857 | \& failed, try continuation... |
| 858 | \& 7 <bcdefg> <__gh__> | 27: NOTHING |
| 859 | \& 7 <bcdefg> <__gh__> | 28: EXACT <h> |
| 860 | \& failed... |
| 861 | \& failed... |
| 862 | .Ve |
| 863 | .PP |
| 864 | The most significant information in the output is about the particular \fInode\fR |
| 865 | of the compiled regex that is currently being tested against the target string. |
| 866 | The format of these lines is |
| 867 | .PP |
| 868 | \&\f(CW\*(C` \*(C'\fR\fISTRING-OFFSET\fR <\fIPRE-STRING\fR> <\fIPOST-STRING\fR> |\fI\s-1ID\s0\fR: \fI\s-1TYPE\s0\fR |
| 869 | .PP |
| 870 | The \fI\s-1TYPE\s0\fR info is indented with respect to the backtracking level. |
| 871 | Other incidental information appears interspersed within. |
| 872 | .SH "Debugging Perl memory usage" |
| 873 | .IX Header "Debugging Perl memory usage" |
| 874 | Perl is a profligate wastrel when it comes to memory use. There |
| 875 | is a saying that to estimate memory usage of Perl, assume a reasonable |
| 876 | algorithm for memory allocation, multiply that estimate by 10, and |
| 877 | while you still may miss the mark, at least you won't be quite so |
| 878 | astonished. This is not absolutely true, but may provide a good |
| 879 | grasp of what happens. |
| 880 | .PP |
| 881 | Assume that an integer cannot take less than 20 bytes of memory, a |
| 882 | float cannot take less than 24 bytes, a string cannot take less |
| 883 | than 32 bytes (all these examples assume 32\-bit architectures, the |
| 884 | result are quite a bit worse on 64\-bit architectures). If a variable |
| 885 | is accessed in two of three different ways (which require an integer, |
| 886 | a float, or a string), the memory footprint may increase yet another |
| 887 | 20 bytes. A sloppy \fImalloc\fR\|(3) implementation can inflate these |
| 888 | numbers dramatically. |
| 889 | .PP |
| 890 | On the opposite end of the scale, a declaration like |
| 891 | .PP |
| 892 | .Vb 1 |
| 893 | \& sub foo; |
| 894 | .Ve |
| 895 | .PP |
| 896 | may take up to 500 bytes of memory, depending on which release of Perl |
| 897 | you're running. |
| 898 | .PP |
| 899 | Anecdotal estimates of source-to-compiled code bloat suggest an |
| 900 | eightfold increase. This means that the compiled form of reasonable |
| 901 | (normally commented, properly indented etc.) code will take |
| 902 | about eight times more space in memory than the code took |
| 903 | on disk. |
| 904 | .PP |
| 905 | There are two Perl-specific ways to analyze memory usage: |
| 906 | \&\f(CW$ENV\fR{\s-1PERL_DEBUG_MSTATS\s0} and \fB\-DL\fR command-line switch. The first |
| 907 | is available only if Perl is compiled with Perl's \fImalloc()\fR; the |
| 908 | second only if Perl was built with \f(CW\*(C`\-DDEBUGGING\*(C'\fR. See the |
| 909 | instructions for how to do this in the \fI\s-1INSTALL\s0\fR podpage at |
| 910 | the top level of the Perl source tree. |
| 911 | .ie n .Sh "Using $ENV{PERL_DEBUG_MSTATS}" |
| 912 | .el .Sh "Using \f(CW$ENV{PERL_DEBUG_MSTATS}\fP" |
| 913 | .IX Subsection "Using $ENV{PERL_DEBUG_MSTATS}" |
| 914 | If your perl is using Perl's \fImalloc()\fR and was compiled with the |
| 915 | necessary switches (this is the default), then it will print memory |
| 916 | usage statistics after compiling your code when \f(CW\*(C`$ENV{PERL_DEBUG_MSTATS} |
| 917 | > 1\*(C'\fR, and before termination of the program when \f(CW\*(C`$ENV{PERL_DEBUG_MSTATS} >= 1\*(C'\fR. The report format is similar to |
| 918 | the following example: |
| 919 | .PP |
| 920 | .Vb 13 |
| 921 | \& $ PERL_DEBUG_MSTATS=2 perl -e "require Carp" |
| 922 | \& Memory allocation statistics after compilation: (buckets 4(4)..8188(8192) |
| 923 | \& 14216 free: 130 117 28 7 9 0 2 2 1 0 0 |
| 924 | \& 437 61 36 0 5 |
| 925 | \& 60924 used: 125 137 161 55 7 8 6 16 2 0 1 |
| 926 | \& 74 109 304 84 20 |
| 927 | \& Total sbrk(): 77824/21:119. Odd ends: pad+heads+chain+tail: 0+636+0+2048. |
| 928 | \& Memory allocation statistics after execution: (buckets 4(4)..8188(8192) |
| 929 | \& 30888 free: 245 78 85 13 6 2 1 3 2 0 1 |
| 930 | \& 315 162 39 42 11 |
| 931 | \& 175816 used: 265 176 1112 111 26 22 11 27 2 1 1 |
| 932 | \& 196 178 1066 798 39 |
| 933 | \& Total sbrk(): 215040/47:145. Odd ends: pad+heads+chain+tail: 0+2192+0+6144. |
| 934 | .Ve |
| 935 | .PP |
| 936 | It is possible to ask for such a statistic at arbitrary points in |
| 937 | your execution using the \fImstat()\fR function out of the standard |
| 938 | Devel::Peek module. |
| 939 | .PP |
| 940 | Here is some explanation of that format: |
| 941 | .ie n .IP """buckets SMALLEST(APPROX)..GREATEST(APPROX)""" 4 |
| 942 | .el .IP "\f(CWbuckets SMALLEST(APPROX)..GREATEST(APPROX)\fR" 4 |
| 943 | .IX Item "buckets SMALLEST(APPROX)..GREATEST(APPROX)" |
| 944 | Perl's \fImalloc()\fR uses bucketed allocations. Every request is rounded |
| 945 | up to the closest bucket size available, and a bucket is taken from |
| 946 | the pool of buckets of that size. |
| 947 | .Sp |
| 948 | The line above describes the limits of buckets currently in use. |
| 949 | Each bucket has two sizes: memory footprint and the maximal size |
| 950 | of user data that can fit into this bucket. Suppose in the above |
| 951 | example that the smallest bucket were size 4. The biggest bucket |
| 952 | would have usable size 8188, and the memory footprint would be 8192. |
| 953 | .Sp |
| 954 | In a Perl built for debugging, some buckets may have negative usable |
| 955 | size. This means that these buckets cannot (and will not) be used. |
| 956 | For larger buckets, the memory footprint may be one page greater |
| 957 | than a power of 2. If so, case the corresponding power of two is |
| 958 | printed in the \f(CW\*(C`APPROX\*(C'\fR field above. |
| 959 | .IP "Free/Used" 4 |
| 960 | .IX Item "Free/Used" |
| 961 | The 1 or 2 rows of numbers following that correspond to the number |
| 962 | of buckets of each size between \f(CW\*(C`SMALLEST\*(C'\fR and \f(CW\*(C`GREATEST\*(C'\fR. In |
| 963 | the first row, the sizes (memory footprints) of buckets are powers |
| 964 | of two\*(--or possibly one page greater. In the second row, if present, |
| 965 | the memory footprints of the buckets are between the memory footprints |
| 966 | of two buckets \*(L"above\*(R". |
| 967 | .Sp |
| 968 | For example, suppose under the previous example, the memory footprints |
| 969 | were |
| 970 | .Sp |
| 971 | .Vb 2 |
| 972 | \& free: 8 16 32 64 128 256 512 1024 2048 4096 8192 |
| 973 | \& 4 12 24 48 80 |
| 974 | .Ve |
| 975 | .Sp |
| 976 | With non\-\f(CW\*(C`DEBUGGING\*(C'\fR perl, the buckets starting from \f(CW128\fR have |
| 977 | a 4\-byte overhead, and thus an 8192\-long bucket may take up to |
| 978 | 8188\-byte allocations. |
| 979 | .ie n .IP """Total sbrk(): SBRKed/SBRKs:CONTINUOUS""" 4 |
| 980 | .el .IP "\f(CWTotal sbrk(): SBRKed/SBRKs:CONTINUOUS\fR" 4 |
| 981 | .IX Item "Total sbrk(): SBRKed/SBRKs:CONTINUOUS" |
| 982 | The first two fields give the total amount of memory perl \fIsbrk\fR\|(2)ed |
| 983 | (ess\-broken? :\-) and number of \fIsbrk\fR\|(2)s used. The third number is |
| 984 | what perl thinks about continuity of returned chunks. So long as |
| 985 | this number is positive, \fImalloc()\fR will assume that it is probable |
| 986 | that \fIsbrk\fR\|(2) will provide continuous memory. |
| 987 | .Sp |
| 988 | Memory allocated by external libraries is not counted. |
| 989 | .ie n .IP """pad: 0""" 4 |
| 990 | .el .IP "\f(CWpad: 0\fR" 4 |
| 991 | .IX Item "pad: 0" |
| 992 | The amount of \fIsbrk\fR\|(2)ed memory needed to keep buckets aligned. |
| 993 | .ie n .IP """heads: 2192""" 4 |
| 994 | .el .IP "\f(CWheads: 2192\fR" 4 |
| 995 | .IX Item "heads: 2192" |
| 996 | Although memory overhead of bigger buckets is kept inside the bucket, for |
| 997 | smaller buckets, it is kept in separate areas. This field gives the |
| 998 | total size of these areas. |
| 999 | .ie n .IP """chain: 0""" 4 |
| 1000 | .el .IP "\f(CWchain: 0\fR" 4 |
| 1001 | .IX Item "chain: 0" |
| 1002 | \&\fImalloc()\fR may want to subdivide a bigger bucket into smaller buckets. |
| 1003 | If only a part of the deceased bucket is left unsubdivided, the rest |
| 1004 | is kept as an element of a linked list. This field gives the total |
| 1005 | size of these chunks. |
| 1006 | .ie n .IP """tail: 6144""" 4 |
| 1007 | .el .IP "\f(CWtail: 6144\fR" 4 |
| 1008 | .IX Item "tail: 6144" |
| 1009 | To minimize the number of \fIsbrk\fR\|(2)s, \fImalloc()\fR asks for more memory. This |
| 1010 | field gives the size of the yet unused part, which is \fIsbrk\fR\|(2)ed, but |
| 1011 | never touched. |
| 1012 | .Sh "Example of using \fB\-DL\fP switch" |
| 1013 | .IX Subsection "Example of using -DL switch" |
| 1014 | Below we show how to analyse memory usage by |
| 1015 | .PP |
| 1016 | .Vb 1 |
| 1017 | \& do 'lib/auto/POSIX/autosplit.ix'; |
| 1018 | .Ve |
| 1019 | .PP |
| 1020 | The file in question contains a header and 146 lines similar to |
| 1021 | .PP |
| 1022 | .Vb 1 |
| 1023 | \& sub getcwd; |
| 1024 | .Ve |
| 1025 | .PP |
| 1026 | \&\fB\s-1WARNING\s0\fR: The discussion below supposes 32\-bit architecture. In |
| 1027 | newer releases of Perl, memory usage of the constructs discussed |
| 1028 | here is greatly improved, but the story discussed below is a real-life |
| 1029 | story. This story is mercilessly terse, and assumes rather more than cursory |
| 1030 | knowledge of Perl internals. Type space to continue, `q' to quit. |
| 1031 | (Actually, you just want to skip to the next section.) |
| 1032 | .PP |
| 1033 | Here is the itemized list of Perl allocations performed during parsing |
| 1034 | of this file: |
| 1035 | .PP |
| 1036 | .Vb 11 |
| 1037 | \& !!! "after" at test.pl line 3. |
| 1038 | \& Id subtot 4 8 12 16 20 24 28 32 36 40 48 56 64 72 80 80+ |
| 1039 | \& 0 02 13752 . . . . 294 . . . . . . . . . . 4 |
| 1040 | \& 0 54 5545 . . 8 124 16 . . . 1 1 . . . . . 3 |
| 1041 | \& 5 05 32 . . . . . . . 1 . . . . . . . . |
| 1042 | \& 6 02 7152 . . . . . . . . . . 149 . . . . . |
| 1043 | \& 7 02 3600 . . . . . 150 . . . . . . . . . . |
| 1044 | \& 7 03 64 . -1 . 1 . . 2 . . . . . . . . . |
| 1045 | \& 7 04 7056 . . . . . . . . . . . . . . . 7 |
| 1046 | \& 7 17 38404 . . . . . . . 1 . . 442 149 . . 147 . |
| 1047 | \& 9 03 2078 17 249 32 . . . . 2 . . . . . . . . |
| 1048 | .Ve |
| 1049 | .PP |
| 1050 | To see this list, insert two \f(CW\*(C`warn('!...')\*(C'\fR statements around the call: |
| 1051 | .PP |
| 1052 | .Vb 3 |
| 1053 | \& warn('!'); |
| 1054 | \& do 'lib/auto/POSIX/autosplit.ix'; |
| 1055 | \& warn('!!! "after"'); |
| 1056 | .Ve |
| 1057 | .PP |
| 1058 | and run it with Perl's \fB\-DL\fR option. The first \fIwarn()\fR will print |
| 1059 | memory allocation info before parsing the file and will memorize |
| 1060 | the statistics at this point (we ignore what it prints). The second |
| 1061 | \&\fIwarn()\fR prints increments with respect to these memorized data. This |
| 1062 | is the printout shown above. |
| 1063 | .PP |
| 1064 | Different \fIId\fRs on the left correspond to different subsystems of |
| 1065 | the perl interpreter. They are just the first argument given to |
| 1066 | the perl memory allocation \s-1API\s0 named \fINew()\fR. To find what \f(CW\*(C`9 03\*(C'\fR |
| 1067 | means, just \fBgrep\fR the perl source for \f(CW903\fR. You'll find it in |
| 1068 | \&\fIutil.c\fR, function \fIsavepvn()\fR. (I know, you wonder why we told you |
| 1069 | to \fBgrep\fR and then gave away the answer. That's because grepping |
| 1070 | the source is good for the soul.) This function is used to store |
| 1071 | a copy of an existing chunk of memory. Using a C debugger, one can |
| 1072 | see that the function was called either directly from \fIgv_init()\fR or |
| 1073 | via \fIsv_magic()\fR, and that \fIgv_init()\fR is called from \fIgv_fetchpv()\fR\-\-which |
| 1074 | was itself called from \fInewSUB()\fR. Please stop to catch your breath now. |
| 1075 | .PP |
| 1076 | \&\fB\s-1NOTE\s0\fR: To reach this point in the debugger and skip the calls to |
| 1077 | \&\fIsavepvn()\fR during the compilation of the main program, you should |
| 1078 | set a C breakpoint |
| 1079 | in \fIPerl_warn()\fR, continue until this point is reached, and \fIthen\fR set |
| 1080 | a C breakpoint in \fIPerl_savepvn()\fR. Note that you may need to skip a |
| 1081 | handful of \fIPerl_savepvn()\fR calls that do not correspond to mass production |
| 1082 | of CVs (there are more \f(CW903\fR allocations than 146 similar lines of |
| 1083 | \&\fIlib/auto/POSIX/autosplit.ix\fR). Note also that \f(CW\*(C`Perl_\*(C'\fR prefixes are |
| 1084 | added by macroization code in perl header files to avoid conflicts |
| 1085 | with external libraries. |
| 1086 | .PP |
| 1087 | Anyway, we see that \f(CW903\fR ids correspond to creation of globs, twice |
| 1088 | per glob \- for glob name, and glob stringification magic. |
| 1089 | .PP |
| 1090 | Here are explanations for other \fIId\fRs above: |
| 1091 | .ie n .IP "717" 4 |
| 1092 | .el .IP "\f(CW717\fR" 4 |
| 1093 | .IX Item "717" |
| 1094 | Creates bigger \f(CW\*(C`XPV*\*(C'\fR structures. In the case above, it |
| 1095 | creates 3 \f(CW\*(C`AV\*(C'\fRs per subroutine, one for a list of lexical variable |
| 1096 | names, one for a scratchpad (which contains lexical variables and |
| 1097 | \&\f(CW\*(C`targets\*(C'\fR), and one for the array of scratchpads needed for |
| 1098 | recursion. |
| 1099 | .Sp |
| 1100 | It also creates a \f(CW\*(C`GV\*(C'\fR and a \f(CW\*(C`CV\*(C'\fR per subroutine, all called from |
| 1101 | \&\fIstart_subparse()\fR. |
| 1102 | .ie n .IP "002" 4 |
| 1103 | .el .IP "\f(CW002\fR" 4 |
| 1104 | .IX Item "002" |
| 1105 | Creates a C array corresponding to the \f(CW\*(C`AV\*(C'\fR of scratchpads and the |
| 1106 | scratchpad itself. The first fake entry of this scratchpad is |
| 1107 | created though the subroutine itself is not defined yet. |
| 1108 | .Sp |
| 1109 | It also creates C arrays to keep data for the stash. This is one \s-1HV\s0, |
| 1110 | but it grows; thus, there are 4 big allocations: the big chunks are not |
| 1111 | freed, but are kept as additional arenas for \f(CW\*(C`SV\*(C'\fR allocations. |
| 1112 | .ie n .IP "054" 4 |
| 1113 | .el .IP "\f(CW054\fR" 4 |
| 1114 | .IX Item "054" |
| 1115 | Creates a \f(CW\*(C`HEK\*(C'\fR for the name of the glob for the subroutine. This |
| 1116 | name is a key in a \fIstash\fR. |
| 1117 | .Sp |
| 1118 | Big allocations with this \fIId\fR correspond to allocations of new |
| 1119 | arenas to keep \f(CW\*(C`HE\*(C'\fR. |
| 1120 | .ie n .IP "602" 4 |
| 1121 | .el .IP "\f(CW602\fR" 4 |
| 1122 | .IX Item "602" |
| 1123 | Creates a \f(CW\*(C`GP\*(C'\fR for the glob for the subroutine. |
| 1124 | .ie n .IP "702" 4 |
| 1125 | .el .IP "\f(CW702\fR" 4 |
| 1126 | .IX Item "702" |
| 1127 | Creates the \f(CW\*(C`MAGIC\*(C'\fR for the glob for the subroutine. |
| 1128 | .ie n .IP "704" 4 |
| 1129 | .el .IP "\f(CW704\fR" 4 |
| 1130 | .IX Item "704" |
| 1131 | Creates \fIarenas\fR which keep SVs. |
| 1132 | .Sh "\fB\-DL\fP details" |
| 1133 | .IX Subsection "-DL details" |
| 1134 | If Perl is run with \fB\-DL\fR option, then \fIwarn()\fRs that start with `!' |
| 1135 | behave specially. They print a list of \fIcategories\fR of memory |
| 1136 | allocations, and statistics of allocations of different sizes for |
| 1137 | these categories. |
| 1138 | .PP |
| 1139 | If \fIwarn()\fR string starts with |
| 1140 | .ie n .IP """!!!""" 4 |
| 1141 | .el .IP "\f(CW!!!\fR" 4 |
| 1142 | .IX Item "!!!" |
| 1143 | print changed categories only, print the differences in counts of allocations. |
| 1144 | .ie n .IP """!!""" 4 |
| 1145 | .el .IP "\f(CW!!\fR" 4 |
| 1146 | .IX Item "!!" |
| 1147 | print grown categories only; print the absolute values of counts, and totals. |
| 1148 | .ie n .IP """!""" 4 |
| 1149 | .el .IP "\f(CW!\fR" 4 |
| 1150 | .IX Item "!" |
| 1151 | print nonempty categories, print the absolute values of counts and totals. |
| 1152 | .Sh "Limitations of \fB\-DL\fP statistics" |
| 1153 | .IX Subsection "Limitations of -DL statistics" |
| 1154 | If an extension or external library does not use the Perl \s-1API\s0 to |
| 1155 | allocate memory, such allocations are not counted. |
| 1156 | .SH "SEE ALSO" |
| 1157 | .IX Header "SEE ALSO" |
| 1158 | perldebug, |
| 1159 | perlguts, |
| 1160 | perlrun |
| 1161 | re, |
| 1162 | and |
| 1163 | Devel::DProf. |