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