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 5.9.4 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::warnings> should be turned into a lexical pragma.
40 C<encoding> should, too (probably).
44 =head2 Needed for a 5.9.5 release
49 Implement L</_ prototype character>
52 Implement L</state variables>
56 =head2 Needed for a 5.9.6 release
58 Stabilisation. If all goes well, this will be the equivalent of a 5.10-beta.
60 =head1 Tasks that only need Perl knowledge
62 =head2 common test code for timed bail out
64 Write portable self destruct code for tests to stop them burning CPU in
65 infinite loops. This needs to avoid using alarm, as some of the tests are
66 testing alarm/sleep or timers.
68 =head2 POD -> HTML conversion in the core still sucks
70 Which is crazy given just how simple POD purports to be, and how simple HTML
71 can be. It's not actually I<as> simple as it sounds, particularly with the
72 flexibility POD allows for C<=item>, but it would be good to improve the
73 visual appeal of the HTML generated, and to avoid it having any validation
74 errors. See also L</make HTML install work>, as the layout of installation tree
75 is needed to improve the cross-linking.
77 The addition of C<Pod::Simple> and its related modules may make this task
80 =head2 Parallel testing
82 The core regression test suite is getting ever more comprehensive, which has
83 the side effect that it takes longer to run. This isn't so good. Investigate
84 whether it would be feasible to give the harness script the B<option> of
85 running sets of tests in parallel. This would be useful for tests in
86 F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
94 How does screen layout work when you're running more than one test?
98 How does the caller of test specify how many tests to run in parallel?
102 How do setup/teardown tests identify themselves?
106 Pugs already does parallel testing - can their approach be re-used?
108 =head2 Make Schwern poorer
110 We should have tests for everything. When all the core's modules are tested,
111 Schwern has promised to donate to $500 to TPF. We may need volunteers to
112 hold him upside down and shake vigorously in order to actually extract the
115 See F<t/lib/1_compile.t> for the 3 remaining modules that need tests.
117 =head2 Improve the coverage of the core tests
119 Use Devel::Cover to ascertain the core's test coverage, then add tests that
120 are currently missing.
124 A full test suite for the B module would be nice.
126 =head2 A decent benchmark
128 C<perlbench> seems impervious to any recent changes made to the perl core. It
129 would be useful to have a reasonable general benchmarking suite that roughly
130 represented what current perl programs do, and measurably reported whether
131 tweaks to the core improve, degrade or don't really affect performance, to
132 guide people attempting to optimise the guts of perl. Gisle would welcome
133 new tests for perlbench.
135 =head2 fix tainting bugs
137 Fix the bugs revealed by running the test suite with the C<-t> switch (via
138 C<make test.taintwarn>).
140 =head2 Dual life everything
142 As part of the "dists" plan, anything that doesn't belong in the smallest perl
143 distribution needs to be dual lifed. Anything else can be too. Figure out what
144 changes would be needed to package that module and its tests up for CPAN, and
145 do so. Test it with older perl releases, and fix the problems you find.
147 =head2 Improving C<threads::shared>
149 Investigate whether C<threads::shared> could share aggregates properly with
150 only Perl level changes to shared.pm
152 =head2 POSIX memory footprint
154 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
155 various times worked to cut it down. There is probably still fat to cut out -
156 for example POSIX passes Exporter some very memory hungry data structures.
158 =head2 embed.pl/makedef.pl
160 There is a script F<embed.pl> that generates several header files to prefix
161 all of Perl's symbols in a consistent way, to provide some semblance of
162 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
163 in F<interpvar.h> and F<thrdvar.h>. Quite a few of the functions and variables
164 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
165 doesn't understand the C macros, so the rules about which symbols are present
166 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
167 It would be good to teach C<embed.pl> to understand the conditional
168 compilation, and hence remove the duplication, and the mistakes it has caused.
175 =head1 Tasks that need a little sysadmin-type knowledge
177 Or if you prefer, tasks that you would learn from, and broaden your skills
180 =head2 make HTML install work
182 There is an C<installhtml> target in the Makefile. It's marked as
183 "experimental". It would be good to get this tested, make it work reliably, and
184 remove the "experimental" tag. This would include
190 Checking that cross linking between various parts of the documentation works.
191 In particular that links work between the modules (files with POD in F<lib/>)
192 and the core documentation (files in F<pod/>)
196 Work out how to split C<perlfunc> into chunks, preferably one per function
197 group, preferably with general case code that could be used elsewhere.
198 Challenges here are correctly identifying the groups of functions that go
199 together, and making the right named external cross-links point to the right
200 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
201 C<endservent>, two or more C<=items> giving the different parameter lists, such
204 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
205 =item substr EXPR,OFFSET,LENGTH
206 =item substr EXPR,OFFSET
208 and different parameter lists having different meanings. (eg C<select>)
212 =head2 compressed man pages
214 Be able to install them. This would probably need a configure test to see how
215 the system does compressed man pages (same directory/different directory?
216 same filename/different filename), as well as tweaking the F<installman> script
217 to compress as necessary.
219 =head2 Add a code coverage target to the Makefile
221 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
222 to do this manually are roughly
228 do a normal C<Configure>, but include Devel::Cover as a module to install
229 (see F<INSTALL> for how to do this)
237 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
241 Process the resulting Devel::Cover database
245 This just give you the coverage of the F<.pm>s. To also get the C level
252 Additionally tell C<Configure> to use the appropriate C compiler flags for
259 (instead of C<make perl>)
263 After running the tests run C<gcov> to generate all the F<.gcov> files.
264 (Including down in the subdirectories of F<ext/>
268 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
269 to get their stats into the cover_db directory.
273 Then process the Devel::Cover database
277 It would be good to add a single switch to C<Configure> to specify that you
278 wanted to perform perl level coverage, and another to specify C level
279 coverage, and have C<Configure> and the F<Makefile> do all the right things
282 =head2 Make Config.pm cope with differences between build and installed perl
284 Quite often vendors ship a perl binary compiled with their (pay-for)
285 compilers. People install a free compiler, such as gcc. To work out how to
286 build extensions, Perl interrogates C<%Config>, so in this situation
287 C<%Config> describes compilers that aren't there, and extension building
288 fails. This forces people into choosing between re-compiling perl themselves
289 using the compiler they have, or only using modules that the vendor ships.
291 It would be good to find a way teach C<Config.pm> about the installation setup,
292 possibly involving probing at install time or later, so that the C<%Config> in
293 a binary distribution better describes the installed machine, when the
294 installed machine differs from the build machine in some significant way.
296 =head2 linker specification files
298 Some platforms mandate that you provide a list of a shared library's external
299 symbols to the linker, so the core already has the infrastructure in place to
300 do this for generating shared perl libraries. My understanding is that the
301 GNU toolchain can accept an optional linker specification file, and restrict
302 visibility just to symbols declared in that file. It would be good to extend
303 F<makedef.pl> to support this format, and to provide a means within
304 C<Configure> to enable it. This would allow Unix users to test that the
305 export list is correct, and to build a perl that does not pollute the global
306 namespace with private symbols.
311 =head1 Tasks that need a little C knowledge
313 These tasks would need a little C knowledge, but don't need any specific
314 background or experience with XS, or how the Perl interpreter works
316 =head2 Make it clear from -v if this is the exact official release
318 Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
319 usually defines one local patch, of the form "MAINT12345" or "RC1". The output
320 of perl -v doesn't report that a perl isn't an official release, and this
321 information can get lost in bugs reports. Because of this, the minor version
322 isn't bumped up until RC time, to minimise the possibility of versions of perl
323 escaping that believe themselves to be newer than they actually are.
325 It would be useful to find an elegant way to have the "this is an interim
326 maintenance release" or "this is a release candidate" in the terse -v output,
327 and have it so that it's easy for the pumpking to remove this just as the
328 release tarball is rolled up. This way the version pulled out of rsync would
329 always say "I'm a development release" and it would be safe to bump the
330 reported minor version as soon as a release ships, which would aid perl
333 This task is really about thinking of an elegant way to arrange the C source
334 such that it's trivial for the Pumpking to flag "this is an official release"
335 when making a tarball, yet leave the default source saying "I'm not the
338 =head2 Ordering of "global" variables.
340 F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
341 per-thread under ithreads, where the variables are actually elements in a
342 structure. As C dictates, the variables must be laid out in order of
343 declaration. There is a comment
344 C</* Important ones in the first cache line (if alignment is done right) */>
345 which implies that at some point in the past the ordering was carefully chosen
346 (at least in part). However, it's clear that the ordering is less than perfect,
347 as currently there are things such as 7 C<bool>s in a row, then something
348 typically requiring 4 byte alignment, and then an odd C<bool> later on.
349 (C<bool>s are typically defined as C<char>s). So it would be good for someone
350 to review the ordering of the variables, to see how much alignment padding can
353 It's also worth checking that all variables are actually used. Perl 5.8.0
354 shipped with C<PL_nrs> still defined in F<thrdvar.h>, despite it being unused
355 since a change over a year earlier. Had this been spotted before release, it
356 could have been removed, but now it has to remain in the 5.8.x releases to
357 keep the structure the same size, to retain binary compatibility.
359 It's probably worth checking if all need to be the types they are. For example
361 PERLVAR(Ierror_count, I32) /* how many errors so far, max 10 */
363 might work as well if stored in a signed (or unsigned) 8 bit value, if the
364 comment is accurate. C<PL_multi_open> and C<PL_multi_close> can probably
365 become C<char>s. Finding variables to downsize coupled with rearrangement
366 could shrink the interpreter structure; a size saving which is multiplied by
367 the number of threads running.
369 =head2 Profile Perl - am I hot or not?
371 The Perl source code is stable enough that it makes sense to profile it,
372 identify and optimise the hotspots. It would be good to measure the
373 performance of the Perl interpreter using free tools such as cachegrind,
374 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
376 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
377 the ops that are most commonly used. The idea is that by grouping them, their
378 object code will be adjacent in the executable, so they have a greater chance
379 of already being in the CPU cache (or swapped in) due to being near another op
382 Except that it's not clear if these really are the most commonly used ops. So
383 as part of exercising your skills with coverage and profiling tools you might
384 want to determine what ops I<really> are the most commonly used. And in turn
385 suggest evictions and promotions to achieve a better F<pp_hot.c>.
387 =head2 Shrink struct context
392 U32 cx_type; /* what kind of context this is */
395 struct subst cx_subst;
399 There are less than 256 values for C<cx_type>, and the constituent parts
400 C<struct block> and C<struct subst> both contain some C<U8> and C<U16> fields,
401 so it should be possible to move them to the first word, and share space with
402 a C<U8> C<cx_type>, saving 1 word.
404 =head2 Allocate OPs from arenas
406 Currently all new OP structures are individually malloc()ed and free()d.
407 All C<malloc> implementations have space overheads, and are now as fast as
408 custom allocates so it would both use less memory and less CPU to allocate
409 the various OP structures from arenas. The SV arena code can probably be
412 =head2 Merge the win32 and wince codebases
414 Currently, code used to build Perl on Win32 and WinCE are maintained
415 separately, but use much of the same code. We currently have a very high
416 probability of the code diverging when it shouldn't. Ideally, the code
417 for the two systems should be merged so that common code between the two
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 shrink C<PVBM>s
429 By removing unused elements and careful re-ordering, the structures for C<AV>s,
430 C<HV>s, C<CV>s and C<GV>s have recently been shrunk considerably. C<PVIO>s
431 probably aren't worth it, as typical programs don't use more than 8, and
432 (at least) C<Filter::Util::Call> uses C<SvPVX>/C<SvCUR>/C<SvLEN> on a C<PVIO>,
433 so it would mean code changes to modules on CPAN. C<PVBM>s might have some
436 =head2 Implicit Latin 1 => Unicode translation
438 Conversions from byte strings to UTF-8 currently map high bit characters
439 to Unicode without translation (or, depending on how you look at it, by
440 implicitly assuming that the byte strings are in Latin-1). As perl assumes
441 the C locale by default, upgrading a string to UTF-8 may change the
442 meaning of its contents regarding character classes, case mapping, etc.
443 This should probably emit a warning (at least).
445 This task is incremental - even a little bit of work on it will help.
447 =head2 autovivification
449 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
451 This task is incremental - even a little bit of work on it will help.
453 =head2 Unicode in Filenames
455 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
456 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
457 system, truncate, unlink, utime, -X. All these could potentially accept
458 Unicode filenames either as input or output (and in the case of system
459 and qx Unicode in general, as input or output to/from the shell).
460 Whether a filesystem - an operating system pair understands Unicode in
463 Known combinations that have some level of understanding include
464 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
465 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
466 create Unicode filenames, what forms of Unicode are accepted and used
467 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
468 and so on, varies. Finding the right level of interfacing to Perl
469 requires some thought. Remember that an OS does not implicate a
472 (The Windows -C command flag "wide API support" has been at least
473 temporarily retired in 5.8.1, and the -C has been repurposed, see
476 =head2 Unicode in %ENV
478 Currently the %ENV entries are always byte strings.
480 =head2 use less 'memory'
482 Investigate trade offs to switch out perl's choices on memory usage.
483 Particularly perl should be able to give memory back.
485 This task is incremental - even a little bit of work on it will help.
487 =head2 Re-implement C<:unique> in a way that is actually thread-safe
489 The old implementation made bad assumptions on several levels. A good 90%
490 solution might be just to make C<:unique> work to share the string buffer
491 of SvPVs. That way large constant strings can be shared between ithreads,
492 such as the configuration information in F<Config>.
494 =head2 Make tainting consistent
496 Tainting would be easier to use if it didn't take documented shortcuts and
497 allow taint to "leak" everywhere within an expression.
499 =head2 readpipe(LIST)
501 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
502 running a shell. readpipe() (the function behind qx//) could be similarly
509 =head1 Tasks that need a knowledge of the interpreter
511 These tasks would need C knowledge, and knowledge of how the interpreter works,
512 or a willingness to learn.
514 =head2 lexical pragmas
516 Document the new support for lexical pragmas in 5.9.3 and how %^H works.
517 Maybe C<re>, C<encoding>, maybe other pragmas could be made lexical.
519 =head2 Attach/detach debugger from running program
521 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
522 program if you pass the process ID. It would be good to do this with the Perl
523 debugger on a running Perl program, although I'm not sure how it would be
524 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
526 =head2 LVALUE functions for lists
528 The old perltodo notes that lvalue functions don't work for list or hash
529 slices. This would be good to fix.
531 =head2 LVALUE functions in the debugger
533 The old perltodo notes that lvalue functions don't work in the debugger. This
534 would be good to fix.
536 =head2 _ prototype character
538 Study the possibility of adding a new prototype character, C<_>, meaning
539 "this argument defaults to $_".
541 =head2 state variables
543 C<my $foo if 0;> is deprecated, and should be replaced with
544 C<state $x = "initial value\n";> the syntax from Perl 6.
545 Rafael has sent a first cut patch to perl5-porters.
547 =head2 regexp optimiser optional
549 The regexp optimiser is not optional. It should configurable to be, to allow
550 its performance to be measured, and its bugs to be easily demonstrated.
554 Introduce a new special block, UNITCHECK, which is run at the end of a
555 compilation unit (module, file, eval(STRING) block). This will correspond to
556 the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
557 O.pm/B.pm backend framework depends on it.
559 =head2 optional optimizer
561 Make the peephole optimizer optional. Currently it performs two tasks as
562 it walks the optree - genuine peephole optimisations, and necessary fixups of
563 ops. It would be good to find an efficient way to switch out the
564 optimisations whilst keeping the fixups.
566 =head2 You WANT *how* many
568 Currently contexts are void, scalar and list. split has a special mechanism in
569 place to pass in the number of return values wanted. It would be useful to
570 have a general mechanism for this, backwards compatible and little speed hit.
571 This would allow proposals such as short circuiting sort to be implemented
574 =head2 lexical aliases
576 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
578 =head2 entersub XS vs Perl
580 At the moment pp_entersub is huge, and has code to deal with entering both
581 perl and XS subroutines. Subroutine implementations rarely change between
582 perl and XS at run time, so investigate using 2 ops to enter subs (one for
583 XS, one for perl) and swap between if a sub is redefined.
587 self ties are currently illegal because they caused too many segfaults. Maybe
588 the causes of these could be tracked down and self-ties on all types re-
591 =head2 Optimize away @_
593 The old perltodo notes "Look at the "reification" code in C<av.c>".
595 =head2 What hooks would assertions need?
597 Assertions are in the core, and work. However, assertions needed to be added
598 as a core patch, rather than an XS module in ext, or a CPAN module, because
599 the core has no hooks in the necessary places. It would be useful to
600 investigate what hooks would need to be added to make it possible to provide
601 the full assertion support from a CPAN module, so that we aren't constraining
602 the imagination of future CPAN authors.
604 =head2 Properly Unicode safe tokeniser and pads.
606 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
607 variable names are stored in stashes as raw bytes, without the utf-8 flag
608 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
609 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
610 source filters. All this could be fixed.
618 Tasks that will get your name mentioned in the description of the "Highlights
621 =head2 make ithreads more robust
623 Generally make ithreads more robust. See also L</iCOW>
625 This task is incremental - even a little bit of work on it will help, and
626 will be greatly appreciated.
628 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
632 Sarathy and Arthur have a proposal for an improved Copy On Write which
633 specifically will be able to COW new ithreads. If this can be implemented
634 it would be a good thing.
636 =head2 (?{...}) closures in regexps
638 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
640 =head2 A re-entrant regexp engine
642 This will allow the use of a regex from inside (?{ }), (??{ }) and
643 (?(?{ })|) constructs.