From e077a8bde9a7e0d2954d5b422667b40ce3c14240 Mon Sep 17 00:00:00 2001
From: Mark Murray <markm@FreeBSD.org>
Date: Thu, 16 May 2002 10:09:28 +0000
Subject: Perl is no longer in base. Long live the port!
---
contrib/perl5/pod/perldebguts.pod | 925 --------------------------------------
1 file changed, 925 deletions(-)
delete mode 100644 contrib/perl5/pod/perldebguts.pod
(limited to 'contrib/perl5/pod/perldebguts.pod')
diff --git a/contrib/perl5/pod/perldebguts.pod b/contrib/perl5/pod/perldebguts.pod
deleted file mode 100644
index 20cc5460fd44..000000000000
--- a/contrib/perl5/pod/perldebguts.pod
+++ /dev/null
@@ -1,925 +0,0 @@
-=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 ranging
-between difficult and impossible for anyone who isn't incredibly
-intimate with Perl's guts to understand. 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 DB, the arguments that the corresponding stack
-frame was called with are copied to the @DB::args array. The
-general mechanisms is enabled by calling Perl with the B<-d> switch, 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 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 any of the variables
-$DB::trace, $DB::single, or $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 until this is done. For the standard
-debugger, the C<$DB::deep> variable (how many levels of recursion
-deep into the debugger you can go before a mandatory break) gives
-an example of such a dependency.
-
-=head2 Writing Your Own Debugger
-
-The minimal working debugger consists of one line
-
- sub DB::DB {}
-
-which is quite handy as contents of C<PERL5DB> environment
-variable:
-
- $ PERL5DB="sub DB::DB {}" perl -d your-script
-
-Another brief debugger, slightly more useful, could be created
-with only the line:
-
- sub DB::DB {print ++$i; scalar <STDIN>}
-
-This debugger would print the sequential number of encountered
-statement, and would wait for you to hit a newline before continuing.
-
-The following debugger is quite functional:
-
- {
- package DB;
- sub DB {}
- sub sub {print ++$i, " $sub\n"; &$sub}
- }
-
-It prints the sequential number of subroutine call and the name of the
-called subroutine. Note that C<&DB::sub> should be compiled into the
-package C<DB>.
-
-At the start, the debugger reads your rc file (F<./.perldb> or
-F<~/.perldb> under Unix), which can set important options. This file may
-define a subroutine C<&afterinit> to be executed after the debugger is
-initialized.
-
-After the rc file is read, the debugger reads the PERLDB_OPTS
-environment variable and parses this as the remainder of a C<O ...>
-line as one might enter at the debugger prompt.
-
-The debugger also maintains magical internal variables, such as
-C<@DB::dbline>, C<%DB::dbline>, which are aliases for
-C<@{"::_<current_file"}> C<%{"::_<current_file"}>. Here C<current_file>
-is the currently selected file, either explicitly chosen with the
-debugger's C<f> command, or implicitly by flow of execution.
-
-Some functions are provided to simplify customization. See
-L<perldebug/"Options"> for description of options parsed by
-C<DB::parse_options(string)>. The function 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>.
-
-The function 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.
-
-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 4
-
- 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 6
-
- 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 14
-
- 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 30
-
- 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 $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
- scalar context return from Exporter::import: ''
-
-=back
-
-In all cases shown above, the line indentation shows the call tree.
-If bit 2 of C<frame> is set, a line is printed on exit from a
-subroutine as well. If bit 4 is set, the arguments are printed
-along with the caller info. If bit 8 is set, the arguments are
-printed even if they are tied or references. If bit 16 is set, the
-return value is printed, too.
-
-When a package is compiled, a line like this
-
- Package lib/Carp.pm.
-
-is printed with proper indentation.
-
-=head1 Debugging regular expressions
-
-There are two ways to enable debugging output for regular expressions.
-
-If your perl is compiled with C<-DDEBUGGING>, you may use the
-B<-Dr> flag on the command line.
-
-Otherwise, one can C<use re 'debug'>, which has effects at
-compile time and run time. It is not lexically scoped.
-
-=head2 Compile-time output
-
-The debugging output at compile time looks like this:
-
- compiling RE `[bc]d(ef*g)+h[ij]k$'
- size 43 first at 1
- 1: ANYOF(11)
- 11: EXACT <d>(13)
- 13: CURLYX {1,32767}(27)
- 15: OPEN1(17)
- 17: EXACT <e>(19)
- 19: STAR(22)
- 20: EXACT <f>(0)
- 22: EXACT <g>(24)
- 24: CLOSE1(26)
- 26: WHILEM(0)
- 27: NOTHING(28)
- 28: EXACT <h>(30)
- 30: ANYOF(40)
- 40: EXACT <k>(42)
- 42: EOL(43)
- 43: END(0)
- anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating)
- stclass `ANYOF' minlen 7
-
-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 label I<id> of the first node that does a
-match.
-
-The last 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 the match cannot be
-shorter than 7 chars.
-
-The fields of interest which may appear in the last 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 info 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 info is used to avoid entering (a slow) regex
-engine on strings that will not definitely match. If 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.
-
-The rest of the output contains 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.
-
-=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.
-
-There are two Perl-specific ways to analyze memory usage:
-$ENV{PERL_DEBUG_MSTATS} and B<-DL> command-line switch. The first
-is available only if Perl is compiled with Perl's malloc(); the
-second only if Perl was built with C<-DDEBUGGING>. See the
-instructions for how to do this in the F<INSTALL> podpage at
-the top level of the Perl source tree.
-
-=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 a 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
-
-=head2 Example of using B<-DL> switch
-
-Below we show how to analyse memory usage by
-
- do 'lib/auto/POSIX/autosplit.ix';
-
-The file in question contains a header and 146 lines similar to
-
- sub getcwd;
-
-B<WARNING>: The discussion below supposes 32-bit architecture. In
-newer releases of Perl, memory usage of the constructs discussed
-here is greatly improved, but the story discussed below is a real-life
-story. This story is mercilessly terse, and assumes rather more than cursory
-knowledge of Perl internals. Type space to continue, `q' to quit.
-(Actually, you just want to skip to the next section.)
-
-Here is the itemized list of Perl allocations performed during parsing
-of this file:
-
- !!! "after" at test.pl line 3.
- Id subtot 4 8 12 16 20 24 28 32 36 40 48 56 64 72 80 80+
- 0 02 13752 . . . . 294 . . . . . . . . . . 4
- 0 54 5545 . . 8 124 16 . . . 1 1 . . . . . 3
- 5 05 32 . . . . . . . 1 . . . . . . . .
- 6 02 7152 . . . . . . . . . . 149 . . . . .
- 7 02 3600 . . . . . 150 . . . . . . . . . .
- 7 03 64 . -1 . 1 . . 2 . . . . . . . . .
- 7 04 7056 . . . . . . . . . . . . . . . 7
- 7 17 38404 . . . . . . . 1 . . 442 149 . . 147 .
- 9 03 2078 17 249 32 . . . . 2 . . . . . . . .
-
-
-To see this list, insert two C<warn('!...')> statements around the call:
-
- warn('!');
- do 'lib/auto/POSIX/autosplit.ix';
- warn('!!! "after"');
-
-and run it with Perl's B<-DL> option. The first warn() will print
-memory allocation info before parsing the file and will memorize
-the statistics at this point (we ignore what it prints). The second
-warn() prints increments with respect to these memorized data. This
-is the printout shown above.
-
-Different I<Id>s on the left correspond to different subsystems of
-the perl interpreter. They are just the first argument given to
-the perl memory allocation API named New(). To find what C<9 03>
-means, just B<grep> the perl source for C<903>. You'll find it in
-F<util.c>, function savepvn(). (I know, you wonder why we told you
-to B<grep> and then gave away the answer. That's because grepping
-the source is good for the soul.) This function is used to store
-a copy of an existing chunk of memory. Using a C debugger, one can
-see that the function was called either directly from gv_init() or
-via sv_magic(), and that gv_init() is called from gv_fetchpv()--which
-was itself called from newSUB(). Please stop to catch your breath now.
-
-B<NOTE>: To reach this point in the debugger and skip the calls to
-savepvn() during the compilation of the main program, you should
-set a C breakpoint
-in Perl_warn(), continue until this point is reached, and I<then> set
-a C breakpoint in Perl_savepvn(). Note that you may need to skip a
-handful of Perl_savepvn() calls that do not correspond to mass production
-of CVs (there are more C<903> allocations than 146 similar lines of
-F<lib/auto/POSIX/autosplit.ix>). Note also that C<Perl_> prefixes are
-added by macroization code in perl header files to avoid conflicts
-with external libraries.
-
-Anyway, we see that C<903> ids correspond to creation of globs, twice
-per glob - for glob name, and glob stringification magic.
-
-Here are explanations for other I<Id>s above:
-
-=over 4
-
-=item C<717>
-
-Creates bigger C<XPV*> structures. In the case above, it
-creates 3 C<AV>s per subroutine, one for a list of lexical variable
-names, one for a scratchpad (which contains lexical variables and
-C<targets>), and one for the array of scratchpads needed for
-recursion.
-
-It also creates a C<GV> and a C<CV> per subroutine, all called from
-start_subparse().
-
-=item C<002>
-
-Creates a C array corresponding to the C<AV> of scratchpads and the
-scratchpad itself. The first fake entry of this scratchpad is
-created though the subroutine itself is not defined yet.
-
-It also creates C arrays to keep data for the stash. This is one HV,
-but it grows; thus, there are 4 big allocations: the big chunks are not
-freed, but are kept as additional arenas for C<SV> allocations.
-
-=item C<054>
-
-Creates a C<HEK> for the name of the glob for the subroutine. This
-name is a key in a I<stash>.
-
-Big allocations with this I<Id> correspond to allocations of new
-arenas to keep C<HE>.
-
-=item C<602>
-
-Creates a C<GP> for the glob for the subroutine.
-
-=item C<702>
-
-Creates the C<MAGIC> for the glob for the subroutine.
-
-=item C<704>
-
-Creates I<arenas> which keep SVs.
-
-=back
-
-=head2 B<-DL> details
-
-If Perl is run with B<-DL> option, then warn()s that start with `!'
-behave specially. They print a list of I<categories> of memory
-allocations, and statistics of allocations of different sizes for
-these categories.
-
-If warn() string starts with
-
-=over 4
-
-=item C<!!!>
-
-print changed categories only, print the differences in counts of allocations.
-
-=item C<!!>
-
-print grown categories only; print the absolute values of counts, and totals.
-
-=item C<!>
-
-print nonempty categories, print the absolute values of counts and totals.
-
-=back
-
-=head2 Limitations of B<-DL> statistics
-
-If an extension or external library does not use the Perl API to
-allocate memory, such allocations are not counted.
-
-=head1 SEE ALSO
-
-L<perldebug>,
-L<perlguts>,
-L<perlrun>
-L<re>,
-and
-L<Devel::Dprof>.
--
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