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 L<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
19 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/>
21 What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
22 not, but if your patch is incorporated, then we'll add your name to the
23 F<AUTHORS> file, which ships in the official distribution. How many other
24 programming languages offer you 1 line of immortality?
26 =head1 Tasks that only need Perl knowledge
28 =head2 Migrate t/ from custom TAP generation
30 Many tests below F<t/> still generate TAP by "hand", rather than using library
31 functions. As explained in L<perlhack/TESTING>, tests in F<t/> are
32 written in a particular way to test that more complex constructions actually
33 work before using them routinely. Hence they don't use C<Test::More>, but
34 instead there is an intentionally simpler library, F<t/test.pl>. However,
35 quite a few tests in F<t/> have not been refactored to use it. Refactoring
36 any of these tests, one at a time, is a useful thing TODO.
38 The subdirectories F<base>, F<cmd> and F<comp>, that contain the most
39 basic tests, should be excluded from this task.
41 =head2 Automate perldelta generation
43 The perldelta file accompanying each release summaries the major changes.
44 It's mostly manually generated currently, but some of that could be
45 automated with a bit of perl, specifically the generation of
49 =item Modules and Pragmata
51 =item New Documentation
57 See F<Porting/how_to_write_a_perldelta.pod> for details.
59 =head2 Remove duplication of test setup.
61 Schwern notes, that there's duplication of code - lots and lots of tests have
62 some variation on the big block of C<$Is_Foo> checks. We can safely put this
63 into a file, change it to build an C<%Is> hash and require it. Maybe just put
64 it into F<test.pl>. Throw in the handy tainting subroutines.
66 =head2 POD -E<gt> HTML conversion in the core still sucks
68 Which is crazy given just how simple POD purports to be, and how simple HTML
69 can be. It's not actually I<as> simple as it sounds, particularly with the
70 flexibility POD allows for C<=item>, but it would be good to improve the
71 visual appeal of the HTML generated, and to avoid it having any validation
72 errors. See also L</make HTML install work>, as the layout of installation tree
73 is needed to improve the cross-linking.
75 The addition of C<Pod::Simple> and its related modules may make this task
78 =head2 Make Schwern poorer
80 We should have tests for everything. When all the core's modules are tested,
81 Schwern has promised to donate to $500 to TPF. We may need volunteers to
82 hold him upside down and shake vigorously in order to actually extract the
85 =head2 Improve the coverage of the core tests
87 Use Devel::Cover to ascertain the core modules' test coverage, then add
88 tests that are currently missing.
92 A full test suite for the B module would be nice.
94 =head2 A decent benchmark
96 C<perlbench> seems impervious to any recent changes made to the perl core. It
97 would be useful to have a reasonable general benchmarking suite that roughly
98 represented what current perl programs do, and measurably reported whether
99 tweaks to the core improve, degrade or don't really affect performance, to
100 guide people attempting to optimise the guts of perl. Gisle would welcome
101 new tests for perlbench.
103 =head2 fix tainting bugs
105 Fix the bugs revealed by running the test suite with the C<-t> switch (via
106 C<make test.taintwarn>).
108 =head2 Dual life everything
110 As part of the "dists" plan, anything that doesn't belong in the smallest perl
111 distribution needs to be dual lifed. Anything else can be too. Figure out what
112 changes would be needed to package that module and its tests up for CPAN, and
113 do so. Test it with older perl releases, and fix the problems you find.
115 To make a minimal perl distribution, it's useful to look at
116 F<t/lib/commonsense.t>.
118 =head2 POSIX memory footprint
120 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
121 various times worked to cut it down. There is probably still fat to cut out -
122 for example POSIX passes Exporter some very memory hungry data structures.
124 =head2 embed.pl/makedef.pl
126 There is a script F<embed.pl> that generates several header files to prefix
127 all of Perl's symbols in a consistent way, to provide some semblance of
128 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
129 in F<interpvar.h>. Quite a few of the functions and variables
130 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
131 doesn't understand the C macros, so the rules about which symbols are present
132 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
133 It would be good to teach C<embed.pl> to understand the conditional
134 compilation, and hence remove the duplication, and the mistakes it has caused.
136 =head2 use strict; and AutoLoad
138 Currently if you write
141 use AutoLoader 'AUTOLOAD';
146 print join (' ', No, strict, here), "!\n";
149 then C<use strict;> isn't in force within the autoloaded subroutines. It would
150 be more consistent (and less surprising) to arrange for all lexical pragmas
151 in force at the __END__ block to be in force within each autoloaded subroutine.
153 There's a similar problem with SelfLoader.
155 =head2 profile installman
157 The F<installman> script is slow. All it is doing text processing, which we're
158 told is something Perl is good at. So it would be nice to know what it is doing
159 that is taking so much CPU, and where possible address it.
161 =head2 enable lexical enabling/disabling of individual warnings
163 Currently, warnings can only be enabled or disabled by category. There
164 are times when it would be useful to quash a single warning, not a
167 =head2 document diagnostics
169 Many diagnostic messages are not currently documented. The list is at the end
172 =head1 Tasks that need a little sysadmin-type knowledge
174 Or if you prefer, tasks that you would learn from, and broaden your skills
177 =head2 make HTML install work
179 There is an C<installhtml> target in the Makefile. It's marked as
180 "experimental". It would be good to get this tested, make it work reliably, and
181 remove the "experimental" tag. This would include
187 Checking that cross linking between various parts of the documentation works.
188 In particular that links work between the modules (files with POD in F<lib/>)
189 and the core documentation (files in F<pod/>)
193 Work out how to split C<perlfunc> into chunks, preferably one per function
194 group, preferably with general case code that could be used elsewhere.
195 Challenges here are correctly identifying the groups of functions that go
196 together, and making the right named external cross-links point to the right
197 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
198 C<endservent>, two or more C<=items> giving the different parameter lists, such
201 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
202 =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 L<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 built 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 linker specification files
295 Some platforms mandate that you provide a list of a shared library's external
296 symbols to the linker, so the core already has the infrastructure in place to
297 do this for generating shared perl libraries. My understanding is that the
298 GNU toolchain can accept an optional linker specification file, and restrict
299 visibility just to symbols declared in that file. It would be good to extend
300 F<makedef.pl> to support this format, and to provide a means within
301 C<Configure> to enable it. This would allow Unix users to test that the
302 export list is correct, and to build a perl that does not pollute the global
303 namespace with private symbols, and will fail in the same way as msvc or mingw
304 builds or when using PERL_DL_NONLAZY=1.
306 =head2 Cross-compile support
308 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
309 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
310 assumed then to be copied to TARGET machine and used as a replacement of full
313 This could be done little differently. Namely C<miniperl> should be built for
314 HOST and then full C<perl> with extensions should be compiled for TARGET.
315 This, however, might require extra trickery for %Config: we have one config
316 first for HOST and then another for TARGET. Tools like MakeMaker will be
317 mightily confused. Having around two different types of executables and
318 libraries (HOST and TARGET) makes life interesting for Makefiles and
319 shell (and Perl) scripts. There is $Config{run}, normally empty, which
320 can be used as an execution wrapper. Also note that in some
321 cross-compilation/execution environments the HOST and the TARGET do
322 not see the same filesystem(s), the $Config{run} may need to do some
323 file/directory copying back and forth.
325 =head2 Split "linker" from "compiler"
327 Right now, Configure probes for two commands, and sets two variables:
331 =item * C<cc> (in F<cc.U>)
333 This variable holds the name of a command to execute a C compiler which
334 can resolve multiple global references that happen to have the same
335 name. Usual values are F<cc> and F<gcc>.
336 Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>.
338 =item * C<ld> (in F<dlsrc.U>)
340 This variable indicates the program to be used to link
341 libraries for dynamic loading. On some systems, it is F<ld>.
342 On ELF systems, it should be C<$cc>. Mostly, we'll try to respect
343 the hint file setting.
347 There is an implicit historical assumption from around Perl5.000alpha
348 something, that C<$cc> is also the correct command for linking object files
349 together to make an executable. This may be true on Unix, but it's not true
350 on other platforms, and there are a maze of work arounds in other places (such
351 as F<Makefile.SH>) to cope with this.
353 Ideally, we should create a new variable to hold the name of the executable
354 linker program, probe for it in F<Configure>, and centralise all the special
355 case logic there or in hints files.
357 A small bikeshed issue remains - what to call it, given that C<$ld> is already
358 taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command
359 for creating dynamically-loadable modules) and C<$link> could be confused with
360 the Unix command line executable of the same name, which does something
361 completely different. Andy Dougherty makes the counter argument "In parrot, I
362 tried to call the command used to link object files and libraries into an
363 executable F<link>, since that's what my vaguely-remembered DOS and VMS
364 experience suggested. I don't think any real confusion has ensued, so it's
365 probably a reasonable name for perl5 to use."
367 "Alas, I've always worried that introducing it would make things worse,
368 since now the module building utilities would have to look for
369 C<$Config{link}> and institute a fall-back plan if it weren't found."
370 Although I can see that as confusing, given that C<$Config{d_link}> is true
371 when (hard) links are available.
373 =head2 Configure Windows using PowerShell
375 Currently, Windows uses hard-coded config files based to build the
376 config.h for compiling Perl. Makefiles are also hard-coded and need to be
377 hand edited prior to building Perl. While this makes it easy to create a perl.exe
378 that works across multiple Windows versions, being able to accurately
379 configure a perl.exe for a specific Windows versions and VS C++ would be
380 a nice enhancement. With PowerShell available on Windows XP and up, this
381 may now be possible. Step 1 might be to investigate whether this is possible
382 and use this to clean up our current makefile situation. Step 2 would be to
383 see if there would be a way to use our existing metaconfig units to configure a
384 Windows Perl or whether we go in a separate direction and make it so. Of
385 course, we all know what step 3 is.
387 =head1 Tasks that need a little C knowledge
389 These tasks would need a little C knowledge, but don't need any specific
390 background or experience with XS, or how the Perl interpreter works
392 =head2 Weed out needless PERL_UNUSED_ARG
394 The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about
395 unused arguments. Often the arguments can't be removed, as there is an
396 external constraint that determines the prototype of the function, so this
397 approach is valid. However, there are some cases where C<PERL_UNUSED_ARG>
398 could be removed. Specifically
404 The prototypes of (nearly all) static functions can be changed
408 Unused arguments generated by short cut macros are wasteful - the short cut
409 macro used can be changed.
413 =head2 Modernize the order of directories in @INC
415 The way @INC is laid out by default, one cannot upgrade core (dual-life)
416 modules without overwriting files. This causes problems for binary
417 package builders. One possible proposal is laid out in this
419 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>
423 Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
424 On these systems, it might be the default compilation mode, and there
425 is currently no guarantee that passing no use64bitall option to the
426 Configure process will build a 32bit perl. Implementing -Duse32bit*
427 options would be nice for perl 5.14.
429 =head2 Profile Perl - am I hot or not?
431 The Perl source code is stable enough that it makes sense to profile it,
432 identify and optimise the hotspots. It would be good to measure the
433 performance of the Perl interpreter using free tools such as cachegrind,
434 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
436 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
437 the ops that are most commonly used. The idea is that by grouping them, their
438 object code will be adjacent in the executable, so they have a greater chance
439 of already being in the CPU cache (or swapped in) due to being near another op
442 Except that it's not clear if these really are the most commonly used ops. So
443 as part of exercising your skills with coverage and profiling tools you might
444 want to determine what ops I<really> are the most commonly used. And in turn
445 suggest evictions and promotions to achieve a better F<pp_hot.c>.
447 One piece of Perl code that might make a good testbed is F<installman>.
449 =head2 Allocate OPs from arenas
451 Currently all new OP structures are individually malloc()ed and free()d.
452 All C<malloc> implementations have space overheads, and are now as fast as
453 custom allocates so it would both use less memory and less CPU to allocate
454 the various OP structures from arenas. The SV arena code can probably be
457 Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use
458 Perl_Slab_alloc() to pack optrees into a contiguous block, which is
459 probably superior to the use of OP arenas, esp. from a cache locality
460 standpoint. See L<Profile Perl - am I hot or not?>.
462 =head2 Improve win32/wince.c
464 Currently, numerous functions look virtually, if not completely,
465 identical in both F<win32/wince.c> and F<win32/win32.c> files, which can't
468 =head2 Use secure CRT functions when building with VC8 on Win32
470 Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
471 that they were "unsafe" and introduced differently named secure versions of
472 them as replacements, e.g. instead of writing
474 FILE* f = fopen(__FILE__, "r");
479 errno_t err = fopen_s(&f, __FILE__, "r");
481 Currently, the warnings about these deprecations have been disabled by adding
482 -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
483 warning suppressant and actually make use of the new secure CRT functions.
485 There is also a similar issue with POSIX CRT function names like fileno having
486 been deprecated in favour of ISO C++ conformant names like _fileno. These
487 warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It
488 might be nice to do as Microsoft suggest here too, although, unlike the secure
489 functions issue, there is presumably little or no benefit in this case.
491 =head2 Fix POSIX::access() and chdir() on Win32
493 These functions currently take no account of DACLs and therefore do not behave
494 correctly in situations where access is restricted by DACLs (as opposed to the
495 read-only attribute).
497 Furthermore, POSIX::access() behaves differently for directories having the
498 read-only attribute set depending on what CRT library is being used. For
499 example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that
500 such directories are not writable, whereas in fact all directories are writable
501 unless access is denied by DACLs. (In the case of directories, the read-only
502 attribute actually only means that the directory cannot be deleted.) This CRT
503 bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still
504 not actually be writable if access is indeed denied by DACLs).
506 For the chdir() issue, see ActiveState bug #74552:
507 L<http://bugs.activestate.com/show_bug.cgi?id=74552>
509 Therefore, DACLs should be checked both for consistency across CRTs and for
512 (Note that perl's -w operator should not be modified to check DACLs. It has
513 been written so that it reflects the state of the read-only attribute, even
514 for directories (whatever CRT is being used), for symmetry with chmod().)
516 =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
518 Maybe create a utility that checks after each libperl.a creation that
519 none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
520 ever creep back to libperl.a.
522 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
524 Note, of course, that this will only tell whether B<your> platform
525 is using those naughty interfaces.
527 =head2 -D_FORTIFY_SOURCE=2, -fstack-protector
529 Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc
530 (4.1 onwards?) supports C<-fstack-protector>, both of which give
531 protection against various kinds of buffer overflow problems.
532 These should probably be used for compiling Perl whenever available,
533 Configure and/or hints files should be adjusted to probe for the
534 availability of these features and enable them as appropriate.
536 =head2 Arenas for GPs? For MAGIC?
538 C<struct gp> and C<struct magic> are both currently allocated by C<malloc>.
539 It might be a speed or memory saving to change to using arenas. Or it might
540 not. It would need some suitable benchmarking first. In particular, C<GP>s
541 can probably be changed with minimal compatibility impact (probably nothing
542 outside of the core, or even outside of F<gv.c> allocates them), but they
543 probably aren't allocated/deallocated often enough for a speed saving. Whereas
544 C<MAGIC> is allocated/deallocated more often, but in turn, is also something
545 more externally visible, so changing the rules here may bite external code.
549 Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and
550 PVHV, and PVCV and PVFM. It should be possible to allocate and return same
551 sized bodies from the same actual arena, rather than maintaining one arena for
552 each. This could save 4-6K per thread, of memory no longer tied up in the
553 not-yet-allocated part of an arena.
556 =head1 Tasks that need a knowledge of XS
558 These tasks would need C knowledge, and roughly the level of knowledge of
559 the perl API that comes from writing modules that use XS to interface to
562 =head2 Write an XS cookbook
564 Create pod/perlxscookbook.pod with short, task-focused 'recipes' in XS that
565 demonstrate common tasks and good practices. (Some of these might be
566 extracted from perlguts.) The target audience should be XS novices, who need
567 more examples than perlguts but something less overwhelming than perlapi.
568 Recipes should provide "one pretty good way to do it" instead of TIMTOWTDI.
570 Rather than focusing on interfacing Perl to C libraries, such a cookbook
571 should probably focus on how to optimize Perl routines by re-writing them
572 in XS. This will likely be more motivating to those who mostly work in
573 Perl but are looking to take the next step into XS.
575 Deconstructing and explaining some simpler XS modules could be one way to
576 bootstrap a cookbook. (List::Util? Class::XSAccessor? Tree::Ternary_XS?)
577 Another option could be deconstructing the implementation of some simpler
580 =head2 Allow XSUBs to inline themselves as OPs
582 For a simple XSUB, often the subroutine dispatch takes more time than the
583 XSUB itself. The tokeniser already has the ability to inline constant
584 subroutines - it would be good to provide a way to inline other subroutines.
586 Specifically, simplest approach looks to be to allow an XSUB to provide an
587 alternative implementation of itself as a custom OP. A new flag bit in
588 C<CvFLAGS()> would signal to the peephole optimiser to take an optree
591 b <@> leave[1 ref] vKP/REFC ->(end)
593 2 <;> nextstate(main 1 -e:1) v:{ ->3
594 a <2> sassign vKS/2 ->b
595 8 <1> entersub[t2] sKS/TARG,1 ->9
598 4 <$> const(IV 1) sM ->5
599 6 <1> rv2av[t1] lKM/1 ->7
601 - <1> ex-rv2cv sK ->-
602 7 <$> gv(*x) s/EARLYCV ->8
603 - <1> ex-rv2sv sKRM*/1 ->a
606 perform the symbol table lookup of C<rv2cv> and C<gv(*x)>, locate the
607 pointer to the custom OP that provides the direct implementation, and re-
608 write the optree something like:
610 b <@> leave[1 ref] vKP/REFC ->(end)
612 2 <;> nextstate(main 1 -e:1) v:{ ->3
613 a <2> sassign vKS/2 ->b
617 4 <$> const(IV 1) sM ->5
618 6 <1> rv2av[t1] lKM/1 ->7
620 - <1> ex-rv2cv sK ->-
621 - <$> ex-gv(*x) s/EARLYCV ->7
622 - <1> ex-rv2sv sKRM*/1 ->a
625 I<i.e.> the C<gv(*)> OP has been nulled and spliced out of the execution
626 path, and the C<entersub> OP has been replaced by the custom op.
628 This approach should provide a measurable speed up to simple XSUBs inside
629 tight loops. Initially one would have to write the OP alternative
630 implementation by hand, but it's likely that this should be reasonably
631 straightforward for the type of XSUB that would benefit the most. Longer
632 term, once the run-time implementation is proven, it should be possible to
633 progressively update ExtUtils::ParseXS to generate OP implementations for
636 =head2 Remove the use of SVs as temporaries in dump.c
638 F<dump.c> contains debugging routines to dump out the contains of perl data
639 structures, such as C<SV>s, C<AV>s and C<HV>s. Currently, the dumping code
640 B<uses> C<SV>s for its temporary buffers, which was a logical initial
641 implementation choice, as they provide ready made memory handling.
643 However, they also lead to a lot of confusion when it happens that what you're
644 trying to debug is seen by the code in F<dump.c>, correctly or incorrectly, as
645 a temporary scalar it can use for a temporary buffer. It's also not possible
646 to dump scalars before the interpreter is properly set up, such as during
647 ithreads cloning. It would be good to progressively replace the use of scalars
648 as string accumulation buffers with something much simpler, directly allocated
649 by C<malloc>. The F<dump.c> code is (or should be) only producing 7 bit
650 US-ASCII, so output character sets are not an issue.
652 Producing and proving an internal simple buffer allocation would make it easier
653 to re-write the internals of the PerlIO subsystem to avoid using C<SV>s for
654 B<its> buffers, use of which can cause problems similar to those of F<dump.c>,
657 =head2 safely supporting POSIX SA_SIGINFO
659 Some years ago Jarkko supplied patches to provide support for the POSIX
660 SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler.
662 Unfortunately, it only works with "unsafe" signals, because under safe
663 signals, by the time Perl gets to run the signal handler, the extra
664 information has been lost. Moreover, it's not easy to store it somewhere,
665 as you can't call mutexs, or do anything else fancy, from inside a signal
668 So it strikes me that we could provide safe SA_SIGINFO support
674 Provide global variables for two file descriptors
678 When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a
679 pipe, store the reader in one, the writer in the other
683 In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if
684 the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open,
690 serialise signal number, C<struct siginfo_t> (or at least the parts we care
691 about) into a small auto char buff
695 C<write()> that (non-blocking) to the writer fd
701 if it writes 100%, flag the signal in a counter of "signals on the pipe" akin
702 to the current per-signal-number counts
706 if it writes 0%, assume the pipe is full. Flag the data as lost?
710 if it writes partially, croak a panic, as your OS is broken.
718 in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on
719 the pipe", read the data out, deserialise, build the Perl structures on
720 the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as
725 I think that this gets us decent C<SA_SIGINFO> support, without the current risk
726 of running Perl code inside the signal handler context. (With all the dangers
727 of things like C<malloc> corruption that that currently offers us)
729 For more information see the thread starting with this message:
730 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html>
732 =head2 autovivification
734 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
736 This task is incremental - even a little bit of work on it will help.
738 =head2 Unicode in Filenames
740 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
741 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
742 system, truncate, unlink, utime, -X. All these could potentially accept
743 Unicode filenames either as input or output (and in the case of system
744 and qx Unicode in general, as input or output to/from the shell).
745 Whether a filesystem - an operating system pair understands Unicode in
748 Known combinations that have some level of understanding include
749 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
750 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
751 create Unicode filenames, what forms of Unicode are accepted and used
752 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
753 and so on, varies. Finding the right level of interfacing to Perl
754 requires some thought. Remember that an OS does not implicate a
757 (The Windows -C command flag "wide API support" has been at least
758 temporarily retired in 5.8.1, and the -C has been repurposed, see
761 Most probably the right way to do this would be this:
762 L</"Virtualize operating system access">.
764 =head2 Unicode in %ENV
766 Currently the %ENV entries are always byte strings.
767 See L</"Virtualize operating system access">.
769 =head2 Unicode and glob()
771 Currently glob patterns and filenames returned from File::Glob::glob()
772 are always byte strings. See L</"Virtualize operating system access">.
774 =head2 use less 'memory'
776 Investigate trade offs to switch out perl's choices on memory usage.
777 Particularly perl should be able to give memory back.
779 This task is incremental - even a little bit of work on it will help.
781 =head2 Re-implement C<:unique> in a way that is actually thread-safe
783 The old implementation made bad assumptions on several levels. A good 90%
784 solution might be just to make C<:unique> work to share the string buffer
785 of SvPVs. That way large constant strings can be shared between ithreads,
786 such as the configuration information in F<Config>.
788 =head2 Make tainting consistent
790 Tainting would be easier to use if it didn't take documented shortcuts and
791 allow taint to "leak" everywhere within an expression.
793 =head2 readpipe(LIST)
795 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
796 running a shell. readpipe() (the function behind qx//) could be similarly
799 =head2 Audit the code for destruction ordering assumptions
803 /* Need to check SvMAGICAL, as during global destruction it may be that
804 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
805 is now part of the linked list of SV heads, rather than pointing to
806 the original body. */
807 /* FIXME - audit the code for other bugs like this one. */
809 adding the C<SvMAGICAL> check to
811 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
812 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
814 Go through the core and look for similar assumptions that SVs have particular
815 types, as all bets are off during global destruction.
817 =head2 Extend PerlIO and PerlIO::Scalar
819 PerlIO::Scalar doesn't know how to truncate(). Implementing this
820 would require extending the PerlIO vtable.
822 Similarly the PerlIO vtable doesn't know about formats (write()), or
823 about stat(), or chmod()/chown(), utime(), or flock().
825 (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
828 PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
829 opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
832 See also L</"Virtualize operating system access">.
834 =head2 -C on the #! line
836 It should be possible to make -C work correctly if found on the #! line,
837 given that all perl command line options are strict ASCII, and -C changes
838 only the interpretation of non-ASCII characters, and not for the script file
839 handle. To make it work needs some investigation of the ordering of function
840 calls during startup, and (by implication) a bit of tweaking of that order.
842 =head2 Organize error messages
844 Perl's diagnostics (error messages, see L<perldiag>) could use
845 reorganizing and formalizing so that each error message has its
846 stable-for-all-eternity unique id, categorized by severity, type, and
847 subsystem. (The error messages would be listed in a datafile outside
848 of the Perl source code, and the source code would only refer to the
849 messages by the id.) This clean-up and regularizing should apply
850 for all croak() messages.
852 This would enable all sorts of things: easier translation/localization
853 of the messages (though please do keep in mind the caveats of
854 L<Locale::Maketext> about too straightforward approaches to
855 translation), filtering by severity, and instead of grepping for a
856 particular error message one could look for a stable error id. (Of
857 course, changing the error messages by default would break all the
858 existing software depending on some particular error message...)
860 This kind of functionality is known as I<message catalogs>. Look for
861 inspiration for example in the catgets() system, possibly even use it
862 if available-- but B<only> if available, all platforms will B<not>
865 For the really pure at heart, consider extending this item to cover
866 also the warning messages (see L<perllexwarn>, C<warnings.pl>).
868 =head1 Tasks that need a knowledge of the interpreter
870 These tasks would need C knowledge, and knowledge of how the interpreter works,
871 or a willingness to learn.
873 =head2 forbid labels with keyword names
875 Currently C<goto keyword> "computes" the label value:
877 $ perl -e 'goto print'
878 Can't find label 1 at -e line 1.
880 It is controversial if the right way to avoid the confusion is to forbid
881 labels with keyword names, or if it would be better to always treat
882 bareword expressions after a "goto" as a label and never as a keyword.
884 =head2 truncate() prototype
886 The prototype of truncate() is currently C<$$>. It should probably
887 be C<*$> instead. (This is changed in F<opcode.pl>)
889 =head2 decapsulation of smart match argument
891 Currently C<$foo ~~ $object> will die with the message "Smart matching a
892 non-overloaded object breaks encapsulation". It would be nice to allow
893 to bypass this by using explicitly the syntax C<$foo ~~ %$object> or
896 =head2 error reporting of [$a ; $b]
898 Using C<;> inside brackets is a syntax error, and we don't propose to change
899 that by giving it any meaning. However, it's not reported very helpfully:
901 $ perl -e '$a = [$b; $c];'
902 syntax error at -e line 1, near "$b;"
903 syntax error at -e line 1, near "$c]"
904 Execution of -e aborted due to compilation errors.
906 It should be possible to hook into the tokeniser or the lexer, so that when a
907 C<;> is parsed where it is not legal as a statement terminator (ie inside
908 C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like
909 I<';' isn't legal inside an expression - if you need multiple statements use a
910 do {...} block>. See the thread starting at
911 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html>
913 =head2 lexicals used only once
917 $ perl -we '$pie = 42'
918 Name "main::pie" used only once: possible typo at -e line 1.
922 $ perl -we 'my $pie = 42'
924 Logically all lexicals used only once should warn, if the user asks for
925 warnings. An unworked RT ticket (#5087) has been open for almost seven
926 years for this discrepancy.
930 The handling of Unicode is unclean in many places. In the regex engine
931 there are especially many problems. The swash data structure could be
932 replaced my something better. Inversion lists and maps are likely
933 candidates. The whole Unicode database could be placed in-core for a
934 huge speed-up. Only minimal work was done on the optimizer when utf8
935 was added, with the result that the synthetic start class often will
936 fail to narrow down the possible choices when given non-Latin1 input.
938 =head2 Properly Unicode safe tokeniser and pads.
940 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
941 variable names are stored in stashes as raw bytes, without the utf-8 flag
942 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
943 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
944 source filters. All this could be fixed.
946 =head2 state variable initialization in list context
948 Currently this is illegal:
950 state ($a, $b) = foo();
952 In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different
953 semantics, which is tricky to implement in Perl 5 as currently they produce
954 the same opcode trees. The Perl 6 design is firm, so it would be good to
955 implement the necessary code in Perl 5. There are comments in
956 C<Perl_newASSIGNOP()> that show the code paths taken by various assignment
957 constructions involving state variables.
959 =head2 Implement $value ~~ 0 .. $range
961 It would be nice to extend the syntax of the C<~~> operator to also
962 understand numeric (and maybe alphanumeric) ranges.
964 =head2 A does() built-in
966 Like ref(), only useful. It would call the C<DOES> method on objects; it
967 would also tell whether something can be dereferenced as an
968 array/hash/etc., or used as a regexp, etc.
969 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
971 =head2 Tied filehandles and write() don't mix
973 There is no method on tied filehandles to allow them to be called back by
976 =head2 Propagate compilation hints to the debugger
978 Currently a debugger started with -dE on the command-line doesn't see the
979 features enabled by -E. More generally hints (C<$^H> and C<%^H>) aren't
980 propagated to the debugger. Probably it would be a good thing to propagate
981 hints from the innermost non-C<DB::> scope: this would make code eval'ed
982 in the debugger see the features (and strictures, etc.) currently in
985 =head2 Attach/detach debugger from running program
987 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
988 program if you pass the process ID. It would be good to do this with the Perl
989 debugger on a running Perl program, although I'm not sure how it would be
990 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
992 =head2 LVALUE functions for lists
994 The old perltodo notes that lvalue functions don't work for list or hash
995 slices. This would be good to fix.
997 =head2 regexp optimiser optional
999 The regexp optimiser is not optional. It should configurable to be, to allow
1000 its performance to be measured, and its bugs to be easily demonstrated.
1002 =head2 C</w> regex modifier
1004 That flag would enable to match whole words, and also to interpolate
1005 arrays as alternations. With it, C</P/w> would be roughly equivalent to:
1007 do { local $"='|'; /\b(?:P)\b/ }
1010 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
1013 =head2 optional optimizer
1015 Make the peephole optimizer optional. Currently it performs two tasks as
1016 it walks the optree - genuine peephole optimisations, and necessary fixups of
1017 ops. It would be good to find an efficient way to switch out the
1018 optimisations whilst keeping the fixups.
1020 =head2 You WANT *how* many
1022 Currently contexts are void, scalar and list. split has a special mechanism in
1023 place to pass in the number of return values wanted. It would be useful to
1024 have a general mechanism for this, backwards compatible and little speed hit.
1025 This would allow proposals such as short circuiting sort to be implemented
1026 as a module on CPAN.
1028 =head2 lexical aliases
1030 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
1032 =head2 entersub XS vs Perl
1034 At the moment pp_entersub is huge, and has code to deal with entering both
1035 perl and XS subroutines. Subroutine implementations rarely change between
1036 perl and XS at run time, so investigate using 2 ops to enter subs (one for
1037 XS, one for perl) and swap between if a sub is redefined.
1041 Self-ties are currently illegal because they caused too many segfaults. Maybe
1042 the causes of these could be tracked down and self-ties on all types
1045 =head2 Optimize away @_
1047 The old perltodo notes "Look at the "reification" code in C<av.c>".
1049 =head2 Virtualize operating system access
1051 Implement a set of "vtables" that virtualizes operating system access
1052 (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very
1053 least these interfaces should take SVs as "name" arguments instead of
1054 bare char pointers; probably the most flexible and extensible way
1055 would be for the Perl-facing interfaces to accept HVs. The system
1056 needs to be per-operating-system and per-file-system
1057 hookable/filterable, preferably both from XS and Perl level
1058 (L<perlport/"Files and Filesystems"> is good reading at this point,
1059 in fact, all of L<perlport> is.)
1061 This has actually already been implemented (but only for Win32),
1062 take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32
1063 variants go through a set of "vtables" for operating system access,
1064 non-Win32 systems currently go straight for the POSIX/Unix-style
1065 system/library call. Similar system as for Win32 should be
1066 implemented for all platforms. The existing Win32 implementation
1067 probably does not need to survive alongside this proposed new
1068 implementation, the approaches could be merged.
1070 What would this give us? One often-asked-for feature this would
1071 enable is using Unicode for filenames, and other "names" like %ENV,
1072 usernames, hostnames, and so forth.
1073 (See L<perlunicode/"When Unicode Does Not Happen">.)
1075 But this kind of virtualization would also allow for things like
1076 virtual filesystems, virtual networks, and "sandboxes" (though as long
1077 as dynamic loading of random object code is allowed, not very safe
1078 sandboxes since external code of course know not of Perl's vtables).
1079 An example of a smaller "sandbox" is that this feature can be used to
1080 implement per-thread working directories: Win32 already does this.
1082 See also L</"Extend PerlIO and PerlIO::Scalar">.
1084 =head2 Investigate PADTMP hash pessimisation
1086 The peephole optimiser converts constants used for hash key lookups to shared
1087 hash key scalars. Under ithreads, something is undoing this work.
1089 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html>
1091 =head2 Store the current pad in the OP slab allocator
1094 I hope that I got that "current pad" part correct
1096 Currently we leak ops in various cases of parse failure. I suggested that we
1097 could solve this by always using the op slab allocator, and walking it to
1098 free ops. Dave comments that as some ops are already freed during optree
1099 creation one would have to mark which ops are freed, and not double free them
1100 when walking the slab. He notes that one problem with this is that for some ops
1101 you have to know which pad was current at the time of allocation, which does
1102 change. I suggested storing a pointer to the current pad in the memory allocated
1103 for the slab, and swapping to a new slab each time the pad changes. Dave thinks
1104 that this would work.
1106 =head2 repack the optree
1108 Repacking the optree after execution order is determined could allow
1109 removal of NULL ops, and optimal ordering of OPs with respect to cache-line
1110 filling. The slab allocator could be reused for this purpose. I think that
1111 the best way to do this is to make it an optional step just before the
1112 completed optree is attached to anything else, and to use the slab allocator
1113 unchanged, so that freeing ops is identical whether or not this step runs.
1114 Note that the slab allocator allocates ops downwards in memory, so one would
1115 have to actually "allocate" the ops in reverse-execution order to get them
1116 contiguous in memory in execution order.
1119 L<http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html>
1121 Note that running this copy, and then freeing all the old location ops would
1122 cause their slabs to be freed, which would eliminate possible memory wastage if
1123 the previous suggestion is implemented, and we swap slabs more frequently.
1125 =head2 eliminate incorrect line numbers in warnings
1133 } elsif ($undef == 0) {
1136 used to produce this output:
1138 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1139 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1141 where the line of the second warning was misreported - it should be line 5.
1142 Rafael fixed this - the problem arose because there was no nextstate OP
1143 between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still
1144 reports that the currently executing line is line 4. The solution was to inject
1145 a nextstate OPs for each C<elsif>, although it turned out that the nextstate
1146 OP needed to be a nulled OP, rather than a live nextstate OP, else other line
1147 numbers became misreported. (Jenga!)
1149 The problem is more general than C<elsif> (although the C<elsif> case is the
1150 most common and the most confusing). Ideally this code
1160 would produce this output
1162 Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
1163 Use of uninitialized value $undef in addition (+) at wrong.pl line 7.
1165 (rather than lines 4 and 5), but this would seem to require every OP to carry
1166 (at least) line number information.
1168 What might work is to have an optional line number in memory just before the
1169 BASEOP structure, with a flag bit in the op to say whether it's present.
1170 Initially during compile every OP would carry its line number. Then add a late
1171 pass to the optimiser (potentially combined with L</repack the optree>) which
1172 looks at the two ops on every edge of the graph of the execution path. If
1173 the line number changes, flags the destination OP with this information.
1174 Once all paths are traced, replace every op with the flag with a
1175 nextstate-light op (that just updates C<PL_curcop>), which in turn then passes
1176 control on to the true op. All ops would then be replaced by variants that
1177 do not store the line number. (Which, logically, why it would work best in
1178 conjunction with L</repack the optree>, as that is already copying/reallocating
1181 (Although I should note that we're not certain that doing this for the general
1184 =head2 optimize tail-calls
1186 Tail-calls present an opportunity for broadly applicable optimization;
1187 anywhere that C<< return foo(...) >> is called, the outer return can
1188 be replaced by a goto, and foo will return directly to the outer
1189 caller, saving (conservatively) 25% of perl's call&return cost, which
1190 is relatively higher than in C. The scheme language is known to do
1191 this heavily. B::Concise provides good insight into where this
1192 optimization is possible, ie anywhere entersub,leavesub op-sequence
1195 perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'
1197 Bottom line on this is probably a new pp_tailcall function which
1198 combines the code in pp_entersub, pp_leavesub. This should probably
1199 be done 1st in XS, and using B::Generate to patch the new OP into the
1202 =head2 Add C<00dddd>
1204 It has been proposed that octal constants be specifiable through the syntax
1205 C<0oddddd>, parallel to the existing construct to specify hex constants
1210 Tasks that will get your name mentioned in the description of the "Highlights
1213 =head2 make ithreads more robust
1215 Generally make ithreads more robust. See also L</iCOW>
1217 This task is incremental - even a little bit of work on it will help, and
1218 will be greatly appreciated.
1220 One bit would be to determine how to clone directory handles on systems
1221 without a C<fchdir> function (in sv.c:Perl_dirp_dup).
1223 Fix Perl_sv_dup, et al so that threads can return objects.
1227 Sarathy and Arthur have a proposal for an improved Copy On Write which
1228 specifically will be able to COW new ithreads. If this can be implemented
1229 it would be a good thing.
1231 =head2 (?{...}) closures in regexps
1233 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
1235 =head2 Add class set operations to regexp engine
1237 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
1239 demerphq has this on his todo list, but right at the bottom.
1242 =head1 Tasks for microperl
1245 [ Each and every one of these may be obsolete, but they were listed
1246 in the old Todo.micro file]
1249 =head2 make creating uconfig.sh automatic
1251 =head2 make creating Makefile.micro automatic
1253 =head2 do away with fork/exec/wait?
1255 (system, popen should be enough?)
1257 =head2 some of the uconfig.sh really needs to be probed (using cc) in buildtime:
1259 (uConfigure? :-) native datatype widths and endianness come to mind