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 5.9.3 release
33 Implement L</lexical pragmas>
37 =head2 Needed for a 5.9.4 release
42 Review assertions. Review syntax to combine assertions. Can assertions take
43 advantage of the lexical pragams work? L</What hooks would assertions need?>
47 =head2 Needed for a 5.9.5 release
52 Implement L</_ prototype character>
55 Implement L</state variables>
59 =head2 Needed for a 5.9.6 release
61 Stabilisation. If all goes well, this will be the equivalent of a 5.10-beta.
63 =head1 Tasks that only need Perl knowledge
65 =head2 common test code for timed bail out
67 Write portable self destruct code for tests to stop them burning CPU in
68 infinite loops. This needs to avoid using alarm, as some of the tests are
69 testing alarm/sleep or timers.
71 =head2 POD -> HTML conversion in the core still sucks
73 Which is crazy given just how simple POD purports to be, and how simple HTML
74 can be. It's not actually I<as> simple as it sounds, particularly with the
75 flexibility POD allows for C<=item>, but it would be good to improve the
76 visual appeal of the HTML generated, and to avoid it having any validation
77 errors. See also L</make HTML install work>, as the layout of installation tree
78 is needed to improve the cross-linking.
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 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.
164 =head1 Tasks that need a little sysadmin-type knowledge
166 Or if you prefer, tasks that you would learn from, and broaden your skills
169 =head2 Relocatable perl
171 The C level patches needed to create a relocatable perl binary are done, as
172 is the work on F<Config.pm>. All that's left to do is the C<Configure> tweaking
173 to let people specify how they want to do the install.
175 =head2 make HTML install work
177 There is an C<installhtml> target in the Makefile. It's marked as
178 "experimental". It would be good to get this tested, make it work reliably, and
179 remove the "experimental" tag. This would include
185 Checking that cross linking between various parts of the documentation works.
186 In particular that links work between the modules (files with POD in F<lib/>)
187 and the core documentation (files in F<pod/>)
191 Work out how to split C<perlfunc> into chunks, preferably one per function
192 group, preferably with general case code that could be used elsewhere.
193 Challenges here are correctly identifying the groups of functions that go
194 together, and making the right named external cross-links point to the right
195 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
196 C<endservent>, two or more C<=items> giving the different parameter lists, such
199 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
201 =item substr EXPR,OFFSET,LENGTH
203 =item substr EXPR,OFFSET
205 and different parameter lists having different meanings. (eg C<select>)
209 =head2 compressed man pages
211 Be able to install them. This would probably need a configure test to see how
212 the system does compressed man pages (same directory/different directory?
213 same filename/different filename), as well as tweaking the F<installman> script
214 to compress as necessary.
216 =head2 Add a code coverage target to the Makefile
218 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
219 to do this manually are roughly
225 do a normal C<Configure>, but include Devel::Cover as a module to install
226 (see F<INSTALL> for how to do this)
234 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
238 Process the resulting Devel::Cover database
242 This just give you the coverage of the F<.pm>s. To also get the C level
249 Additionally tell C<Configure> to use the appropriate C compiler flags for
256 (instead of C<make perl>)
260 After running the tests run C<gcov> to generate all the F<.gcov> files.
261 (Including down in the subdirectories of F<ext/>
265 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
266 to get their stats into the cover_db directory.
270 Then process the Devel::Cover database
274 It would be good to add a single switch to C<Configure> to specify that you
275 wanted to perform perl level coverage, and another to specify C level
276 coverage, and have C<Configure> and the F<Makefile> do all the right things
279 =head2 Make Config.pm cope with differences between build and installed perl
281 Quite often vendors ship a perl binary compiled with their (pay-for)
282 compilers. People install a free compiler, such as gcc. To work out how to
283 build extensions, Perl interrogates C<%Config>, so in this situation
284 C<%Config> describes compilers that aren't there, and extension building
285 fails. This forces people into choosing between re-compiling perl themselves
286 using the compiler they have, or only using modules that the vendor ships.
288 It would be good to find a way teach C<Config.pm> about the installation setup,
289 possibly involving probing at install time or later, so that the C<%Config> in
290 a binary distribution better describes the installed machine, when the
291 installed machine differs from the build machine in some significant way.
293 =head2 make parallel builds work
295 Currently parallel builds (such as C<make -j3>) don't work reliably. We believe
296 that this is due to incomplete dependency specification in the F<Makefile>.
297 It would be good if someone were able to track down the causes of these
298 problems, so that parallel builds worked properly.
300 =head2 linker specification files
302 Some platforms mandate that you provide a list of a shared library's external
303 symbols to the linker, so the core already has the infrastructure in place to
304 do this for generating shared perl libraries. My understanding is that the
305 GNU toolchain can accept an optional linker specification file, and restrict
306 visibility just to symbols declared in that file. It would be good to extend
307 F<makedef.pl> to support this format, and to provide a means within
308 C<Configure> to enable it. This would allow Unix users to test that the
309 export list is correct, and to build a perl that does not pollute the global
310 namespace with private symbols.
315 =head1 Tasks that need a little C knowledge
317 These tasks would need a little C knowledge, but don't need any specific
318 background or experience with XS, or how the Perl interpreter works
320 =head2 Make it clear from -v if this is the exact official release
322 Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
323 usually defines one local patch, of the form "MAINT12345" or "RC1". The output
324 of perl -v doesn't report that a perl isn't an official release, and this
325 information can get lost in bugs reports. Because of this, the minor version
326 isn't bumped up until RC time, to minimise the possibility of versions of perl
327 escaping that believe themselves to be newer than they actually are.
329 It would be useful to find an elegant way to have the "this is an interim
330 maintenance release" or "this is a release candidate" in the terse -v output,
331 and have it so that it's easy for the pumpking to remove this just as the
332 release tarball is rolled up. This way the version pulled out of rsync would
333 always say "I'm a development release" and it would be safe to bump the
334 reported minor version as soon as a release ships, which would aid perl
337 This task is really about thinking of an elegant way to arrange the C source
338 such that it's trivial for the Pumpking to flag "this is an official release"
339 when making a tarball, yet leave the default source saying "I'm not the
342 =head2 Tidy up global variables
344 There's a note in F<intrpvar.h>
346 /* These two variables are needed to preserve 5.8.x bincompat because
347 we can't change function prototypes of two exported functions.
348 Probably should be taken out of blead soon, and relevant prototypes
351 So doing this, and removing any of the unused variables still present would
354 =head2 Ordering of "global" variables.
356 F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
357 per-thread under ithreads, where the variables are actually elements in a
358 structure. As C dictates, the variables must be laid out in order of
359 declaration. There is a comment
360 C</* Important ones in the first cache line (if alignment is done right) */>
361 which implies that at some point in the past the ordering was carefully chosen
362 (at least in part). However, it's clear that the ordering is less than perfect,
363 as currently there are things such as 7 C<bool>s in a row, then something
364 typically requiring 4 byte alignment, and then an odd C<bool> later on.
365 (C<bool>s are typically defined as C<char>s). So it would be good for someone
366 to review the ordering of the variables, to see how much alignment padding can
369 =head2 bincompat functions
371 There are lots of functions which are retained for binary compatibility.
372 Clean these up. Move them to mathom.c, and don't compile for blead?
374 =head2 am I hot or not?
376 The idea of F<pp_hot.c> is that it contains the I<hot> ops, the ops that are
377 most commonly used. The idea is that by grouping them, their object code will
378 be adjacent in the executable, so they have a greater chance of already being
379 in the CPU cache (or swapped in) due to being near another op already in use.
381 Except that it's not clear if these really are the most commonly used ops. So
382 anyone feeling like exercising their skill with coverage and profiling tools
383 might want to determine what ops I<really> are the most commonly used. And in
384 turn suggest evictions and promotions to achieve a better F<pp_hot.c>.
386 =head2 emulate the per-thread memory pool on Unix
388 For Windows, ithreads allocates memory for each thread from a separate pool,
389 which it discards at thread exit. It also checks that memory is free()d to
390 the correct pool. Neither check is done on Unix, so code developed there won't
391 be subject to such strictures, so can harbour bugs that only show up when the
392 code reaches Windows.
394 It would be good to be able to optionally emulate the Window pool system on
395 Unix, to let developers who only have access to Unix, or want to use
396 Unix-specific debugging tools, check for these problems. To do this would
397 involve figuring out how the C<PerlMem_*> macros wrap C<malloc()> access, and
398 providing a layer that records/checks the identity of the thread making the
399 call, and recording all the memory allocated by each thread via this API so
400 that it can be summarily free()d at thread exit. One implementation idea
401 would be to increase the size of allocation, and store the C<my_perl> pointer
402 (to identify the thread) at the start, along with pointers to make a linked
403 list of blocks for this thread. To avoid alignment problems it would be
404 necessary to do something like
406 union memory_header_padded {
407 struct memory_header {
408 void *thread_id; /* For my_perl */
409 void *next; /* Pointer to next block for this thread */
411 long double padding; /* whatever type has maximal alignment constraint */
415 although C<long double> might not be the only type to add to the padding
418 =head2 reduce duplication in sv_setsv_flags
420 C<Perl_sv_setsv_flags> has a comment
421 C</* There's a lot of redundancy below but we're going for speed here */>
423 Whilst this was true 10 years ago, the growing disparity between RAM and CPU
424 speeds mean that the trade offs have changed. In addition, the duplicate code
425 adds to the maintenance burden. It would be good to see how much of the
426 redundancy can be pruned, particular in the less common paths. (Profiling
427 tools at the ready...). For example, why does the test for
428 "Can't redefine active sort subroutine" need to occur in two places?
433 =head1 Tasks that need a knowledge of XS
435 These tasks would need C knowledge, and roughly the level of knowledge of
436 the perl API that comes from writing modules that use XS to interface to
441 Clean this up. Check everything in core works
443 =head2 shrink C<GV>s, C<CV>s
445 By removing unused elements and careful re-ordering, the structures for C<AV>s
446 and C<HV>s have recently been shrunk considerably. It's probable that the same
447 approach would find savings in C<GV>s and C<CV>s, if not all the other
448 larger-than-C<PVMG> types.
450 =head2 merge Perl_sv_2[inpu]v
452 There's a lot of code shared between C<Perl_sv_2iv_flags>,
453 C<Perl_sv_2uv_flags>, C<Perl_sv_2nv>, and C<Perl_sv_2pv_flags>. It would be
454 interesting to see if some of it can be merged into common shared static
455 functions. In particular, C<Perl_sv_2uv_flags> started out as a cut&paste
456 from C<Perl_sv_2iv_flags> around 5.005_50 time, and it may be possible to
457 replace both with a single function that returns a value or union which is
458 split out by the macros in F<sv.h>
460 =head2 UTF8 caching code
462 The string position/offset cache is not optional. It should be.
464 =head2 Implicit Latin 1 => Unicode translation
466 Conversions from byte strings to UTF-8 currently map high bit characters
467 to Unicode without translation (or, depending on how you look at it, by
468 implicitly assuming that the byte strings are in Latin-1). As perl assumes
469 the C locale by default, upgrading a string to UTF-8 may change the
470 meaning of its contents regarding character classes, case mapping, etc.
471 This should probably emit a warning (at least).
473 This task is incremental - even a little bit of work on it will help.
475 =head2 autovivification
477 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
479 This task is incremental - even a little bit of work on it will help.
481 =head2 Unicode in Filenames
483 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
484 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
485 system, truncate, unlink, utime, -X. All these could potentially accept
486 Unicode filenames either as input or output (and in the case of system
487 and qx Unicode in general, as input or output to/from the shell).
488 Whether a filesystem - an operating system pair understands Unicode in
491 Known combinations that have some level of understanding include
492 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
493 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
494 create Unicode filenames, what forms of Unicode are accepted and used
495 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
496 and so on, varies. Finding the right level of interfacing to Perl
497 requires some thought. Remember that an OS does not implicate a
500 (The Windows -C command flag "wide API support" has been at least
501 temporarily retired in 5.8.1, and the -C has been repurposed, see
504 =head2 Unicode in %ENV
506 Currently the %ENV entries are always byte strings.
508 =head2 use less 'memory'
510 Investigate trade offs to switch out perl's choices on memory usage.
511 Particularly perl should be able to give memory back.
513 This task is incremental - even a little bit of work on it will help.
515 =head2 Re-implement C<:unique> in a way that is actually thread-safe
517 The old implementation made bad assumptions on several levels. A good 90%
518 solution might be just to make C<:unique> work to share the string buffer
519 of SvPVs. That way large constant strings can be shared between ithreads,
520 such as the configuration information in F<Config>.
522 =head2 Make tainting consistent
524 Tainting would be easier to use if it didn't take documented shortcuts and
525 allow taint to "leak" everywhere within an expression.
527 =head2 readpipe(LIST)
529 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
530 running a shell. readpipe() (the function behind qx//) could be similarly
537 =head1 Tasks that need a knowledge of the interpreter
539 These tasks would need C knowledge, and knowledge of how the interpreter works,
540 or a willingness to learn.
542 =head2 lexical pragmas
544 Reimplement the mechanism of lexical pragmas to be more extensible. Fix
545 current pragmas that don't work well (or at all) with lexical scopes or in
546 run-time eval(STRING) (C<sort>, C<re>, C<encoding> for example). MJD has a
547 preliminary patch that implements this.
549 =head2 Attach/detach debugger from running program
551 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
552 program if you pass the process ID. It would be good to do this with the Perl
553 debugger on a running Perl program, although I'm not sure how it would be
554 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
556 =head2 inlining autoloaded constants
558 Currently the optimiser can inline constants when expressed as subroutines
559 with prototype ($) that return a constant. Likewise, many packages wrapping
560 C libraries export lots of constants as subroutines which are AUTOLOADed on
561 demand. However, these have no prototypes, so can't be seen as constants by
562 the optimiser. Some way of cheaply (low syntax, low memory overhead) to the
563 perl compiler that a name is a constant would be great, so that it knows to
564 call the AUTOLOAD routine at compile time, and then inline the constant.
566 =head2 Constant folding
568 The peephole optimiser should trap errors during constant folding, and give
569 up on the folding, rather than bailing out at compile time. It is quite
570 possible that the unfoldable constant is in unreachable code, eg something
571 akin to C<$a = 0/0 if 0;>
573 =head2 LVALUE functions for lists
575 The old perltodo notes that lvalue functions don't work for list or hash
576 slices. This would be good to fix.
578 =head2 LVALUE functions in the debugger
580 The old perltodo notes that lvalue functions don't work in the debugger. This
581 would be good to fix.
583 =head2 _ prototype character
585 Study the possibility of adding a new prototype character, C<_>, meaning
586 "this argument defaults to $_".
588 =head2 state variables
590 C<my $foo if 0;> is deprecated, and should be replaced with
591 C<state $x = "initial value\n";> the syntax from Perl 6.
593 =head2 @INC source filter to Filter::Simple
595 The second return value from a sub in @INC can be a source filter. This isn't
596 documented. It should be changed to use Filter::Simple, tested and documented.
598 =head2 regexp optimiser optional
600 The regexp optimiser is not optional. It should configurable to be, to allow
601 its performance to be measured, and its bugs to be easily demonstrated.
605 Introduce a new special block, UNITCHECK, which is run at the end of a
606 compilation unit (module, file, eval(STRING) block). This will correspond to
607 the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
608 O.pm/B.pm backend framework depends on it.
610 =head2 optional optimizer
612 Make the peephole optimizer optional. Currently it performs two tasks as
613 it walks the optree - genuine peephole optimisations, and necessary fixups of
614 ops. It would be good to find an efficient way to switch out the
615 optimisations whilst keeping the fixups.
617 =head2 You WANT *how* many
619 Currently contexts are void, scalar and list. split has a special mechanism in
620 place to pass in the number of return values wanted. It would be useful to
621 have a general mechanism for this, backwards compatible and little speed hit.
622 This would allow proposals such as short circuiting sort to be implemented
625 =head2 lexical aliases
627 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
629 =head2 entersub XS vs Perl
631 At the moment pp_entersub is huge, and has code to deal with entering both
632 perl and XS subroutines. Subroutine implementations rarely change between
633 perl and XS at run time, so investigate using 2 ops to enter subs (one for
634 XS, one for perl) and swap between if a sub is redefined.
638 self ties are currently illegal because they caused too many segfaults. Maybe
639 the causes of these could be tracked down and self-ties on all types re-
642 =head2 Optimize away @_
644 The old perltodo notes "Look at the "reification" code in C<av.c>".
648 The old perltodo notes "Although we have C<Switch.pm> in core, Larry points to
649 the dormant C<nswitch> and C<cswitch> ops in F<pp.c>; using these opcodes would
652 =head2 What hooks would assertions need?
654 Assertions are in the core, and work. However, assertions needed to be added
655 as a core patch, rather than an XS module in ext, or a CPAN module, because
656 the core has no hooks in the necessary places. It would be useful to
657 investigate what hooks would need to be added to make it possible to provide
658 the full assertion support from a CPAN module, so that we aren't constraining
659 the imagination of future CPAN authors.
669 Tasks that will get your name mentioned in the description of the "Highlights
672 =head2 make ithreads more robust
674 Generally make ithreads more robust. See also L</iCOW>
676 This task is incremental - even a little bit of work on it will help, and
677 will be greatly appreciated.
681 Sarathy and Arthur have a proposal for an improved Copy On Write which
682 specifically will be able to COW new ithreads. If this can be implemented
683 it would be a good thing.
685 =head2 (?{...}) closures in regexps
687 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
689 =head2 A re-entrant regexp engine
691 This will allow the use of a regex from inside (?{ }), (??{ }) and
692 (?(?{ })|) constructs.