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 =head2 Needed for a 5.9.5 release
44 Implement L</_ prototype character>
47 Implement L</state variables>
51 =head2 Needed for a 5.9.6 release
53 Stabilisation. If all goes well, this will be the equivalent of a 5.10-beta.
55 =head1 Tasks that only need Perl knowledge
57 =head2 common test code for timed bail out
59 Write portable self destruct code for tests to stop them burning CPU in
60 infinite loops. This needs to avoid using alarm, as some of the tests are
61 testing alarm/sleep or timers.
63 =head2 POD -> HTML conversion in the core still sucks
65 Which is crazy given just how simple POD purports to be, and how simple HTML
66 can be. It's not actually I<as> simple as it sounds, particularly with the
67 flexibility POD allows for C<=item>, but it would be good to improve the
68 visual appeal of the HTML generated, and to avoid it having any validation
69 errors. See also L</make HTML install work>, as the layout of installation tree
70 is needed to improve the cross-linking.
72 The addition of C<Pod::Simple> and its related modules may make this task
75 =head2 Parallel testing
77 The core regression test suite is getting ever more comprehensive, which has
78 the side effect that it takes longer to run. This isn't so good. Investigate
79 whether it would be feasible to give the harness script the B<option> of
80 running sets of tests in parallel. This would be useful for tests in
81 F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
89 How does screen layout work when you're running more than one test?
93 How does the caller of test specify how many tests to run in parallel?
97 How do setup/teardown tests identify themselves?
101 Pugs already does parallel testing - can their approach be re-used?
103 =head2 Make Schwern poorer
105 We should have for everything. When all the core's modules are tested,
106 Schwern has promised to donate to $500 to TPF. We may need volunteers to
107 hold him upside down and shake vigorously in order to actually extract the
110 See F<t/lib/1_compile.t> for the 3 remaining modules that need tests.
112 =head2 Improve the coverage of the core tests
114 Use Devel::Cover to ascertain the core's test coverage, then add tests that
115 are currently missing.
119 A full test suite for the B module would be nice.
121 =head2 A decent benchmark
123 C<perlbench> seems impervious to any recent changes made to the perl core. It
124 would be useful to have a reasonable general benchmarking suite that roughly
125 represented what current perl programs do, and measurably reported whether
126 tweaks to the core improve, degrade or don't really affect performance, to
127 guide people attempting to optimise the guts of perl. Gisle would welcome
128 new tests for perlbench.
130 =head2 fix tainting bugs
132 Fix the bugs revealed by running the test suite with the C<-t> switch (via
133 C<make test.taintwarn>).
135 =head2 Dual life everything
137 As part of the "dists" plan, anything that doesn't belong in the smallest perl
138 distribution needs to be dual lifed. Anything else can be too. Figure out what
139 changes would be needed to package that module and its tests up for CPAN, and
140 do so. Test it with older perl releases, and fix the problems you find.
142 =head2 Improving C<threads::shared>
144 Investigate whether C<threads::shared> could share aggregates properly with
145 only Perl level changes to shared.pm
147 =head2 POSIX memory footprint
149 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
150 various times worked to cut it down. There is probably still fat to cut out -
151 for example POSIX passes Exporter some very memory hungry data structures.
159 =head1 Tasks that need a little sysadmin-type knowledge
161 Or if you prefer, tasks that you would learn from, and broaden your skills
164 =head2 Relocatable perl
166 The C level patches needed to create a relocatable perl binary are done, as
167 is the work on F<Config.pm>. All that's left to do is the C<Configure> tweaking
168 to let people specify how they want to do the install.
170 =head2 make HTML install work
172 There is an C<installhtml> target in the Makefile. It's marked as
173 "experimental". It would be good to get this tested, make it work reliably, and
174 remove the "experimental" tag. This would include
180 Checking that cross linking between various parts of the documentation works.
181 In particular that links work between the modules (files with POD in F<lib/>)
182 and the core documentation (files in F<pod/>)
186 Work out how to split C<perlfunc> into chunks, preferably one per function
187 group, preferably with general case code that could be used elsewhere.
188 Challenges here are correctly identifying the groups of functions that go
189 together, and making the right named external cross-links point to the right
190 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
191 C<endservent>, two or more C<=items> giving the different parameter lists, such
194 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
196 =item substr EXPR,OFFSET,LENGTH
198 =item substr EXPR,OFFSET
200 and different parameter lists having different meanings. (eg C<select>)
204 =head2 compressed man pages
206 Be able to install them. This would probably need a configure test to see how
207 the system does compressed man pages (same directory/different directory?
208 same filename/different filename), as well as tweaking the F<installman> script
209 to compress as necessary.
211 =head2 Add a code coverage target to the Makefile
213 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
214 to do this manually are roughly
220 do a normal C<Configure>, but include Devel::Cover as a module to install
221 (see F<INSTALL> for how to do this)
229 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
233 Process the resulting Devel::Cover database
237 This just give you the coverage of the F<.pm>s. To also get the C level
244 Additionally tell C<Configure> to use the appropriate C compiler flags for
251 (instead of C<make perl>)
255 After running the tests run C<gcov> to generate all the F<.gcov> files.
256 (Including down in the subdirectories of F<ext/>
260 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
261 to get their stats into the cover_db directory.
265 Then process the Devel::Cover database
269 It would be good to add a single switch to C<Configure> to specify that you
270 wanted to perform perl level coverage, and another to specify C level
271 coverage, and have C<Configure> and the F<Makefile> do all the right things
274 =head2 Make Config.pm cope with differences between build and installed perl
276 Quite often vendors ship a perl binary compiled with their (pay-for)
277 compilers. People install a free compiler, such as gcc. To work out how to
278 build extensions, Perl interrogates C<%Config>, so in this situation
279 C<%Config> describes compilers that aren't there, and extension building
280 fails. This forces people into choosing between re-compiling perl themselves
281 using the compiler they have, or only using modules that the vendor ships.
283 It would be good to find a way teach C<Config.pm> about the installation setup,
284 possibly involving probing at install time or later, so that the C<%Config> in
285 a binary distribution better describes the installed machine, when the
286 installed machine differs from the build machine in some significant way.
288 =head2 make parallel builds work
290 Currently parallel builds (such as C<make -j3>) don't work reliably. We believe
291 that this is due to incomplete dependency specification in the F<Makefile>.
292 It would be good if someone were able to track down the causes of these
293 problems, so that parallel builds worked properly.
295 =head2 linker specification files
297 Some platforms mandate that you provide a list of a shared library's external
298 symbols to the linker, so the core already has the infrastructure in place to
299 do this for generating shared perl libraries. My understanding is that the
300 GNU toolchain can accept an optional linker specification file, and restrict
301 visibility just to symbols declared in that file. It would be good to extend
302 F<makedef.pl> to support this format, and to provide a means within
303 C<Configure> to enable it. This would allow Unix users to test that the
304 export list is correct, and to build a perl that does not pollute the global
305 namespace with private symbols.
310 =head1 Tasks that need a little C knowledge
312 These tasks would need a little C knowledge, but don't need any specific
313 background or experience with XS, or how the Perl interpreter works
315 =head2 Make it clear from -v if this is the exact official release
317 Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
318 usually defines one local patch, of the form "MAINT12345" or "RC1". The output
319 of perl -v doesn't report that a perl isn't an official release, and this
320 information can get lost in bugs reports. Because of this, the minor version
321 isn't bumped up until RC time, to minimise the possibility of versions of perl
322 escaping that believe themselves to be newer than they actually are.
324 It would be useful to find an elegant way to have the "this is an interim
325 maintenance release" or "this is a release candidate" in the terse -v output,
326 and have it so that it's easy for the pumpking to remove this just as the
327 release tarball is rolled up. This way the version pulled out of rsync would
328 always say "I'm a development release" and it would be safe to bump the
329 reported minor version as soon as a release ships, which would aid perl
332 This task is really about thinking of an elegant way to arrange the C source
333 such that it's trivial for the Pumpking to flag "this is an official release"
334 when making a tarball, yet leave the default source saying "I'm not the
337 =head2 Ordering of "global" variables.
339 F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
340 per-thread under ithreads, where the variables are actually elements in a
341 structure. As C dictates, the variables must be laid out in order of
342 declaration. There is a comment
343 C</* Important ones in the first cache line (if alignment is done right) */>
344 which implies that at some point in the past the ordering was carefully chosen
345 (at least in part). However, it's clear that the ordering is less than perfect,
346 as currently there are things such as 7 C<bool>s in a row, then something
347 typically requiring 4 byte alignment, and then an odd C<bool> later on.
348 (C<bool>s are typically defined as C<char>s). So it would be good for someone
349 to review the ordering of the variables, to see how much alignment padding can
352 It's also worth checking that all variables are actually used. Perl 5.8.0
353 shipped with C<PL_nrs> still defined in F<thrdvar.h>, despite it being unused
354 since a change over a year earlier. Had this been spotted before release, it
355 could have been removed, but now it has to remain in the 5.8.x releases to
356 keep the structure the same size, to retain binary compatibility.
358 =head2 am I hot or not?
360 The idea of F<pp_hot.c> is that it contains the I<hot> ops, the ops that are
361 most commonly used. The idea is that by grouping them, their object code will
362 be adjacent in the executable, so they have a greater chance of already being
363 in the CPU cache (or swapped in) due to being near another op already in use.
365 Except that it's not clear if these really are the most commonly used ops. So
366 anyone feeling like exercising their skill with coverage and profiling tools
367 might want to determine what ops I<really> are the most commonly used. And in
368 turn suggest evictions and promotions to achieve a better F<pp_hot.c>.
373 =head1 Tasks that need a knowledge of XS
375 These tasks would need C knowledge, and roughly the level of knowledge of
376 the perl API that comes from writing modules that use XS to interface to
381 Clean this up. Check everything in core works
383 =head2 shrink C<GV>s, C<CV>s
385 By removing unused elements and careful re-ordering, the structures for C<AV>s
386 and C<HV>s have recently been shrunk considerably. It's probable that the same
387 approach would find savings in C<GV>s and C<CV>s, if not all the other
388 larger-than-C<PVMG> types.
390 =head2 UTF8 caching code
392 The string position/offset cache is not optional. It should be.
394 =head2 Implicit Latin 1 => Unicode translation
396 Conversions from byte strings to UTF-8 currently map high bit characters
397 to Unicode without translation (or, depending on how you look at it, by
398 implicitly assuming that the byte strings are in Latin-1). As perl assumes
399 the C locale by default, upgrading a string to UTF-8 may change the
400 meaning of its contents regarding character classes, case mapping, etc.
401 This should probably emit a warning (at least).
403 This task is incremental - even a little bit of work on it will help.
405 =head2 autovivification
407 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
409 This task is incremental - even a little bit of work on it will help.
411 =head2 Unicode in Filenames
413 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
414 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
415 system, truncate, unlink, utime, -X. All these could potentially accept
416 Unicode filenames either as input or output (and in the case of system
417 and qx Unicode in general, as input or output to/from the shell).
418 Whether a filesystem - an operating system pair understands Unicode in
421 Known combinations that have some level of understanding include
422 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
423 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
424 create Unicode filenames, what forms of Unicode are accepted and used
425 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
426 and so on, varies. Finding the right level of interfacing to Perl
427 requires some thought. Remember that an OS does not implicate a
430 (The Windows -C command flag "wide API support" has been at least
431 temporarily retired in 5.8.1, and the -C has been repurposed, see
434 =head2 Unicode in %ENV
436 Currently the %ENV entries are always byte strings.
438 =head2 use less 'memory'
440 Investigate trade offs to switch out perl's choices on memory usage.
441 Particularly perl should be able to give memory back.
443 This task is incremental - even a little bit of work on it will help.
445 =head2 Re-implement C<:unique> in a way that is actually thread-safe
447 The old implementation made bad assumptions on several levels. A good 90%
448 solution might be just to make C<:unique> work to share the string buffer
449 of SvPVs. That way large constant strings can be shared between ithreads,
450 such as the configuration information in F<Config>.
452 =head2 Make tainting consistent
454 Tainting would be easier to use if it didn't take documented shortcuts and
455 allow taint to "leak" everywhere within an expression.
457 =head2 readpipe(LIST)
459 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
460 running a shell. readpipe() (the function behind qx//) could be similarly
467 =head1 Tasks that need a knowledge of the interpreter
469 These tasks would need C knowledge, and knowledge of how the interpreter works,
470 or a willingness to learn.
472 =head2 lexical pragmas
474 Document the new support for lexical pragmas in 5.9.3 and how %^H works.
475 Maybe C<re>, C<encoding>, maybe other pragmas could be made lexical.
477 =head2 Attach/detach debugger from running program
479 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
480 program if you pass the process ID. It would be good to do this with the Perl
481 debugger on a running Perl program, although I'm not sure how it would be
482 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
484 =head2 Constant folding
486 The peephole optimiser should trap errors during constant folding, and give
487 up on the folding, rather than bailing out at compile time. It is quite
488 possible that the unfoldable constant is in unreachable code, eg something
489 akin to C<$a = 0/0 if 0;>
491 =head2 LVALUE functions for lists
493 The old perltodo notes that lvalue functions don't work for list or hash
494 slices. This would be good to fix.
496 =head2 LVALUE functions in the debugger
498 The old perltodo notes that lvalue functions don't work in the debugger. This
499 would be good to fix.
501 =head2 _ prototype character
503 Study the possibility of adding a new prototype character, C<_>, meaning
504 "this argument defaults to $_".
506 =head2 state variables
508 C<my $foo if 0;> is deprecated, and should be replaced with
509 C<state $x = "initial value\n";> the syntax from Perl 6.
511 =head2 @INC source filter to Filter::Simple
513 The second return value from a sub in @INC can be a source filter. This isn't
514 documented. It should be changed to use Filter::Simple, tested and documented.
516 =head2 regexp optimiser optional
518 The regexp optimiser is not optional. It should configurable to be, to allow
519 its performance to be measured, and its bugs to be easily demonstrated.
523 Introduce a new special block, UNITCHECK, which is run at the end of a
524 compilation unit (module, file, eval(STRING) block). This will correspond to
525 the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
526 O.pm/B.pm backend framework depends on it.
528 =head2 optional optimizer
530 Make the peephole optimizer optional. Currently it performs two tasks as
531 it walks the optree - genuine peephole optimisations, and necessary fixups of
532 ops. It would be good to find an efficient way to switch out the
533 optimisations whilst keeping the fixups.
535 =head2 You WANT *how* many
537 Currently contexts are void, scalar and list. split has a special mechanism in
538 place to pass in the number of return values wanted. It would be useful to
539 have a general mechanism for this, backwards compatible and little speed hit.
540 This would allow proposals such as short circuiting sort to be implemented
543 =head2 lexical aliases
545 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
547 =head2 entersub XS vs Perl
549 At the moment pp_entersub is huge, and has code to deal with entering both
550 perl and XS subroutines. Subroutine implementations rarely change between
551 perl and XS at run time, so investigate using 2 ops to enter subs (one for
552 XS, one for perl) and swap between if a sub is redefined.
556 self ties are currently illegal because they caused too many segfaults. Maybe
557 the causes of these could be tracked down and self-ties on all types re-
560 =head2 Optimize away @_
562 The old perltodo notes "Look at the "reification" code in C<av.c>".
564 =head2 What hooks would assertions need?
566 Assertions are in the core, and work. However, assertions needed to be added
567 as a core patch, rather than an XS module in ext, or a CPAN module, because
568 the core has no hooks in the necessary places. It would be useful to
569 investigate what hooks would need to be added to make it possible to provide
570 the full assertion support from a CPAN module, so that we aren't constraining
571 the imagination of future CPAN authors.
579 Tasks that will get your name mentioned in the description of the "Highlights
582 =head2 make ithreads more robust
584 Generally make ithreads more robust. See also L</iCOW>
586 This task is incremental - even a little bit of work on it will help, and
587 will be greatly appreciated.
589 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
593 Sarathy and Arthur have a proposal for an improved Copy On Write which
594 specifically will be able to COW new ithreads. If this can be implemented
595 it would be a good thing.
597 =head2 (?{...}) closures in regexps
599 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
601 =head2 A re-entrant regexp engine
603 This will allow the use of a regex from inside (?{ }), (??{ }) and
604 (?(?{ })|) constructs.