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 the final 5.10.0 release
30 Review perlguts. Significant changes have occured since 5.8, and we can't
31 release a new version without making sure these are covered.
33 =head1 Tasks that only need Perl knowledge
35 =head2 common test code for timed bail out
37 Write portable self destruct code for tests to stop them burning CPU in
38 infinite loops. This needs to avoid using alarm, as some of the tests are
39 testing alarm/sleep or timers.
41 =head2 POD -> HTML conversion in the core still sucks
43 Which is crazy given just how simple POD purports to be, and how simple HTML
44 can be. It's not actually I<as> simple as it sounds, particularly with the
45 flexibility POD allows for C<=item>, but it would be good to improve the
46 visual appeal of the HTML generated, and to avoid it having any validation
47 errors. See also L</make HTML install work>, as the layout of installation tree
48 is needed to improve the cross-linking.
50 The addition of C<Pod::Simple> and its related modules may make this task
53 =head2 Parallel testing
55 (This probably impacts much more than the core: also the Test::Harness
56 and TAP::* modules on CPAN.)
58 The core regression test suite is getting ever more comprehensive, which has
59 the side effect that it takes longer to run. This isn't so good. Investigate
60 whether it would be feasible to give the harness script the B<option> of
61 running sets of tests in parallel. This would be useful for tests in
62 F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
70 How does screen layout work when you're running more than one test?
74 How does the caller of test specify how many tests to run in parallel?
78 How do setup/teardown tests identify themselves?
82 Pugs already does parallel testing - can their approach be re-used?
84 =head2 Make Schwern poorer
86 We should have tests for everything. When all the core's modules are tested,
87 Schwern has promised to donate to $500 to TPF. We may need volunteers to
88 hold him upside down and shake vigorously in order to actually extract the
91 =head2 Improve the coverage of the core tests
93 Use Devel::Cover to ascertain the core modules's test coverage, then add
94 tests that are currently missing.
98 A full test suite for the B module would be nice.
100 =head2 A decent benchmark
102 C<perlbench> seems impervious to any recent changes made to the perl core. It
103 would be useful to have a reasonable general benchmarking suite that roughly
104 represented what current perl programs do, and measurably reported whether
105 tweaks to the core improve, degrade or don't really affect performance, to
106 guide people attempting to optimise the guts of perl. Gisle would welcome
107 new tests for perlbench.
109 =head2 fix tainting bugs
111 Fix the bugs revealed by running the test suite with the C<-t> switch (via
112 C<make test.taintwarn>).
114 =head2 Dual life everything
116 As part of the "dists" plan, anything that doesn't belong in the smallest perl
117 distribution needs to be dual lifed. Anything else can be too. Figure out what
118 changes would be needed to package that module and its tests up for CPAN, and
119 do so. Test it with older perl releases, and fix the problems you find.
121 =head2 Improving C<threads::shared>
123 Investigate whether C<threads::shared> could share aggregates properly with
124 only Perl level changes to shared.pm
126 =head2 POSIX memory footprint
128 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
129 various times worked to cut it down. There is probably still fat to cut out -
130 for example POSIX passes Exporter some very memory hungry data structures.
132 =head2 embed.pl/makedef.pl
134 There is a script F<embed.pl> that generates several header files to prefix
135 all of Perl's symbols in a consistent way, to provide some semblance of
136 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
137 in F<interpvar.h> and F<thrdvar.h>. Quite a few of the functions and variables
138 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
139 doesn't understand the C macros, so the rules about which symbols are present
140 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
141 It would be good to teach C<embed.pl> to understand the conditional
142 compilation, and hence remove the duplication, and the mistakes it has caused.
144 =head2 use strict; and AutoLoad
146 Currently if you write
149 use AutoLoader 'AUTOLOAD';
154 print join (' ', No, strict, here), "!\n";
157 then C<use strict;> isn't in force within the autoloaded subroutines. It would
158 be more consistent (and less surprising) to arrange for all lexical pragmas
159 in force at the __END__ block to be in force within each autoloaded subroutine.
161 There's a similar problem with SelfLoader.
163 =head1 Tasks that need a little sysadmin-type knowledge
165 Or if you prefer, tasks that you would learn from, and broaden your skills
168 =head2 make HTML install work
170 There is an C<installhtml> target in the Makefile. It's marked as
171 "experimental". It would be good to get this tested, make it work reliably, and
172 remove the "experimental" tag. This would include
178 Checking that cross linking between various parts of the documentation works.
179 In particular that links work between the modules (files with POD in F<lib/>)
180 and the core documentation (files in F<pod/>)
184 Work out how to split C<perlfunc> into chunks, preferably one per function
185 group, preferably with general case code that could be used elsewhere.
186 Challenges here are correctly identifying the groups of functions that go
187 together, and making the right named external cross-links point to the right
188 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
189 C<endservent>, two or more C<=items> giving the different parameter lists, such
192 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
193 =item substr EXPR,OFFSET,LENGTH
194 =item substr EXPR,OFFSET
196 and different parameter lists having different meanings. (eg C<select>)
200 =head2 compressed man pages
202 Be able to install them. This would probably need a configure test to see how
203 the system does compressed man pages (same directory/different directory?
204 same filename/different filename), as well as tweaking the F<installman> script
205 to compress as necessary.
207 =head2 Add a code coverage target to the Makefile
209 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
210 to do this manually are roughly
216 do a normal C<Configure>, but include Devel::Cover as a module to install
217 (see F<INSTALL> for how to do this)
225 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
229 Process the resulting Devel::Cover database
233 This just give you the coverage of the F<.pm>s. To also get the C level
240 Additionally tell C<Configure> to use the appropriate C compiler flags for
247 (instead of C<make perl>)
251 After running the tests run C<gcov> to generate all the F<.gcov> files.
252 (Including down in the subdirectories of F<ext/>
256 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
257 to get their stats into the cover_db directory.
261 Then process the Devel::Cover database
265 It would be good to add a single switch to C<Configure> to specify that you
266 wanted to perform perl level coverage, and another to specify C level
267 coverage, and have C<Configure> and the F<Makefile> do all the right things
270 =head2 Make Config.pm cope with differences between built and installed perl
272 Quite often vendors ship a perl binary compiled with their (pay-for)
273 compilers. People install a free compiler, such as gcc. To work out how to
274 build extensions, Perl interrogates C<%Config>, so in this situation
275 C<%Config> describes compilers that aren't there, and extension building
276 fails. This forces people into choosing between re-compiling perl themselves
277 using the compiler they have, or only using modules that the vendor ships.
279 It would be good to find a way teach C<Config.pm> about the installation setup,
280 possibly involving probing at install time or later, so that the C<%Config> in
281 a binary distribution better describes the installed machine, when the
282 installed machine differs from the build machine in some significant way.
284 =head2 linker specification files
286 Some platforms mandate that you provide a list of a shared library's external
287 symbols to the linker, so the core already has the infrastructure in place to
288 do this for generating shared perl libraries. My understanding is that the
289 GNU toolchain can accept an optional linker specification file, and restrict
290 visibility just to symbols declared in that file. It would be good to extend
291 F<makedef.pl> to support this format, and to provide a means within
292 C<Configure> to enable it. This would allow Unix users to test that the
293 export list is correct, and to build a perl that does not pollute the global
294 namespace with private symbols.
296 =head2 Cross-compile support
298 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
299 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
300 assumed then to be copied to TARGET machine and used as a replacement of full
303 This could be done little differently. Namely C<miniperl> should be built for
304 HOST and then full C<perl> with extensions should be compiled for TARGET.
305 This, however, might require extra trickery for %Config: we have one config
306 first for HOST and then another for TARGET.
308 =head1 Tasks that need a little C knowledge
310 These tasks would need a little C knowledge, but don't need any specific
311 background or experience with XS, or how the Perl interpreter works
313 =head2 Make it clear from -v if this is the exact official release
315 Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
316 usually defines one local patch, of the form "MAINT12345" or "RC1". The output
317 of perl -v doesn't report that a perl isn't an official release, and this
318 information can get lost in bugs reports. Because of this, the minor version
319 isn't bumped up until RC time, to minimise the possibility of versions of perl
320 escaping that believe themselves to be newer than they actually are.
322 It would be useful to find an elegant way to have the "this is an interim
323 maintenance release" or "this is a release candidate" in the terse -v output,
324 and have it so that it's easy for the pumpking to remove this just as the
325 release tarball is rolled up. This way the version pulled out of rsync would
326 always say "I'm a development release" and it would be safe to bump the
327 reported minor version as soon as a release ships, which would aid perl
330 This task is really about thinking of an elegant way to arrange the C source
331 such that it's trivial for the Pumpking to flag "this is an official release"
332 when making a tarball, yet leave the default source saying "I'm not the
335 =head2 Ordering of "global" variables.
337 F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
338 per-thread under ithreads, where the variables are actually elements in a
339 structure. As C dictates, the variables must be laid out in order of
340 declaration. There is a comment
341 C</* Important ones in the first cache line (if alignment is done right) */>
342 which implies that at some point in the past the ordering was carefully chosen
343 (at least in part). However, it's clear that the ordering is less than perfect,
344 as currently there are things such as 7 C<bool>s in a row, then something
345 typically requiring 4 byte alignment, and then an odd C<bool> later on.
346 (C<bool>s are typically defined as C<char>s). So it would be good for someone
347 to review the ordering of the variables, to see how much alignment padding can
350 It's also worth checking that all variables are actually used. Perl 5.8.0
351 shipped with C<PL_nrs> still defined in F<thrdvar.h>, despite it being unused
352 since a change over a year earlier. Had this been spotted before release, it
353 could have been removed, but now it has to remain in the 5.8.x releases to
354 keep the structure the same size, to retain binary compatibility.
356 It's probably worth checking if all need to be the types they are. For example
358 PERLVAR(Ierror_count, I32) /* how many errors so far, max 10 */
360 might work as well if stored in a signed (or unsigned) 8 bit value, if the
361 comment is accurate. C<PL_multi_open> and C<PL_multi_close> can probably
362 become C<char>s. Finding variables to downsize coupled with rearrangement
363 could shrink the interpreter structure; a size saving which is multiplied by
364 the number of threads running.
366 =head2 Profile Perl - am I hot or not?
368 The Perl source code is stable enough that it makes sense to profile it,
369 identify and optimise the hotspots. It would be good to measure the
370 performance of the Perl interpreter using free tools such as cachegrind,
371 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
373 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
374 the ops that are most commonly used. The idea is that by grouping them, their
375 object code will be adjacent in the executable, so they have a greater chance
376 of already being in the CPU cache (or swapped in) due to being near another op
379 Except that it's not clear if these really are the most commonly used ops. So
380 as part of exercising your skills with coverage and profiling tools you might
381 want to determine what ops I<really> are the most commonly used. And in turn
382 suggest evictions and promotions to achieve a better F<pp_hot.c>.
384 =head2 Allocate OPs from arenas
386 Currently all new OP structures are individually malloc()ed and free()d.
387 All C<malloc> implementations have space overheads, and are now as fast as
388 custom allocates so it would both use less memory and less CPU to allocate
389 the various OP structures from arenas. The SV arena code can probably be
392 =head2 Improve win32/wince.c
394 Currently, numerous functions look virtually, if not completely,
395 identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
398 =head2 Use secure CRT functions when building with VC8 on Win32
400 Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
401 that they were "unsafe" and introduced differently named secure versions of
402 them as replacements, e.g. instead of writing
404 FILE* f = fopen(__FILE__, "r");
409 errno_t err = fopen_s(&f, __FILE__, "r");
411 Currently, the warnings about these deprecations have been disabled by adding
412 -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
413 warning suppressant and actually make use of the new secure CRT functions.
415 There is also a similar issue with POSIX CRT function names like fileno having
416 been deprecated in favour of ISO C++ conformant names like _fileno. These
417 warnings are also currently suppressed with the compiler option /wd4996. It
418 might be nice to do as Microsoft suggest here too, although, unlike the secure
419 functions issue, there is presumably little or no benefit in this case.
421 =head1 Tasks that need a knowledge of XS
423 These tasks would need C knowledge, and roughly the level of knowledge of
424 the perl API that comes from writing modules that use XS to interface to
427 =head2 autovivification
429 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
431 This task is incremental - even a little bit of work on it will help.
433 =head2 Unicode in Filenames
435 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
436 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
437 system, truncate, unlink, utime, -X. All these could potentially accept
438 Unicode filenames either as input or output (and in the case of system
439 and qx Unicode in general, as input or output to/from the shell).
440 Whether a filesystem - an operating system pair understands Unicode in
443 Known combinations that have some level of understanding include
444 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
445 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
446 create Unicode filenames, what forms of Unicode are accepted and used
447 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
448 and so on, varies. Finding the right level of interfacing to Perl
449 requires some thought. Remember that an OS does not implicate a
452 (The Windows -C command flag "wide API support" has been at least
453 temporarily retired in 5.8.1, and the -C has been repurposed, see
456 =head2 Unicode in %ENV
458 Currently the %ENV entries are always byte strings.
460 =head2 Unicode and glob()
462 Currently glob patterns and filenames returned from File::Glob::glob()
463 are always byte strings.
465 =head2 use less 'memory'
467 Investigate trade offs to switch out perl's choices on memory usage.
468 Particularly perl should be able to give memory back.
470 This task is incremental - even a little bit of work on it will help.
472 =head2 Re-implement C<:unique> in a way that is actually thread-safe
474 The old implementation made bad assumptions on several levels. A good 90%
475 solution might be just to make C<:unique> work to share the string buffer
476 of SvPVs. That way large constant strings can be shared between ithreads,
477 such as the configuration information in F<Config>.
479 =head2 Make tainting consistent
481 Tainting would be easier to use if it didn't take documented shortcuts and
482 allow taint to "leak" everywhere within an expression.
484 =head2 readpipe(LIST)
486 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
487 running a shell. readpipe() (the function behind qx//) could be similarly
490 =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
492 Maybe create a utility that checks after each libperl.a creation that
493 none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
494 ever creep back to libperl.a.
496 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
498 Note, of course, that this will only tell whether B<your> platform
499 is using those naughty interfaces.
501 =head2 Audit the code for destruction ordering assumptions
505 /* Need to check SvMAGICAL, as during global destruction it may be that
506 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
507 is now part of the linked list of SV heads, rather than pointing to
508 the original body. */
509 /* FIXME - audit the code for other bugs like this one. */
511 adding the C<SvMAGICAL> check to
513 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
514 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
516 Go through the core and look for similar assumptions that SVs have particular
517 types, as all bets are off during global destruction.
519 =head2 Extend PerlIO and PerlIO::Scalar
521 PerlIO::Scalar doesn't know how to truncate(). Implementing this
522 would require extending the PerlIO vtable.
524 Similarly the PerlIO vtable doesn't know about formats (write()), or
525 about stat(), or chmod()/chown(), utime(), or flock().
527 (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
530 PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
531 opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
534 =head2 -C on the #! line
536 It should be possible to make -C work correctly if found on the #! line,
537 given that all perl command line options are strict ASCII, and -C changes
538 only the interpretation of non-ASCII characters, and not for the script file
539 handle. To make it work needs some investigation of the ordering of function
540 calls during startup, and (by implication) a bit of tweaking of that order.
543 =head1 Tasks that need a knowledge of the interpreter
545 These tasks would need C knowledge, and knowledge of how the interpreter works,
546 or a willingness to learn.
548 =head2 Implement $value ~~ 0 .. $range
550 It would be nice to extend the syntax of the C<~~> operator to also
551 understand numeric (and maybe alphanumeric) ranges.
553 =head2 Attach/detach debugger from running program
555 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
556 program if you pass the process ID. It would be good to do this with the Perl
557 debugger on a running Perl program, although I'm not sure how it would be
558 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
560 =head2 LVALUE functions for lists
562 The old perltodo notes that lvalue functions don't work for list or hash
563 slices. This would be good to fix.
565 =head2 LVALUE functions in the debugger
567 The old perltodo notes that lvalue functions don't work in the debugger. This
568 would be good to fix.
570 =head2 regexp optimiser optional
572 The regexp optimiser is not optional. It should configurable to be, to allow
573 its performance to be measured, and its bugs to be easily demonstrated.
575 =head2 delete &function
577 Allow to delete functions. One can already undef them, but they're still
580 =head2 C</w> regex modifier
582 That flag would enable to match whole words, and also to interpolate
583 arrays as alternations. With it, C</P/w> would be roughly equivalent to:
585 do { local $"='|'; /\b(?:P)\b/ }
587 See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
590 =head2 optional optimizer
592 Make the peephole optimizer optional. Currently it performs two tasks as
593 it walks the optree - genuine peephole optimisations, and necessary fixups of
594 ops. It would be good to find an efficient way to switch out the
595 optimisations whilst keeping the fixups.
597 =head2 You WANT *how* many
599 Currently contexts are void, scalar and list. split has a special mechanism in
600 place to pass in the number of return values wanted. It would be useful to
601 have a general mechanism for this, backwards compatible and little speed hit.
602 This would allow proposals such as short circuiting sort to be implemented
605 =head2 lexical aliases
607 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
609 =head2 entersub XS vs Perl
611 At the moment pp_entersub is huge, and has code to deal with entering both
612 perl and XS subroutines. Subroutine implementations rarely change between
613 perl and XS at run time, so investigate using 2 ops to enter subs (one for
614 XS, one for perl) and swap between if a sub is redefined.
618 self ties are currently illegal because they caused too many segfaults. Maybe
619 the causes of these could be tracked down and self-ties on all types re-
622 =head2 Optimize away @_
624 The old perltodo notes "Look at the "reification" code in C<av.c>".
626 =head2 What hooks would assertions need?
628 Assertions are in the core, and work. However, assertions needed to be added
629 as a core patch, rather than an XS module in ext, or a CPAN module, because
630 the core has no hooks in the necessary places. It would be useful to
631 investigate what hooks would need to be added to make it possible to provide
632 the full assertion support from a CPAN module, so that we aren't constraining
633 the imagination of future CPAN authors.
635 =head2 Properly Unicode safe tokeniser and pads.
637 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
638 variable names are stored in stashes as raw bytes, without the utf-8 flag
639 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
640 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
641 source filters. All this could be fixed.
643 =head2 The yada yada yada operators
645 Perl 6's Synopsis 3 says:
647 I<The ... operator is the "yada, yada, yada" list operator, which is used as
648 the body in function prototypes. It complains bitterly (by calling fail)
649 if it is ever executed. Variant ??? calls warn, and !!! calls die.>
651 Those would be nice to add to Perl 5. That could be done without new ops.
655 Tasks that will get your name mentioned in the description of the "Highlights
658 =head2 make ithreads more robust
660 Generally make ithreads more robust. See also L</iCOW>
662 This task is incremental - even a little bit of work on it will help, and
663 will be greatly appreciated.
665 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
667 Fix Perl_sv_dup, et al so that threads can return objects.
671 Sarathy and Arthur have a proposal for an improved Copy On Write which
672 specifically will be able to COW new ithreads. If this can be implemented
673 it would be a good thing.
675 =head2 (?{...}) closures in regexps
677 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
679 =head2 A re-entrant regexp engine
681 This will allow the use of a regex from inside (?{ }), (??{ }) and
682 (?(?{ })|) constructs.
684 =head2 Add class set operations to regexp engine
686 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
688 demerphq has this on his todo list, but right at the bottom.