3 perltodo - Perl TO-DO List
7 This is a list of wishes for Perl. The tasks we think are smaller or
8 easier are listed first. Anyone is welcome to work on any of these,
9 but it's a good idea to first contact I<perl5-porters@perl.org> to
10 avoid duplication of effort, and to learn from any previous attempts.
11 By all means contact a pumpking privately first if you prefer.
13 Whilst patches to make the list shorter are most welcome, ideas to add to
14 the list are also encouraged. Check the perl5-porters archives for past
15 ideas, and any discussion about them. One set of archives may be found at:
17 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
19 What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
20 not, but if your patch is incorporated, then we'll add your name to the
21 F<AUTHORS> file, which ships in the official distribution. How many other
22 programming languages offer you 1 line of immortality?
24 =head1 Tasks that only need Perl knowledge
26 =head2 Remove duplication of test setup.
28 Schwern notes, that there's duplication of code - lots and lots of tests have
29 some variation on the big block of C<$Is_Foo> checks. We can safely put this
30 into a file, change it to build an C<%Is> hash and require it. Maybe just put
31 it into F<test.pl>. Throw in the handy tainting subroutines.
33 =head2 common test code for timed bail out
35 Write portable self destruct code for tests to stop them burning CPU in
36 infinite loops. This needs to avoid using alarm, as some of the tests are
37 testing alarm/sleep or timers.
39 =head2 POD -E<gt> HTML conversion in the core still sucks
41 Which is crazy given just how simple POD purports to be, and how simple HTML
42 can be. It's not actually I<as> simple as it sounds, particularly with the
43 flexibility POD allows for C<=item>, but it would be good to improve the
44 visual appeal of the HTML generated, and to avoid it having any validation
45 errors. See also L</make HTML install work>, as the layout of installation tree
46 is needed to improve the cross-linking.
48 The addition of C<Pod::Simple> and its related modules may make this task
51 =head2 merge checkpods and podchecker
53 F<pod/checkpods.PL> (and C<make check> in the F<pod/> subdirectory)
54 implements a very basic check for pod files, but the errors it discovers
55 aren't found by podchecker. Add this check to podchecker, get rid of
56 checkpods and have C<make check> use podchecker.
58 =head2 Parallel testing
60 (This probably impacts much more than the core: also the Test::Harness
61 and TAP::* modules on CPAN.)
63 The core regression test suite is getting ever more comprehensive, which has
64 the side effect that it takes longer to run. This isn't so good. Investigate
65 whether it would be feasible to give the harness script the B<option> of
66 running sets of tests in parallel. This would be useful for tests in
67 F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
75 How does screen layout work when you're running more than one test?
79 How does the caller of test specify how many tests to run in parallel?
83 How do setup/teardown tests identify themselves?
87 Pugs already does parallel testing - can their approach be re-used?
89 =head2 Make Schwern poorer
91 We should have tests for everything. When all the core's modules are tested,
92 Schwern has promised to donate to $500 to TPF. We may need volunteers to
93 hold him upside down and shake vigorously in order to actually extract the
96 =head2 Improve the coverage of the core tests
98 Use Devel::Cover to ascertain the core modules's test coverage, then add
99 tests that are currently missing.
103 A full test suite for the B module would be nice.
105 =head2 Deparse inlined constants
109 use constant PI => 4;
112 will currently deparse as
114 use constant ('PI', 4);
117 because the tokenizer inlines the value of the constant subroutine C<PI>.
118 This allows various compile time optimisations, such as constant folding
119 and dead code elimination. Where these haven't happened (such as the example
120 above) it ought be possible to make B::Deparse work out the name of the
121 original constant, because just enough information survives in the symbol
122 table to do this. Specifically, the same scalar is used for the constant in
123 the optree as is used for the constant subroutine, so by iterating over all
124 symbol tables and generating a mapping of SV address to constant name, it
125 would be possible to provide B::Deparse with this functionality.
127 =head2 A decent benchmark
129 C<perlbench> seems impervious to any recent changes made to the perl core. It
130 would be useful to have a reasonable general benchmarking suite that roughly
131 represented what current perl programs do, and measurably reported whether
132 tweaks to the core improve, degrade or don't really affect performance, to
133 guide people attempting to optimise the guts of perl. Gisle would welcome
134 new tests for perlbench.
136 =head2 fix tainting bugs
138 Fix the bugs revealed by running the test suite with the C<-t> switch (via
139 C<make test.taintwarn>).
141 =head2 Dual life everything
143 As part of the "dists" plan, anything that doesn't belong in the smallest perl
144 distribution needs to be dual lifed. Anything else can be too. Figure out what
145 changes would be needed to package that module and its tests up for CPAN, and
146 do so. Test it with older perl releases, and fix the problems you find.
148 To make a minimal perl distribution, it's useful to look at
149 F<t/lib/commonsense.t>.
151 =head2 Bundle dual life modules in ext/
153 For maintenance (and branch merging) reasons, it would be useful to move
154 some architecture-independent dual-life modules from lib/ to ext/, if this
155 has no negative impact on the build of perl itself.
157 However, we need to make sure that they are still installed in
158 architecture-independent directories by C<make install>.
160 =head2 Improving C<threads::shared>
162 Investigate whether C<threads::shared> could share aggregates properly with
163 only Perl level changes to shared.pm
165 =head2 POSIX memory footprint
167 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
168 various times worked to cut it down. There is probably still fat to cut out -
169 for example POSIX passes Exporter some very memory hungry data structures.
171 =head2 embed.pl/makedef.pl
173 There is a script F<embed.pl> that generates several header files to prefix
174 all of Perl's symbols in a consistent way, to provide some semblance of
175 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
176 in F<interpvar.h>. Quite a few of the functions and variables
177 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
178 doesn't understand the C macros, so the rules about which symbols are present
179 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
180 It would be good to teach C<embed.pl> to understand the conditional
181 compilation, and hence remove the duplication, and the mistakes it has caused.
183 =head2 use strict; and AutoLoad
185 Currently if you write
188 use AutoLoader 'AUTOLOAD';
193 print join (' ', No, strict, here), "!\n";
196 then C<use strict;> isn't in force within the autoloaded subroutines. It would
197 be more consistent (and less surprising) to arrange for all lexical pragmas
198 in force at the __END__ block to be in force within each autoloaded subroutine.
200 There's a similar problem with SelfLoader.
202 =head1 Tasks that need a little sysadmin-type knowledge
204 Or if you prefer, tasks that you would learn from, and broaden your skills
207 =head2 make HTML install work
209 There is an C<installhtml> target in the Makefile. It's marked as
210 "experimental". It would be good to get this tested, make it work reliably, and
211 remove the "experimental" tag. This would include
217 Checking that cross linking between various parts of the documentation works.
218 In particular that links work between the modules (files with POD in F<lib/>)
219 and the core documentation (files in F<pod/>)
223 Work out how to split C<perlfunc> into chunks, preferably one per function
224 group, preferably with general case code that could be used elsewhere.
225 Challenges here are correctly identifying the groups of functions that go
226 together, and making the right named external cross-links point to the right
227 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
228 C<endservent>, two or more C<=items> giving the different parameter lists, such
231 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
232 =item substr EXPR,OFFSET,LENGTH
233 =item substr EXPR,OFFSET
235 and different parameter lists having different meanings. (eg C<select>)
239 =head2 compressed man pages
241 Be able to install them. This would probably need a configure test to see how
242 the system does compressed man pages (same directory/different directory?
243 same filename/different filename), as well as tweaking the F<installman> script
244 to compress as necessary.
246 =head2 Add a code coverage target to the Makefile
248 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
249 to do this manually are roughly
255 do a normal C<Configure>, but include Devel::Cover as a module to install
256 (see F<INSTALL> for how to do this)
264 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
268 Process the resulting Devel::Cover database
272 This just give you the coverage of the F<.pm>s. To also get the C level
279 Additionally tell C<Configure> to use the appropriate C compiler flags for
286 (instead of C<make perl>)
290 After running the tests run C<gcov> to generate all the F<.gcov> files.
291 (Including down in the subdirectories of F<ext/>
295 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
296 to get their stats into the cover_db directory.
300 Then process the Devel::Cover database
304 It would be good to add a single switch to C<Configure> to specify that you
305 wanted to perform perl level coverage, and another to specify C level
306 coverage, and have C<Configure> and the F<Makefile> do all the right things
309 =head2 Make Config.pm cope with differences between built and installed perl
311 Quite often vendors ship a perl binary compiled with their (pay-for)
312 compilers. People install a free compiler, such as gcc. To work out how to
313 build extensions, Perl interrogates C<%Config>, so in this situation
314 C<%Config> describes compilers that aren't there, and extension building
315 fails. This forces people into choosing between re-compiling perl themselves
316 using the compiler they have, or only using modules that the vendor ships.
318 It would be good to find a way teach C<Config.pm> about the installation setup,
319 possibly involving probing at install time or later, so that the C<%Config> in
320 a binary distribution better describes the installed machine, when the
321 installed machine differs from the build machine in some significant way.
323 =head2 linker specification files
325 Some platforms mandate that you provide a list of a shared library's external
326 symbols to the linker, so the core already has the infrastructure in place to
327 do this for generating shared perl libraries. My understanding is that the
328 GNU toolchain can accept an optional linker specification file, and restrict
329 visibility just to symbols declared in that file. It would be good to extend
330 F<makedef.pl> to support this format, and to provide a means within
331 C<Configure> to enable it. This would allow Unix users to test that the
332 export list is correct, and to build a perl that does not pollute the global
333 namespace with private symbols.
335 =head2 Cross-compile support
337 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
338 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
339 assumed then to be copied to TARGET machine and used as a replacement of full
342 This could be done little differently. Namely C<miniperl> should be built for
343 HOST and then full C<perl> with extensions should be compiled for TARGET.
344 This, however, might require extra trickery for %Config: we have one config
345 first for HOST and then another for TARGET. Tools like MakeMaker will be
346 mightily confused. Having around two different types of executables and
347 libraries (HOST and TARGET) makes life interesting for Makefiles and
348 shell (and Perl) scripts. There is $Config{run}, normally empty, which
349 can be used as an execution wrapper. Also note that in some
350 cross-compilation/execution environments the HOST and the TARGET do
351 not see the same filesystem(s), the $Config{run} may need to do some
352 file/directory copying back and forth.
356 Make F<pod/roffitall> be updated by F<pod/buildtoc>.
358 =head1 Tasks that need a little C knowledge
360 These tasks would need a little C knowledge, but don't need any specific
361 background or experience with XS, or how the Perl interpreter works
363 =head2 Weed out needless PERL_UNUSED_ARG
365 The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about
366 unused arguments. Often the arguments can't be removed, as there is an
367 external constraint that determines the prototype of the function, so this
368 approach is valid. However, there are some cases where C<PERL_UNUSED_ARG>
369 could be removed. Specifically
375 The prototypes of (nearly all) static functions can be changed
379 Unused arguments generated by short cut macros are wasteful - the short cut
380 macro used can be changed.
384 =head2 Modernize the order of directories in @INC
386 The way @INC is laid out by default, one cannot upgrade core (dual-life)
387 modules without overwriting files. This causes problems for binary
388 package builders. One possible proposal is laid out in this
390 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.
394 Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
395 On these systems, it might be the default compilation mode, and there
396 is currently no guarantee that passing no use64bitall option to the
397 Configure process will build a 32bit perl. Implementing -Duse32bit*
398 options would be nice for perl 5.12.
400 =head2 Make it clear from -v if this is the exact official release
402 Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
403 usually defines one local patch, of the form "MAINT12345" or "RC1". The output
404 of perl -v doesn't report that a perl isn't an official release, and this
405 information can get lost in bugs reports. Because of this, the minor version
406 isn't bumped up until RC time, to minimise the possibility of versions of perl
407 escaping that believe themselves to be newer than they actually are.
409 It would be useful to find an elegant way to have the "this is an interim
410 maintenance release" or "this is a release candidate" in the terse -v output,
411 and have it so that it's easy for the pumpking to remove this just as the
412 release tarball is rolled up. This way the version pulled out of rsync would
413 always say "I'm a development release" and it would be safe to bump the
414 reported minor version as soon as a release ships, which would aid perl
417 This task is really about thinking of an elegant way to arrange the C source
418 such that it's trivial for the Pumpking to flag "this is an official release"
419 when making a tarball, yet leave the default source saying "I'm not the
422 =head2 Profile Perl - am I hot or not?
424 The Perl source code is stable enough that it makes sense to profile it,
425 identify and optimise the hotspots. It would be good to measure the
426 performance of the Perl interpreter using free tools such as cachegrind,
427 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
429 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
430 the ops that are most commonly used. The idea is that by grouping them, their
431 object code will be adjacent in the executable, so they have a greater chance
432 of already being in the CPU cache (or swapped in) due to being near another op
435 Except that it's not clear if these really are the most commonly used ops. So
436 as part of exercising your skills with coverage and profiling tools you might
437 want to determine what ops I<really> are the most commonly used. And in turn
438 suggest evictions and promotions to achieve a better F<pp_hot.c>.
440 =head2 Allocate OPs from arenas
442 Currently all new OP structures are individually malloc()ed and free()d.
443 All C<malloc> implementations have space overheads, and are now as fast as
444 custom allocates so it would both use less memory and less CPU to allocate
445 the various OP structures from arenas. The SV arena code can probably be
448 Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use
449 Perl_Slab_alloc() to pack optrees into a contiguous block, which is
450 probably superior to the use of OP arenas, esp. from a cache locality
451 standpoint. See L<Profile Perl - am I hot or not?>.
453 =head2 Improve win32/wince.c
455 Currently, numerous functions look virtually, if not completely,
456 identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
459 =head2 Use secure CRT functions when building with VC8 on Win32
461 Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
462 that they were "unsafe" and introduced differently named secure versions of
463 them as replacements, e.g. instead of writing
465 FILE* f = fopen(__FILE__, "r");
470 errno_t err = fopen_s(&f, __FILE__, "r");
472 Currently, the warnings about these deprecations have been disabled by adding
473 -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
474 warning suppressant and actually make use of the new secure CRT functions.
476 There is also a similar issue with POSIX CRT function names like fileno having
477 been deprecated in favour of ISO C++ conformant names like _fileno. These
478 warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It
479 might be nice to do as Microsoft suggest here too, although, unlike the secure
480 functions issue, there is presumably little or no benefit in this case.
482 =head2 Fix POSIX::access() and chdir() on Win32
484 These functions currently take no account of DACLs and therefore do not behave
485 correctly in situations where access is restricted by DACLs (as opposed to the
486 read-only attribute).
488 Furthermore, POSIX::access() behaves differently for directories having the
489 read-only attribute set depending on what CRT library is being used. For
490 example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that
491 such directories are not writable, whereas in fact all directories are writable
492 unless access is denied by DACLs. (In the case of directories, the read-only
493 attribute actually only means that the directory cannot be deleted.) This CRT
494 bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still
495 not actually be writable if access is indeed denied by DACLs).
497 For the chdir() issue, see ActiveState bug #74552:
498 http://bugs.activestate.com/show_bug.cgi?id=74552
500 Therefore, DACLs should be checked both for consistency across CRTs and for
503 (Note that perl's -w operator should not be modified to check DACLs. It has
504 been written so that it reflects the state of the read-only attribute, even
505 for directories (whatever CRT is being used), for symmetry with chmod().)
507 =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
509 Maybe create a utility that checks after each libperl.a creation that
510 none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
511 ever creep back to libperl.a.
513 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
515 Note, of course, that this will only tell whether B<your> platform
516 is using those naughty interfaces.
518 =head2 -D_FORTIFY_SOURCE=2, -fstack-protector
520 Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc
521 (4.1 onwards?) supports C<-fstack-protector>, both of which give
522 protection against various kinds of buffer overflow problems.
523 These should probably be used for compiling Perl whenever available,
524 Configure and/or hints files should be adjusted to probe for the
525 availability of these features and enable them as appropriate.
527 =head2 Arenas for GPs? For MAGIC?
529 C<struct gp> and C<struct magic> are both currently allocated by C<malloc>.
530 It might be a speed or memory saving to change to using arenas. Or it might
531 not. It would need some suitable benchmarking first. In particular, C<GP>s
532 can probably be changed with minimal compatibility impact (probably nothing
533 outside of the core, or even outside of F<gv.c> allocates them), but they
534 probably aren't allocated/deallocated often enough for a speed saving. Whereas
535 C<MAGIC> is allocated/deallocated more often, but in turn, is also something
536 more externally visible, so changing the rules here may bite external code.
539 =head1 Tasks that need a knowledge of XS
541 These tasks would need C knowledge, and roughly the level of knowledge of
542 the perl API that comes from writing modules that use XS to interface to
545 =head2 investigate removing int_macro_int from POSIX.xs
547 As a hang over from the original C<constant> implementation, F<POSIX.xs>
548 contains a function C<int_macro_int> which in conjunction with C<AUTOLOAD> is
549 used to wrap the C functions C<WEXITSTATUS>, C<WIFEXITED>, C<WIFSIGNALED>,
550 C<WIFSTOPPED>, C<WSTOPSIG> and C<WTERMSIG>. It's probably worth replacing
551 this complexity with 5 simple direct wrappings of those 5 functions.
553 However, it would be interesting if someone could measure the memory usage
554 before and after, both for the case of C<use POSIX();> and the case of
555 actually calling the Perl space functions.
557 =head2 safely supporting POSIX SA_SIGINFO
559 Some years ago Jarkko supplied patches to provide support for the POSIX
560 SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler.
562 Unfortunately, it only works with "unsafe" signals, because under safe
563 signals, by the time Perl gets to run the signal handler, the extra
564 information has been lost. Moreover, it's not easy to store it somewhere,
565 as you can't call mutexs, or do anything else fancy, from inside a signal
568 So it strikes me that we could provide safe SA_SIGINFO support
574 Provide global variables for two file descriptors
578 When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a
579 pipe, store the reader in one, the writer in the other
583 In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if
584 the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open,
590 serialise signal number, C<struct siginfo_t> (or at least the parts we care
591 about) into a small auto char buff
595 C<write()> that (non-blocking) to the writer fd
601 if it writes 100%, flag the signal in a counter of "signals on the pipe" akin
602 to the current per-signal-number counts
606 if it writes 0%, assume the pipe is full. Flag the data as lost?
610 if it writes partially, croak a panic, as your OS is broken.
618 in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on
619 the pipe", read the data out, deserialise, build the Perl structures on
620 the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as
625 I think that this gets us decent C<SA_SIGINFO> support, without the current risk
626 of running Perl code inside the signal handler context. (With all the dangers
627 of things like C<malloc> corruption that that currently offers us)
629 For more information see the thread starting with this message:
630 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html
632 =head2 autovivification
634 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
636 This task is incremental - even a little bit of work on it will help.
638 =head2 Unicode in Filenames
640 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
641 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
642 system, truncate, unlink, utime, -X. All these could potentially accept
643 Unicode filenames either as input or output (and in the case of system
644 and qx Unicode in general, as input or output to/from the shell).
645 Whether a filesystem - an operating system pair understands Unicode in
648 Known combinations that have some level of understanding include
649 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
650 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
651 create Unicode filenames, what forms of Unicode are accepted and used
652 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
653 and so on, varies. Finding the right level of interfacing to Perl
654 requires some thought. Remember that an OS does not implicate a
657 (The Windows -C command flag "wide API support" has been at least
658 temporarily retired in 5.8.1, and the -C has been repurposed, see
661 Most probably the right way to do this would be this:
662 L</"Virtualize operating system access">.
664 =head2 Unicode in %ENV
666 Currently the %ENV entries are always byte strings.
667 See L</"Virtualize operating system access">.
669 =head2 Unicode and glob()
671 Currently glob patterns and filenames returned from File::Glob::glob()
672 are always byte strings. See L</"Virtualize operating system access">.
674 =head2 Unicode and lc/uc operators
676 Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on
677 what the internal encoding of their argument is. That should not be the
678 case. Maybe add a pragma to switch behaviour.
680 =head2 use less 'memory'
682 Investigate trade offs to switch out perl's choices on memory usage.
683 Particularly perl should be able to give memory back.
685 This task is incremental - even a little bit of work on it will help.
687 =head2 Re-implement C<:unique> in a way that is actually thread-safe
689 The old implementation made bad assumptions on several levels. A good 90%
690 solution might be just to make C<:unique> work to share the string buffer
691 of SvPVs. That way large constant strings can be shared between ithreads,
692 such as the configuration information in F<Config>.
694 =head2 Make tainting consistent
696 Tainting would be easier to use if it didn't take documented shortcuts and
697 allow taint to "leak" everywhere within an expression.
699 =head2 readpipe(LIST)
701 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
702 running a shell. readpipe() (the function behind qx//) could be similarly
705 =head2 Audit the code for destruction ordering assumptions
709 /* Need to check SvMAGICAL, as during global destruction it may be that
710 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
711 is now part of the linked list of SV heads, rather than pointing to
712 the original body. */
713 /* FIXME - audit the code for other bugs like this one. */
715 adding the C<SvMAGICAL> check to
717 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
718 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
720 Go through the core and look for similar assumptions that SVs have particular
721 types, as all bets are off during global destruction.
723 =head2 Extend PerlIO and PerlIO::Scalar
725 PerlIO::Scalar doesn't know how to truncate(). Implementing this
726 would require extending the PerlIO vtable.
728 Similarly the PerlIO vtable doesn't know about formats (write()), or
729 about stat(), or chmod()/chown(), utime(), or flock().
731 (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
734 PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
735 opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
738 See also L</"Virtualize operating system access">.
740 =head2 -C on the #! line
742 It should be possible to make -C work correctly if found on the #! line,
743 given that all perl command line options are strict ASCII, and -C changes
744 only the interpretation of non-ASCII characters, and not for the script file
745 handle. To make it work needs some investigation of the ordering of function
746 calls during startup, and (by implication) a bit of tweaking of that order.
748 =head2 Organize error messages
750 Perl's diagnostics (error messages, see L<perldiag>) could use
751 reorganizing and formalizing so that each error message has its
752 stable-for-all-eternity unique id, categorized by severity, type, and
753 subsystem. (The error messages would be listed in a datafile outside
754 of the Perl source code, and the source code would only refer to the
755 messages by the id.) This clean-up and regularizing should apply
756 for all croak() messages.
758 This would enable all sorts of things: easier translation/localization
759 of the messages (though please do keep in mind the caveats of
760 L<Locale::Maketext> about too straightforward approaches to
761 translation), filtering by severity, and instead of grepping for a
762 particular error message one could look for a stable error id. (Of
763 course, changing the error messages by default would break all the
764 existing software depending on some particular error message...)
766 This kind of functionality is known as I<message catalogs>. Look for
767 inspiration for example in the catgets() system, possibly even use it
768 if available-- but B<only> if available, all platforms will B<not>
771 For the really pure at heart, consider extending this item to cover
772 also the warning messages (see L<perllexwarn>, C<warnings.pl>).
774 =head1 Tasks that need a knowledge of the interpreter
776 These tasks would need C knowledge, and knowledge of how the interpreter works,
777 or a willingness to learn.
779 =head2 lexicals used only once
783 $ perl -we '$pie = 42'
784 Name "main::pie" used only once: possible typo at -e line 1.
788 $ perl -we 'my $pie = 42'
790 Logically all lexicals used only once should warn, if the user asks for
791 warnings. An unworked RT ticket (#5087) has been open for almost seven
792 years for this discrepancy.
796 The handling of Unicode is unclean in many places. For example, the regexp
797 engine matches in Unicode semantics whenever the string or the pattern is
798 flagged as UTF-8, but that should not be dependent on an internal storage
799 detail of the string. Likewise, case folding behaviour is dependent on the
800 UTF8 internal flag being on or off.
802 =head2 Properly Unicode safe tokeniser and pads.
804 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
805 variable names are stored in stashes as raw bytes, without the utf-8 flag
806 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
807 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
808 source filters. All this could be fixed.
810 =head2 state variable initialization in list context
812 Currently this is illegal:
814 state ($a, $b) = foo();
816 In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different
817 semantics, which is tricky to implement in Perl 5 as currently they produce
818 the same opcode trees. The Perl 6 design is firm, so it would be good to
819 implement the necessary code in Perl 5. There are comments in
820 C<Perl_newASSIGNOP()> that show the code paths taken by various assignment
821 constructions involving state variables.
823 =head2 Implement $value ~~ 0 .. $range
825 It would be nice to extend the syntax of the C<~~> operator to also
826 understand numeric (and maybe alphanumeric) ranges.
828 =head2 A does() built-in
830 Like ref(), only useful. It would call the C<DOES> method on objects; it
831 would also tell whether something can be dereferenced as an
832 array/hash/etc., or used as a regexp, etc.
833 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
835 =head2 Tied filehandles and write() don't mix
837 There is no method on tied filehandles to allow them to be called back by
840 =head2 Attach/detach debugger from running program
842 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
843 program if you pass the process ID. It would be good to do this with the Perl
844 debugger on a running Perl program, although I'm not sure how it would be
845 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
847 =head2 Optimize away empty destructors
849 Defining an empty DESTROY method might be useful (notably in
850 AUTOLOAD-enabled classes), but it's still a bit expensive to call. That
851 could probably be optimized.
853 =head2 LVALUE functions for lists
855 The old perltodo notes that lvalue functions don't work for list or hash
856 slices. This would be good to fix.
858 =head2 LVALUE functions in the debugger
860 The old perltodo notes that lvalue functions don't work in the debugger. This
861 would be good to fix.
863 =head2 regexp optimiser optional
865 The regexp optimiser is not optional. It should configurable to be, to allow
866 its performance to be measured, and its bugs to be easily demonstrated.
868 =head2 delete &function
870 Allow to delete functions. One can already undef them, but they're still
873 =head2 C</w> regex modifier
875 That flag would enable to match whole words, and also to interpolate
876 arrays as alternations. With it, C</P/w> would be roughly equivalent to:
878 do { local $"='|'; /\b(?:P)\b/ }
880 See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
883 =head2 optional optimizer
885 Make the peephole optimizer optional. Currently it performs two tasks as
886 it walks the optree - genuine peephole optimisations, and necessary fixups of
887 ops. It would be good to find an efficient way to switch out the
888 optimisations whilst keeping the fixups.
890 =head2 You WANT *how* many
892 Currently contexts are void, scalar and list. split has a special mechanism in
893 place to pass in the number of return values wanted. It would be useful to
894 have a general mechanism for this, backwards compatible and little speed hit.
895 This would allow proposals such as short circuiting sort to be implemented
898 =head2 lexical aliases
900 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
902 =head2 entersub XS vs Perl
904 At the moment pp_entersub is huge, and has code to deal with entering both
905 perl and XS subroutines. Subroutine implementations rarely change between
906 perl and XS at run time, so investigate using 2 ops to enter subs (one for
907 XS, one for perl) and swap between if a sub is redefined.
911 Self-ties are currently illegal because they caused too many segfaults. Maybe
912 the causes of these could be tracked down and self-ties on all types
915 =head2 Optimize away @_
917 The old perltodo notes "Look at the "reification" code in C<av.c>".
919 =head2 Virtualize operating system access
921 Implement a set of "vtables" that virtualizes operating system access
922 (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very
923 least these interfaces should take SVs as "name" arguments instead of
924 bare char pointers; probably the most flexible and extensible way
925 would be for the Perl-facing interfaces to accept HVs. The system
926 needs to be per-operating-system and per-file-system
927 hookable/filterable, preferably both from XS and Perl level
928 (L<perlport/"Files and Filesystems"> is good reading at this point,
929 in fact, all of L<perlport> is.)
931 This has actually already been implemented (but only for Win32),
932 take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32
933 variants go through a set of "vtables" for operating system access,
934 non-Win32 systems currently go straight for the POSIX/UNIX-style
935 system/library call. Similar system as for Win32 should be
936 implemented for all platforms. The existing Win32 implementation
937 probably does not need to survive alongside this proposed new
938 implementation, the approaches could be merged.
940 What would this give us? One often-asked-for feature this would
941 enable is using Unicode for filenames, and other "names" like %ENV,
942 usernames, hostnames, and so forth.
943 (See L<perlunicode/"When Unicode Does Not Happen">.)
945 But this kind of virtualization would also allow for things like
946 virtual filesystems, virtual networks, and "sandboxes" (though as long
947 as dynamic loading of random object code is allowed, not very safe
948 sandboxes since external code of course know not of Perl's vtables).
949 An example of a smaller "sandbox" is that this feature can be used to
950 implement per-thread working directories: Win32 already does this.
952 See also L</"Extend PerlIO and PerlIO::Scalar">.
954 =head2 Investigate PADTMP hash pessimisation
956 The peephole optimier converts constants used for hash key lookups to shared
957 hash key scalars. Under ithreads, something is undoing this work.
958 See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html
960 =head2 Store the current pad in the OP slab allocator
963 I hope that I got that "current pad" part correct
965 Currently we leak ops in various cases of parse failure. I suggested that we
966 could solve this by always using the op slab allocator, and walking it to
967 free ops. Dave comments that as some ops are already freed during optree
968 creation one would have to mark which ops are freed, and not double free them
969 when walking the slab. He notes that one problem with this is that for some ops
970 you have to know which pad was current at the time of allocation, which does
971 change. I suggested storing a pointer to the current pad in the memory allocated
972 for the slab, and swapping to a new slab each time the pad changes. Dave thinks
973 that this would work.
975 =head2 repack the optree
977 Repacking the optree after execution order is determined could allow
978 removal of NULL ops, and optimal ordering of OPs with respect to cache-line
979 filling. The slab allocator could be reused for this purpose. I think that
980 the best way to do this is to make it an optional step just before the
981 completed optree is attached to anything else, and to use the slab allocator
982 unchanged, so that freeing ops is identical whether or not this step runs.
983 Note that the slab allocator allocates ops downwards in memory, so one would
984 have to actually "allocate" the ops in reverse-execution order to get them
985 contiguous in memory in execution order.
987 See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html
989 Note that running this copy, and then freeing all the old location ops would
990 cause their slabs to be freed, which would eliminate possible memory wastage if
991 the previous suggestion is implemented, and we swap slabs more frequently.
993 =head2 eliminate incorrect line numbers in warnings
1001 } elsif ($undef == 0) {
1004 used to produce this output:
1006 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1007 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1009 where the line of the second warning was misreported - it should be line 5.
1010 Rafael fixed this - the problem arose because there was no nextstate OP
1011 between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still
1012 reports that the currently executing line is line 4. The solution was to inject
1013 a nextstate OPs for each C<elsif>, although it turned out that the nextstate
1014 OP needed to be a nulled OP, rather than a live nextstate OP, else other line
1015 numbers became misreported. (Jenga!)
1017 The problem is more general than C<elsif> (although the C<elsif> case is the
1018 most common and the most confusing). Ideally this code
1028 would produce this output
1030 Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
1031 Use of uninitialized value $undef in addition (+) at wrong.pl line 7.
1033 (rather than lines 4 and 5), but this would seem to require every OP to carry
1034 (at least) line number information.
1036 What might work is to have an optional line number in memory just before the
1037 BASEOP structure, with a flag bit in the op to say whether it's present.
1038 Initially during compile every OP would carry its line number. Then add a late
1039 pass to the optimiser (potentially combined with L</repack the optree>) which
1040 looks at the two ops on every edge of the graph of the execution path. If
1041 the line number changes, flags the destination OP with this information.
1042 Once all paths are traced, replace every op with the flag with a
1043 nextstate-light op (that just updates C<PL_curcop>), which in turn then passes
1044 control on to the true op. All ops would then be replaced by variants that
1045 do not store the line number. (Which, logically, why it would work best in
1046 conjunction with L</repack the optree>, as that is already copying/reallocating
1049 (Although I should note that we're not certain that doing this for the general
1052 =head2 optimize tail-calls
1054 Tail-calls present an opportunity for broadly applicable optimization;
1055 anywhere that C<< return foo(...) >> is called, the outer return can
1056 be replaced by a goto, and foo will return directly to the outer
1057 caller, saving (conservatively) 25% of perl's call&return cost, which
1058 is relatively higher than in C. The scheme language is known to do
1059 this heavily. B::Concise provides good insight into where this
1060 optimization is possible, ie anywhere entersub,leavesub op-sequence
1063 perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'
1065 Bottom line on this is probably a new pp_tailcall function which
1066 combines the code in pp_entersub, pp_leavesub. This should probably
1067 be done 1st in XS, and using B::Generate to patch the new OP into the
1072 Tasks that will get your name mentioned in the description of the "Highlights
1075 =head2 make ithreads more robust
1077 Generally make ithreads more robust. See also L</iCOW>
1079 This task is incremental - even a little bit of work on it will help, and
1080 will be greatly appreciated.
1082 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
1084 Fix Perl_sv_dup, et al so that threads can return objects.
1088 Sarathy and Arthur have a proposal for an improved Copy On Write which
1089 specifically will be able to COW new ithreads. If this can be implemented
1090 it would be a good thing.
1092 =head2 (?{...}) closures in regexps
1094 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
1096 =head2 A re-entrant regexp engine
1098 This will allow the use of a regex from inside (?{ }), (??{ }) and
1099 (?(?{ })|) constructs.
1101 =head2 Add class set operations to regexp engine
1103 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
1105 demerphq has this on his todo list, but right at the bottom.