3 perltodo - Perl TO-DO List
7 This is a list of wishes for Perl. The tasks we think are smaller or easier
8 are listed first. Anyone is welcome to work on any of these, but it's a good
9 idea to first contact I<perl5-porters@perl.org> to avoid duplication of
10 effort. By all means contact a pumpking privately first if you prefer.
12 Whilst patches to make the list shorter are most welcome, ideas to add to
13 the list are also encouraged. Check the perl5-porters archives for past
14 ideas, and any discussion about them. One set of archives may be found at:
16 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
18 What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
19 not, but if your patch is incorporated, then we'll add your name to the
20 F<AUTHORS> file, which ships in the official distribution. How many other
21 programming languages offer you 1 line of immortality?
23 =head1 The roadmap to 5.10
25 The roadmap to 5.10 envisages feature based releases, as various items in this
28 =head2 Needed for a 5.9.5 release
34 Review assertions. Review syntax to combine assertions. Assertions could take
35 advantage of the lexical pragmas work. L</What hooks would assertions need?>
39 C<encoding> should be turned into a lexical pragma (probably).
43 =head2 Needed for a 5.9.6 release
45 Stabilisation. If all goes well, this will be the equivalent of a 5.10-beta.
47 =head1 Tasks that only need Perl knowledge
49 =head2 common test code for timed bail out
51 Write portable self destruct code for tests to stop them burning CPU in
52 infinite loops. This needs to avoid using alarm, as some of the tests are
53 testing alarm/sleep or timers.
55 =head2 POD -> HTML conversion in the core still sucks
57 Which is crazy given just how simple POD purports to be, and how simple HTML
58 can be. It's not actually I<as> simple as it sounds, particularly with the
59 flexibility POD allows for C<=item>, but it would be good to improve the
60 visual appeal of the HTML generated, and to avoid it having any validation
61 errors. See also L</make HTML install work>, as the layout of installation tree
62 is needed to improve the cross-linking.
64 The addition of C<Pod::Simple> and its related modules may make this task
67 =head2 Parallel testing
69 (This probably impacts much more than the core: also the Test::Harness
70 and TAP::* modules on CPAN.)
72 The core regression test suite is getting ever more comprehensive, which has
73 the side effect that it takes longer to run. This isn't so good. Investigate
74 whether it would be feasible to give the harness script the B<option> of
75 running sets of tests in parallel. This would be useful for tests in
76 F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
84 How does screen layout work when you're running more than one test?
88 How does the caller of test specify how many tests to run in parallel?
92 How do setup/teardown tests identify themselves?
96 Pugs already does parallel testing - can their approach be re-used?
98 =head2 Make Schwern poorer
100 We should have tests for everything. When all the core's modules are tested,
101 Schwern has promised to donate to $500 to TPF. We may need volunteers to
102 hold him upside down and shake vigorously in order to actually extract the
105 =head2 Improve the coverage of the core tests
107 Use Devel::Cover to ascertain the core modules's test coverage, then add
108 tests that are currently missing.
112 A full test suite for the B module would be nice.
114 =head2 A decent benchmark
116 C<perlbench> seems impervious to any recent changes made to the perl core. It
117 would be useful to have a reasonable general benchmarking suite that roughly
118 represented what current perl programs do, and measurably reported whether
119 tweaks to the core improve, degrade or don't really affect performance, to
120 guide people attempting to optimise the guts of perl. Gisle would welcome
121 new tests for perlbench.
123 =head2 fix tainting bugs
125 Fix the bugs revealed by running the test suite with the C<-t> switch (via
126 C<make test.taintwarn>).
128 =head2 Dual life everything
130 As part of the "dists" plan, anything that doesn't belong in the smallest perl
131 distribution needs to be dual lifed. Anything else can be too. Figure out what
132 changes would be needed to package that module and its tests up for CPAN, and
133 do so. Test it with older perl releases, and fix the problems you find.
135 =head2 Improving C<threads::shared>
137 Investigate whether C<threads::shared> could share aggregates properly with
138 only Perl level changes to shared.pm
140 =head2 POSIX memory footprint
142 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
143 various times worked to cut it down. There is probably still fat to cut out -
144 for example POSIX passes Exporter some very memory hungry data structures.
146 =head2 embed.pl/makedef.pl
148 There is a script F<embed.pl> that generates several header files to prefix
149 all of Perl's symbols in a consistent way, to provide some semblance of
150 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
151 in F<interpvar.h> and F<thrdvar.h>. Quite a few of the functions and variables
152 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
153 doesn't understand the C macros, so the rules about which symbols are present
154 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
155 It would be good to teach C<embed.pl> to understand the conditional
156 compilation, and hence remove the duplication, and the mistakes it has caused.
158 =head1 Tasks that need a little sysadmin-type knowledge
160 Or if you prefer, tasks that you would learn from, and broaden your skills
163 =head2 make HTML install work
165 There is an C<installhtml> target in the Makefile. It's marked as
166 "experimental". It would be good to get this tested, make it work reliably, and
167 remove the "experimental" tag. This would include
173 Checking that cross linking between various parts of the documentation works.
174 In particular that links work between the modules (files with POD in F<lib/>)
175 and the core documentation (files in F<pod/>)
179 Work out how to split C<perlfunc> into chunks, preferably one per function
180 group, preferably with general case code that could be used elsewhere.
181 Challenges here are correctly identifying the groups of functions that go
182 together, and making the right named external cross-links point to the right
183 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
184 C<endservent>, two or more C<=items> giving the different parameter lists, such
187 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
188 =item substr EXPR,OFFSET,LENGTH
189 =item substr EXPR,OFFSET
191 and different parameter lists having different meanings. (eg C<select>)
195 =head2 compressed man pages
197 Be able to install them. This would probably need a configure test to see how
198 the system does compressed man pages (same directory/different directory?
199 same filename/different filename), as well as tweaking the F<installman> script
200 to compress as necessary.
202 =head2 Add a code coverage target to the Makefile
204 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
205 to do this manually are roughly
211 do a normal C<Configure>, but include Devel::Cover as a module to install
212 (see F<INSTALL> for how to do this)
220 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
224 Process the resulting Devel::Cover database
228 This just give you the coverage of the F<.pm>s. To also get the C level
235 Additionally tell C<Configure> to use the appropriate C compiler flags for
242 (instead of C<make perl>)
246 After running the tests run C<gcov> to generate all the F<.gcov> files.
247 (Including down in the subdirectories of F<ext/>
251 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
252 to get their stats into the cover_db directory.
256 Then process the Devel::Cover database
260 It would be good to add a single switch to C<Configure> to specify that you
261 wanted to perform perl level coverage, and another to specify C level
262 coverage, and have C<Configure> and the F<Makefile> do all the right things
265 =head2 Make Config.pm cope with differences between built and installed perl
267 Quite often vendors ship a perl binary compiled with their (pay-for)
268 compilers. People install a free compiler, such as gcc. To work out how to
269 build extensions, Perl interrogates C<%Config>, so in this situation
270 C<%Config> describes compilers that aren't there, and extension building
271 fails. This forces people into choosing between re-compiling perl themselves
272 using the compiler they have, or only using modules that the vendor ships.
274 It would be good to find a way teach C<Config.pm> about the installation setup,
275 possibly involving probing at install time or later, so that the C<%Config> in
276 a binary distribution better describes the installed machine, when the
277 installed machine differs from the build machine in some significant way.
279 =head2 linker specification files
281 Some platforms mandate that you provide a list of a shared library's external
282 symbols to the linker, so the core already has the infrastructure in place to
283 do this for generating shared perl libraries. My understanding is that the
284 GNU toolchain can accept an optional linker specification file, and restrict
285 visibility just to symbols declared in that file. It would be good to extend
286 F<makedef.pl> to support this format, and to provide a means within
287 C<Configure> to enable it. This would allow Unix users to test that the
288 export list is correct, and to build a perl that does not pollute the global
289 namespace with private symbols.
291 =head2 Cross-compile support
293 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
294 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
295 assumed then to be copied to TARGET machine and used as a replacement of full
298 This could be done little differently. Namely C<miniperl> should be built for
299 HOST and then full C<perl> with extensions should be compiled for TARGET.
300 This, however, might require extra trickery for %Config: we have one config
301 first for HOST and then another for TARGET.
303 =head1 Tasks that need a little C knowledge
305 These tasks would need a little C knowledge, but don't need any specific
306 background or experience with XS, or how the Perl interpreter works
308 =head2 Make it clear from -v if this is the exact official release
310 Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
311 usually defines one local patch, of the form "MAINT12345" or "RC1". The output
312 of perl -v doesn't report that a perl isn't an official release, and this
313 information can get lost in bugs reports. Because of this, the minor version
314 isn't bumped up until RC time, to minimise the possibility of versions of perl
315 escaping that believe themselves to be newer than they actually are.
317 It would be useful to find an elegant way to have the "this is an interim
318 maintenance release" or "this is a release candidate" in the terse -v output,
319 and have it so that it's easy for the pumpking to remove this just as the
320 release tarball is rolled up. This way the version pulled out of rsync would
321 always say "I'm a development release" and it would be safe to bump the
322 reported minor version as soon as a release ships, which would aid perl
325 This task is really about thinking of an elegant way to arrange the C source
326 such that it's trivial for the Pumpking to flag "this is an official release"
327 when making a tarball, yet leave the default source saying "I'm not the
330 =head2 Ordering of "global" variables.
332 F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
333 per-thread under ithreads, where the variables are actually elements in a
334 structure. As C dictates, the variables must be laid out in order of
335 declaration. There is a comment
336 C</* Important ones in the first cache line (if alignment is done right) */>
337 which implies that at some point in the past the ordering was carefully chosen
338 (at least in part). However, it's clear that the ordering is less than perfect,
339 as currently there are things such as 7 C<bool>s in a row, then something
340 typically requiring 4 byte alignment, and then an odd C<bool> later on.
341 (C<bool>s are typically defined as C<char>s). So it would be good for someone
342 to review the ordering of the variables, to see how much alignment padding can
345 It's also worth checking that all variables are actually used. Perl 5.8.0
346 shipped with C<PL_nrs> still defined in F<thrdvar.h>, despite it being unused
347 since a change over a year earlier. Had this been spotted before release, it
348 could have been removed, but now it has to remain in the 5.8.x releases to
349 keep the structure the same size, to retain binary compatibility.
351 It's probably worth checking if all need to be the types they are. For example
353 PERLVAR(Ierror_count, I32) /* how many errors so far, max 10 */
355 might work as well if stored in a signed (or unsigned) 8 bit value, if the
356 comment is accurate. C<PL_multi_open> and C<PL_multi_close> can probably
357 become C<char>s. Finding variables to downsize coupled with rearrangement
358 could shrink the interpreter structure; a size saving which is multiplied by
359 the number of threads running.
361 =head2 Profile Perl - am I hot or not?
363 The Perl source code is stable enough that it makes sense to profile it,
364 identify and optimise the hotspots. It would be good to measure the
365 performance of the Perl interpreter using free tools such as cachegrind,
366 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
368 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
369 the ops that are most commonly used. The idea is that by grouping them, their
370 object code will be adjacent in the executable, so they have a greater chance
371 of already being in the CPU cache (or swapped in) due to being near another op
374 Except that it's not clear if these really are the most commonly used ops. So
375 as part of exercising your skills with coverage and profiling tools you might
376 want to determine what ops I<really> are the most commonly used. And in turn
377 suggest evictions and promotions to achieve a better F<pp_hot.c>.
379 =head2 Allocate OPs from arenas
381 Currently all new OP structures are individually malloc()ed and free()d.
382 All C<malloc> implementations have space overheads, and are now as fast as
383 custom allocates so it would both use less memory and less CPU to allocate
384 the various OP structures from arenas. The SV arena code can probably be
387 =head2 Improve win32/wince.c
389 Currently, numerous functions look virtually, if not completely,
390 identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
393 =head1 Tasks that need a knowledge of XS
395 These tasks would need C knowledge, and roughly the level of knowledge of
396 the perl API that comes from writing modules that use XS to interface to
399 =head2 shrink C<PVBM>s
401 By removing unused elements and careful re-ordering, the structures for C<AV>s,
402 C<HV>s, C<CV>s and C<GV>s have recently been shrunk considerably. C<PVIO>s
403 probably aren't worth it, as typical programs don't use more than 8, and
404 (at least) C<Filter::Util::Call> uses C<SvPVX>/C<SvCUR>/C<SvLEN> on a C<PVIO>,
405 so it would mean code changes to modules on CPAN. C<PVBM>s might have some
408 =head2 autovivification
410 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
412 This task is incremental - even a little bit of work on it will help.
414 =head2 Unicode in Filenames
416 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
417 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
418 system, truncate, unlink, utime, -X. All these could potentially accept
419 Unicode filenames either as input or output (and in the case of system
420 and qx Unicode in general, as input or output to/from the shell).
421 Whether a filesystem - an operating system pair understands Unicode in
424 Known combinations that have some level of understanding include
425 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
426 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
427 create Unicode filenames, what forms of Unicode are accepted and used
428 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
429 and so on, varies. Finding the right level of interfacing to Perl
430 requires some thought. Remember that an OS does not implicate a
433 (The Windows -C command flag "wide API support" has been at least
434 temporarily retired in 5.8.1, and the -C has been repurposed, see
437 =head2 Unicode in %ENV
439 Currently the %ENV entries are always byte strings.
441 =head2 use less 'memory'
443 Investigate trade offs to switch out perl's choices on memory usage.
444 Particularly perl should be able to give memory back.
446 This task is incremental - even a little bit of work on it will help.
448 =head2 Re-implement C<:unique> in a way that is actually thread-safe
450 The old implementation made bad assumptions on several levels. A good 90%
451 solution might be just to make C<:unique> work to share the string buffer
452 of SvPVs. That way large constant strings can be shared between ithreads,
453 such as the configuration information in F<Config>.
455 =head2 Make tainting consistent
457 Tainting would be easier to use if it didn't take documented shortcuts and
458 allow taint to "leak" everywhere within an expression.
460 =head2 readpipe(LIST)
462 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
463 running a shell. readpipe() (the function behind qx//) could be similarly
466 =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
468 Maybe create a utility that checks after each libperl.a creation that
469 none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
470 ever creep back to libperl.a.
472 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
474 Note, of course, that this will only tell whether B<your> platform
475 is using those naughty interfaces.
477 =head2 Audit the code for destruction ordering assumptions
481 /* Need to check SvMAGICAL, as during global destruction it may be that
482 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
483 is now part of the linked list of SV heads, rather than pointing to
484 the original body. */
485 /* FIXME - audit the code for other bugs like this one. */
487 adding the C<SvMAGICAL> check to
489 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
490 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
492 Go through the core and look for similar assumptions that SVs have particular
493 types, as all bets are off during global destruction.
495 =head1 Tasks that need a knowledge of the interpreter
497 These tasks would need C knowledge, and knowledge of how the interpreter works,
498 or a willingness to learn.
500 =head2 Implement $value ~~ 0 .. $range
502 It would be nice to extend the syntax of the C<~~> operator to also
503 understand numeric (and maybe alphanumeric) ranges.
505 =head2 Attach/detach debugger from running program
507 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
508 program if you pass the process ID. It would be good to do this with the Perl
509 debugger on a running Perl program, although I'm not sure how it would be
510 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
512 =head2 LVALUE functions for lists
514 The old perltodo notes that lvalue functions don't work for list or hash
515 slices. This would be good to fix.
517 =head2 LVALUE functions in the debugger
519 The old perltodo notes that lvalue functions don't work in the debugger. This
520 would be good to fix.
522 =head2 regexp optimiser optional
524 The regexp optimiser is not optional. It should configurable to be, to allow
525 its performance to be measured, and its bugs to be easily demonstrated.
527 =head2 delete &function
529 Allow to delete functions. One can already undef them, but they're still
532 =head2 optional optimizer
534 Make the peephole optimizer optional. Currently it performs two tasks as
535 it walks the optree - genuine peephole optimisations, and necessary fixups of
536 ops. It would be good to find an efficient way to switch out the
537 optimisations whilst keeping the fixups.
539 =head2 You WANT *how* many
541 Currently contexts are void, scalar and list. split has a special mechanism in
542 place to pass in the number of return values wanted. It would be useful to
543 have a general mechanism for this, backwards compatible and little speed hit.
544 This would allow proposals such as short circuiting sort to be implemented
547 =head2 lexical aliases
549 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
551 =head2 entersub XS vs Perl
553 At the moment pp_entersub is huge, and has code to deal with entering both
554 perl and XS subroutines. Subroutine implementations rarely change between
555 perl and XS at run time, so investigate using 2 ops to enter subs (one for
556 XS, one for perl) and swap between if a sub is redefined.
560 self ties are currently illegal because they caused too many segfaults. Maybe
561 the causes of these could be tracked down and self-ties on all types re-
564 =head2 Optimize away @_
566 The old perltodo notes "Look at the "reification" code in C<av.c>".
568 =head2 What hooks would assertions need?
570 Assertions are in the core, and work. However, assertions needed to be added
571 as a core patch, rather than an XS module in ext, or a CPAN module, because
572 the core has no hooks in the necessary places. It would be useful to
573 investigate what hooks would need to be added to make it possible to provide
574 the full assertion support from a CPAN module, so that we aren't constraining
575 the imagination of future CPAN authors.
577 =head2 Properly Unicode safe tokeniser and pads.
579 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
580 variable names are stored in stashes as raw bytes, without the utf-8 flag
581 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
582 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
583 source filters. All this could be fixed.
587 Tasks that will get your name mentioned in the description of the "Highlights
590 =head2 make ithreads more robust
592 Generally make ithreads more robust. See also L</iCOW>
594 This task is incremental - even a little bit of work on it will help, and
595 will be greatly appreciated.
597 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
601 Sarathy and Arthur have a proposal for an improved Copy On Write which
602 specifically will be able to COW new ithreads. If this can be implemented
603 it would be a good thing.
605 =head2 (?{...}) closures in regexps
607 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
609 =head2 A re-entrant regexp engine
611 This will allow the use of a regex from inside (?{ }), (??{ }) and
612 (?(?{ })|) constructs.
614 =head2 Add (?YES) (?NO) to regexp enigne
616 YES/NO would allow a subpattern to be passed/failed but allow backtracking.
617 Basically a more efficient (?=), (?!).
619 demerphq has this on his todo list
621 =head2 Add (?SUCCEED) (?FAIL) to regexp engine
623 SUCCEED/FAIL would allow a pattern to be passed/failed but without backtracking.
624 Thus you could signal that a pattern has matched or not, and return (regardless
625 that there is more pattern following).
627 demerphq has this on his todo list
629 =head2 Add (?CUT) (?COMMIT) to regexp engine
631 CUT would allow a pattern to say "do not backtrack beyond here".
632 COMMIT would say match from here or don't, but don't try the pattern from
633 another starting pattern.
635 These correspond to the \v and \V that Jeffrey Friedl mentions in
636 Mastering Regular Expressions 2nd edition.
638 demerphq has this on his todo list
640 =head2 Add class set operations to regexp engine
642 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
644 demerphq has this on his todo list, but right at the bottom.