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Deparse inlined constants.
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1=head1 NAME
2
3perltodo - Perl TO-DO List
4
5=head1 DESCRIPTION
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7This is a list of wishes for Perl. The tasks we think are smaller or
8easier are listed first. Anyone is welcome to work on any of these,
9but it's a good idea to first contact I<perl5-porters@perl.org> to
10avoid duplication of effort, and to learn from any previous attempts.
11By all means contact a pumpking privately first if you prefer.
e50bb9a1 12
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13Whilst patches to make the list shorter are most welcome, ideas to add to
14the list are also encouraged. Check the perl5-porters archives for past
15ideas, and any discussion about them. One set of archives may be found at:
e50bb9a1 16
0bdfc961 17 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
938c8732 18
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19What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
20not, but if your patch is incorporated, then we'll add your name to the
21F<AUTHORS> file, which ships in the official distribution. How many other
22programming languages offer you 1 line of immortality?
938c8732 23
0bdfc961 24=head1 Tasks that only need Perl knowledge
e50bb9a1 25
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26=head2 Smartmatch design issues
27
28In 5.10.0 the smartmatch operator C<~~> isn't working quite "right". But
29before we can fix the implementation, we need to define what "right" is.
30The first problem is that Robin Houston implemented the Perl 6 smart match
31spec as of February 2006, when smart match was axiomatically symmetrical:
32L<http://groups.google.com/group/perl.perl6.language/msg/bf2b486f089ad021>
33
34Since then the Perl 6 target moved, but the Perl 5 implementation did not.
35
36So it would be useful for someone to compare the Perl 6 smartmatch table
37as of February 2006 L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=markup&pathrev=7615>
38and the current table L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?revision=14556&view=markup>
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39and tabulate the differences in Perl 6. The annotated view of changes is
40L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=annotate> and the diff is
162f8c67 41C<svn diff -r7615:14556 http://svn.perl.org/perl6/doc/trunk/design/syn/S03.pod>
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42-- search for C<=head1 Smart matching>. (In theory F<viewvc> can generate that,
43but in practice when I tried it hung forever, I assume "thinking")
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44
45With that done and published, someone (else) can then map any changed Perl 6
46semantics back to Perl 5, based on how the existing semantics map to Perl 5:
47L<http://search.cpan.org/~rgarcia/perl-5.10.0/pod/perlsyn.pod#Smart_matching_in_detail>
48
49
50There are also some questions that need answering:
51
52=over 4
53
54=item *
55
56How do you negate one? (documentation issue)
57http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-01/msg00071.html
58
59=item *
60
61Array behaviors
62http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00799.html
63
64* Should smart matches be symmetrical? (Perl 6 says no)
65
66* Other differences between Perl 5 and Perl 6 smart match?
67
68=item *
69
70Objects and smart match
71http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00865.html
72
73=back
74
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75=head2 Remove duplication of test setup.
76
77Schwern notes, that there's duplication of code - lots and lots of tests have
78some variation on the big block of C<$Is_Foo> checks. We can safely put this
79into a file, change it to build an C<%Is> hash and require it. Maybe just put
80it into F<test.pl>. Throw in the handy tainting subroutines.
81
87a942b1 82=head2 POD -E<gt> HTML conversion in the core still sucks
e50bb9a1 83
938c8732 84Which is crazy given just how simple POD purports to be, and how simple HTML
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85can be. It's not actually I<as> simple as it sounds, particularly with the
86flexibility POD allows for C<=item>, but it would be good to improve the
87visual appeal of the HTML generated, and to avoid it having any validation
88errors. See also L</make HTML install work>, as the layout of installation tree
89is needed to improve the cross-linking.
938c8732 90
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91The addition of C<Pod::Simple> and its related modules may make this task
92easier to complete.
93
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94=head2 merge checkpods and podchecker
95
96F<pod/checkpods.PL> (and C<make check> in the F<pod/> subdirectory)
97implements a very basic check for pod files, but the errors it discovers
98aren't found by podchecker. Add this check to podchecker, get rid of
99checkpods and have C<make check> use podchecker.
100
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101=head2 Parallel testing
102
b2e2905c 103(This probably impacts much more than the core: also the Test::Harness
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104and TAP::* modules on CPAN.)
105
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106All of the tests in F<t/> can now be run in parallel, if C<$ENV{TEST_JOBS}>
107is set. However, tests within each directory in F<ext> and F<lib> are still
108run in series, with directories run in parallel. This is an adequate
109heuristic, but it might be possible to relax it further, and get more
110throughput. Specifically, it would be good to audit all of F<lib/*.t>, and
111make them use C<File::Temp>.
aa237293 112
0bdfc961 113=head2 Make Schwern poorer
e50bb9a1 114
613bd4f7 115We should have tests for everything. When all the core's modules are tested,
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116Schwern has promised to donate to $500 to TPF. We may need volunteers to
117hold him upside down and shake vigorously in order to actually extract the
118cash.
3958b146 119
0bdfc961 120=head2 Improve the coverage of the core tests
e50bb9a1 121
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122Use Devel::Cover to ascertain the core modules's test coverage, then add
123tests that are currently missing.
30222c0f 124
0bdfc961 125=head2 test B
e50bb9a1 126
0bdfc961 127A full test suite for the B module would be nice.
e50bb9a1 128
0bdfc961 129=head2 A decent benchmark
e50bb9a1 130
617eabfa 131C<perlbench> seems impervious to any recent changes made to the perl core. It
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132would be useful to have a reasonable general benchmarking suite that roughly
133represented what current perl programs do, and measurably reported whether
134tweaks to the core improve, degrade or don't really affect performance, to
135guide people attempting to optimise the guts of perl. Gisle would welcome
136new tests for perlbench.
6168cf99 137
0bdfc961 138=head2 fix tainting bugs
6168cf99 139
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140Fix the bugs revealed by running the test suite with the C<-t> switch (via
141C<make test.taintwarn>).
e50bb9a1 142
0bdfc961 143=head2 Dual life everything
e50bb9a1 144
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145As part of the "dists" plan, anything that doesn't belong in the smallest perl
146distribution needs to be dual lifed. Anything else can be too. Figure out what
147changes would be needed to package that module and its tests up for CPAN, and
148do so. Test it with older perl releases, and fix the problems you find.
e50bb9a1 149
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150To make a minimal perl distribution, it's useful to look at
151F<t/lib/commonsense.t>.
152
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153=head2 Bundle dual life modules in ext/
154
155For maintenance (and branch merging) reasons, it would be useful to move
156some architecture-independent dual-life modules from lib/ to ext/, if this
157has no negative impact on the build of perl itself.
158
0bdfc961 159=head2 POSIX memory footprint
e50bb9a1 160
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161Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
162various times worked to cut it down. There is probably still fat to cut out -
163for example POSIX passes Exporter some very memory hungry data structures.
e50bb9a1 164
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165=head2 embed.pl/makedef.pl
166
167There is a script F<embed.pl> that generates several header files to prefix
168all of Perl's symbols in a consistent way, to provide some semblance of
169namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
907b3e23 170in F<interpvar.h>. Quite a few of the functions and variables
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171are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
172doesn't understand the C macros, so the rules about which symbols are present
173when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
174It would be good to teach C<embed.pl> to understand the conditional
175compilation, and hence remove the duplication, and the mistakes it has caused.
e50bb9a1 176
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177=head2 use strict; and AutoLoad
178
179Currently if you write
180
181 package Whack;
182 use AutoLoader 'AUTOLOAD';
183 use strict;
184 1;
185 __END__
186 sub bloop {
187 print join (' ', No, strict, here), "!\n";
188 }
189
190then C<use strict;> isn't in force within the autoloaded subroutines. It would
191be more consistent (and less surprising) to arrange for all lexical pragmas
192in force at the __END__ block to be in force within each autoloaded subroutine.
193
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194There's a similar problem with SelfLoader.
195
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196=head2 profile installman
197
198The F<installman> script is slow. All it is doing text processing, which we're
199told is something Perl is good at. So it would be nice to know what it is doing
200that is taking so much CPU, and where possible address it.
201
202
0bdfc961 203=head1 Tasks that need a little sysadmin-type knowledge
e50bb9a1 204
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205Or if you prefer, tasks that you would learn from, and broaden your skills
206base...
e50bb9a1 207
cd793d32 208=head2 make HTML install work
e50bb9a1 209
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210There is an C<installhtml> target in the Makefile. It's marked as
211"experimental". It would be good to get this tested, make it work reliably, and
212remove the "experimental" tag. This would include
213
214=over 4
215
216=item 1
217
218Checking that cross linking between various parts of the documentation works.
219In particular that links work between the modules (files with POD in F<lib/>)
220and the core documentation (files in F<pod/>)
221
222=item 2
223
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224Work out how to split C<perlfunc> into chunks, preferably one per function
225group, preferably with general case code that could be used elsewhere.
226Challenges here are correctly identifying the groups of functions that go
227together, and making the right named external cross-links point to the right
228page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
229C<endservent>, two or more C<=items> giving the different parameter lists, such
230as
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231
232 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
adebf063 233 =item substr EXPR,OFFSET,LENGTH
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234 =item substr EXPR,OFFSET
235
236and different parameter lists having different meanings. (eg C<select>)
237
238=back
3a89a73c 239
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240=head2 compressed man pages
241
242Be able to install them. This would probably need a configure test to see how
243the system does compressed man pages (same directory/different directory?
244same filename/different filename), as well as tweaking the F<installman> script
245to compress as necessary.
246
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247=head2 Add a code coverage target to the Makefile
248
249Make it easy for anyone to run Devel::Cover on the core's tests. The steps
250to do this manually are roughly
251
252=over 4
253
254=item *
255
256do a normal C<Configure>, but include Devel::Cover as a module to install
257(see F<INSTALL> for how to do this)
258
259=item *
260
261 make perl
262
263=item *
264
265 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
266
267=item *
268
269Process the resulting Devel::Cover database
270
271=back
272
273This just give you the coverage of the F<.pm>s. To also get the C level
274coverage you need to
275
276=over 4
277
278=item *
279
280Additionally tell C<Configure> to use the appropriate C compiler flags for
281C<gcov>
282
283=item *
284
285 make perl.gcov
286
287(instead of C<make perl>)
288
289=item *
290
291After running the tests run C<gcov> to generate all the F<.gcov> files.
292(Including down in the subdirectories of F<ext/>
293
294=item *
295
296(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
297to get their stats into the cover_db directory.
298
299=item *
300
301Then process the Devel::Cover database
302
303=back
304
305It would be good to add a single switch to C<Configure> to specify that you
306wanted to perform perl level coverage, and another to specify C level
307coverage, and have C<Configure> and the F<Makefile> do all the right things
308automatically.
309
02f21748 310=head2 Make Config.pm cope with differences between built and installed perl
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311
312Quite often vendors ship a perl binary compiled with their (pay-for)
313compilers. People install a free compiler, such as gcc. To work out how to
314build extensions, Perl interrogates C<%Config>, so in this situation
315C<%Config> describes compilers that aren't there, and extension building
316fails. This forces people into choosing between re-compiling perl themselves
317using the compiler they have, or only using modules that the vendor ships.
318
319It would be good to find a way teach C<Config.pm> about the installation setup,
320possibly involving probing at install time or later, so that the C<%Config> in
321a binary distribution better describes the installed machine, when the
322installed machine differs from the build machine in some significant way.
323
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324=head2 linker specification files
325
326Some platforms mandate that you provide a list of a shared library's external
327symbols to the linker, so the core already has the infrastructure in place to
328do this for generating shared perl libraries. My understanding is that the
329GNU toolchain can accept an optional linker specification file, and restrict
330visibility just to symbols declared in that file. It would be good to extend
331F<makedef.pl> to support this format, and to provide a means within
332C<Configure> to enable it. This would allow Unix users to test that the
333export list is correct, and to build a perl that does not pollute the global
334namespace with private symbols.
335
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336=head2 Cross-compile support
337
338Currently C<Configure> understands C<-Dusecrosscompile> option. This option
339arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
340assumed then to be copied to TARGET machine and used as a replacement of full
341C<perl> executable.
342
d1307786 343This could be done little differently. Namely C<miniperl> should be built for
a229ae3b 344HOST and then full C<perl> with extensions should be compiled for TARGET.
d1307786 345This, however, might require extra trickery for %Config: we have one config
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346first for HOST and then another for TARGET. Tools like MakeMaker will be
347mightily confused. Having around two different types of executables and
348libraries (HOST and TARGET) makes life interesting for Makefiles and
349shell (and Perl) scripts. There is $Config{run}, normally empty, which
350can be used as an execution wrapper. Also note that in some
351cross-compilation/execution environments the HOST and the TARGET do
352not see the same filesystem(s), the $Config{run} may need to do some
353file/directory copying back and forth.
0bdfc961 354
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355=head2 roffitall
356
357Make F<pod/roffitall> be updated by F<pod/buildtoc>.
358
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359=head2 Split "linker" from "compiler"
360
361Right now, Configure probes for two commands, and sets two variables:
362
363=over 4
364
b91dd380 365=item * C<cc> (in F<cc.U>)
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366
367This variable holds the name of a command to execute a C compiler which
368can resolve multiple global references that happen to have the same
369name. Usual values are F<cc> and F<gcc>.
370Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>.
371
b91dd380 372=item * C<ld> (in F<dlsrc.U>)
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373
374This variable indicates the program to be used to link
375libraries for dynamic loading. On some systems, it is F<ld>.
376On ELF systems, it should be C<$cc>. Mostly, we'll try to respect
377the hint file setting.
378
379=back
380
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381There is an implicit historical assumption from around Perl5.000alpha
382something, that C<$cc> is also the correct command for linking object files
383together to make an executable. This may be true on Unix, but it's not true
384on other platforms, and there are a maze of work arounds in other places (such
385as F<Makefile.SH>) to cope with this.
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386
387Ideally, we should create a new variable to hold the name of the executable
388linker program, probe for it in F<Configure>, and centralise all the special
389case logic there or in hints files.
390
391A small bikeshed issue remains - what to call it, given that C<$ld> is already
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392taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command
393for creating dynamically-loadable modules) and C<$link> could be confused with
394the Unix command line executable of the same name, which does something
395completely different. Andy Dougherty makes the counter argument "In parrot, I
396tried to call the command used to link object files and libraries into an
397executable F<link>, since that's what my vaguely-remembered DOS and VMS
398experience suggested. I don't think any real confusion has ensued, so it's
399probably a reasonable name for perl5 to use."
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400
401"Alas, I've always worried that introducing it would make things worse,
402since now the module building utilities would have to look for
403C<$Config{link}> and institute a fall-back plan if it weren't found."
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404Although I can see that as confusing, given that C<$Config{d_link}> is true
405when (hard) links are available.
98fca0e8 406
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407=head1 Tasks that need a little C knowledge
408
409These tasks would need a little C knowledge, but don't need any specific
410background or experience with XS, or how the Perl interpreter works
411
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412=head2 Weed out needless PERL_UNUSED_ARG
413
414The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about
415unused arguments. Often the arguments can't be removed, as there is an
416external constraint that determines the prototype of the function, so this
417approach is valid. However, there are some cases where C<PERL_UNUSED_ARG>
418could be removed. Specifically
419
420=over 4
421
422=item *
423
424The prototypes of (nearly all) static functions can be changed
425
426=item *
427
428Unused arguments generated by short cut macros are wasteful - the short cut
429macro used can be changed.
430
431=back
432
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433=head2 Modernize the order of directories in @INC
434
435The way @INC is laid out by default, one cannot upgrade core (dual-life)
436modules without overwriting files. This causes problems for binary
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437package builders. One possible proposal is laid out in this
438message:
439L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.
fbf638cb 440
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441=head2 -Duse32bit*
442
443Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
444On these systems, it might be the default compilation mode, and there
445is currently no guarantee that passing no use64bitall option to the
446Configure process will build a 32bit perl. Implementing -Duse32bit*
447options would be nice for perl 5.12.
448
0bdfc961 449=head2 Make it clear from -v if this is the exact official release
89007cb3 450
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451Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
452usually defines one local patch, of the form "MAINT12345" or "RC1". The output
453of perl -v doesn't report that a perl isn't an official release, and this
89007cb3 454information can get lost in bugs reports. Because of this, the minor version
fa11829f 455isn't bumped up until RC time, to minimise the possibility of versions of perl
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456escaping that believe themselves to be newer than they actually are.
457
458It would be useful to find an elegant way to have the "this is an interim
459maintenance release" or "this is a release candidate" in the terse -v output,
460and have it so that it's easy for the pumpking to remove this just as the
461release tarball is rolled up. This way the version pulled out of rsync would
462always say "I'm a development release" and it would be safe to bump the
463reported minor version as soon as a release ships, which would aid perl
464developers.
465
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466This task is really about thinking of an elegant way to arrange the C source
467such that it's trivial for the Pumpking to flag "this is an official release"
468when making a tarball, yet leave the default source saying "I'm not the
469official release".
470
fee0a0f7 471=head2 Profile Perl - am I hot or not?
62403a3c 472
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473The Perl source code is stable enough that it makes sense to profile it,
474identify and optimise the hotspots. It would be good to measure the
475performance of the Perl interpreter using free tools such as cachegrind,
476gprof, and dtrace, and work to reduce the bottlenecks they reveal.
477
478As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
479the ops that are most commonly used. The idea is that by grouping them, their
480object code will be adjacent in the executable, so they have a greater chance
481of already being in the CPU cache (or swapped in) due to being near another op
482already in use.
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483
484Except that it's not clear if these really are the most commonly used ops. So
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485as part of exercising your skills with coverage and profiling tools you might
486want to determine what ops I<really> are the most commonly used. And in turn
487suggest evictions and promotions to achieve a better F<pp_hot.c>.
62403a3c 488
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489One piece of Perl code that might make a good testbed is F<installman>.
490
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491=head2 Allocate OPs from arenas
492
493Currently all new OP structures are individually malloc()ed and free()d.
494All C<malloc> implementations have space overheads, and are now as fast as
495custom allocates so it would both use less memory and less CPU to allocate
496the various OP structures from arenas. The SV arena code can probably be
497re-used for this.
498
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499Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use
500Perl_Slab_alloc() to pack optrees into a contiguous block, which is
501probably superior to the use of OP arenas, esp. from a cache locality
502standpoint. See L<Profile Perl - am I hot or not?>.
503
a229ae3b 504=head2 Improve win32/wince.c
0bdfc961 505
a229ae3b 506Currently, numerous functions look virtually, if not completely,
02f21748 507identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
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508be good.
509
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510=head2 Use secure CRT functions when building with VC8 on Win32
511
512Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
513that they were "unsafe" and introduced differently named secure versions of
514them as replacements, e.g. instead of writing
515
516 FILE* f = fopen(__FILE__, "r");
517
518one should now write
519
520 FILE* f;
521 errno_t err = fopen_s(&f, __FILE__, "r");
522
523Currently, the warnings about these deprecations have been disabled by adding
524-D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
525warning suppressant and actually make use of the new secure CRT functions.
526
527There is also a similar issue with POSIX CRT function names like fileno having
528been deprecated in favour of ISO C++ conformant names like _fileno. These
26a6faa8 529warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It
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530might be nice to do as Microsoft suggest here too, although, unlike the secure
531functions issue, there is presumably little or no benefit in this case.
532
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533=head2 Fix POSIX::access() and chdir() on Win32
534
535These functions currently take no account of DACLs and therefore do not behave
536correctly in situations where access is restricted by DACLs (as opposed to the
537read-only attribute).
538
539Furthermore, POSIX::access() behaves differently for directories having the
540read-only attribute set depending on what CRT library is being used. For
541example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that
542such directories are not writable, whereas in fact all directories are writable
543unless access is denied by DACLs. (In the case of directories, the read-only
544attribute actually only means that the directory cannot be deleted.) This CRT
545bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still
546not actually be writable if access is indeed denied by DACLs).
547
548For the chdir() issue, see ActiveState bug #74552:
549http://bugs.activestate.com/show_bug.cgi?id=74552
550
551Therefore, DACLs should be checked both for consistency across CRTs and for
552the correct answer.
553
554(Note that perl's -w operator should not be modified to check DACLs. It has
555been written so that it reflects the state of the read-only attribute, even
556for directories (whatever CRT is being used), for symmetry with chmod().)
557
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558=head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
559
560Maybe create a utility that checks after each libperl.a creation that
561none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
562ever creep back to libperl.a.
563
564 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
565
566Note, of course, that this will only tell whether B<your> platform
567is using those naughty interfaces.
568
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569=head2 -D_FORTIFY_SOURCE=2, -fstack-protector
570
571Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc
572(4.1 onwards?) supports C<-fstack-protector>, both of which give
573protection against various kinds of buffer overflow problems.
574These should probably be used for compiling Perl whenever available,
575Configure and/or hints files should be adjusted to probe for the
576availability of these features and enable them as appropriate.
16815324 577
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578=head2 Arenas for GPs? For MAGIC?
579
580C<struct gp> and C<struct magic> are both currently allocated by C<malloc>.
581It might be a speed or memory saving to change to using arenas. Or it might
582not. It would need some suitable benchmarking first. In particular, C<GP>s
583can probably be changed with minimal compatibility impact (probably nothing
584outside of the core, or even outside of F<gv.c> allocates them), but they
585probably aren't allocated/deallocated often enough for a speed saving. Whereas
586C<MAGIC> is allocated/deallocated more often, but in turn, is also something
587more externally visible, so changing the rules here may bite external code.
588
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589=head2 Shared arenas
590
591Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and
592PVHV, and PVCV and PVFM. It should be possible to allocate and return same
593sized bodies from the same actual arena, rather than maintaining one arena for
594each. This could save 4-6K per thread, of memory no longer tied up in the
595not-yet-allocated part of an arena.
596
8964cfe0 597
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598=head1 Tasks that need a knowledge of XS
599
600These tasks would need C knowledge, and roughly the level of knowledge of
601the perl API that comes from writing modules that use XS to interface to
602C.
603
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604=head2 safely supporting POSIX SA_SIGINFO
605
606Some years ago Jarkko supplied patches to provide support for the POSIX
607SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler.
608
609Unfortunately, it only works with "unsafe" signals, because under safe
610signals, by the time Perl gets to run the signal handler, the extra
611information has been lost. Moreover, it's not easy to store it somewhere,
612as you can't call mutexs, or do anything else fancy, from inside a signal
613handler.
614
615So it strikes me that we could provide safe SA_SIGINFO support
616
617=over 4
618
619=item 1
620
621Provide global variables for two file descriptors
622
623=item 2
624
625When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a
626pipe, store the reader in one, the writer in the other
627
628=item 3
629
630In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if
631the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open,
632
633=over 8
634
635=item 1
636
637serialise signal number, C<struct siginfo_t> (or at least the parts we care
638about) into a small auto char buff
639
640=item 2
641
642C<write()> that (non-blocking) to the writer fd
643
644=over 12
645
646=item 1
647
648if it writes 100%, flag the signal in a counter of "signals on the pipe" akin
649to the current per-signal-number counts
650
651=item 2
652
653if it writes 0%, assume the pipe is full. Flag the data as lost?
654
655=item 3
656
657if it writes partially, croak a panic, as your OS is broken.
658
659=back
660
661=back
662
663=item 4
664
665in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on
666the pipe", read the data out, deserialise, build the Perl structures on
667the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as
668usual.
669
670=back
671
672I think that this gets us decent C<SA_SIGINFO> support, without the current risk
673of running Perl code inside the signal handler context. (With all the dangers
674of things like C<malloc> corruption that that currently offers us)
675
676For more information see the thread starting with this message:
677http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html
678
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679=head2 autovivification
680
681Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
682
683This task is incremental - even a little bit of work on it will help.
684
685=head2 Unicode in Filenames
686
687chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
688opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
689system, truncate, unlink, utime, -X. All these could potentially accept
690Unicode filenames either as input or output (and in the case of system
691and qx Unicode in general, as input or output to/from the shell).
692Whether a filesystem - an operating system pair understands Unicode in
693filenames varies.
694
695Known combinations that have some level of understanding include
696Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
697OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
698create Unicode filenames, what forms of Unicode are accepted and used
699(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
700and so on, varies. Finding the right level of interfacing to Perl
701requires some thought. Remember that an OS does not implicate a
702filesystem.
703
704(The Windows -C command flag "wide API support" has been at least
705temporarily retired in 5.8.1, and the -C has been repurposed, see
706L<perlrun>.)
707
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708Most probably the right way to do this would be this:
709L</"Virtualize operating system access">.
710
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711=head2 Unicode in %ENV
712
713Currently the %ENV entries are always byte strings.
87a942b1 714See L</"Virtualize operating system access">.
6d71adcd 715
1f2e7916
JD
716=head2 Unicode and glob()
717
718Currently glob patterns and filenames returned from File::Glob::glob()
87a942b1 719are always byte strings. See L</"Virtualize operating system access">.
1f2e7916 720
dbb0c492
RGS
721=head2 Unicode and lc/uc operators
722
723Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on
724what the internal encoding of their argument is. That should not be the
725case. Maybe add a pragma to switch behaviour.
726
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727=head2 use less 'memory'
728
729Investigate trade offs to switch out perl's choices on memory usage.
730Particularly perl should be able to give memory back.
731
732This task is incremental - even a little bit of work on it will help.
733
734=head2 Re-implement C<:unique> in a way that is actually thread-safe
735
736The old implementation made bad assumptions on several levels. A good 90%
737solution might be just to make C<:unique> work to share the string buffer
738of SvPVs. That way large constant strings can be shared between ithreads,
739such as the configuration information in F<Config>.
740
741=head2 Make tainting consistent
742
743Tainting would be easier to use if it didn't take documented shortcuts and
744allow taint to "leak" everywhere within an expression.
745
746=head2 readpipe(LIST)
747
748system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
749running a shell. readpipe() (the function behind qx//) could be similarly
750extended.
751
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752=head2 Audit the code for destruction ordering assumptions
753
754Change 25773 notes
755
756 /* Need to check SvMAGICAL, as during global destruction it may be that
757 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
758 is now part of the linked list of SV heads, rather than pointing to
759 the original body. */
760 /* FIXME - audit the code for other bugs like this one. */
761
762adding the C<SvMAGICAL> check to
763
764 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
765 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
766
767Go through the core and look for similar assumptions that SVs have particular
768types, as all bets are off during global destruction.
769
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770=head2 Extend PerlIO and PerlIO::Scalar
771
772PerlIO::Scalar doesn't know how to truncate(). Implementing this
773would require extending the PerlIO vtable.
774
775Similarly the PerlIO vtable doesn't know about formats (write()), or
776about stat(), or chmod()/chown(), utime(), or flock().
777
778(For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
779would mean.)
780
781PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
782opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
783readlink().
784
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785See also L</"Virtualize operating system access">.
786
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787=head2 -C on the #! line
788
789It should be possible to make -C work correctly if found on the #! line,
790given that all perl command line options are strict ASCII, and -C changes
791only the interpretation of non-ASCII characters, and not for the script file
792handle. To make it work needs some investigation of the ordering of function
793calls during startup, and (by implication) a bit of tweaking of that order.
794
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795=head2 Organize error messages
796
797Perl's diagnostics (error messages, see L<perldiag>) could use
a8d0aeb9 798reorganizing and formalizing so that each error message has its
d6c1e11f
JH
799stable-for-all-eternity unique id, categorized by severity, type, and
800subsystem. (The error messages would be listed in a datafile outside
c4bd451b
CB
801of the Perl source code, and the source code would only refer to the
802messages by the id.) This clean-up and regularizing should apply
d6c1e11f
JH
803for all croak() messages.
804
805This would enable all sorts of things: easier translation/localization
806of the messages (though please do keep in mind the caveats of
807L<Locale::Maketext> about too straightforward approaches to
808translation), filtering by severity, and instead of grepping for a
809particular error message one could look for a stable error id. (Of
810course, changing the error messages by default would break all the
811existing software depending on some particular error message...)
812
813This kind of functionality is known as I<message catalogs>. Look for
814inspiration for example in the catgets() system, possibly even use it
815if available-- but B<only> if available, all platforms will B<not>
de96509d 816have catgets().
d6c1e11f
JH
817
818For the really pure at heart, consider extending this item to cover
819also the warning messages (see L<perllexwarn>, C<warnings.pl>).
3236f110 820
0bdfc961 821=head1 Tasks that need a knowledge of the interpreter
3298bd4d 822
0bdfc961
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823These tasks would need C knowledge, and knowledge of how the interpreter works,
824or a willingness to learn.
3298bd4d 825
565590b5
NC
826=head2 error reporting of [$a ; $b]
827
828Using C<;> inside brackets is a syntax error, and we don't propose to change
829that by giving it any meaning. However, it's not reported very helpfully:
830
831 $ perl -e '$a = [$b; $c];'
832 syntax error at -e line 1, near "$b;"
833 syntax error at -e line 1, near "$c]"
834 Execution of -e aborted due to compilation errors.
835
836It should be possible to hook into the tokeniser or the lexer, so that when a
837C<;> is parsed where it is not legal as a statement terminator (ie inside
838C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like
839I<';' isn't legal inside an expression - if you need multiple statements use a
840do {...} block>. See the thread starting at
841http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html
842
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843=head2 lexicals used only once
844
845This warns:
846
847 $ perl -we '$pie = 42'
848 Name "main::pie" used only once: possible typo at -e line 1.
849
850This does not:
851
852 $ perl -we 'my $pie = 42'
853
854Logically all lexicals used only once should warn, if the user asks for
d6f4ea2e
SP
855warnings. An unworked RT ticket (#5087) has been open for almost seven
856years for this discrepancy.
718140ec 857
a3d15f9a
RGS
858=head2 UTF-8 revamp
859
860The handling of Unicode is unclean in many places. For example, the regexp
861engine matches in Unicode semantics whenever the string or the pattern is
862flagged as UTF-8, but that should not be dependent on an internal storage
863detail of the string. Likewise, case folding behaviour is dependent on the
864UTF8 internal flag being on or off.
865
866=head2 Properly Unicode safe tokeniser and pads.
867
868The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
869variable names are stored in stashes as raw bytes, without the utf-8 flag
870set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
871tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
872source filters. All this could be fixed.
873
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874=head2 state variable initialization in list context
875
876Currently this is illegal:
877
878 state ($a, $b) = foo();
879
a2874905 880In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different
a8d0aeb9 881semantics, which is tricky to implement in Perl 5 as currently they produce
a2874905 882the same opcode trees. The Perl 6 design is firm, so it would be good to
a8d0aeb9 883implement the necessary code in Perl 5. There are comments in
a2874905
NC
884C<Perl_newASSIGNOP()> that show the code paths taken by various assignment
885constructions involving state variables.
636e63cb 886
4fedb12c
RGS
887=head2 Implement $value ~~ 0 .. $range
888
889It would be nice to extend the syntax of the C<~~> operator to also
890understand numeric (and maybe alphanumeric) ranges.
a393eb28
RGS
891
892=head2 A does() built-in
893
894Like ref(), only useful. It would call the C<DOES> method on objects; it
895would also tell whether something can be dereferenced as an
896array/hash/etc., or used as a regexp, etc.
897L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
898
899=head2 Tied filehandles and write() don't mix
900
901There is no method on tied filehandles to allow them to be called back by
902formats.
4fedb12c 903
d10fc472 904=head2 Attach/detach debugger from running program
1626a787 905
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906The old perltodo notes "With C<gdb>, you can attach the debugger to a running
907program if you pass the process ID. It would be good to do this with the Perl
0bdfc961
NC
908debugger on a running Perl program, although I'm not sure how it would be
909done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
1626a787 910
a8cb5b9e
RGS
911=head2 Optimize away empty destructors
912
913Defining an empty DESTROY method might be useful (notably in
914AUTOLOAD-enabled classes), but it's still a bit expensive to call. That
915could probably be optimized.
916
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917=head2 LVALUE functions for lists
918
919The old perltodo notes that lvalue functions don't work for list or hash
920slices. This would be good to fix.
921
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922=head2 regexp optimiser optional
923
924The regexp optimiser is not optional. It should configurable to be, to allow
925its performance to be measured, and its bugs to be easily demonstrated.
926
02f21748
RGS
927=head2 delete &function
928
929Allow to delete functions. One can already undef them, but they're still
930in the stash.
931
ef36c6a7
RGS
932=head2 C</w> regex modifier
933
934That flag would enable to match whole words, and also to interpolate
935arrays as alternations. With it, C</P/w> would be roughly equivalent to:
936
937 do { local $"='|'; /\b(?:P)\b/ }
938
939See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
940for the discussion.
941
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942=head2 optional optimizer
943
944Make the peephole optimizer optional. Currently it performs two tasks as
945it walks the optree - genuine peephole optimisations, and necessary fixups of
946ops. It would be good to find an efficient way to switch out the
947optimisations whilst keeping the fixups.
948
949=head2 You WANT *how* many
950
951Currently contexts are void, scalar and list. split has a special mechanism in
952place to pass in the number of return values wanted. It would be useful to
953have a general mechanism for this, backwards compatible and little speed hit.
954This would allow proposals such as short circuiting sort to be implemented
955as a module on CPAN.
956
957=head2 lexical aliases
958
959Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
960
961=head2 entersub XS vs Perl
962
963At the moment pp_entersub is huge, and has code to deal with entering both
964perl and XS subroutines. Subroutine implementations rarely change between
965perl and XS at run time, so investigate using 2 ops to enter subs (one for
966XS, one for perl) and swap between if a sub is redefined.
2810d901 967
de535794 968=head2 Self-ties
2810d901 969
de535794 970Self-ties are currently illegal because they caused too many segfaults. Maybe
a8d0aeb9 971the causes of these could be tracked down and self-ties on all types
de535794 972reinstated.
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973
974=head2 Optimize away @_
975
976The old perltodo notes "Look at the "reification" code in C<av.c>".
977
87a942b1
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978=head2 Virtualize operating system access
979
980Implement a set of "vtables" that virtualizes operating system access
981(open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very
982least these interfaces should take SVs as "name" arguments instead of
983bare char pointers; probably the most flexible and extensible way
e1a3d5d1
JH
984would be for the Perl-facing interfaces to accept HVs. The system
985needs to be per-operating-system and per-file-system
986hookable/filterable, preferably both from XS and Perl level
87a942b1
JH
987(L<perlport/"Files and Filesystems"> is good reading at this point,
988in fact, all of L<perlport> is.)
989
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990This has actually already been implemented (but only for Win32),
991take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32
992variants go through a set of "vtables" for operating system access,
993non-Win32 systems currently go straight for the POSIX/UNIX-style
994system/library call. Similar system as for Win32 should be
995implemented for all platforms. The existing Win32 implementation
996probably does not need to survive alongside this proposed new
997implementation, the approaches could be merged.
87a942b1
JH
998
999What would this give us? One often-asked-for feature this would
94da6c29
JH
1000enable is using Unicode for filenames, and other "names" like %ENV,
1001usernames, hostnames, and so forth.
1002(See L<perlunicode/"When Unicode Does Not Happen">.)
1003
1004But this kind of virtualization would also allow for things like
1005virtual filesystems, virtual networks, and "sandboxes" (though as long
1006as dynamic loading of random object code is allowed, not very safe
1007sandboxes since external code of course know not of Perl's vtables).
1008An example of a smaller "sandbox" is that this feature can be used to
1009implement per-thread working directories: Win32 already does this.
1010
1011See also L</"Extend PerlIO and PerlIO::Scalar">.
87a942b1 1012
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1013=head2 Investigate PADTMP hash pessimisation
1014
1015The peephole optimier converts constants used for hash key lookups to shared
057163d7 1016hash key scalars. Under ithreads, something is undoing this work.
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1017See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html
1018
057163d7
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1019=head2 Store the current pad in the OP slab allocator
1020
1021=for clarification
1022I hope that I got that "current pad" part correct
1023
1024Currently we leak ops in various cases of parse failure. I suggested that we
1025could solve this by always using the op slab allocator, and walking it to
1026free ops. Dave comments that as some ops are already freed during optree
1027creation one would have to mark which ops are freed, and not double free them
1028when walking the slab. He notes that one problem with this is that for some ops
1029you have to know which pad was current at the time of allocation, which does
1030change. I suggested storing a pointer to the current pad in the memory allocated
1031for the slab, and swapping to a new slab each time the pad changes. Dave thinks
1032that this would work.
1033
52960e22
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1034=head2 repack the optree
1035
1036Repacking the optree after execution order is determined could allow
057163d7
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1037removal of NULL ops, and optimal ordering of OPs with respect to cache-line
1038filling. The slab allocator could be reused for this purpose. I think that
1039the best way to do this is to make it an optional step just before the
1040completed optree is attached to anything else, and to use the slab allocator
1041unchanged, so that freeing ops is identical whether or not this step runs.
1042Note that the slab allocator allocates ops downwards in memory, so one would
1043have to actually "allocate" the ops in reverse-execution order to get them
1044contiguous in memory in execution order.
1045
1046See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html
1047
1048Note that running this copy, and then freeing all the old location ops would
1049cause their slabs to be freed, which would eliminate possible memory wastage if
1050the previous suggestion is implemented, and we swap slabs more frequently.
52960e22 1051
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1052=head2 eliminate incorrect line numbers in warnings
1053
1054This code
1055
1056 use warnings;
1057 my $undef;
1058
1059 if ($undef == 3) {
1060 } elsif ($undef == 0) {
1061 }
1062
18a16cc5 1063used to produce this output:
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1064
1065 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1066 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1067
18a16cc5
NC
1068where the line of the second warning was misreported - it should be line 5.
1069Rafael fixed this - the problem arose because there was no nextstate OP
1070between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still
1071reports that the currently executing line is line 4. The solution was to inject
1072a nextstate OPs for each C<elsif>, although it turned out that the nextstate
1073OP needed to be a nulled OP, rather than a live nextstate OP, else other line
1074numbers became misreported. (Jenga!)
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1075
1076The problem is more general than C<elsif> (although the C<elsif> case is the
1077most common and the most confusing). Ideally this code
1078
1079 use warnings;
1080 my $undef;
1081
1082 my $a = $undef + 1;
1083 my $b
1084 = $undef
1085 + 1;
1086
1087would produce this output
1088
1089 Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
1090 Use of uninitialized value $undef in addition (+) at wrong.pl line 7.
1091
1092(rather than lines 4 and 5), but this would seem to require every OP to carry
1093(at least) line number information.
1094
1095What might work is to have an optional line number in memory just before the
1096BASEOP structure, with a flag bit in the op to say whether it's present.
1097Initially during compile every OP would carry its line number. Then add a late
1098pass to the optimiser (potentially combined with L</repack the optree>) which
1099looks at the two ops on every edge of the graph of the execution path. If
1100the line number changes, flags the destination OP with this information.
1101Once all paths are traced, replace every op with the flag with a
1102nextstate-light op (that just updates C<PL_curcop>), which in turn then passes
1103control on to the true op. All ops would then be replaced by variants that
1104do not store the line number. (Which, logically, why it would work best in
1105conjunction with L</repack the optree>, as that is already copying/reallocating
1106all the OPs)
1107
18a16cc5
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1108(Although I should note that we're not certain that doing this for the general
1109case is worth it)
1110
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JC
1111=head2 optimize tail-calls
1112
1113Tail-calls present an opportunity for broadly applicable optimization;
1114anywhere that C<< return foo(...) >> is called, the outer return can
1115be replaced by a goto, and foo will return directly to the outer
1116caller, saving (conservatively) 25% of perl's call&return cost, which
1117is relatively higher than in C. The scheme language is known to do
1118this heavily. B::Concise provides good insight into where this
1119optimization is possible, ie anywhere entersub,leavesub op-sequence
1120occurs.
1121
1122 perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'
1123
1124Bottom line on this is probably a new pp_tailcall function which
1125combines the code in pp_entersub, pp_leavesub. This should probably
1126be done 1st in XS, and using B::Generate to patch the new OP into the
1127optrees.
1128
0bdfc961
NC
1129=head1 Big projects
1130
1131Tasks that will get your name mentioned in the description of the "Highlights
87a942b1 1132of 5.12"
0bdfc961
NC
1133
1134=head2 make ithreads more robust
1135
4e577f8b 1136Generally make ithreads more robust. See also L</iCOW>
0bdfc961
NC
1137
1138This task is incremental - even a little bit of work on it will help, and
1139will be greatly appreciated.
1140
6c047da7
YST
1141One bit would be to write the missing code in sv.c:Perl_dirp_dup.
1142
59c7f7d5
RGS
1143Fix Perl_sv_dup, et al so that threads can return objects.
1144
0bdfc961
NC
1145=head2 iCOW
1146
1147Sarathy and Arthur have a proposal for an improved Copy On Write which
1148specifically will be able to COW new ithreads. If this can be implemented
1149it would be a good thing.
1150
1151=head2 (?{...}) closures in regexps
1152
1153Fix (or rewrite) the implementation of the C</(?{...})/> closures.
1154
1155=head2 A re-entrant regexp engine
1156
1157This will allow the use of a regex from inside (?{ }), (??{ }) and
1158(?(?{ })|) constructs.
6bda09f9 1159
6bda09f9
YO
1160=head2 Add class set operations to regexp engine
1161
1162Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
1163
1164demerphq has this on his todo list, but right at the bottom.