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diff --git a/Master/tlpkg/tlperl/lib/pods/perldebguts.pod b/Master/tlpkg/tlperl/lib/pods/perldebguts.pod new file mode 100755 index 00000000000..55f237b7557 --- /dev/null +++ b/Master/tlpkg/tlperl/lib/pods/perldebguts.pod @@ -0,0 +1,878 @@ +=head1 NAME + +perldebguts - Guts of Perl debugging + +=head1 DESCRIPTION + +This is not the perldebug(1) manpage, which tells you how to use +the debugger. This manpage describes low-level details concerning +the debugger's internals, which range from difficult to impossible +to understand for anyone who isn't incredibly intimate with Perl's guts. +Caveat lector. + +=head1 Debugger Internals + +Perl has special debugging hooks at compile-time and run-time used +to create debugging environments. These hooks are not to be confused +with the I<perl -Dxxx> command described in L<perlrun>, which is +usable only if a special Perl is built per the instructions in the +F<INSTALL> podpage in the Perl source tree. + +For example, whenever you call Perl's built-in C<caller> function +from the package C<DB>, the arguments that the corresponding stack +frame was called with are copied to the C<@DB::args> array. These +mechanisms are enabled by calling Perl with the B<-d> switch. +Specifically, the following additional features are enabled +(cf. L<perlvar/$^P>): + +=over 4 + +=item * + +Perl inserts the contents of C<$ENV{PERL5DB}> (or C<BEGIN {require +'perl5db.pl'}> if not present) before the first line of your program. + +=item * + +Each array C<@{"_<$filename"}> holds the lines of $filename for a +file compiled by Perl. The same is also true for C<eval>ed strings +that contain subroutines, or which are currently being executed. +The $filename for C<eval>ed strings looks like C<(eval 34)>. +Code assertions in regexes look like C<(re_eval 19)>. + +Values in this array are magical in numeric context: they compare +equal to zero only if the line is not breakable. + +=item * + +Each hash C<%{"_<$filename"}> contains breakpoints and actions keyed +by line number. Individual entries (as opposed to the whole hash) +are settable. Perl only cares about Boolean true here, although +the values used by F<perl5db.pl> have the form +C<"$break_condition\0$action">. + +The same holds for evaluated strings that contain subroutines, or +which are currently being executed. The $filename for C<eval>ed strings +looks like C<(eval 34)> or C<(re_eval 19)>. + +=item * + +Each scalar C<${"_<$filename"}> contains C<"_<$filename">. This is +also the case for evaluated strings that contain subroutines, or +which are currently being executed. The $filename for C<eval>ed +strings looks like C<(eval 34)> or C<(re_eval 19)>. + +=item * + +After each C<require>d file is compiled, but before it is executed, +C<DB::postponed(*{"_<$filename"})> is called if the subroutine +C<DB::postponed> exists. Here, the $filename is the expanded name of +the C<require>d file, as found in the values of %INC. + +=item * + +After each subroutine C<subname> is compiled, the existence of +C<$DB::postponed{subname}> is checked. If this key exists, +C<DB::postponed(subname)> is called if the C<DB::postponed> subroutine +also exists. + +=item * + +A hash C<%DB::sub> is maintained, whose keys are subroutine names +and whose values have the form C<filename:startline-endline>. +C<filename> has the form C<(eval 34)> for subroutines defined inside +C<eval>s, or C<(re_eval 19)> for those within regex code assertions. + +=item * + +When the execution of your program reaches a point that can hold a +breakpoint, the C<DB::DB()> subroutine is called if any of the variables +C<$DB::trace>, C<$DB::single>, or C<$DB::signal> is true. These variables +are not C<local>izable. This feature is disabled when executing +inside C<DB::DB()>, including functions called from it +unless C<< $^D & (1<<30) >> is true. + +=item * + +When execution of the program reaches a subroutine call, a call to +C<&DB::sub>(I<args>) is made instead, with C<$DB::sub> holding the +name of the called subroutine. (This doesn't happen if the subroutine +was compiled in the C<DB> package.) + +=back + +Note that if C<&DB::sub> needs external data for it to work, no +subroutine call is possible without it. As an example, the standard +debugger's C<&DB::sub> depends on the C<$DB::deep> variable +(it defines how many levels of recursion deep into the debugger you can go +before a mandatory break). If C<$DB::deep> is not defined, subroutine +calls are not possible, even though C<&DB::sub> exists. + +=head2 Writing Your Own Debugger + +=head3 Environment Variables + +The C<PERL5DB> environment variable can be used to define a debugger. +For example, the minimal "working" debugger (it actually doesn't do anything) +consists of one line: + + sub DB::DB {} + +It can easily be defined like this: + + $ PERL5DB="sub DB::DB {}" perl -d your-script + +Another brief debugger, slightly more useful, can be created +with only the line: + + sub DB::DB {print ++$i; scalar <STDIN>} + +This debugger prints a number which increments for each statement +encountered and waits for you to hit a newline before continuing +to the next statement. + +The following debugger is actually useful: + + { + package DB; + sub DB {} + sub sub {print ++$i, " $sub\n"; &$sub} + } + +It prints the sequence number of each subroutine call and the name of the +called subroutine. Note that C<&DB::sub> is being compiled into the +package C<DB> through the use of the C<package> directive. + +When it starts, the debugger reads your rc file (F<./.perldb> or +F<~/.perldb> under Unix), which can set important options. +(A subroutine (C<&afterinit>) can be defined here as well; it is executed +after the debugger completes its own initialization.) + +After the rc file is read, the debugger reads the PERLDB_OPTS +environment variable and uses it to set debugger options. The +contents of this variable are treated as if they were the argument +of an C<o ...> debugger command (q.v. in L<perldebug/Options>). + +=head3 Debugger internal variables + +In addition to the file and subroutine-related variables mentioned above, +the debugger also maintains various magical internal variables. + +=over 4 + +=item * + +C<@DB::dbline> is an alias for C<@{"::_<current_file"}>, which +holds the lines of the currently-selected file (compiled by Perl), either +explicitly chosen with the debugger's C<f> command, or implicitly by flow +of execution. + +Values in this array are magical in numeric context: they compare +equal to zero only if the line is not breakable. + +=item * + +C<%DB::dbline>, is an alias for C<%{"::_<current_file"}>, which +contains breakpoints and actions keyed by line number in +the currently-selected file, either explicitly chosen with the +debugger's C<f> command, or implicitly by flow of execution. + +As previously noted, individual entries (as opposed to the whole hash) +are settable. Perl only cares about Boolean true here, although +the values used by F<perl5db.pl> have the form +C<"$break_condition\0$action">. + +=back + +=head3 Debugger customization functions + +Some functions are provided to simplify customization. + +=over 4 + +=item * + +See L<perldebug/"Configurable Options"> for a description of options parsed by +C<DB::parse_options(string)>. + +=item * + +C<DB::dump_trace(skip[,count])> skips the specified number of frames +and returns a list containing information about the calling frames (all +of them, if C<count> is missing). Each entry is reference to a hash +with keys C<context> (either C<.>, C<$>, or C<@>), C<sub> (subroutine +name, or info about C<eval>), C<args> (C<undef> or a reference to +an array), C<file>, and C<line>. + +=item * + +C<DB::print_trace(FH, skip[, count[, short]])> prints +formatted info about caller frames. The last two functions may be +convenient as arguments to C<< < >>, C<< << >> commands. + +=back + +Note that any variables and functions that are not documented in +this manpages (or in L<perldebug>) are considered for internal +use only, and as such are subject to change without notice. + +=head1 Frame Listing Output Examples + +The C<frame> option can be used to control the output of frame +information. For example, contrast this expression trace: + + $ perl -de 42 + Stack dump during die enabled outside of evals. + + Loading DB routines from perl5db.pl patch level 0.94 + Emacs support available. + + Enter h or `h h' for help. + + main::(-e:1): 0 + DB<1> sub foo { 14 } + + DB<2> sub bar { 3 } + + DB<3> t print foo() * bar() + main::((eval 172):3): print foo() + bar(); + main::foo((eval 168):2): + main::bar((eval 170):2): + 42 + +with this one, once the C<o>ption C<frame=2> has been set: + + DB<4> o f=2 + frame = '2' + DB<5> t print foo() * bar() + 3: foo() * bar() + entering main::foo + 2: sub foo { 14 }; + exited main::foo + entering main::bar + 2: sub bar { 3 }; + exited main::bar + 42 + +By way of demonstration, we present below a laborious listing +resulting from setting your C<PERLDB_OPTS> environment variable to +the value C<f=n N>, and running I<perl -d -V> from the command line. +Examples use various values of C<n> are shown to give you a feel +for the difference between settings. Long those it may be, this +is not a complete listing, but only excerpts. + +=over 4 + +=item 1 + + entering main::BEGIN + entering Config::BEGIN + Package lib/Exporter.pm. + Package lib/Carp.pm. + Package lib/Config.pm. + entering Config::TIEHASH + entering Exporter::import + entering Exporter::export + entering Config::myconfig + entering Config::FETCH + entering Config::FETCH + entering Config::FETCH + entering Config::FETCH + +=item 2 + + entering main::BEGIN + entering Config::BEGIN + Package lib/Exporter.pm. + Package lib/Carp.pm. + exited Config::BEGIN + Package lib/Config.pm. + entering Config::TIEHASH + exited Config::TIEHASH + entering Exporter::import + entering Exporter::export + exited Exporter::export + exited Exporter::import + exited main::BEGIN + entering Config::myconfig + entering Config::FETCH + exited Config::FETCH + entering Config::FETCH + exited Config::FETCH + entering Config::FETCH + +=item 3 + + in $=main::BEGIN() from /dev/null:0 + in $=Config::BEGIN() from lib/Config.pm:2 + Package lib/Exporter.pm. + Package lib/Carp.pm. + Package lib/Config.pm. + in $=Config::TIEHASH('Config') from lib/Config.pm:644 + in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 + in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li + in @=Config::myconfig() from /dev/null:0 + in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 + in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 + in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 + in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574 + in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574 + in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574 + +=item 4 + + in $=main::BEGIN() from /dev/null:0 + in $=Config::BEGIN() from lib/Config.pm:2 + Package lib/Exporter.pm. + Package lib/Carp.pm. + out $=Config::BEGIN() from lib/Config.pm:0 + Package lib/Config.pm. + in $=Config::TIEHASH('Config') from lib/Config.pm:644 + out $=Config::TIEHASH('Config') from lib/Config.pm:644 + in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 + in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/ + out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/ + out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 + out $=main::BEGIN() from /dev/null:0 + in @=Config::myconfig() from /dev/null:0 + in $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 + out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574 + in $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 + out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574 + in $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 + out $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574 + in $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574 + +=item 5 + + in $=main::BEGIN() from /dev/null:0 + in $=Config::BEGIN() from lib/Config.pm:2 + Package lib/Exporter.pm. + Package lib/Carp.pm. + out $=Config::BEGIN() from lib/Config.pm:0 + Package lib/Config.pm. + in $=Config::TIEHASH('Config') from lib/Config.pm:644 + out $=Config::TIEHASH('Config') from lib/Config.pm:644 + in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 + in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E + out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E + out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 + out $=main::BEGIN() from /dev/null:0 + in @=Config::myconfig() from /dev/null:0 + in $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574 + out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574 + in $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574 + out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574 + +=item 6 + + in $=CODE(0x15eca4)() from /dev/null:0 + in $=CODE(0x182528)() from lib/Config.pm:2 + Package lib/Exporter.pm. + out $=CODE(0x182528)() from lib/Config.pm:0 + scalar context return from CODE(0x182528): undef + Package lib/Config.pm. + in $=Config::TIEHASH('Config') from lib/Config.pm:628 + out $=Config::TIEHASH('Config') from lib/Config.pm:628 + scalar context return from Config::TIEHASH: empty hash + in $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 + in $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171 + out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171 + scalar context return from Exporter::export: '' + out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0 + scalar context return from Exporter::import: '' + +=back + +In all cases shown above, the line indentation shows the call tree. +If bit 2 of C<frame> is set, a line is printed on exit from a +subroutine as well. If bit 4 is set, the arguments are printed +along with the caller info. If bit 8 is set, the arguments are +printed even if they are tied or references. If bit 16 is set, the +return value is printed, too. + +When a package is compiled, a line like this + + Package lib/Carp.pm. + +is printed with proper indentation. + +=head1 Debugging regular expressions + +There are two ways to enable debugging output for regular expressions. + +If your perl is compiled with C<-DDEBUGGING>, you may use the +B<-Dr> flag on the command line. + +Otherwise, one can C<use re 'debug'>, which has effects at +compile time and run time. It is not lexically scoped. + +=head2 Compile-time output + +The debugging output at compile time looks like this: + + Compiling REx `[bc]d(ef*g)+h[ij]k$' + size 45 Got 364 bytes for offset annotations. + first at 1 + rarest char g at 0 + rarest char d at 0 + 1: ANYOF[bc](12) + 12: EXACT <d>(14) + 14: CURLYX[0] {1,32767}(28) + 16: OPEN1(18) + 18: EXACT <e>(20) + 20: STAR(23) + 21: EXACT <f>(0) + 23: EXACT <g>(25) + 25: CLOSE1(27) + 27: WHILEM[1/1](0) + 28: NOTHING(29) + 29: EXACT <h>(31) + 31: ANYOF[ij](42) + 42: EXACT <k>(44) + 44: EOL(45) + 45: END(0) + anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating) + stclass `ANYOF[bc]' minlen 7 + Offsets: [45] + 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1] + 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0] + 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0] + 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0] + Omitting $` $& $' support. + +The first line shows the pre-compiled form of the regex. The second +shows the size of the compiled form (in arbitrary units, usually +4-byte words) and the total number of bytes allocated for the +offset/length table, usually 4+C<size>*8. The next line shows the +label I<id> of the first node that does a match. + +The + + anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating) + stclass `ANYOF[bc]' minlen 7 + +line (split into two lines above) contains optimizer +information. In the example shown, the optimizer found that the match +should contain a substring C<de> at offset 1, plus substring C<gh> +at some offset between 3 and infinity. Moreover, when checking for +these substrings (to abandon impossible matches quickly), Perl will check +for the substring C<gh> before checking for the substring C<de>. The +optimizer may also use the knowledge that the match starts (at the +C<first> I<id>) with a character class, and no string +shorter than 7 characters can possibly match. + +The fields of interest which may appear in this line are + +=over 4 + +=item C<anchored> I<STRING> C<at> I<POS> + +=item C<floating> I<STRING> C<at> I<POS1..POS2> + +See above. + +=item C<matching floating/anchored> + +Which substring to check first. + +=item C<minlen> + +The minimal length of the match. + +=item C<stclass> I<TYPE> + +Type of first matching node. + +=item C<noscan> + +Don't scan for the found substrings. + +=item C<isall> + +Means that the optimizer information is all that the regular +expression contains, and thus one does not need to enter the regex engine at +all. + +=item C<GPOS> + +Set if the pattern contains C<\G>. + +=item C<plus> + +Set if the pattern starts with a repeated char (as in C<x+y>). + +=item C<implicit> + +Set if the pattern starts with C<.*>. + +=item C<with eval> + +Set if the pattern contain eval-groups, such as C<(?{ code })> and +C<(??{ code })>. + +=item C<anchored(TYPE)> + +If the pattern may match only at a handful of places, (with C<TYPE> +being C<BOL>, C<MBOL>, or C<GPOS>. See the table below. + +=back + +If a substring is known to match at end-of-line only, it may be +followed by C<$>, as in C<floating `k'$>. + +The optimizer-specific information is used to avoid entering (a slow) regex +engine on strings that will not definitely match. If the C<isall> flag +is set, a call to the regex engine may be avoided even when the optimizer +found an appropriate place for the match. + +Above the optimizer section is the list of I<nodes> of the compiled +form of the regex. Each line has format + +C< >I<id>: I<TYPE> I<OPTIONAL-INFO> (I<next-id>) + +=head2 Types of nodes + +Here are the possible types, with short descriptions: + + # TYPE arg-description [num-args] [longjump-len] DESCRIPTION + + # Exit points + END no End of program. + SUCCEED no Return from a subroutine, basically. + + # Anchors: + BOL no Match "" at beginning of line. + MBOL no Same, assuming multiline. + SBOL no Same, assuming singleline. + EOS no Match "" at end of string. + EOL no Match "" at end of line. + MEOL no Same, assuming multiline. + SEOL no Same, assuming singleline. + BOUND no Match "" at any word boundary + BOUNDL no Match "" at any word boundary + NBOUND no Match "" at any word non-boundary + NBOUNDL no Match "" at any word non-boundary + GPOS no Matches where last m//g left off. + + # [Special] alternatives + ANY no Match any one character (except newline). + SANY no Match any one character. + ANYOF sv Match character in (or not in) this class. + ALNUM no Match any alphanumeric character + ALNUML no Match any alphanumeric char in locale + NALNUM no Match any non-alphanumeric character + NALNUML no Match any non-alphanumeric char in locale + SPACE no Match any whitespace character + SPACEL no Match any whitespace char in locale + NSPACE no Match any non-whitespace character + NSPACEL no Match any non-whitespace char in locale + DIGIT no Match any numeric character + NDIGIT no Match any non-numeric character + + # BRANCH The set of branches constituting a single choice are hooked + # together with their "next" pointers, since precedence prevents + # anything being concatenated to any individual branch. The + # "next" pointer of the last BRANCH in a choice points to the + # thing following the whole choice. This is also where the + # final "next" pointer of each individual branch points; each + # branch starts with the operand node of a BRANCH node. + # + BRANCH node Match this alternative, or the next... + + # BACK Normal "next" pointers all implicitly point forward; BACK + # exists to make loop structures possible. + # not used + BACK no Match "", "next" ptr points backward. + + # Literals + EXACT sv Match this string (preceded by length). + EXACTF sv Match this string, folded (prec. by length). + EXACTFL sv Match this string, folded in locale (w/len). + + # Do nothing + NOTHING no Match empty string. + # A variant of above which delimits a group, thus stops optimizations + TAIL no Match empty string. Can jump here from outside. + + # STAR,PLUS '?', and complex '*' and '+', are implemented as circular + # BRANCH structures using BACK. Simple cases (one character + # per match) are implemented with STAR and PLUS for speed + # and to minimize recursive plunges. + # + STAR node Match this (simple) thing 0 or more times. + PLUS node Match this (simple) thing 1 or more times. + + CURLY sv 2 Match this simple thing {n,m} times. + CURLYN no 2 Match next-after-this simple thing + # {n,m} times, set parens. + CURLYM no 2 Match this medium-complex thing {n,m} times. + CURLYX sv 2 Match this complex thing {n,m} times. + + # This terminator creates a loop structure for CURLYX + WHILEM no Do curly processing and see if rest matches. + + # OPEN,CLOSE,GROUPP ...are numbered at compile time. + OPEN num 1 Mark this point in input as start of #n. + CLOSE num 1 Analogous to OPEN. + + REF num 1 Match some already matched string + REFF num 1 Match already matched string, folded + REFFL num 1 Match already matched string, folded in loc. + + # grouping assertions + IFMATCH off 1 2 Succeeds if the following matches. + UNLESSM off 1 2 Fails if the following matches. + SUSPEND off 1 1 "Independent" sub-regex. + IFTHEN off 1 1 Switch, should be preceded by switcher . + GROUPP num 1 Whether the group matched. + + # Support for long regex + LONGJMP off 1 1 Jump far away. + BRANCHJ off 1 1 BRANCH with long offset. + + # The heavy worker + EVAL evl 1 Execute some Perl code. + + # Modifiers + MINMOD no Next operator is not greedy. + LOGICAL no Next opcode should set the flag only. + + # This is not used yet + RENUM off 1 1 Group with independently numbered parens. + + # This is not really a node, but an optimized away piece of a "long" node. + # To simplify debugging output, we mark it as if it were a node + OPTIMIZED off Placeholder for dump. + +=for unprinted-credits +Next section M-J. Dominus (mjd-perl-patch+@plover.com) 20010421 + +Following the optimizer information is a dump of the offset/length +table, here split across several lines: + + Offsets: [45] + 1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1] + 0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0] + 11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0] + 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0] + +The first line here indicates that the offset/length table contains 45 +entries. Each entry is a pair of integers, denoted by C<offset[length]>. +Entries are numbered starting with 1, so entry #1 here is C<1[4]> and +entry #12 is C<5[1]>. C<1[4]> indicates that the node labeled C<1:> +(the C<1: ANYOF[bc]>) begins at character position 1 in the +pre-compiled form of the regex, and has a length of 4 characters. +C<5[1]> in position 12 +indicates that the node labeled C<12:> +(the C<< 12: EXACT <d> >>) begins at character position 5 in the +pre-compiled form of the regex, and has a length of 1 character. +C<12[1]> in position 14 +indicates that the node labeled C<14:> +(the C<< 14: CURLYX[0] {1,32767} >>) begins at character position 12 in the +pre-compiled form of the regex, and has a length of 1 character---that +is, it corresponds to the C<+> symbol in the precompiled regex. + +C<0[0]> items indicate that there is no corresponding node. + +=head2 Run-time output + +First of all, when doing a match, one may get no run-time output even +if debugging is enabled. This means that the regex engine was never +entered and that all of the job was therefore done by the optimizer. + +If the regex engine was entered, the output may look like this: + + Matching `[bc]d(ef*g)+h[ij]k$' against `abcdefg__gh__' + Setting an EVAL scope, savestack=3 + 2 <ab> <cdefg__gh_> | 1: ANYOF + 3 <abc> <defg__gh_> | 11: EXACT <d> + 4 <abcd> <efg__gh_> | 13: CURLYX {1,32767} + 4 <abcd> <efg__gh_> | 26: WHILEM + 0 out of 1..32767 cc=effff31c + 4 <abcd> <efg__gh_> | 15: OPEN1 + 4 <abcd> <efg__gh_> | 17: EXACT <e> + 5 <abcde> <fg__gh_> | 19: STAR + EXACT <f> can match 1 times out of 32767... + Setting an EVAL scope, savestack=3 + 6 <bcdef> <g__gh__> | 22: EXACT <g> + 7 <bcdefg> <__gh__> | 24: CLOSE1 + 7 <bcdefg> <__gh__> | 26: WHILEM + 1 out of 1..32767 cc=effff31c + Setting an EVAL scope, savestack=12 + 7 <bcdefg> <__gh__> | 15: OPEN1 + 7 <bcdefg> <__gh__> | 17: EXACT <e> + restoring \1 to 4(4)..7 + failed, try continuation... + 7 <bcdefg> <__gh__> | 27: NOTHING + 7 <bcdefg> <__gh__> | 28: EXACT <h> + failed... + failed... + +The most significant information in the output is about the particular I<node> +of the compiled regex that is currently being tested against the target string. +The format of these lines is + +C< >I<STRING-OFFSET> <I<PRE-STRING>> <I<POST-STRING>> |I<ID>: I<TYPE> + +The I<TYPE> info is indented with respect to the backtracking level. +Other incidental information appears interspersed within. + +=head1 Debugging Perl memory usage + +Perl is a profligate wastrel when it comes to memory use. There +is a saying that to estimate memory usage of Perl, assume a reasonable +algorithm for memory allocation, multiply that estimate by 10, and +while you still may miss the mark, at least you won't be quite so +astonished. This is not absolutely true, but may provide a good +grasp of what happens. + +Assume that an integer cannot take less than 20 bytes of memory, a +float cannot take less than 24 bytes, a string cannot take less +than 32 bytes (all these examples assume 32-bit architectures, the +result are quite a bit worse on 64-bit architectures). If a variable +is accessed in two of three different ways (which require an integer, +a float, or a string), the memory footprint may increase yet another +20 bytes. A sloppy malloc(3) implementation can inflate these +numbers dramatically. + +On the opposite end of the scale, a declaration like + + sub foo; + +may take up to 500 bytes of memory, depending on which release of Perl +you're running. + +Anecdotal estimates of source-to-compiled code bloat suggest an +eightfold increase. This means that the compiled form of reasonable +(normally commented, properly indented etc.) code will take +about eight times more space in memory than the code took +on disk. + +The B<-DL> command-line switch is obsolete since circa Perl 5.6.0 +(it was available only if Perl was built with C<-DDEBUGGING>). +The switch was used to track Perl's memory allocations and possible +memory leaks. These days the use of malloc debugging tools like +F<Purify> or F<valgrind> is suggested instead. See also +L<perlhack/PERL_MEM_LOG>. + +One way to find out how much memory is being used by Perl data +structures is to install the Devel::Size module from CPAN: it gives +you the minimum number of bytes required to store a particular data +structure. Please be mindful of the difference between the size() +and total_size(). + +If Perl has been compiled using Perl's malloc you can analyze Perl +memory usage by setting the $ENV{PERL_DEBUG_MSTATS}. + +=head2 Using C<$ENV{PERL_DEBUG_MSTATS}> + +If your perl is using Perl's malloc() and was compiled with the +necessary switches (this is the default), then it will print memory +usage statistics after compiling your code when C<< $ENV{PERL_DEBUG_MSTATS} +> 1 >>, and before termination of the program when C<< +$ENV{PERL_DEBUG_MSTATS} >= 1 >>. The report format is similar to +the following example: + + $ PERL_DEBUG_MSTATS=2 perl -e "require Carp" + Memory allocation statistics after compilation: (buckets 4(4)..8188(8192) + 14216 free: 130 117 28 7 9 0 2 2 1 0 0 + 437 61 36 0 5 + 60924 used: 125 137 161 55 7 8 6 16 2 0 1 + 74 109 304 84 20 + Total sbrk(): 77824/21:119. Odd ends: pad+heads+chain+tail: 0+636+0+2048. + Memory allocation statistics after execution: (buckets 4(4)..8188(8192) + 30888 free: 245 78 85 13 6 2 1 3 2 0 1 + 315 162 39 42 11 + 175816 used: 265 176 1112 111 26 22 11 27 2 1 1 + 196 178 1066 798 39 + Total sbrk(): 215040/47:145. Odd ends: pad+heads+chain+tail: 0+2192+0+6144. + +It is possible to ask for such a statistic at arbitrary points in +your execution using the mstat() function out of the standard +Devel::Peek module. + +Here is some explanation of that format: + +=over 4 + +=item C<buckets SMALLEST(APPROX)..GREATEST(APPROX)> + +Perl's malloc() uses bucketed allocations. Every request is rounded +up to the closest bucket size available, and a bucket is taken from +the pool of buckets of that size. + +The line above describes the limits of buckets currently in use. +Each bucket has two sizes: memory footprint and the maximal size +of user data that can fit into this bucket. Suppose in the above +example that the smallest bucket were size 4. The biggest bucket +would have usable size 8188, and the memory footprint would be 8192. + +In a Perl built for debugging, some buckets may have negative usable +size. This means that these buckets cannot (and will not) be used. +For larger buckets, the memory footprint may be one page greater +than a power of 2. If so, case the corresponding power of two is +printed in the C<APPROX> field above. + +=item Free/Used + +The 1 or 2 rows of numbers following that correspond to the number +of buckets of each size between C<SMALLEST> and C<GREATEST>. In +the first row, the sizes (memory footprints) of buckets are powers +of two--or possibly one page greater. In the second row, if present, +the memory footprints of the buckets are between the memory footprints +of two buckets "above". + +For example, suppose under the previous example, the memory footprints +were + + free: 8 16 32 64 128 256 512 1024 2048 4096 8192 + 4 12 24 48 80 + +With non-C<DEBUGGING> perl, the buckets starting from C<128> have +a 4-byte overhead, and thus an 8192-long bucket may take up to +8188-byte allocations. + +=item C<Total sbrk(): SBRKed/SBRKs:CONTINUOUS> + +The first two fields give the total amount of memory perl sbrk(2)ed +(ess-broken? :-) and number of sbrk(2)s used. The third number is +what perl thinks about continuity of returned chunks. So long as +this number is positive, malloc() will assume that it is probable +that sbrk(2) will provide continuous memory. + +Memory allocated by external libraries is not counted. + +=item C<pad: 0> + +The amount of sbrk(2)ed memory needed to keep buckets aligned. + +=item C<heads: 2192> + +Although memory overhead of bigger buckets is kept inside the bucket, for +smaller buckets, it is kept in separate areas. This field gives the +total size of these areas. + +=item C<chain: 0> + +malloc() may want to subdivide a bigger bucket into smaller buckets. +If only a part of the deceased bucket is left unsubdivided, the rest +is kept as an element of a linked list. This field gives the total +size of these chunks. + +=item C<tail: 6144> + +To minimize the number of sbrk(2)s, malloc() asks for more memory. This +field gives the size of the yet unused part, which is sbrk(2)ed, but +never touched. + +=back + +=head1 SEE ALSO + +L<perldebug>, +L<perlguts>, +L<perlrun> +L<re>, +and +L<Devel::DProf>. |