=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.
+This is not L<perldebug>, 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
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/$^P>):
+from the package C<DB>, the arguments that the corresponding stack
+frame was called with are copied to the C<@DB::args> array. These
+mechanisms are enabled by calling Perl with the B<-d> switch.
+Specifically, the following additional features are enabled
+(cf. L<perlvar/$^P>):
=over 4
=item *
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)>.
+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)>.
Values in this array are magical in numeric context: they compare
equal to zero only if the line is not breakable.
The same holds for evaluated strings that contain subroutines, or
which are currently being executed. The $filename for C<eval>ed strings
-looks like C<(eval 34)> or C<(re_eval 19)>.
+looks like C<(eval 34)>.
=item *
Each scalar C<${"_<$filename"}> contains C<"_<$filename">. This is
also the case for evaluated strings that contain subroutines, or
which are currently being executed. The $filename for C<eval>ed
-strings looks like C<(eval 34)> or C<(re_eval 19)>.
+strings looks like C<(eval 34)>.
=item *
A hash C<%DB::sub> is maintained, whose keys are subroutine names
and whose values have the form C<filename:startline-endline>.
C<filename> has the form C<(eval 34)> for subroutines defined inside
-C<eval>s, or C<(re_eval 19)> for those within regex code assertions.
+C<eval>s.
=item *
When the execution of your program reaches a point that can hold a
-breakpoint, the C<DB::DB()> subroutine is called any of the variables
-$DB::trace, $DB::single, or $DB::signal is true. These variables
+breakpoint, the C<DB::DB()> subroutine is called if any of the variables
+C<$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<< $^D & (1<<30) >> is true.
When execution of the program reaches a subroutine call, a call to
C<&DB::sub>(I<args>) is made instead, with C<$DB::sub> holding the
-name of the called subroutine. This doesn't happen if the subroutine
+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<$DB::deep> variable (how many levels of recursion
-deep into the debugger you can go before a mandatory break) gives
-an example of such a dependency.
+subroutine call is possible without it. As an example, the standard
+debugger's C<&DB::sub> depends on the C<$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
-The minimal working debugger consists of one line
+=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 {}
-which is quite handy as contents of C<PERL5DB> environment
-variable:
+It can easily be defined like this:
$ PERL5DB="sub DB::DB {}" perl -d your-script
-Another brief debugger, slightly more useful, could be created
+Another brief debugger, slightly more useful, can be created
with only the line:
sub DB::DB {print ++$i; scalar <STDIN>}
-This debugger would print the sequential number of encountered
-statement, and would wait for you to hit a newline before continuing.
+This debugger prints a number which increments for each statement
+encountered and waits for you to hit a newline before continuing
+to the next statement.
-The following debugger is quite functional:
+The following debugger is actually useful:
{
package DB;
sub sub {print ++$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>.
+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.
-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.
+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 parses this as the remainder of a C<O ...>
-line as one might enter at the debugger prompt.
+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/"Configurable 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.
-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
+=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.
-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<$>, or C<@>), C<sub> (subroutine
+As previously noted, individual entries (as opposed to the whole hash)
+are settable. Perl only cares about Boolean true here, although
+the values used by F<perl5db.pl> have the form
+C<"$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>.
-The function C<DB::print_trace(FH, skip[, count[, short]])> prints
+=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.
Loading DB routines from perl5db.pl patch level 0.94
Emacs support available.
- Enter h or `h h' for help.
+ Enter h or 'h h' for help.
main::(-e:1): 0
DB<1> sub foo { 14 }
main::bar((eval 170):2):
42
-with this one, once the C<O>ption C<frame=2> has been set:
+with this one, once the C<o>ption C<frame=2> has been set:
- DB<4> O f=2
+ DB<4> o f=2
frame = '2'
DB<5> t print foo() * bar()
3: foo() * bar()
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
+Examples using various values of C<n> are shown to give you a feel
+for the difference between settings. Long though it may be, this
is not a complete listing, but only excerpts.
=over 4
exited Config::FETCH
entering Config::FETCH
-=item 4
+=item 3
in $=main::BEGIN() from /dev/null:0
in $=Config::BEGIN() from lib/Config.pm:2
in $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574
in $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574
-=item 6
+=item 4
in $=main::BEGIN() from /dev/null:0
in $=Config::BEGIN() from lib/Config.pm:2
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
+=item 5
in $=main::BEGIN() from /dev/null:0
in $=Config::BEGIN() from lib/Config.pm:2
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
+=item 6
in $=CODE(0x15eca4)() from /dev/null:0
in $=CODE(0x182528)() from lib/Config.pm:2
is printed with proper indentation.
-=head1 Debugging regular expressions
+=head1 Debugging Regular Expressions
There are two ways to enable debugging output for regular expressions.
B<-Dr> flag on the command line.
Otherwise, one can C<use re 'debug'>, which has effects at
-compile time and run time. It is not lexically scoped.
+compile time and run time. Since Perl 5.9.5, this pragma is lexically
+scoped.
-=head2 Compile-time output
+=head2 Compile-time Output
The debugging output at compile time looks like this:
- Compiling REx `[bc]d(ef*g)+h[ij]k$'
+ Compiling REx '[bc]d(ef*g)+h[ij]k$'
size 45 Got 364 bytes for offset annotations.
first at 1
rarest char g at 0
42: EXACT <k>(44)
44: EOL(45)
45: END(0)
- anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating)
- stclass `ANYOF[bc]' minlen 7
+ anchored 'de' at 1 floating 'gh' at 3..2147483647 (checking floating)
+ stclass 'ANYOF[bc]' minlen 7
Offsets: [45]
1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1]
0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0]
The
- anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating)
- stclass `ANYOF[bc]' minlen 7
+ anchored 'de' at 1 floating 'gh' at 3..2147483647 (checking floating)
+ stclass 'ANYOF[bc]' minlen 7
line (split into two lines above) contains optimizer
information. In the example shown, the optimizer found that the match
=item C<anchored(TYPE)>
-If the pattern may match only at a handful of places, (with C<TYPE>
+If the pattern may match only at a handful of places, with C<TYPE>
being C<BOL>, C<MBOL>, or C<GPOS>. See the table below.
=back
If a substring is known to match at end-of-line only, it may be
-followed by C<$>, as in C<floating `k'$>.
+followed by C<$>, 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
C< >I<id>: I<TYPE> I<OPTIONAL-INFO> (I<next-id>)
-=head2 Types of nodes
+=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 comment
+This table is generated by regen/regcomp.pl. Any changes made here
+will be lost.
+
+=for regcomp.pl begin
+
+ # 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 using
+ native charset semantics for non-utf8
+ BOUNDL no Match "" at any locale word boundary
+ BOUNDU no Match "" at any word boundary using
+ Unicode semantics
+ BOUNDA no Match "" at any word boundary using ASCII
+ semantics
+ NBOUND no Match "" at any word non-boundary using
+ native charset semantics for non-utf8
+ NBOUNDL no Match "" at any locale word non-boundary
+ NBOUNDU no Match "" at any word non-boundary using
+ Unicode semantics
+ NBOUNDA no Match "" at any word non-boundary using
+ ASCII semantics
+ GPOS no Matches where last m//g left off.
+
+ # [Special] alternatives:
+
+ REG_ANY no Match any one character (except newline).
+ SANY no Match any one character.
+ CANY no Match any one byte.
+ ANYOF sv Match character in (or not in) this
+ class, single char match only
+ ANYOF_WARN_SUPER sv Match character in (or not in) this
+ class, warn (if enabled) upon matching a
+ char above Unicode max;
+ ANYOF_SYNTHETIC sv Synthetic start class
+
+ POSIXD none Some [[:class:]] under /d; the FLAGS
+ field gives which one
+ POSIXL none Some [[:class:]] under /l; the FLAGS
+ field gives which one
+ POSIXU none Some [[:class:]] under /u; the FLAGS
+ field gives which one
+ POSIXA none Some [[:class:]] under /a; the FLAGS
+ field gives which one
+ NPOSIXD none complement of POSIXD, [[:^class:]]
+ NPOSIXL none complement of POSIXL, [[:^class:]]
+ NPOSIXU none complement of POSIXU, [[:^class:]]
+ NPOSIXA none complement of POSIXA, [[:^class:]]
+
+ CLUMP no Match any extended grapheme cluster
+ sequence
+
+ # Alternation
+
+ # 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 pointer
+
+ # 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 str Match this string (preceded by length).
+ EXACTF str Match this non-UTF-8 string (not
+ guaranteed to be folded) using /id rules
+ (w/len).
+ EXACTFL str Match this string (not guaranteed to be
+ folded) using /il rules (w/len).
+ EXACTFU str Match this string (folded iff in UTF-8,
+ length in folding doesn't change if not
+ in UTF-8) using /iu rules (w/len).
+ EXACTFA str Match this string (not guaranteed to be
+ folded) using /iaa rules (w/len).
+ EXACTFU_SS str Match this string (folded iff in UTF-8,
+ length in folding may change even if not
+ in UTF-8) using /iu rules (w/len).
+ EXACTFU_TRICKYFOLD str Match this folded UTF-8 string using /iu
+ rules
+
+ # Do nothing types
+
+ 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.
+
+ # Loops
+
+ # 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 Capture next-after-this simple thing
+ CURLYM no 2 Capture 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.
+
+ # Buffer related
+
+ # 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
+ using native charset semantics for non-
+ utf8
+ REFFL num 1 Match already matched string, folded in
+ loc.
+ REFFU num 1 Match already matched string, folded
+ using unicode semantics for non-utf8
+ REFFA num 1 Match already matched string, folded
+ using unicode semantics for non-utf8, no
+ mixing ASCII, non-ASCII
+
+ # Named references. Code in regcomp.c assumes that these all are after
+ # the numbered references
+ NREF no-sv 1 Match some already matched string
+ NREFF no-sv 1 Match already matched string, folded
+ using native charset semantics for non-
+ utf8
+ NREFFL no-sv 1 Match already matched string, folded in
+ loc.
+ NREFFU num 1 Match already matched string, folded
+ using unicode semantics for non-utf8
+ NREFFA num 1 Match already matched string, folded
+ using unicode semantics for non-utf8, no
+ mixing ASCII, non-ASCII
+
+ IFMATCH off 1 2 Succeeds if the following matches.
+ UNLESSM off 1 2 Fails if the following matches.
+ SUSPEND off 1 1 "Independent" sub-RE.
+ IFTHEN off 1 1 Switch, should be preceded by switcher.
+ GROUPP num 1 Whether the group matched.
+
+ # Support for long RE
+
+ 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.
+
+ # Trie Related
+
+ # Behave the same as A|LIST|OF|WORDS would. The '..C' variants
+ # have inline charclass data (ascii only), the 'C' store it in the
+ # structure.
+
+ TRIE trie 1 Match many EXACT(F[ALU]?)? at once.
+ flags==type
+ TRIEC trie Same as TRIE, but with embedded charclass
+ charclass data
+
+ AHOCORASICK trie 1 Aho Corasick stclass. flags==type
+ AHOCORASICKC trie Same as AHOCORASICK, but with embedded
+ charclass charclass data
+
+ # Regex Subroutines
+ GOSUB num/ofs 2L recurse to paren arg1 at (signed) ofs
+ arg2
+ GOSTART no recurse to start of pattern
+
+ # Special conditionals
+ NGROUPP no-sv 1 Whether the group matched.
+ INSUBP num 1 Whether we are in a specific recurse.
+ DEFINEP none 1 Never execute directly.
+
+ # Backtracking Verbs
+ ENDLIKE none Used only for the type field of verbs
+ OPFAIL none Same as (?!)
+ ACCEPT parno 1 Accepts the current matched string.
+
+ # Verbs With Arguments
+ VERB no-sv 1 Used only for the type field of verbs
+ PRUNE no-sv 1 Pattern fails at this startpoint if no-
+ backtracking through this
+ MARKPOINT no-sv 1 Push the current location for rollback by
+ cut.
+ SKIP no-sv 1 On failure skip forward (to the mark)
+ before retrying
+ COMMIT no-sv 1 Pattern fails outright if backtracking
+ through this
+ CUTGROUP no-sv 1 On failure go to the next alternation in
+ the group
+
+ # Control what to keep in $&.
+ KEEPS no $& begins here.
+
+ # New charclass like patterns
+ LNBREAK none generic newline pattern
+
+ # SPECIAL REGOPS
+
+ # This is not really a node, but an optimized away piece of a "long"
+ # node. To simplify debugging output, we mark it as if it were a node
+ OPTIMIZED off Placeholder for dump.
+
+ # Special opcode with the property that no opcode in a compiled program
+ # will ever be of this type. Thus it can be used as a flag value that
+ # no other opcode has been seen. END is used similarly, in that an END
+ # node cant be optimized. So END implies "unoptimizable" and PSEUDO
+ # mean "not seen anything to optimize yet".
+ PSEUDO off Pseudo opcode for internal use.
+
+=for regcomp.pl end
=for unprinted-credits
Next section M-J. Dominus (mjd-perl-patch+@plover.com) 20010421
C<0[0]> items indicate that there is no corresponding node.
-=head2 Run-time output
+=head2 Run-time Output
First of all, when doing a match, one may get no run-time output even
if debugging is enabled. This means that the regex engine was never
If the regex engine was entered, the output may look like this:
- Matching `[bc]d(ef*g)+h[ij]k$' against `abcdefg__gh__'
+ Matching '[bc]d(ef*g)+h[ij]k$' against 'abcdefg__gh__'
Setting an EVAL scope, savestack=3
2 <ab> <cdefg__gh_> | 1: ANYOF
3 <abc> <defg__gh_> | 11: EXACT <d>
The I<TYPE> info is indented with respect to the backtracking level.
Other incidental information appears interspersed within.
-=head1 Debugging Perl memory usage
+=head1 Debugging Perl Memory Usage
Perl is a profligate wastrel when it comes to memory use. There
is a saying that to estimate memory usage of Perl, assume a reasonable
about eight times more space in memory than the code took
on disk.
-There are two Perl-specific ways to analyze memory usage:
-$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.
+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<perlhacktips/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 $ENV{PERL_DEBUG_MSTATS}.
=head2 Using C<$ENV{PERL_DEBUG_MSTATS}>
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
+than a power of 2. If so, the corresponding power of two is
printed in the C<APPROX> field above.
=item Free/Used
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
+With a 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>
=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<perlrun>
L<re>,
and
-L<Devel::Dprof>.
+L<Devel::DProf>.
https://perl5.git.perl.org / perl5.git / blobdiff