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