(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.
+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
=back
-=head2 Example of using B<-DL> switch
-
-(Note that -DL is obsolete since circa 5.6.0, and even before that
-Perl needed to be compiled with -DDEBUGGING.)
-
-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>,
projects / p5sagit/p5-mst-13.2.git / commitdiff