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 =head1 Tasks that need a little sysadmin-type knowledge
146 Or if you prefer, tasks that you would learn from, and broaden your skills
149 =head2 make HTML install work
151 There is an C<installhtml> target in the Makefile. It's marked as
152 "experimental". It would be good to get this tested, make it work reliably, and
153 remove the "experimental" tag. This would include
159 Checking that cross linking between various parts of the documentation works.
160 In particular that links work between the modules (files with POD in F<lib/>)
161 and the core documentation (files in F<pod/>)
165 Work out how to split C<perlfunc> into chunks, preferably one per function
166 group, preferably with general case code that could be used elsewhere.
167 Challenges here are correctly identifying the groups of functions that go
168 together, and making the right named external cross-links point to the right
169 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
170 C<endservent>, two or more C<=items> giving the different parameter lists, such
173 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
174 =item substr EXPR,OFFSET,LENGTH
175 =item substr EXPR,OFFSET
177 and different parameter lists having different meanings. (eg C<select>)
181 =head2 compressed man pages
183 Be able to install them. This would probably need a configure test to see how
184 the system does compressed man pages (same directory/different directory?
185 same filename/different filename), as well as tweaking the F<installman> script
186 to compress as necessary.
188 =head2 Add a code coverage target to the Makefile
190 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
191 to do this manually are roughly
197 do a normal C<Configure>, but include Devel::Cover as a module to install
198 (see F<INSTALL> for how to do this)
206 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
210 Process the resulting Devel::Cover database
214 This just give you the coverage of the F<.pm>s. To also get the C level
221 Additionally tell C<Configure> to use the appropriate C compiler flags for
228 (instead of C<make perl>)
232 After running the tests run C<gcov> to generate all the F<.gcov> files.
233 (Including down in the subdirectories of F<ext/>
237 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
238 to get their stats into the cover_db directory.
242 Then process the Devel::Cover database
246 It would be good to add a single switch to C<Configure> to specify that you
247 wanted to perform perl level coverage, and another to specify C level
248 coverage, and have C<Configure> and the F<Makefile> do all the right things
251 =head2 Make Config.pm cope with differences between built and installed perl
253 Quite often vendors ship a perl binary compiled with their (pay-for)
254 compilers. People install a free compiler, such as gcc. To work out how to
255 build extensions, Perl interrogates C<%Config>, so in this situation
256 C<%Config> describes compilers that aren't there, and extension building
257 fails. This forces people into choosing between re-compiling perl themselves
258 using the compiler they have, or only using modules that the vendor ships.
260 It would be good to find a way teach C<Config.pm> about the installation setup,
261 possibly involving probing at install time or later, so that the C<%Config> in
262 a binary distribution better describes the installed machine, when the
263 installed machine differs from the build machine in some significant way.
265 =head2 linker specification files
267 Some platforms mandate that you provide a list of a shared library's external
268 symbols to the linker, so the core already has the infrastructure in place to
269 do this for generating shared perl libraries. My understanding is that the
270 GNU toolchain can accept an optional linker specification file, and restrict
271 visibility just to symbols declared in that file. It would be good to extend
272 F<makedef.pl> to support this format, and to provide a means within
273 C<Configure> to enable it. This would allow Unix users to test that the
274 export list is correct, and to build a perl that does not pollute the global
275 namespace with private symbols.
277 =head2 Cross-compile support
279 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
280 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
281 assumed then to be copied to TARGET machine and used as a replacement of full
284 This could be done little differently. Namely C<miniperl> should be built for
285 HOST and then full C<perl> with extensions should be compiled for TARGET.
286 This, however, might require extra trickery for %Config: we have one config
287 first for HOST and then another for TARGET.
289 =head1 Tasks that need a little C knowledge
291 These tasks would need a little C knowledge, but don't need any specific
292 background or experience with XS, or how the Perl interpreter works
294 =head2 Make it clear from -v if this is the exact official release
296 Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
297 usually defines one local patch, of the form "MAINT12345" or "RC1". The output
298 of perl -v doesn't report that a perl isn't an official release, and this
299 information can get lost in bugs reports. Because of this, the minor version
300 isn't bumped up until RC time, to minimise the possibility of versions of perl
301 escaping that believe themselves to be newer than they actually are.
303 It would be useful to find an elegant way to have the "this is an interim
304 maintenance release" or "this is a release candidate" in the terse -v output,
305 and have it so that it's easy for the pumpking to remove this just as the
306 release tarball is rolled up. This way the version pulled out of rsync would
307 always say "I'm a development release" and it would be safe to bump the
308 reported minor version as soon as a release ships, which would aid perl
311 This task is really about thinking of an elegant way to arrange the C source
312 such that it's trivial for the Pumpking to flag "this is an official release"
313 when making a tarball, yet leave the default source saying "I'm not the
316 =head2 Ordering of "global" variables.
318 F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
319 per-thread under ithreads, where the variables are actually elements in a
320 structure. As C dictates, the variables must be laid out in order of
321 declaration. There is a comment
322 C</* Important ones in the first cache line (if alignment is done right) */>
323 which implies that at some point in the past the ordering was carefully chosen
324 (at least in part). However, it's clear that the ordering is less than perfect,
325 as currently there are things such as 7 C<bool>s in a row, then something
326 typically requiring 4 byte alignment, and then an odd C<bool> later on.
327 (C<bool>s are typically defined as C<char>s). So it would be good for someone
328 to review the ordering of the variables, to see how much alignment padding can
331 It's also worth checking that all variables are actually used. Perl 5.8.0
332 shipped with C<PL_nrs> still defined in F<thrdvar.h>, despite it being unused
333 since a change over a year earlier. Had this been spotted before release, it
334 could have been removed, but now it has to remain in the 5.8.x releases to
335 keep the structure the same size, to retain binary compatibility.
337 It's probably worth checking if all need to be the types they are. For example
339 PERLVAR(Ierror_count, I32) /* how many errors so far, max 10 */
341 might work as well if stored in a signed (or unsigned) 8 bit value, if the
342 comment is accurate. C<PL_multi_open> and C<PL_multi_close> can probably
343 become C<char>s. Finding variables to downsize coupled with rearrangement
344 could shrink the interpreter structure; a size saving which is multiplied by
345 the number of threads running.
347 =head2 Profile Perl - am I hot or not?
349 The Perl source code is stable enough that it makes sense to profile it,
350 identify and optimise the hotspots. It would be good to measure the
351 performance of the Perl interpreter using free tools such as cachegrind,
352 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
354 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
355 the ops that are most commonly used. The idea is that by grouping them, their
356 object code will be adjacent in the executable, so they have a greater chance
357 of already being in the CPU cache (or swapped in) due to being near another op
360 Except that it's not clear if these really are the most commonly used ops. So
361 as part of exercising your skills with coverage and profiling tools you might
362 want to determine what ops I<really> are the most commonly used. And in turn
363 suggest evictions and promotions to achieve a better F<pp_hot.c>.
365 =head2 Allocate OPs from arenas
367 Currently all new OP structures are individually malloc()ed and free()d.
368 All C<malloc> implementations have space overheads, and are now as fast as
369 custom allocates so it would both use less memory and less CPU to allocate
370 the various OP structures from arenas. The SV arena code can probably be
373 =head2 Improve win32/wince.c
375 Currently, numerous functions look virtually, if not completely,
376 identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
379 =head2 Use secure CRT functions when building with VC8 on Win32
381 Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
382 that they were "unsafe" and introduced differently named secure versions of
383 them as replacements, e.g. instead of writing
385 FILE* f = fopen(__FILE__, "r");
390 errno_t err = fopen_s(&f, __FILE__, "r");
392 Currently, the warnings about these deprecations have been disabled by adding
393 -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
394 warning suppressant and actually make use of the new secure CRT functions.
396 There is also a similar issue with POSIX CRT function names like fileno having
397 been deprecated in favour of ISO C++ conformant names like _fileno. These
398 warnings are also currently suppressed with the compiler option /wd4996. It
399 might be nice to do as Microsoft suggest here too, although, unlike the secure
400 functions issue, there is presumably little or no benefit in this case.
402 =head1 Tasks that need a knowledge of XS
404 These tasks would need C knowledge, and roughly the level of knowledge of
405 the perl API that comes from writing modules that use XS to interface to
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 =head2 Extend PerlIO and PerlIO::Scalar
497 PerlIO::Scalar doesn't know how to truncate(). Implementing this
498 would require extending the PerlIO vtable.
500 Similarly the PerlIO vtable doesn't know about formats (write()), or
501 about stat(), or chmod()/chown(), utime(), or flock().
503 (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
506 PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
507 opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
510 =head1 Tasks that need a knowledge of the interpreter
512 These tasks would need C knowledge, and knowledge of how the interpreter works,
513 or a willingness to learn.
515 =head2 Implement $value ~~ 0 .. $range
517 It would be nice to extend the syntax of the C<~~> operator to also
518 understand numeric (and maybe alphanumeric) ranges.
520 =head2 Attach/detach debugger from running program
522 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
523 program if you pass the process ID. It would be good to do this with the Perl
524 debugger on a running Perl program, although I'm not sure how it would be
525 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
527 =head2 LVALUE functions for lists
529 The old perltodo notes that lvalue functions don't work for list or hash
530 slices. This would be good to fix.
532 =head2 LVALUE functions in the debugger
534 The old perltodo notes that lvalue functions don't work in the debugger. This
535 would be good to fix.
537 =head2 regexp optimiser optional
539 The regexp optimiser is not optional. It should configurable to be, to allow
540 its performance to be measured, and its bugs to be easily demonstrated.
542 =head2 delete &function
544 Allow to delete functions. One can already undef them, but they're still
547 =head2 optional optimizer
549 Make the peephole optimizer optional. Currently it performs two tasks as
550 it walks the optree - genuine peephole optimisations, and necessary fixups of
551 ops. It would be good to find an efficient way to switch out the
552 optimisations whilst keeping the fixups.
554 =head2 You WANT *how* many
556 Currently contexts are void, scalar and list. split has a special mechanism in
557 place to pass in the number of return values wanted. It would be useful to
558 have a general mechanism for this, backwards compatible and little speed hit.
559 This would allow proposals such as short circuiting sort to be implemented
562 =head2 lexical aliases
564 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
566 =head2 entersub XS vs Perl
568 At the moment pp_entersub is huge, and has code to deal with entering both
569 perl and XS subroutines. Subroutine implementations rarely change between
570 perl and XS at run time, so investigate using 2 ops to enter subs (one for
571 XS, one for perl) and swap between if a sub is redefined.
575 self ties are currently illegal because they caused too many segfaults. Maybe
576 the causes of these could be tracked down and self-ties on all types re-
579 =head2 Optimize away @_
581 The old perltodo notes "Look at the "reification" code in C<av.c>".
583 =head2 What hooks would assertions need?
585 Assertions are in the core, and work. However, assertions needed to be added
586 as a core patch, rather than an XS module in ext, or a CPAN module, because
587 the core has no hooks in the necessary places. It would be useful to
588 investigate what hooks would need to be added to make it possible to provide
589 the full assertion support from a CPAN module, so that we aren't constraining
590 the imagination of future CPAN authors.
592 =head2 Properly Unicode safe tokeniser and pads.
594 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
595 variable names are stored in stashes as raw bytes, without the utf-8 flag
596 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
597 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
598 source filters. All this could be fixed.
602 Tasks that will get your name mentioned in the description of the "Highlights
605 =head2 make ithreads more robust
607 Generally make ithreads more robust. See also L</iCOW>
609 This task is incremental - even a little bit of work on it will help, and
610 will be greatly appreciated.
612 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
616 Sarathy and Arthur have a proposal for an improved Copy On Write which
617 specifically will be able to COW new ithreads. If this can be implemented
618 it would be a good thing.
620 =head2 (?{...}) closures in regexps
622 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
624 =head2 A re-entrant regexp engine
626 This will allow the use of a regex from inside (?{ }), (??{ }) and
627 (?(?{ })|) constructs.
629 =head2 Add class set operations to regexp engine
631 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
633 demerphq has this on his todo list, but right at the bottom.