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 Tasks that only need Perl knowledge
25 =head2 common test code for timed bail out
27 Write portable self destruct code for tests to stop them burning CPU in
28 infinite loops. This needs to avoid using alarm, as some of the tests are
29 testing alarm/sleep or timers.
31 =head2 POD -E<gt> HTML conversion in the core still sucks
33 Which is crazy given just how simple POD purports to be, and how simple HTML
34 can be. It's not actually I<as> simple as it sounds, particularly with the
35 flexibility POD allows for C<=item>, but it would be good to improve the
36 visual appeal of the HTML generated, and to avoid it having any validation
37 errors. See also L</make HTML install work>, as the layout of installation tree
38 is needed to improve the cross-linking.
40 The addition of C<Pod::Simple> and its related modules may make this task
43 =head2 Parallel testing
45 (This probably impacts much more than the core: also the Test::Harness
46 and TAP::* modules on CPAN.)
48 The core regression test suite is getting ever more comprehensive, which has
49 the side effect that it takes longer to run. This isn't so good. Investigate
50 whether it would be feasible to give the harness script the B<option> of
51 running sets of tests in parallel. This would be useful for tests in
52 F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
60 How does screen layout work when you're running more than one test?
64 How does the caller of test specify how many tests to run in parallel?
68 How do setup/teardown tests identify themselves?
72 Pugs already does parallel testing - can their approach be re-used?
74 =head2 Make Schwern poorer
76 We should have tests for everything. When all the core's modules are tested,
77 Schwern has promised to donate to $500 to TPF. We may need volunteers to
78 hold him upside down and shake vigorously in order to actually extract the
81 =head2 Improve the coverage of the core tests
83 Use Devel::Cover to ascertain the core modules's test coverage, then add
84 tests that are currently missing.
88 A full test suite for the B module would be nice.
90 =head2 A decent benchmark
92 C<perlbench> seems impervious to any recent changes made to the perl core. It
93 would be useful to have a reasonable general benchmarking suite that roughly
94 represented what current perl programs do, and measurably reported whether
95 tweaks to the core improve, degrade or don't really affect performance, to
96 guide people attempting to optimise the guts of perl. Gisle would welcome
97 new tests for perlbench.
99 =head2 fix tainting bugs
101 Fix the bugs revealed by running the test suite with the C<-t> switch (via
102 C<make test.taintwarn>).
104 =head2 Dual life everything
106 As part of the "dists" plan, anything that doesn't belong in the smallest perl
107 distribution needs to be dual lifed. Anything else can be too. Figure out what
108 changes would be needed to package that module and its tests up for CPAN, and
109 do so. Test it with older perl releases, and fix the problems you find.
111 To make a minimal perl distribution, it's useful to look at
112 F<t/lib/commonsense.t>.
114 =head2 Improving C<threads::shared>
116 Investigate whether C<threads::shared> could share aggregates properly with
117 only Perl level changes to shared.pm
119 =head2 POSIX memory footprint
121 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
122 various times worked to cut it down. There is probably still fat to cut out -
123 for example POSIX passes Exporter some very memory hungry data structures.
125 =head2 embed.pl/makedef.pl
127 There is a script F<embed.pl> that generates several header files to prefix
128 all of Perl's symbols in a consistent way, to provide some semblance of
129 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
130 in F<interpvar.h>. Quite a few of the functions and variables
131 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
132 doesn't understand the C macros, so the rules about which symbols are present
133 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
134 It would be good to teach C<embed.pl> to understand the conditional
135 compilation, and hence remove the duplication, and the mistakes it has caused.
137 =head2 use strict; and AutoLoad
139 Currently if you write
142 use AutoLoader 'AUTOLOAD';
147 print join (' ', No, strict, here), "!\n";
150 then C<use strict;> isn't in force within the autoloaded subroutines. It would
151 be more consistent (and less surprising) to arrange for all lexical pragmas
152 in force at the __END__ block to be in force within each autoloaded subroutine.
154 There's a similar problem with SelfLoader.
156 =head1 Tasks that need a little sysadmin-type knowledge
158 Or if you prefer, tasks that you would learn from, and broaden your skills
161 =head2 make HTML install work
163 There is an C<installhtml> target in the Makefile. It's marked as
164 "experimental". It would be good to get this tested, make it work reliably, and
165 remove the "experimental" tag. This would include
171 Checking that cross linking between various parts of the documentation works.
172 In particular that links work between the modules (files with POD in F<lib/>)
173 and the core documentation (files in F<pod/>)
177 Work out how to split C<perlfunc> into chunks, preferably one per function
178 group, preferably with general case code that could be used elsewhere.
179 Challenges here are correctly identifying the groups of functions that go
180 together, and making the right named external cross-links point to the right
181 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
182 C<endservent>, two or more C<=items> giving the different parameter lists, such
185 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
186 =item substr EXPR,OFFSET,LENGTH
187 =item substr EXPR,OFFSET
189 and different parameter lists having different meanings. (eg C<select>)
193 =head2 compressed man pages
195 Be able to install them. This would probably need a configure test to see how
196 the system does compressed man pages (same directory/different directory?
197 same filename/different filename), as well as tweaking the F<installman> script
198 to compress as necessary.
200 =head2 Add a code coverage target to the Makefile
202 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
203 to do this manually are roughly
209 do a normal C<Configure>, but include Devel::Cover as a module to install
210 (see F<INSTALL> for how to do this)
218 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
222 Process the resulting Devel::Cover database
226 This just give you the coverage of the F<.pm>s. To also get the C level
233 Additionally tell C<Configure> to use the appropriate C compiler flags for
240 (instead of C<make perl>)
244 After running the tests run C<gcov> to generate all the F<.gcov> files.
245 (Including down in the subdirectories of F<ext/>
249 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
250 to get their stats into the cover_db directory.
254 Then process the Devel::Cover database
258 It would be good to add a single switch to C<Configure> to specify that you
259 wanted to perform perl level coverage, and another to specify C level
260 coverage, and have C<Configure> and the F<Makefile> do all the right things
263 =head2 Make Config.pm cope with differences between built and installed perl
265 Quite often vendors ship a perl binary compiled with their (pay-for)
266 compilers. People install a free compiler, such as gcc. To work out how to
267 build extensions, Perl interrogates C<%Config>, so in this situation
268 C<%Config> describes compilers that aren't there, and extension building
269 fails. This forces people into choosing between re-compiling perl themselves
270 using the compiler they have, or only using modules that the vendor ships.
272 It would be good to find a way teach C<Config.pm> about the installation setup,
273 possibly involving probing at install time or later, so that the C<%Config> in
274 a binary distribution better describes the installed machine, when the
275 installed machine differs from the build machine in some significant way.
277 =head2 linker specification files
279 Some platforms mandate that you provide a list of a shared library's external
280 symbols to the linker, so the core already has the infrastructure in place to
281 do this for generating shared perl libraries. My understanding is that the
282 GNU toolchain can accept an optional linker specification file, and restrict
283 visibility just to symbols declared in that file. It would be good to extend
284 F<makedef.pl> to support this format, and to provide a means within
285 C<Configure> to enable it. This would allow Unix users to test that the
286 export list is correct, and to build a perl that does not pollute the global
287 namespace with private symbols.
289 =head2 Cross-compile support
291 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
292 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
293 assumed then to be copied to TARGET machine and used as a replacement of full
296 This could be done little differently. Namely C<miniperl> should be built for
297 HOST and then full C<perl> with extensions should be compiled for TARGET.
298 This, however, might require extra trickery for %Config: we have one config
299 first for HOST and then another for TARGET. Tools like MakeMaker will be
300 mightily confused. Having around two different types of executables and
301 libraries (HOST and TARGET) makes life interesting for Makefiles and
302 shell (and Perl) scripts. There is $Config{run}, normally empty, which
303 can be used as an execution wrapper. Also note that in some
304 cross-compilation/execution environments the HOST and the TARGET do
305 not see the same filesystem(s), the $Config{run} may need to do some
306 file/directory copying back and forth.
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 Profile Perl - am I hot or not?
337 The Perl source code is stable enough that it makes sense to profile it,
338 identify and optimise the hotspots. It would be good to measure the
339 performance of the Perl interpreter using free tools such as cachegrind,
340 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
342 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
343 the ops that are most commonly used. The idea is that by grouping them, their
344 object code will be adjacent in the executable, so they have a greater chance
345 of already being in the CPU cache (or swapped in) due to being near another op
348 Except that it's not clear if these really are the most commonly used ops. So
349 as part of exercising your skills with coverage and profiling tools you might
350 want to determine what ops I<really> are the most commonly used. And in turn
351 suggest evictions and promotions to achieve a better F<pp_hot.c>.
353 =head2 Allocate OPs from arenas
355 Currently all new OP structures are individually malloc()ed and free()d.
356 All C<malloc> implementations have space overheads, and are now as fast as
357 custom allocates so it would both use less memory and less CPU to allocate
358 the various OP structures from arenas. The SV arena code can probably be
361 =head2 Improve win32/wince.c
363 Currently, numerous functions look virtually, if not completely,
364 identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
367 =head2 Use secure CRT functions when building with VC8 on Win32
369 Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
370 that they were "unsafe" and introduced differently named secure versions of
371 them as replacements, e.g. instead of writing
373 FILE* f = fopen(__FILE__, "r");
378 errno_t err = fopen_s(&f, __FILE__, "r");
380 Currently, the warnings about these deprecations have been disabled by adding
381 -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
382 warning suppressant and actually make use of the new secure CRT functions.
384 There is also a similar issue with POSIX CRT function names like fileno having
385 been deprecated in favour of ISO C++ conformant names like _fileno. These
386 warnings are also currently suppressed with the compiler option /wd4996. It
387 might be nice to do as Microsoft suggest here too, although, unlike the secure
388 functions issue, there is presumably little or no benefit in this case.
390 =head1 Tasks that need a knowledge of XS
392 These tasks would need C knowledge, and roughly the level of knowledge of
393 the perl API that comes from writing modules that use XS to interface to
396 =head2 autovivification
398 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
400 This task is incremental - even a little bit of work on it will help.
402 =head2 Unicode in Filenames
404 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
405 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
406 system, truncate, unlink, utime, -X. All these could potentially accept
407 Unicode filenames either as input or output (and in the case of system
408 and qx Unicode in general, as input or output to/from the shell).
409 Whether a filesystem - an operating system pair understands Unicode in
412 Known combinations that have some level of understanding include
413 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
414 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
415 create Unicode filenames, what forms of Unicode are accepted and used
416 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
417 and so on, varies. Finding the right level of interfacing to Perl
418 requires some thought. Remember that an OS does not implicate a
421 (The Windows -C command flag "wide API support" has been at least
422 temporarily retired in 5.8.1, and the -C has been repurposed, see
425 Most probably the right way to do this would be this:
426 L</"Virtualize operating system access">.
428 =head2 Unicode in %ENV
430 Currently the %ENV entries are always byte strings.
431 See L</"Virtualize operating system access">.
433 =head2 Unicode and glob()
435 Currently glob patterns and filenames returned from File::Glob::glob()
436 are always byte strings. See L</"Virtualize operating system access">.
438 =head2 Unicode and lc/uc operators
440 Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on
441 what the internal encoding of their argument is. That should not be the
442 case. Maybe add a pragma to switch behaviour.
444 =head2 use less 'memory'
446 Investigate trade offs to switch out perl's choices on memory usage.
447 Particularly perl should be able to give memory back.
449 This task is incremental - even a little bit of work on it will help.
451 =head2 Re-implement C<:unique> in a way that is actually thread-safe
453 The old implementation made bad assumptions on several levels. A good 90%
454 solution might be just to make C<:unique> work to share the string buffer
455 of SvPVs. That way large constant strings can be shared between ithreads,
456 such as the configuration information in F<Config>.
458 =head2 Make tainting consistent
460 Tainting would be easier to use if it didn't take documented shortcuts and
461 allow taint to "leak" everywhere within an expression.
463 =head2 readpipe(LIST)
465 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
466 running a shell. readpipe() (the function behind qx//) could be similarly
469 =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
471 Maybe create a utility that checks after each libperl.a creation that
472 none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
473 ever creep back to libperl.a.
475 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
477 Note, of course, that this will only tell whether B<your> platform
478 is using those naughty interfaces.
480 =head2 Audit the code for destruction ordering assumptions
484 /* Need to check SvMAGICAL, as during global destruction it may be that
485 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
486 is now part of the linked list of SV heads, rather than pointing to
487 the original body. */
488 /* FIXME - audit the code for other bugs like this one. */
490 adding the C<SvMAGICAL> check to
492 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
493 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
495 Go through the core and look for similar assumptions that SVs have particular
496 types, as all bets are off during global destruction.
498 =head2 Extend PerlIO and PerlIO::Scalar
500 PerlIO::Scalar doesn't know how to truncate(). Implementing this
501 would require extending the PerlIO vtable.
503 Similarly the PerlIO vtable doesn't know about formats (write()), or
504 about stat(), or chmod()/chown(), utime(), or flock().
506 (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
509 PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
510 opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
513 See also L</"Virtualize operating system access">.
515 =head2 -C on the #! line
517 It should be possible to make -C work correctly if found on the #! line,
518 given that all perl command line options are strict ASCII, and -C changes
519 only the interpretation of non-ASCII characters, and not for the script file
520 handle. To make it work needs some investigation of the ordering of function
521 calls during startup, and (by implication) a bit of tweaking of that order.
524 =head1 Tasks that need a knowledge of the interpreter
526 These tasks would need C knowledge, and knowledge of how the interpreter works,
527 or a willingness to learn.
529 =head2 Implement $value ~~ 0 .. $range
531 It would be nice to extend the syntax of the C<~~> operator to also
532 understand numeric (and maybe alphanumeric) ranges.
534 =head2 A does() built-in
536 Like ref(), only useful. It would call the C<DOES> method on objects; it
537 would also tell whether something can be dereferenced as an
538 array/hash/etc., or used as a regexp, etc.
539 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
541 =head2 Tied filehandles and write() don't mix
543 There is no method on tied filehandles to allow them to be called back by
546 =head2 Attach/detach debugger from running program
548 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
549 program if you pass the process ID. It would be good to do this with the Perl
550 debugger on a running Perl program, although I'm not sure how it would be
551 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
553 =head2 LVALUE functions for lists
555 The old perltodo notes that lvalue functions don't work for list or hash
556 slices. This would be good to fix.
558 =head2 LVALUE functions in the debugger
560 The old perltodo notes that lvalue functions don't work in the debugger. This
561 would be good to fix.
563 =head2 regexp optimiser optional
565 The regexp optimiser is not optional. It should configurable to be, to allow
566 its performance to be measured, and its bugs to be easily demonstrated.
568 =head2 delete &function
570 Allow to delete functions. One can already undef them, but they're still
573 =head2 C</w> regex modifier
575 That flag would enable to match whole words, and also to interpolate
576 arrays as alternations. With it, C</P/w> would be roughly equivalent to:
578 do { local $"='|'; /\b(?:P)\b/ }
580 See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
583 =head2 optional optimizer
585 Make the peephole optimizer optional. Currently it performs two tasks as
586 it walks the optree - genuine peephole optimisations, and necessary fixups of
587 ops. It would be good to find an efficient way to switch out the
588 optimisations whilst keeping the fixups.
590 =head2 You WANT *how* many
592 Currently contexts are void, scalar and list. split has a special mechanism in
593 place to pass in the number of return values wanted. It would be useful to
594 have a general mechanism for this, backwards compatible and little speed hit.
595 This would allow proposals such as short circuiting sort to be implemented
598 =head2 lexical aliases
600 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
602 =head2 entersub XS vs Perl
604 At the moment pp_entersub is huge, and has code to deal with entering both
605 perl and XS subroutines. Subroutine implementations rarely change between
606 perl and XS at run time, so investigate using 2 ops to enter subs (one for
607 XS, one for perl) and swap between if a sub is redefined.
611 self ties are currently illegal because they caused too many segfaults. Maybe
612 the causes of these could be tracked down and self-ties on all types re-
615 =head2 Optimize away @_
617 The old perltodo notes "Look at the "reification" code in C<av.c>".
619 =head2 Properly Unicode safe tokeniser and pads.
621 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
622 variable names are stored in stashes as raw bytes, without the utf-8 flag
623 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
624 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
625 source filters. All this could be fixed.
627 =head2 The yada yada yada operators
629 Perl 6's Synopsis 3 says:
631 I<The ... operator is the "yada, yada, yada" list operator, which is used as
632 the body in function prototypes. It complains bitterly (by calling fail)
633 if it is ever executed. Variant ??? calls warn, and !!! calls die.>
635 Those would be nice to add to Perl 5. That could be done without new ops.
637 =head2 Virtualize operating system access
639 Implement a set of "vtables" that virtualizes operating system access
640 (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very
641 least these interfaces should take SVs as "name" arguments instead of
642 bare char pointers; probably the most flexible and extensible way
643 would be for the Perl-facing interfaces to accept HVs. The system
644 needs to be per-operating-system and per-file-system
645 hookable/filterable, preferably both from XS and Perl level
646 (L<perlport/"Files and Filesystems"> is good reading at this point,
647 in fact, all of L<perlport> is.)
649 This has actually already been implemented (but only for Win32),
650 take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32
651 variants go through a set of "vtables" for operating system access,
652 non-Win32 systems currently go straight for the POSIX/UNIX-style
653 system/library call. Similar system as for Win32 should be
654 implemented for all platforms. The existing Win32 implementation
655 probably does not need to survive alongside this proposed new
656 implementation, the approaches could be merged.
658 What would this give us? One often-asked-for feature this would
659 enable is using Unicode for filenames, and other "names" like %ENV,
660 usernames, hostnames, and so forth.
661 (See L<perlunicode/"When Unicode Does Not Happen">.)
663 But this kind of virtualization would also allow for things like
664 virtual filesystems, virtual networks, and "sandboxes" (though as long
665 as dynamic loading of random object code is allowed, not very safe
666 sandboxes since external code of course know not of Perl's vtables).
667 An example of a smaller "sandbox" is that this feature can be used to
668 implement per-thread working directories: Win32 already does this.
670 See also L</"Extend PerlIO and PerlIO::Scalar">.
674 Tasks that will get your name mentioned in the description of the "Highlights
677 =head2 make ithreads more robust
679 Generally make ithreads more robust. See also L</iCOW>
681 This task is incremental - even a little bit of work on it will help, and
682 will be greatly appreciated.
684 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
686 Fix Perl_sv_dup, et al so that threads can return objects.
690 Sarathy and Arthur have a proposal for an improved Copy On Write which
691 specifically will be able to COW new ithreads. If this can be implemented
692 it would be a good thing.
694 =head2 (?{...}) closures in regexps
696 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
698 =head2 A re-entrant regexp engine
700 This will allow the use of a regex from inside (?{ }), (??{ }) and
701 (?(?{ })|) constructs.
703 =head2 Add class set operations to regexp engine
705 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
707 demerphq has this on his todo list, but right at the bottom.