3 perltodo - Perl TO-DO List
7 This is a list of wishes for Perl. The most up to date version of this file
8 is at http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod
10 The tasks we think are smaller or easier are listed first. Anyone is welcome
11 to work on any of these, but it's a good idea to first contact
12 I<perl5-porters@perl.org> to avoid duplication of effort, and to learn from
13 any previous attempts. By all means contact a pumpking privately first if you
16 Whilst patches to make the list shorter are most welcome, ideas to add to
17 the list are also encouraged. Check the perl5-porters archives for past
18 ideas, and any discussion about them. One set of archives may be found at:
20 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
22 What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
23 not, but if your patch is incorporated, then we'll add your name to the
24 F<AUTHORS> file, which ships in the official distribution. How many other
25 programming languages offer you 1 line of immortality?
27 =head1 Tasks that only need Perl knowledge
29 =head2 Smartmatch design issues
31 In 5.10.0 the smartmatch operator C<~~> isn't working quite "right". But
32 before we can fix the implementation, we need to define what "right" is.
33 The first problem is that Robin Houston implemented the Perl 6 smart match
34 spec as of February 2006, when smart match was axiomatically symmetrical:
35 L<http://groups.google.com/group/perl.perl6.language/msg/bf2b486f089ad021>
37 Since then the Perl 6 target moved, but the Perl 5 implementation did not.
39 So it would be useful for someone to compare the Perl 6 smartmatch table
40 as of February 2006 L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=markup&pathrev=7615>
41 and the current table L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?revision=14556&view=markup>
42 and tabulate the differences in Perl 6. The annotated view of changes is
43 L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=annotate> and the diff is
44 C<svn diff -r7615:14556 http://svn.perl.org/perl6/doc/trunk/design/syn/S03.pod>
45 -- search for C<=head1 Smart matching>. (In theory F<viewvc> can generate that,
46 but in practice when I tried it hung forever, I assume "thinking")
48 With that done and published, someone (else) can then map any changed Perl 6
49 semantics back to Perl 5, based on how the existing semantics map to Perl 5:
50 L<http://search.cpan.org/~rgarcia/perl-5.10.0/pod/perlsyn.pod#Smart_matching_in_detail>
53 There are also some questions that need answering:
59 How do you negate one? (documentation issue)
60 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-01/msg00071.html
65 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00799.html
67 * Should smart matches be symmetrical? (Perl 6 says no)
69 * Other differences between Perl 5 and Perl 6 smart match?
73 Objects and smart match
74 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00865.html
78 =head2 Remove duplication of test setup.
80 Schwern notes, that there's duplication of code - lots and lots of tests have
81 some variation on the big block of C<$Is_Foo> checks. We can safely put this
82 into a file, change it to build an C<%Is> hash and require it. Maybe just put
83 it into F<test.pl>. Throw in the handy tainting subroutines.
85 =head2 POD -E<gt> HTML conversion in the core still sucks
87 Which is crazy given just how simple POD purports to be, and how simple HTML
88 can be. It's not actually I<as> simple as it sounds, particularly with the
89 flexibility POD allows for C<=item>, but it would be good to improve the
90 visual appeal of the HTML generated, and to avoid it having any validation
91 errors. See also L</make HTML install work>, as the layout of installation tree
92 is needed to improve the cross-linking.
94 The addition of C<Pod::Simple> and its related modules may make this task
97 =head2 Parallel testing
99 (This probably impacts much more than the core: also the Test::Harness
100 and TAP::* modules on CPAN.)
102 All of the tests in F<t/> can now be run in parallel, if C<$ENV{TEST_JOBS}>
103 is set. However, tests within each directory in F<ext> and F<lib> are still
104 run in series, with directories run in parallel. This is an adequate
105 heuristic, but it might be possible to relax it further, and get more
106 throughput. Specifically, it would be good to audit all of F<lib/*.t>, and
107 make them use C<File::Temp>.
109 =head2 Make Schwern poorer
111 We should have tests for everything. When all the core's modules are tested,
112 Schwern has promised to donate to $500 to TPF. We may need volunteers to
113 hold him upside down and shake vigorously in order to actually extract the
116 =head2 Improve the coverage of the core tests
118 Use Devel::Cover to ascertain the core modules's test coverage, then add
119 tests that are currently missing.
123 A full test suite for the B module would be nice.
125 =head2 A decent benchmark
127 C<perlbench> seems impervious to any recent changes made to the perl core. It
128 would be useful to have a reasonable general benchmarking suite that roughly
129 represented what current perl programs do, and measurably reported whether
130 tweaks to the core improve, degrade or don't really affect performance, to
131 guide people attempting to optimise the guts of perl. Gisle would welcome
132 new tests for perlbench.
134 =head2 fix tainting bugs
136 Fix the bugs revealed by running the test suite with the C<-t> switch (via
137 C<make test.taintwarn>).
139 =head2 Dual life everything
141 As part of the "dists" plan, anything that doesn't belong in the smallest perl
142 distribution needs to be dual lifed. Anything else can be too. Figure out what
143 changes would be needed to package that module and its tests up for CPAN, and
144 do so. Test it with older perl releases, and fix the problems you find.
146 To make a minimal perl distribution, it's useful to look at
147 F<t/lib/commonsense.t>.
149 =head2 Bundle dual life modules in ext/
151 For maintenance (and branch merging) reasons, it would be useful to move
152 some architecture-independent dual-life modules from lib/ to ext/, if this
153 has no negative impact on the build of perl itself.
155 =head2 POSIX memory footprint
157 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
158 various times worked to cut it down. There is probably still fat to cut out -
159 for example POSIX passes Exporter some very memory hungry data structures.
161 =head2 embed.pl/makedef.pl
163 There is a script F<embed.pl> that generates several header files to prefix
164 all of Perl's symbols in a consistent way, to provide some semblance of
165 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
166 in F<interpvar.h>. Quite a few of the functions and variables
167 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
168 doesn't understand the C macros, so the rules about which symbols are present
169 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
170 It would be good to teach C<embed.pl> to understand the conditional
171 compilation, and hence remove the duplication, and the mistakes it has caused.
173 =head2 use strict; and AutoLoad
175 Currently if you write
178 use AutoLoader 'AUTOLOAD';
183 print join (' ', No, strict, here), "!\n";
186 then C<use strict;> isn't in force within the autoloaded subroutines. It would
187 be more consistent (and less surprising) to arrange for all lexical pragmas
188 in force at the __END__ block to be in force within each autoloaded subroutine.
190 There's a similar problem with SelfLoader.
192 =head2 profile installman
194 The F<installman> script is slow. All it is doing text processing, which we're
195 told is something Perl is good at. So it would be nice to know what it is doing
196 that is taking so much CPU, and where possible address it.
199 =head1 Tasks that need a little sysadmin-type knowledge
201 Or if you prefer, tasks that you would learn from, and broaden your skills
204 =head2 make HTML install work
206 There is an C<installhtml> target in the Makefile. It's marked as
207 "experimental". It would be good to get this tested, make it work reliably, and
208 remove the "experimental" tag. This would include
214 Checking that cross linking between various parts of the documentation works.
215 In particular that links work between the modules (files with POD in F<lib/>)
216 and the core documentation (files in F<pod/>)
220 Work out how to split C<perlfunc> into chunks, preferably one per function
221 group, preferably with general case code that could be used elsewhere.
222 Challenges here are correctly identifying the groups of functions that go
223 together, and making the right named external cross-links point to the right
224 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
225 C<endservent>, two or more C<=items> giving the different parameter lists, such
228 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
229 =item substr EXPR,OFFSET,LENGTH
230 =item substr EXPR,OFFSET
232 and different parameter lists having different meanings. (eg C<select>)
236 =head2 compressed man pages
238 Be able to install them. This would probably need a configure test to see how
239 the system does compressed man pages (same directory/different directory?
240 same filename/different filename), as well as tweaking the F<installman> script
241 to compress as necessary.
243 =head2 Add a code coverage target to the Makefile
245 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
246 to do this manually are roughly
252 do a normal C<Configure>, but include Devel::Cover as a module to install
253 (see F<INSTALL> for how to do this)
261 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
265 Process the resulting Devel::Cover database
269 This just give you the coverage of the F<.pm>s. To also get the C level
276 Additionally tell C<Configure> to use the appropriate C compiler flags for
283 (instead of C<make perl>)
287 After running the tests run C<gcov> to generate all the F<.gcov> files.
288 (Including down in the subdirectories of F<ext/>
292 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
293 to get their stats into the cover_db directory.
297 Then process the Devel::Cover database
301 It would be good to add a single switch to C<Configure> to specify that you
302 wanted to perform perl level coverage, and another to specify C level
303 coverage, and have C<Configure> and the F<Makefile> do all the right things
306 =head2 Make Config.pm cope with differences between built and installed perl
308 Quite often vendors ship a perl binary compiled with their (pay-for)
309 compilers. People install a free compiler, such as gcc. To work out how to
310 build extensions, Perl interrogates C<%Config>, so in this situation
311 C<%Config> describes compilers that aren't there, and extension building
312 fails. This forces people into choosing between re-compiling perl themselves
313 using the compiler they have, or only using modules that the vendor ships.
315 It would be good to find a way teach C<Config.pm> about the installation setup,
316 possibly involving probing at install time or later, so that the C<%Config> in
317 a binary distribution better describes the installed machine, when the
318 installed machine differs from the build machine in some significant way.
320 =head2 linker specification files
322 Some platforms mandate that you provide a list of a shared library's external
323 symbols to the linker, so the core already has the infrastructure in place to
324 do this for generating shared perl libraries. My understanding is that the
325 GNU toolchain can accept an optional linker specification file, and restrict
326 visibility just to symbols declared in that file. It would be good to extend
327 F<makedef.pl> to support this format, and to provide a means within
328 C<Configure> to enable it. This would allow Unix users to test that the
329 export list is correct, and to build a perl that does not pollute the global
330 namespace with private symbols.
332 =head2 Cross-compile support
334 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
335 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
336 assumed then to be copied to TARGET machine and used as a replacement of full
339 This could be done little differently. Namely C<miniperl> should be built for
340 HOST and then full C<perl> with extensions should be compiled for TARGET.
341 This, however, might require extra trickery for %Config: we have one config
342 first for HOST and then another for TARGET. Tools like MakeMaker will be
343 mightily confused. Having around two different types of executables and
344 libraries (HOST and TARGET) makes life interesting for Makefiles and
345 shell (and Perl) scripts. There is $Config{run}, normally empty, which
346 can be used as an execution wrapper. Also note that in some
347 cross-compilation/execution environments the HOST and the TARGET do
348 not see the same filesystem(s), the $Config{run} may need to do some
349 file/directory copying back and forth.
353 Make F<pod/roffitall> be updated by F<pod/buildtoc>.
355 =head2 Split "linker" from "compiler"
357 Right now, Configure probes for two commands, and sets two variables:
361 =item * C<cc> (in F<cc.U>)
363 This variable holds the name of a command to execute a C compiler which
364 can resolve multiple global references that happen to have the same
365 name. Usual values are F<cc> and F<gcc>.
366 Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>.
368 =item * C<ld> (in F<dlsrc.U>)
370 This variable indicates the program to be used to link
371 libraries for dynamic loading. On some systems, it is F<ld>.
372 On ELF systems, it should be C<$cc>. Mostly, we'll try to respect
373 the hint file setting.
377 There is an implicit historical assumption from around Perl5.000alpha
378 something, that C<$cc> is also the correct command for linking object files
379 together to make an executable. This may be true on Unix, but it's not true
380 on other platforms, and there are a maze of work arounds in other places (such
381 as F<Makefile.SH>) to cope with this.
383 Ideally, we should create a new variable to hold the name of the executable
384 linker program, probe for it in F<Configure>, and centralise all the special
385 case logic there or in hints files.
387 A small bikeshed issue remains - what to call it, given that C<$ld> is already
388 taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command
389 for creating dynamically-loadable modules) and C<$link> could be confused with
390 the Unix command line executable of the same name, which does something
391 completely different. Andy Dougherty makes the counter argument "In parrot, I
392 tried to call the command used to link object files and libraries into an
393 executable F<link>, since that's what my vaguely-remembered DOS and VMS
394 experience suggested. I don't think any real confusion has ensued, so it's
395 probably a reasonable name for perl5 to use."
397 "Alas, I've always worried that introducing it would make things worse,
398 since now the module building utilities would have to look for
399 C<$Config{link}> and institute a fall-back plan if it weren't found."
400 Although I can see that as confusing, given that C<$Config{d_link}> is true
401 when (hard) links are available.
403 =head1 Tasks that need a little C knowledge
405 These tasks would need a little C knowledge, but don't need any specific
406 background or experience with XS, or how the Perl interpreter works
408 =head2 Weed out needless PERL_UNUSED_ARG
410 The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about
411 unused arguments. Often the arguments can't be removed, as there is an
412 external constraint that determines the prototype of the function, so this
413 approach is valid. However, there are some cases where C<PERL_UNUSED_ARG>
414 could be removed. Specifically
420 The prototypes of (nearly all) static functions can be changed
424 Unused arguments generated by short cut macros are wasteful - the short cut
425 macro used can be changed.
429 =head2 Modernize the order of directories in @INC
431 The way @INC is laid out by default, one cannot upgrade core (dual-life)
432 modules without overwriting files. This causes problems for binary
433 package builders. One possible proposal is laid out in this
435 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.
439 Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
440 On these systems, it might be the default compilation mode, and there
441 is currently no guarantee that passing no use64bitall option to the
442 Configure process will build a 32bit perl. Implementing -Duse32bit*
443 options would be nice for perl 5.12.
445 =head2 Profile Perl - am I hot or not?
447 The Perl source code is stable enough that it makes sense to profile it,
448 identify and optimise the hotspots. It would be good to measure the
449 performance of the Perl interpreter using free tools such as cachegrind,
450 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
452 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
453 the ops that are most commonly used. The idea is that by grouping them, their
454 object code will be adjacent in the executable, so they have a greater chance
455 of already being in the CPU cache (or swapped in) due to being near another op
458 Except that it's not clear if these really are the most commonly used ops. So
459 as part of exercising your skills with coverage and profiling tools you might
460 want to determine what ops I<really> are the most commonly used. And in turn
461 suggest evictions and promotions to achieve a better F<pp_hot.c>.
463 One piece of Perl code that might make a good testbed is F<installman>.
465 =head2 Allocate OPs from arenas
467 Currently all new OP structures are individually malloc()ed and free()d.
468 All C<malloc> implementations have space overheads, and are now as fast as
469 custom allocates so it would both use less memory and less CPU to allocate
470 the various OP structures from arenas. The SV arena code can probably be
473 Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use
474 Perl_Slab_alloc() to pack optrees into a contiguous block, which is
475 probably superior to the use of OP arenas, esp. from a cache locality
476 standpoint. See L<Profile Perl - am I hot or not?>.
478 =head2 Improve win32/wince.c
480 Currently, numerous functions look virtually, if not completely,
481 identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
484 =head2 Use secure CRT functions when building with VC8 on Win32
486 Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
487 that they were "unsafe" and introduced differently named secure versions of
488 them as replacements, e.g. instead of writing
490 FILE* f = fopen(__FILE__, "r");
495 errno_t err = fopen_s(&f, __FILE__, "r");
497 Currently, the warnings about these deprecations have been disabled by adding
498 -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
499 warning suppressant and actually make use of the new secure CRT functions.
501 There is also a similar issue with POSIX CRT function names like fileno having
502 been deprecated in favour of ISO C++ conformant names like _fileno. These
503 warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It
504 might be nice to do as Microsoft suggest here too, although, unlike the secure
505 functions issue, there is presumably little or no benefit in this case.
507 =head2 Fix POSIX::access() and chdir() on Win32
509 These functions currently take no account of DACLs and therefore do not behave
510 correctly in situations where access is restricted by DACLs (as opposed to the
511 read-only attribute).
513 Furthermore, POSIX::access() behaves differently for directories having the
514 read-only attribute set depending on what CRT library is being used. For
515 example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that
516 such directories are not writable, whereas in fact all directories are writable
517 unless access is denied by DACLs. (In the case of directories, the read-only
518 attribute actually only means that the directory cannot be deleted.) This CRT
519 bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still
520 not actually be writable if access is indeed denied by DACLs).
522 For the chdir() issue, see ActiveState bug #74552:
523 http://bugs.activestate.com/show_bug.cgi?id=74552
525 Therefore, DACLs should be checked both for consistency across CRTs and for
528 (Note that perl's -w operator should not be modified to check DACLs. It has
529 been written so that it reflects the state of the read-only attribute, even
530 for directories (whatever CRT is being used), for symmetry with chmod().)
532 =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
534 Maybe create a utility that checks after each libperl.a creation that
535 none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
536 ever creep back to libperl.a.
538 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
540 Note, of course, that this will only tell whether B<your> platform
541 is using those naughty interfaces.
543 =head2 -D_FORTIFY_SOURCE=2, -fstack-protector
545 Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc
546 (4.1 onwards?) supports C<-fstack-protector>, both of which give
547 protection against various kinds of buffer overflow problems.
548 These should probably be used for compiling Perl whenever available,
549 Configure and/or hints files should be adjusted to probe for the
550 availability of these features and enable them as appropriate.
552 =head2 Arenas for GPs? For MAGIC?
554 C<struct gp> and C<struct magic> are both currently allocated by C<malloc>.
555 It might be a speed or memory saving to change to using arenas. Or it might
556 not. It would need some suitable benchmarking first. In particular, C<GP>s
557 can probably be changed with minimal compatibility impact (probably nothing
558 outside of the core, or even outside of F<gv.c> allocates them), but they
559 probably aren't allocated/deallocated often enough for a speed saving. Whereas
560 C<MAGIC> is allocated/deallocated more often, but in turn, is also something
561 more externally visible, so changing the rules here may bite external code.
565 Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and
566 PVHV, and PVCV and PVFM. It should be possible to allocate and return same
567 sized bodies from the same actual arena, rather than maintaining one arena for
568 each. This could save 4-6K per thread, of memory no longer tied up in the
569 not-yet-allocated part of an arena.
572 =head1 Tasks that need a knowledge of XS
574 These tasks would need C knowledge, and roughly the level of knowledge of
575 the perl API that comes from writing modules that use XS to interface to
578 =head2 safely supporting POSIX SA_SIGINFO
580 Some years ago Jarkko supplied patches to provide support for the POSIX
581 SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler.
583 Unfortunately, it only works with "unsafe" signals, because under safe
584 signals, by the time Perl gets to run the signal handler, the extra
585 information has been lost. Moreover, it's not easy to store it somewhere,
586 as you can't call mutexs, or do anything else fancy, from inside a signal
589 So it strikes me that we could provide safe SA_SIGINFO support
595 Provide global variables for two file descriptors
599 When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a
600 pipe, store the reader in one, the writer in the other
604 In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if
605 the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open,
611 serialise signal number, C<struct siginfo_t> (or at least the parts we care
612 about) into a small auto char buff
616 C<write()> that (non-blocking) to the writer fd
622 if it writes 100%, flag the signal in a counter of "signals on the pipe" akin
623 to the current per-signal-number counts
627 if it writes 0%, assume the pipe is full. Flag the data as lost?
631 if it writes partially, croak a panic, as your OS is broken.
639 in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on
640 the pipe", read the data out, deserialise, build the Perl structures on
641 the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as
646 I think that this gets us decent C<SA_SIGINFO> support, without the current risk
647 of running Perl code inside the signal handler context. (With all the dangers
648 of things like C<malloc> corruption that that currently offers us)
650 For more information see the thread starting with this message:
651 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html
653 =head2 autovivification
655 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
657 This task is incremental - even a little bit of work on it will help.
659 =head2 Unicode in Filenames
661 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
662 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
663 system, truncate, unlink, utime, -X. All these could potentially accept
664 Unicode filenames either as input or output (and in the case of system
665 and qx Unicode in general, as input or output to/from the shell).
666 Whether a filesystem - an operating system pair understands Unicode in
669 Known combinations that have some level of understanding include
670 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
671 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
672 create Unicode filenames, what forms of Unicode are accepted and used
673 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
674 and so on, varies. Finding the right level of interfacing to Perl
675 requires some thought. Remember that an OS does not implicate a
678 (The Windows -C command flag "wide API support" has been at least
679 temporarily retired in 5.8.1, and the -C has been repurposed, see
682 Most probably the right way to do this would be this:
683 L</"Virtualize operating system access">.
685 =head2 Unicode in %ENV
687 Currently the %ENV entries are always byte strings.
688 See L</"Virtualize operating system access">.
690 =head2 Unicode and glob()
692 Currently glob patterns and filenames returned from File::Glob::glob()
693 are always byte strings. See L</"Virtualize operating system access">.
695 =head2 Unicode and lc/uc operators
697 Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on
698 what the internal encoding of their argument is. That should not be the
699 case. Maybe add a pragma to switch behaviour.
701 =head2 use less 'memory'
703 Investigate trade offs to switch out perl's choices on memory usage.
704 Particularly perl should be able to give memory back.
706 This task is incremental - even a little bit of work on it will help.
708 =head2 Re-implement C<:unique> in a way that is actually thread-safe
710 The old implementation made bad assumptions on several levels. A good 90%
711 solution might be just to make C<:unique> work to share the string buffer
712 of SvPVs. That way large constant strings can be shared between ithreads,
713 such as the configuration information in F<Config>.
715 =head2 Make tainting consistent
717 Tainting would be easier to use if it didn't take documented shortcuts and
718 allow taint to "leak" everywhere within an expression.
720 =head2 readpipe(LIST)
722 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
723 running a shell. readpipe() (the function behind qx//) could be similarly
726 =head2 Audit the code for destruction ordering assumptions
730 /* Need to check SvMAGICAL, as during global destruction it may be that
731 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
732 is now part of the linked list of SV heads, rather than pointing to
733 the original body. */
734 /* FIXME - audit the code for other bugs like this one. */
736 adding the C<SvMAGICAL> check to
738 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
739 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
741 Go through the core and look for similar assumptions that SVs have particular
742 types, as all bets are off during global destruction.
744 =head2 Extend PerlIO and PerlIO::Scalar
746 PerlIO::Scalar doesn't know how to truncate(). Implementing this
747 would require extending the PerlIO vtable.
749 Similarly the PerlIO vtable doesn't know about formats (write()), or
750 about stat(), or chmod()/chown(), utime(), or flock().
752 (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
755 PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
756 opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
759 See also L</"Virtualize operating system access">.
761 =head2 -C on the #! line
763 It should be possible to make -C work correctly if found on the #! line,
764 given that all perl command line options are strict ASCII, and -C changes
765 only the interpretation of non-ASCII characters, and not for the script file
766 handle. To make it work needs some investigation of the ordering of function
767 calls during startup, and (by implication) a bit of tweaking of that order.
769 =head2 Organize error messages
771 Perl's diagnostics (error messages, see L<perldiag>) could use
772 reorganizing and formalizing so that each error message has its
773 stable-for-all-eternity unique id, categorized by severity, type, and
774 subsystem. (The error messages would be listed in a datafile outside
775 of the Perl source code, and the source code would only refer to the
776 messages by the id.) This clean-up and regularizing should apply
777 for all croak() messages.
779 This would enable all sorts of things: easier translation/localization
780 of the messages (though please do keep in mind the caveats of
781 L<Locale::Maketext> about too straightforward approaches to
782 translation), filtering by severity, and instead of grepping for a
783 particular error message one could look for a stable error id. (Of
784 course, changing the error messages by default would break all the
785 existing software depending on some particular error message...)
787 This kind of functionality is known as I<message catalogs>. Look for
788 inspiration for example in the catgets() system, possibly even use it
789 if available-- but B<only> if available, all platforms will B<not>
792 For the really pure at heart, consider extending this item to cover
793 also the warning messages (see L<perllexwarn>, C<warnings.pl>).
795 =head1 Tasks that need a knowledge of the interpreter
797 These tasks would need C knowledge, and knowledge of how the interpreter works,
798 or a willingness to learn.
800 =head2 error reporting of [$a ; $b]
802 Using C<;> inside brackets is a syntax error, and we don't propose to change
803 that by giving it any meaning. However, it's not reported very helpfully:
805 $ perl -e '$a = [$b; $c];'
806 syntax error at -e line 1, near "$b;"
807 syntax error at -e line 1, near "$c]"
808 Execution of -e aborted due to compilation errors.
810 It should be possible to hook into the tokeniser or the lexer, so that when a
811 C<;> is parsed where it is not legal as a statement terminator (ie inside
812 C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like
813 I<';' isn't legal inside an expression - if you need multiple statements use a
814 do {...} block>. See the thread starting at
815 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html
817 =head2 lexicals used only once
821 $ perl -we '$pie = 42'
822 Name "main::pie" used only once: possible typo at -e line 1.
826 $ perl -we 'my $pie = 42'
828 Logically all lexicals used only once should warn, if the user asks for
829 warnings. An unworked RT ticket (#5087) has been open for almost seven
830 years for this discrepancy.
834 The handling of Unicode is unclean in many places. For example, the regexp
835 engine matches in Unicode semantics whenever the string or the pattern is
836 flagged as UTF-8, but that should not be dependent on an internal storage
837 detail of the string. Likewise, case folding behaviour is dependent on the
838 UTF8 internal flag being on or off.
840 =head2 Properly Unicode safe tokeniser and pads.
842 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
843 variable names are stored in stashes as raw bytes, without the utf-8 flag
844 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
845 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
846 source filters. All this could be fixed.
848 =head2 state variable initialization in list context
850 Currently this is illegal:
852 state ($a, $b) = foo();
854 In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different
855 semantics, which is tricky to implement in Perl 5 as currently they produce
856 the same opcode trees. The Perl 6 design is firm, so it would be good to
857 implement the necessary code in Perl 5. There are comments in
858 C<Perl_newASSIGNOP()> that show the code paths taken by various assignment
859 constructions involving state variables.
861 =head2 Implement $value ~~ 0 .. $range
863 It would be nice to extend the syntax of the C<~~> operator to also
864 understand numeric (and maybe alphanumeric) ranges.
866 =head2 A does() built-in
868 Like ref(), only useful. It would call the C<DOES> method on objects; it
869 would also tell whether something can be dereferenced as an
870 array/hash/etc., or used as a regexp, etc.
871 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
873 =head2 Tied filehandles and write() don't mix
875 There is no method on tied filehandles to allow them to be called back by
878 =head2 Attach/detach debugger from running program
880 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
881 program if you pass the process ID. It would be good to do this with the Perl
882 debugger on a running Perl program, although I'm not sure how it would be
883 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
885 =head2 Optimize away empty destructors
887 Defining an empty DESTROY method might be useful (notably in
888 AUTOLOAD-enabled classes), but it's still a bit expensive to call. That
889 could probably be optimized.
891 =head2 LVALUE functions for lists
893 The old perltodo notes that lvalue functions don't work for list or hash
894 slices. This would be good to fix.
896 =head2 regexp optimiser optional
898 The regexp optimiser is not optional. It should configurable to be, to allow
899 its performance to be measured, and its bugs to be easily demonstrated.
901 =head2 delete &function
903 Allow to delete functions. One can already undef them, but they're still
906 =head2 C</w> regex modifier
908 That flag would enable to match whole words, and also to interpolate
909 arrays as alternations. With it, C</P/w> would be roughly equivalent to:
911 do { local $"='|'; /\b(?:P)\b/ }
913 See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
916 =head2 optional optimizer
918 Make the peephole optimizer optional. Currently it performs two tasks as
919 it walks the optree - genuine peephole optimisations, and necessary fixups of
920 ops. It would be good to find an efficient way to switch out the
921 optimisations whilst keeping the fixups.
923 =head2 You WANT *how* many
925 Currently contexts are void, scalar and list. split has a special mechanism in
926 place to pass in the number of return values wanted. It would be useful to
927 have a general mechanism for this, backwards compatible and little speed hit.
928 This would allow proposals such as short circuiting sort to be implemented
931 =head2 lexical aliases
933 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
935 =head2 entersub XS vs Perl
937 At the moment pp_entersub is huge, and has code to deal with entering both
938 perl and XS subroutines. Subroutine implementations rarely change between
939 perl and XS at run time, so investigate using 2 ops to enter subs (one for
940 XS, one for perl) and swap between if a sub is redefined.
944 Self-ties are currently illegal because they caused too many segfaults. Maybe
945 the causes of these could be tracked down and self-ties on all types
948 =head2 Optimize away @_
950 The old perltodo notes "Look at the "reification" code in C<av.c>".
952 =head2 Virtualize operating system access
954 Implement a set of "vtables" that virtualizes operating system access
955 (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very
956 least these interfaces should take SVs as "name" arguments instead of
957 bare char pointers; probably the most flexible and extensible way
958 would be for the Perl-facing interfaces to accept HVs. The system
959 needs to be per-operating-system and per-file-system
960 hookable/filterable, preferably both from XS and Perl level
961 (L<perlport/"Files and Filesystems"> is good reading at this point,
962 in fact, all of L<perlport> is.)
964 This has actually already been implemented (but only for Win32),
965 take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32
966 variants go through a set of "vtables" for operating system access,
967 non-Win32 systems currently go straight for the POSIX/UNIX-style
968 system/library call. Similar system as for Win32 should be
969 implemented for all platforms. The existing Win32 implementation
970 probably does not need to survive alongside this proposed new
971 implementation, the approaches could be merged.
973 What would this give us? One often-asked-for feature this would
974 enable is using Unicode for filenames, and other "names" like %ENV,
975 usernames, hostnames, and so forth.
976 (See L<perlunicode/"When Unicode Does Not Happen">.)
978 But this kind of virtualization would also allow for things like
979 virtual filesystems, virtual networks, and "sandboxes" (though as long
980 as dynamic loading of random object code is allowed, not very safe
981 sandboxes since external code of course know not of Perl's vtables).
982 An example of a smaller "sandbox" is that this feature can be used to
983 implement per-thread working directories: Win32 already does this.
985 See also L</"Extend PerlIO and PerlIO::Scalar">.
987 =head2 Investigate PADTMP hash pessimisation
989 The peephole optimiser converts constants used for hash key lookups to shared
990 hash key scalars. Under ithreads, something is undoing this work.
991 See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html
993 =head2 Store the current pad in the OP slab allocator
996 I hope that I got that "current pad" part correct
998 Currently we leak ops in various cases of parse failure. I suggested that we
999 could solve this by always using the op slab allocator, and walking it to
1000 free ops. Dave comments that as some ops are already freed during optree
1001 creation one would have to mark which ops are freed, and not double free them
1002 when walking the slab. He notes that one problem with this is that for some ops
1003 you have to know which pad was current at the time of allocation, which does
1004 change. I suggested storing a pointer to the current pad in the memory allocated
1005 for the slab, and swapping to a new slab each time the pad changes. Dave thinks
1006 that this would work.
1008 =head2 repack the optree
1010 Repacking the optree after execution order is determined could allow
1011 removal of NULL ops, and optimal ordering of OPs with respect to cache-line
1012 filling. The slab allocator could be reused for this purpose. I think that
1013 the best way to do this is to make it an optional step just before the
1014 completed optree is attached to anything else, and to use the slab allocator
1015 unchanged, so that freeing ops is identical whether or not this step runs.
1016 Note that the slab allocator allocates ops downwards in memory, so one would
1017 have to actually "allocate" the ops in reverse-execution order to get them
1018 contiguous in memory in execution order.
1020 See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html
1022 Note that running this copy, and then freeing all the old location ops would
1023 cause their slabs to be freed, which would eliminate possible memory wastage if
1024 the previous suggestion is implemented, and we swap slabs more frequently.
1026 =head2 eliminate incorrect line numbers in warnings
1034 } elsif ($undef == 0) {
1037 used to produce this output:
1039 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1040 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1042 where the line of the second warning was misreported - it should be line 5.
1043 Rafael fixed this - the problem arose because there was no nextstate OP
1044 between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still
1045 reports that the currently executing line is line 4. The solution was to inject
1046 a nextstate OPs for each C<elsif>, although it turned out that the nextstate
1047 OP needed to be a nulled OP, rather than a live nextstate OP, else other line
1048 numbers became misreported. (Jenga!)
1050 The problem is more general than C<elsif> (although the C<elsif> case is the
1051 most common and the most confusing). Ideally this code
1061 would produce this output
1063 Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
1064 Use of uninitialized value $undef in addition (+) at wrong.pl line 7.
1066 (rather than lines 4 and 5), but this would seem to require every OP to carry
1067 (at least) line number information.
1069 What might work is to have an optional line number in memory just before the
1070 BASEOP structure, with a flag bit in the op to say whether it's present.
1071 Initially during compile every OP would carry its line number. Then add a late
1072 pass to the optimiser (potentially combined with L</repack the optree>) which
1073 looks at the two ops on every edge of the graph of the execution path. If
1074 the line number changes, flags the destination OP with this information.
1075 Once all paths are traced, replace every op with the flag with a
1076 nextstate-light op (that just updates C<PL_curcop>), which in turn then passes
1077 control on to the true op. All ops would then be replaced by variants that
1078 do not store the line number. (Which, logically, why it would work best in
1079 conjunction with L</repack the optree>, as that is already copying/reallocating
1082 (Although I should note that we're not certain that doing this for the general
1085 =head2 optimize tail-calls
1087 Tail-calls present an opportunity for broadly applicable optimization;
1088 anywhere that C<< return foo(...) >> is called, the outer return can
1089 be replaced by a goto, and foo will return directly to the outer
1090 caller, saving (conservatively) 25% of perl's call&return cost, which
1091 is relatively higher than in C. The scheme language is known to do
1092 this heavily. B::Concise provides good insight into where this
1093 optimization is possible, ie anywhere entersub,leavesub op-sequence
1096 perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'
1098 Bottom line on this is probably a new pp_tailcall function which
1099 combines the code in pp_entersub, pp_leavesub. This should probably
1100 be done 1st in XS, and using B::Generate to patch the new OP into the
1105 Tasks that will get your name mentioned in the description of the "Highlights
1108 =head2 make ithreads more robust
1110 Generally make ithreads more robust. See also L</iCOW>
1112 This task is incremental - even a little bit of work on it will help, and
1113 will be greatly appreciated.
1115 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
1117 Fix Perl_sv_dup, et al so that threads can return objects.
1121 Sarathy and Arthur have a proposal for an improved Copy On Write which
1122 specifically will be able to COW new ithreads. If this can be implemented
1123 it would be a good thing.
1125 =head2 (?{...}) closures in regexps
1127 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
1129 =head2 A re-entrant regexp engine
1131 This will allow the use of a regex from inside (?{ }), (??{ }) and
1132 (?(?{ })|) constructs.
1134 =head2 Add class set operations to regexp engine
1136 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
1138 demerphq has this on his todo list, but right at the bottom.