3 perltodo - Perl TO-DO List
7 This is a list of wishes for Perl. The most up to date version of this file
8 is at http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod
10 The tasks we think are smaller or easier are listed first. Anyone is welcome
11 to work on any of these, but it's a good idea to first contact
12 I<perl5-porters@perl.org> to avoid duplication of effort, and to learn from
13 any previous attempts. By all means contact a pumpking privately first if you
16 Whilst patches to make the list shorter are most welcome, ideas to add to
17 the list are also encouraged. Check the perl5-porters archives for past
18 ideas, and any discussion about them. One set of archives may be found at:
20 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
22 What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
23 not, but if your patch is incorporated, then we'll add your name to the
24 F<AUTHORS> file, which ships in the official distribution. How many other
25 programming languages offer you 1 line of immortality?
27 =head1 Tasks that only need Perl knowledge
29 =head2 Migrate t/ from custom TAP generation
31 Many tests below F<t/> still generate TAP by "hand", rather than using library
32 functions. As explained in L<perlhack/Writing a test>, tests in F<t/> are
33 written in a particular way to test that more complex constructions actually
34 work before using them routinely. Hence they don't use C<Test::More>, but
35 instead there is an intentionally simpler library, F<t/test.pl>. However,
36 quite a few tests in F<t/> have not been refactored to use it. Refactoring
37 any of these tests, one at a time, is a useful thing TODO.
39 =head2 Test that regen.pl was run
41 There are various generated files shipped with the perl distribution, for
42 things like header files generate from data. The generation scripts are
43 written in perl, and all can be run by F<regen.pl>. However, because they're
44 written in perl, we can't run them before we've built perl. We can't run them
45 as part of the F<Makefile>, because changing files underneath F<make> confuses
46 it completely, and we don't want to run them automatically anyway, as they
47 change files shipped by the distribution, something we seek not do to.
49 If someone changes the data, but forgets to re-run F<regen.pl> then the
50 generated files are out of sync. It would be good to have a test in
51 F<t/porting> that checks that the generated files are in sync, and fails
52 otherwise, to alert someone before they make a poor commit. I suspect that this
53 would require adapting the scripts run from F<regen.pl> to have dry-run
54 options, and invoking them with these, or by refactoring them into a library
55 that does the generation, which can be called by the scripts, and by the test.
57 =head2 Automate perldelta generation
59 The perldelta file accompanying each release summaries the major changes.
60 It's mostly manually generated currently, but some of that could be
61 automated with a bit of perl, specifically the generation of
65 =item Modules and Pragmata
67 =item New Documentation
73 See F<Porting/how_to_write_a_perldelta.pod> for details.
75 =head2 Remove duplication of test setup.
77 Schwern notes, that there's duplication of code - lots and lots of tests have
78 some variation on the big block of C<$Is_Foo> checks. We can safely put this
79 into a file, change it to build an C<%Is> hash and require it. Maybe just put
80 it into F<test.pl>. Throw in the handy tainting subroutines.
82 =head2 POD -E<gt> HTML conversion in the core still sucks
84 Which is crazy given just how simple POD purports to be, and how simple HTML
85 can be. It's not actually I<as> simple as it sounds, particularly with the
86 flexibility POD allows for C<=item>, but it would be good to improve the
87 visual appeal of the HTML generated, and to avoid it having any validation
88 errors. See also L</make HTML install work>, as the layout of installation tree
89 is needed to improve the cross-linking.
91 The addition of C<Pod::Simple> and its related modules may make this task
94 =head2 Make ExtUtils::ParseXS use strict;
96 F<lib/ExtUtils/ParseXS.pm> contains this line
98 # use strict; # One of these days...
100 Simply uncomment it, and fix all the resulting issues :-)
102 The more practical approach, to break the task down into manageable chunks, is
103 to work your way though the code from bottom to top, or if necessary adding
104 extra C<{ ... }> blocks, and turning on strict within them.
106 =head2 Make Schwern poorer
108 We should have tests for everything. When all the core's modules are tested,
109 Schwern has promised to donate to $500 to TPF. We may need volunteers to
110 hold him upside down and shake vigorously in order to actually extract the
113 =head2 Improve the coverage of the core tests
115 Use Devel::Cover to ascertain the core modules's test coverage, then add
116 tests that are currently missing.
120 A full test suite for the B module would be nice.
122 =head2 A decent benchmark
124 C<perlbench> seems impervious to any recent changes made to the perl core. It
125 would be useful to have a reasonable general benchmarking suite that roughly
126 represented what current perl programs do, and measurably reported whether
127 tweaks to the core improve, degrade or don't really affect performance, to
128 guide people attempting to optimise the guts of perl. Gisle would welcome
129 new tests for perlbench.
131 =head2 fix tainting bugs
133 Fix the bugs revealed by running the test suite with the C<-t> switch (via
134 C<make test.taintwarn>).
136 =head2 Dual life everything
138 As part of the "dists" plan, anything that doesn't belong in the smallest perl
139 distribution needs to be dual lifed. Anything else can be too. Figure out what
140 changes would be needed to package that module and its tests up for CPAN, and
141 do so. Test it with older perl releases, and fix the problems you find.
143 To make a minimal perl distribution, it's useful to look at
144 F<t/lib/commonsense.t>.
146 =head2 Move dual-life pod/*.PL into ext
148 Nearly all the dual-life modules have been moved to F<ext>. However, we
149 still need to move F<pod/*.PL> into their respective directories
150 in F<ext/>. They're referenced by (at least) C<plextract> in F<Makefile.SH>
151 and C<utils> in F<win32/Makefile> and F<win32/makefile.ml>, and listed
152 explicitly in F<win32/pod.mak>, F<vms/descrip_mms.template> and F<utils.lst>
154 =head2 POSIX memory footprint
156 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
157 various times worked to cut it down. There is probably still fat to cut out -
158 for example POSIX passes Exporter some very memory hungry data structures.
160 =head2 embed.pl/makedef.pl
162 There is a script F<embed.pl> that generates several header files to prefix
163 all of Perl's symbols in a consistent way, to provide some semblance of
164 namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
165 in F<interpvar.h>. Quite a few of the functions and variables
166 are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
167 doesn't understand the C macros, so the rules about which symbols are present
168 when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
169 It would be good to teach C<embed.pl> to understand the conditional
170 compilation, and hence remove the duplication, and the mistakes it has caused.
172 =head2 use strict; and AutoLoad
174 Currently if you write
177 use AutoLoader 'AUTOLOAD';
182 print join (' ', No, strict, here), "!\n";
185 then C<use strict;> isn't in force within the autoloaded subroutines. It would
186 be more consistent (and less surprising) to arrange for all lexical pragmas
187 in force at the __END__ block to be in force within each autoloaded subroutine.
189 There's a similar problem with SelfLoader.
191 =head2 profile installman
193 The F<installman> script is slow. All it is doing text processing, which we're
194 told is something Perl is good at. So it would be nice to know what it is doing
195 that is taking so much CPU, and where possible address it.
198 =head1 Tasks that need a little sysadmin-type knowledge
200 Or if you prefer, tasks that you would learn from, and broaden your skills
203 =head2 make HTML install work
205 There is an C<installhtml> target in the Makefile. It's marked as
206 "experimental". It would be good to get this tested, make it work reliably, and
207 remove the "experimental" tag. This would include
213 Checking that cross linking between various parts of the documentation works.
214 In particular that links work between the modules (files with POD in F<lib/>)
215 and the core documentation (files in F<pod/>)
219 Work out how to split C<perlfunc> into chunks, preferably one per function
220 group, preferably with general case code that could be used elsewhere.
221 Challenges here are correctly identifying the groups of functions that go
222 together, and making the right named external cross-links point to the right
223 page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
224 C<endservent>, two or more C<=items> giving the different parameter lists, such
227 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
228 =item substr EXPR,OFFSET,LENGTH
229 =item substr EXPR,OFFSET
231 and different parameter lists having different meanings. (eg C<select>)
235 =head2 compressed man pages
237 Be able to install them. This would probably need a configure test to see how
238 the system does compressed man pages (same directory/different directory?
239 same filename/different filename), as well as tweaking the F<installman> script
240 to compress as necessary.
242 =head2 Add a code coverage target to the Makefile
244 Make it easy for anyone to run Devel::Cover on the core's tests. The steps
245 to do this manually are roughly
251 do a normal C<Configure>, but include Devel::Cover as a module to install
252 (see F<INSTALL> for how to do this)
260 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
264 Process the resulting Devel::Cover database
268 This just give you the coverage of the F<.pm>s. To also get the C level
275 Additionally tell C<Configure> to use the appropriate C compiler flags for
282 (instead of C<make perl>)
286 After running the tests run C<gcov> to generate all the F<.gcov> files.
287 (Including down in the subdirectories of F<ext/>
291 (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
292 to get their stats into the cover_db directory.
296 Then process the Devel::Cover database
300 It would be good to add a single switch to C<Configure> to specify that you
301 wanted to perform perl level coverage, and another to specify C level
302 coverage, and have C<Configure> and the F<Makefile> do all the right things
305 =head2 Make Config.pm cope with differences between built and installed perl
307 Quite often vendors ship a perl binary compiled with their (pay-for)
308 compilers. People install a free compiler, such as gcc. To work out how to
309 build extensions, Perl interrogates C<%Config>, so in this situation
310 C<%Config> describes compilers that aren't there, and extension building
311 fails. This forces people into choosing between re-compiling perl themselves
312 using the compiler they have, or only using modules that the vendor ships.
314 It would be good to find a way teach C<Config.pm> about the installation setup,
315 possibly involving probing at install time or later, so that the C<%Config> in
316 a binary distribution better describes the installed machine, when the
317 installed machine differs from the build machine in some significant way.
319 =head2 linker specification files
321 Some platforms mandate that you provide a list of a shared library's external
322 symbols to the linker, so the core already has the infrastructure in place to
323 do this for generating shared perl libraries. My understanding is that the
324 GNU toolchain can accept an optional linker specification file, and restrict
325 visibility just to symbols declared in that file. It would be good to extend
326 F<makedef.pl> to support this format, and to provide a means within
327 C<Configure> to enable it. This would allow Unix users to test that the
328 export list is correct, and to build a perl that does not pollute the global
329 namespace with private symbols.
331 =head2 Cross-compile support
333 Currently C<Configure> understands C<-Dusecrosscompile> option. This option
334 arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
335 assumed then to be copied to TARGET machine and used as a replacement of full
338 This could be done little differently. Namely C<miniperl> should be built for
339 HOST and then full C<perl> with extensions should be compiled for TARGET.
340 This, however, might require extra trickery for %Config: we have one config
341 first for HOST and then another for TARGET. Tools like MakeMaker will be
342 mightily confused. Having around two different types of executables and
343 libraries (HOST and TARGET) makes life interesting for Makefiles and
344 shell (and Perl) scripts. There is $Config{run}, normally empty, which
345 can be used as an execution wrapper. Also note that in some
346 cross-compilation/execution environments the HOST and the TARGET do
347 not see the same filesystem(s), the $Config{run} may need to do some
348 file/directory copying back and forth.
352 Make F<pod/roffitall> be updated by F<pod/buildtoc>.
354 =head2 Split "linker" from "compiler"
356 Right now, Configure probes for two commands, and sets two variables:
360 =item * C<cc> (in F<cc.U>)
362 This variable holds the name of a command to execute a C compiler which
363 can resolve multiple global references that happen to have the same
364 name. Usual values are F<cc> and F<gcc>.
365 Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>.
367 =item * C<ld> (in F<dlsrc.U>)
369 This variable indicates the program to be used to link
370 libraries for dynamic loading. On some systems, it is F<ld>.
371 On ELF systems, it should be C<$cc>. Mostly, we'll try to respect
372 the hint file setting.
376 There is an implicit historical assumption from around Perl5.000alpha
377 something, that C<$cc> is also the correct command for linking object files
378 together to make an executable. This may be true on Unix, but it's not true
379 on other platforms, and there are a maze of work arounds in other places (such
380 as F<Makefile.SH>) to cope with this.
382 Ideally, we should create a new variable to hold the name of the executable
383 linker program, probe for it in F<Configure>, and centralise all the special
384 case logic there or in hints files.
386 A small bikeshed issue remains - what to call it, given that C<$ld> is already
387 taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command
388 for creating dynamically-loadable modules) and C<$link> could be confused with
389 the Unix command line executable of the same name, which does something
390 completely different. Andy Dougherty makes the counter argument "In parrot, I
391 tried to call the command used to link object files and libraries into an
392 executable F<link>, since that's what my vaguely-remembered DOS and VMS
393 experience suggested. I don't think any real confusion has ensued, so it's
394 probably a reasonable name for perl5 to use."
396 "Alas, I've always worried that introducing it would make things worse,
397 since now the module building utilities would have to look for
398 C<$Config{link}> and institute a fall-back plan if it weren't found."
399 Although I can see that as confusing, given that C<$Config{d_link}> is true
400 when (hard) links are available.
402 =head2 Configure Windows using PowerShell
404 Currently, Windows uses hard-coded config files based to build the
405 config.h for compiling Perl. Makefiles are also hard-coded and need to be
406 hand edited prior to building Perl. While this makes it easy to create a perl.exe
407 that works across multiple Windows versions, being able to accurately
408 configure a perl.exe for a specific Windows versions and VS C++ would be
409 a nice enhancement. With PowerShell available on Windows XP and up, this
410 may now be possible. Step 1 might be to investigate whether this is possible
411 and use this to clean up our current makefile situation. Step 2 would be to
412 see if there would be a way to use our existing metaconfig units to configure a
413 Windows Perl or whether we go in a separate direction and make it so. Of
414 course, we all know what step 3 is.
416 =head2 decouple -g and -DDEBUGGING
418 Currently F<Configure> automatically adds C<-DDEBUGGING> to the C compiler
419 flags if it spots C<-g> in the optimiser flags. The pre-processor directive
420 C<DEBUGGING> enables F<perl>'s command line C<-D> options, but in the process
421 makes F<perl> slower. It would be good to disentangle this logic, so that
422 C-level debugging with C<-g> and Perl level debugging with C<-D> can easily
423 be enabled independently.
425 =head1 Tasks that need a little C knowledge
427 These tasks would need a little C knowledge, but don't need any specific
428 background or experience with XS, or how the Perl interpreter works
430 =head2 Weed out needless PERL_UNUSED_ARG
432 The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about
433 unused arguments. Often the arguments can't be removed, as there is an
434 external constraint that determines the prototype of the function, so this
435 approach is valid. However, there are some cases where C<PERL_UNUSED_ARG>
436 could be removed. Specifically
442 The prototypes of (nearly all) static functions can be changed
446 Unused arguments generated by short cut macros are wasteful - the short cut
447 macro used can be changed.
451 =head2 Modernize the order of directories in @INC
453 The way @INC is laid out by default, one cannot upgrade core (dual-life)
454 modules without overwriting files. This causes problems for binary
455 package builders. One possible proposal is laid out in this
457 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.
461 Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
462 On these systems, it might be the default compilation mode, and there
463 is currently no guarantee that passing no use64bitall option to the
464 Configure process will build a 32bit perl. Implementing -Duse32bit*
465 options would be nice for perl 5.12.
467 =head2 Profile Perl - am I hot or not?
469 The Perl source code is stable enough that it makes sense to profile it,
470 identify and optimise the hotspots. It would be good to measure the
471 performance of the Perl interpreter using free tools such as cachegrind,
472 gprof, and dtrace, and work to reduce the bottlenecks they reveal.
474 As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
475 the ops that are most commonly used. The idea is that by grouping them, their
476 object code will be adjacent in the executable, so they have a greater chance
477 of already being in the CPU cache (or swapped in) due to being near another op
480 Except that it's not clear if these really are the most commonly used ops. So
481 as part of exercising your skills with coverage and profiling tools you might
482 want to determine what ops I<really> are the most commonly used. And in turn
483 suggest evictions and promotions to achieve a better F<pp_hot.c>.
485 One piece of Perl code that might make a good testbed is F<installman>.
487 =head2 Allocate OPs from arenas
489 Currently all new OP structures are individually malloc()ed and free()d.
490 All C<malloc> implementations have space overheads, and are now as fast as
491 custom allocates so it would both use less memory and less CPU to allocate
492 the various OP structures from arenas. The SV arena code can probably be
495 Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use
496 Perl_Slab_alloc() to pack optrees into a contiguous block, which is
497 probably superior to the use of OP arenas, esp. from a cache locality
498 standpoint. See L<Profile Perl - am I hot or not?>.
500 =head2 Improve win32/wince.c
502 Currently, numerous functions look virtually, if not completely,
503 identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
506 =head2 Use secure CRT functions when building with VC8 on Win32
508 Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
509 that they were "unsafe" and introduced differently named secure versions of
510 them as replacements, e.g. instead of writing
512 FILE* f = fopen(__FILE__, "r");
517 errno_t err = fopen_s(&f, __FILE__, "r");
519 Currently, the warnings about these deprecations have been disabled by adding
520 -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
521 warning suppressant and actually make use of the new secure CRT functions.
523 There is also a similar issue with POSIX CRT function names like fileno having
524 been deprecated in favour of ISO C++ conformant names like _fileno. These
525 warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It
526 might be nice to do as Microsoft suggest here too, although, unlike the secure
527 functions issue, there is presumably little or no benefit in this case.
529 =head2 Fix POSIX::access() and chdir() on Win32
531 These functions currently take no account of DACLs and therefore do not behave
532 correctly in situations where access is restricted by DACLs (as opposed to the
533 read-only attribute).
535 Furthermore, POSIX::access() behaves differently for directories having the
536 read-only attribute set depending on what CRT library is being used. For
537 example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that
538 such directories are not writable, whereas in fact all directories are writable
539 unless access is denied by DACLs. (In the case of directories, the read-only
540 attribute actually only means that the directory cannot be deleted.) This CRT
541 bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still
542 not actually be writable if access is indeed denied by DACLs).
544 For the chdir() issue, see ActiveState bug #74552:
545 http://bugs.activestate.com/show_bug.cgi?id=74552
547 Therefore, DACLs should be checked both for consistency across CRTs and for
550 (Note that perl's -w operator should not be modified to check DACLs. It has
551 been written so that it reflects the state of the read-only attribute, even
552 for directories (whatever CRT is being used), for symmetry with chmod().)
554 =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
556 Maybe create a utility that checks after each libperl.a creation that
557 none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
558 ever creep back to libperl.a.
560 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
562 Note, of course, that this will only tell whether B<your> platform
563 is using those naughty interfaces.
565 =head2 -D_FORTIFY_SOURCE=2, -fstack-protector
567 Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc
568 (4.1 onwards?) supports C<-fstack-protector>, both of which give
569 protection against various kinds of buffer overflow problems.
570 These should probably be used for compiling Perl whenever available,
571 Configure and/or hints files should be adjusted to probe for the
572 availability of these features and enable them as appropriate.
574 =head2 Arenas for GPs? For MAGIC?
576 C<struct gp> and C<struct magic> are both currently allocated by C<malloc>.
577 It might be a speed or memory saving to change to using arenas. Or it might
578 not. It would need some suitable benchmarking first. In particular, C<GP>s
579 can probably be changed with minimal compatibility impact (probably nothing
580 outside of the core, or even outside of F<gv.c> allocates them), but they
581 probably aren't allocated/deallocated often enough for a speed saving. Whereas
582 C<MAGIC> is allocated/deallocated more often, but in turn, is also something
583 more externally visible, so changing the rules here may bite external code.
587 Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and
588 PVHV, and PVCV and PVFM. It should be possible to allocate and return same
589 sized bodies from the same actual arena, rather than maintaining one arena for
590 each. This could save 4-6K per thread, of memory no longer tied up in the
591 not-yet-allocated part of an arena.
594 =head1 Tasks that need a knowledge of XS
596 These tasks would need C knowledge, and roughly the level of knowledge of
597 the perl API that comes from writing modules that use XS to interface to
600 =head2 Write an XS cookbook
602 Create pod/perlxscookbook.pod with short, task-focused 'recipes' in XS that
603 demonstrate common tasks and good practices. (Some of these might be
604 extracted from perlguts.) The target audience should be XS novices, who need
605 more examples than perlguts but something less overwhelming than perlapi.
606 Recipes should provide "one pretty good way to do it" instead of TIMTOWTDI.
608 Rather than focusing on interfacing Perl to C libraries, such a cookbook
609 should probably focus on how to optimize Perl routines by re-writing them
610 in XS. This will likely be more motivating to those who mostly work in
611 Perl but are looking to take the next step into XS.
613 Deconstructing and explaining some simpler XS modules could be one way to
614 bootstrap a cookbook. (List::Util? Class::XSAccessor? Tree::Ternary_XS?)
615 Another option could be deconstructing the implementation of some simpler
618 =head2 Remove the use of SVs as temporaries in dump.c
620 F<dump.c> contains debugging routines to dump out the contains of perl data
621 structures, such as C<SV>s, C<AV>s and C<HV>s. Currently, the dumping code
622 B<uses> C<SV>s for its temporary buffers, which was a logical initial
623 implementation choice, as they provide ready made memory handling.
625 However, they also lead to a lot of confusion when it happens that what you're
626 trying to debug is seen by the code in F<dump.c>, correctly or incorrectly, as
627 a temporary scalar it can use for a temporary buffer. It's also not possible
628 to dump scalars before the interpreter is properly set up, such as during
629 ithreads cloning. It would be good to progressively replace the use of scalars
630 as string accumulation buffers with something much simpler, directly allocated
631 by C<malloc>. The F<dump.c> code is (or should be) only producing 7 bit
632 US-ASCII, so output character sets are not an issue.
634 Producing and proving an internal simple buffer allocation would make it easier
635 to re-write the internals of the PerlIO subsystem to avoid using C<SV>s for
636 B<its> buffers, use of which can cause problems similar to those of F<dump.c>,
639 =head2 safely supporting POSIX SA_SIGINFO
641 Some years ago Jarkko supplied patches to provide support for the POSIX
642 SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler.
644 Unfortunately, it only works with "unsafe" signals, because under safe
645 signals, by the time Perl gets to run the signal handler, the extra
646 information has been lost. Moreover, it's not easy to store it somewhere,
647 as you can't call mutexs, or do anything else fancy, from inside a signal
650 So it strikes me that we could provide safe SA_SIGINFO support
656 Provide global variables for two file descriptors
660 When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a
661 pipe, store the reader in one, the writer in the other
665 In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if
666 the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open,
672 serialise signal number, C<struct siginfo_t> (or at least the parts we care
673 about) into a small auto char buff
677 C<write()> that (non-blocking) to the writer fd
683 if it writes 100%, flag the signal in a counter of "signals on the pipe" akin
684 to the current per-signal-number counts
688 if it writes 0%, assume the pipe is full. Flag the data as lost?
692 if it writes partially, croak a panic, as your OS is broken.
700 in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on
701 the pipe", read the data out, deserialise, build the Perl structures on
702 the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as
707 I think that this gets us decent C<SA_SIGINFO> support, without the current risk
708 of running Perl code inside the signal handler context. (With all the dangers
709 of things like C<malloc> corruption that that currently offers us)
711 For more information see the thread starting with this message:
712 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html
714 =head2 autovivification
716 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
718 This task is incremental - even a little bit of work on it will help.
720 =head2 Unicode in Filenames
722 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
723 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
724 system, truncate, unlink, utime, -X. All these could potentially accept
725 Unicode filenames either as input or output (and in the case of system
726 and qx Unicode in general, as input or output to/from the shell).
727 Whether a filesystem - an operating system pair understands Unicode in
730 Known combinations that have some level of understanding include
731 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
732 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
733 create Unicode filenames, what forms of Unicode are accepted and used
734 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
735 and so on, varies. Finding the right level of interfacing to Perl
736 requires some thought. Remember that an OS does not implicate a
739 (The Windows -C command flag "wide API support" has been at least
740 temporarily retired in 5.8.1, and the -C has been repurposed, see
743 Most probably the right way to do this would be this:
744 L</"Virtualize operating system access">.
746 =head2 Unicode in %ENV
748 Currently the %ENV entries are always byte strings.
749 See L</"Virtualize operating system access">.
751 =head2 Unicode and glob()
753 Currently glob patterns and filenames returned from File::Glob::glob()
754 are always byte strings. See L</"Virtualize operating system access">.
756 =head2 Unicode and lc/uc operators
758 Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on
759 what the internal encoding of their argument is. That should not be the
760 case. Maybe add a pragma to switch behaviour.
762 =head2 use less 'memory'
764 Investigate trade offs to switch out perl's choices on memory usage.
765 Particularly perl should be able to give memory back.
767 This task is incremental - even a little bit of work on it will help.
769 =head2 Re-implement C<:unique> in a way that is actually thread-safe
771 The old implementation made bad assumptions on several levels. A good 90%
772 solution might be just to make C<:unique> work to share the string buffer
773 of SvPVs. That way large constant strings can be shared between ithreads,
774 such as the configuration information in F<Config>.
776 =head2 Make tainting consistent
778 Tainting would be easier to use if it didn't take documented shortcuts and
779 allow taint to "leak" everywhere within an expression.
781 =head2 readpipe(LIST)
783 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
784 running a shell. readpipe() (the function behind qx//) could be similarly
787 =head2 Audit the code for destruction ordering assumptions
791 /* Need to check SvMAGICAL, as during global destruction it may be that
792 AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
793 is now part of the linked list of SV heads, rather than pointing to
794 the original body. */
795 /* FIXME - audit the code for other bugs like this one. */
797 adding the C<SvMAGICAL> check to
799 if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
800 MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
802 Go through the core and look for similar assumptions that SVs have particular
803 types, as all bets are off during global destruction.
805 =head2 Extend PerlIO and PerlIO::Scalar
807 PerlIO::Scalar doesn't know how to truncate(). Implementing this
808 would require extending the PerlIO vtable.
810 Similarly the PerlIO vtable doesn't know about formats (write()), or
811 about stat(), or chmod()/chown(), utime(), or flock().
813 (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
816 PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
817 opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
820 See also L</"Virtualize operating system access">.
822 =head2 -C on the #! line
824 It should be possible to make -C work correctly if found on the #! line,
825 given that all perl command line options are strict ASCII, and -C changes
826 only the interpretation of non-ASCII characters, and not for the script file
827 handle. To make it work needs some investigation of the ordering of function
828 calls during startup, and (by implication) a bit of tweaking of that order.
830 =head2 Organize error messages
832 Perl's diagnostics (error messages, see L<perldiag>) could use
833 reorganizing and formalizing so that each error message has its
834 stable-for-all-eternity unique id, categorized by severity, type, and
835 subsystem. (The error messages would be listed in a datafile outside
836 of the Perl source code, and the source code would only refer to the
837 messages by the id.) This clean-up and regularizing should apply
838 for all croak() messages.
840 This would enable all sorts of things: easier translation/localization
841 of the messages (though please do keep in mind the caveats of
842 L<Locale::Maketext> about too straightforward approaches to
843 translation), filtering by severity, and instead of grepping for a
844 particular error message one could look for a stable error id. (Of
845 course, changing the error messages by default would break all the
846 existing software depending on some particular error message...)
848 This kind of functionality is known as I<message catalogs>. Look for
849 inspiration for example in the catgets() system, possibly even use it
850 if available-- but B<only> if available, all platforms will B<not>
853 For the really pure at heart, consider extending this item to cover
854 also the warning messages (see L<perllexwarn>, C<warnings.pl>).
856 =head1 Tasks that need a knowledge of the interpreter
858 These tasks would need C knowledge, and knowledge of how the interpreter works,
859 or a willingness to learn.
861 =head2 truncate() prototype
863 The prototype of truncate() is currently C<$$>. It should probably
864 be C<*$> instead. (This is changed in F<opcode.pl>)
866 =head2 decapsulation of smart match argument
868 Currently C<$foo ~~ $object> will die with the message "Smart matching a
869 non-overloaded object breaks encapsulation". It would be nice to allow
870 to bypass this by using explictly the syntax C<$foo ~~ %$object> or
873 =head2 error reporting of [$a ; $b]
875 Using C<;> inside brackets is a syntax error, and we don't propose to change
876 that by giving it any meaning. However, it's not reported very helpfully:
878 $ perl -e '$a = [$b; $c];'
879 syntax error at -e line 1, near "$b;"
880 syntax error at -e line 1, near "$c]"
881 Execution of -e aborted due to compilation errors.
883 It should be possible to hook into the tokeniser or the lexer, so that when a
884 C<;> is parsed where it is not legal as a statement terminator (ie inside
885 C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like
886 I<';' isn't legal inside an expression - if you need multiple statements use a
887 do {...} block>. See the thread starting at
888 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html
890 =head2 lexicals used only once
894 $ perl -we '$pie = 42'
895 Name "main::pie" used only once: possible typo at -e line 1.
899 $ perl -we 'my $pie = 42'
901 Logically all lexicals used only once should warn, if the user asks for
902 warnings. An unworked RT ticket (#5087) has been open for almost seven
903 years for this discrepancy.
907 The handling of Unicode is unclean in many places. For example, the regexp
908 engine matches in Unicode semantics whenever the string or the pattern is
909 flagged as UTF-8, but that should not be dependent on an internal storage
910 detail of the string. Likewise, case folding behaviour is dependent on the
911 UTF8 internal flag being on or off.
913 =head2 Properly Unicode safe tokeniser and pads.
915 The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
916 variable names are stored in stashes as raw bytes, without the utf-8 flag
917 set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
918 tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
919 source filters. All this could be fixed.
921 =head2 state variable initialization in list context
923 Currently this is illegal:
925 state ($a, $b) = foo();
927 In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different
928 semantics, which is tricky to implement in Perl 5 as currently they produce
929 the same opcode trees. The Perl 6 design is firm, so it would be good to
930 implement the necessary code in Perl 5. There are comments in
931 C<Perl_newASSIGNOP()> that show the code paths taken by various assignment
932 constructions involving state variables.
934 =head2 Implement $value ~~ 0 .. $range
936 It would be nice to extend the syntax of the C<~~> operator to also
937 understand numeric (and maybe alphanumeric) ranges.
939 =head2 A does() built-in
941 Like ref(), only useful. It would call the C<DOES> method on objects; it
942 would also tell whether something can be dereferenced as an
943 array/hash/etc., or used as a regexp, etc.
944 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
946 =head2 Tied filehandles and write() don't mix
948 There is no method on tied filehandles to allow them to be called back by
951 =head2 Propagate compilation hints to the debugger
953 Currently a debugger started with -dE on the command-line doesn't see the
954 features enabled by -E. More generally hints (C<$^H> and C<%^H>) aren't
955 propagated to the debugger. Probably it would be a good thing to propagate
956 hints from the innermost non-C<DB::> scope: this would make code eval'ed
957 in the debugger see the features (and strictures, etc.) currently in
960 =head2 Attach/detach debugger from running program
962 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
963 program if you pass the process ID. It would be good to do this with the Perl
964 debugger on a running Perl program, although I'm not sure how it would be
965 done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
967 =head2 LVALUE functions for lists
969 The old perltodo notes that lvalue functions don't work for list or hash
970 slices. This would be good to fix.
972 =head2 regexp optimiser optional
974 The regexp optimiser is not optional. It should configurable to be, to allow
975 its performance to be measured, and its bugs to be easily demonstrated.
977 =head2 delete &function
979 Allow to delete functions. One can already undef them, but they're still
982 =head2 C</w> regex modifier
984 That flag would enable to match whole words, and also to interpolate
985 arrays as alternations. With it, C</P/w> would be roughly equivalent to:
987 do { local $"='|'; /\b(?:P)\b/ }
989 See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
992 =head2 optional optimizer
994 Make the peephole optimizer optional. Currently it performs two tasks as
995 it walks the optree - genuine peephole optimisations, and necessary fixups of
996 ops. It would be good to find an efficient way to switch out the
997 optimisations whilst keeping the fixups.
999 =head2 You WANT *how* many
1001 Currently contexts are void, scalar and list. split has a special mechanism in
1002 place to pass in the number of return values wanted. It would be useful to
1003 have a general mechanism for this, backwards compatible and little speed hit.
1004 This would allow proposals such as short circuiting sort to be implemented
1005 as a module on CPAN.
1007 =head2 lexical aliases
1009 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
1011 =head2 entersub XS vs Perl
1013 At the moment pp_entersub is huge, and has code to deal with entering both
1014 perl and XS subroutines. Subroutine implementations rarely change between
1015 perl and XS at run time, so investigate using 2 ops to enter subs (one for
1016 XS, one for perl) and swap between if a sub is redefined.
1020 Self-ties are currently illegal because they caused too many segfaults. Maybe
1021 the causes of these could be tracked down and self-ties on all types
1024 =head2 Optimize away @_
1026 The old perltodo notes "Look at the "reification" code in C<av.c>".
1028 =head2 Virtualize operating system access
1030 Implement a set of "vtables" that virtualizes operating system access
1031 (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very
1032 least these interfaces should take SVs as "name" arguments instead of
1033 bare char pointers; probably the most flexible and extensible way
1034 would be for the Perl-facing interfaces to accept HVs. The system
1035 needs to be per-operating-system and per-file-system
1036 hookable/filterable, preferably both from XS and Perl level
1037 (L<perlport/"Files and Filesystems"> is good reading at this point,
1038 in fact, all of L<perlport> is.)
1040 This has actually already been implemented (but only for Win32),
1041 take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32
1042 variants go through a set of "vtables" for operating system access,
1043 non-Win32 systems currently go straight for the POSIX/UNIX-style
1044 system/library call. Similar system as for Win32 should be
1045 implemented for all platforms. The existing Win32 implementation
1046 probably does not need to survive alongside this proposed new
1047 implementation, the approaches could be merged.
1049 What would this give us? One often-asked-for feature this would
1050 enable is using Unicode for filenames, and other "names" like %ENV,
1051 usernames, hostnames, and so forth.
1052 (See L<perlunicode/"When Unicode Does Not Happen">.)
1054 But this kind of virtualization would also allow for things like
1055 virtual filesystems, virtual networks, and "sandboxes" (though as long
1056 as dynamic loading of random object code is allowed, not very safe
1057 sandboxes since external code of course know not of Perl's vtables).
1058 An example of a smaller "sandbox" is that this feature can be used to
1059 implement per-thread working directories: Win32 already does this.
1061 See also L</"Extend PerlIO and PerlIO::Scalar">.
1063 =head2 Investigate PADTMP hash pessimisation
1065 The peephole optimiser converts constants used for hash key lookups to shared
1066 hash key scalars. Under ithreads, something is undoing this work.
1067 See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html
1069 =head2 Store the current pad in the OP slab allocator
1072 I hope that I got that "current pad" part correct
1074 Currently we leak ops in various cases of parse failure. I suggested that we
1075 could solve this by always using the op slab allocator, and walking it to
1076 free ops. Dave comments that as some ops are already freed during optree
1077 creation one would have to mark which ops are freed, and not double free them
1078 when walking the slab. He notes that one problem with this is that for some ops
1079 you have to know which pad was current at the time of allocation, which does
1080 change. I suggested storing a pointer to the current pad in the memory allocated
1081 for the slab, and swapping to a new slab each time the pad changes. Dave thinks
1082 that this would work.
1084 =head2 repack the optree
1086 Repacking the optree after execution order is determined could allow
1087 removal of NULL ops, and optimal ordering of OPs with respect to cache-line
1088 filling. The slab allocator could be reused for this purpose. I think that
1089 the best way to do this is to make it an optional step just before the
1090 completed optree is attached to anything else, and to use the slab allocator
1091 unchanged, so that freeing ops is identical whether or not this step runs.
1092 Note that the slab allocator allocates ops downwards in memory, so one would
1093 have to actually "allocate" the ops in reverse-execution order to get them
1094 contiguous in memory in execution order.
1096 See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html
1098 Note that running this copy, and then freeing all the old location ops would
1099 cause their slabs to be freed, which would eliminate possible memory wastage if
1100 the previous suggestion is implemented, and we swap slabs more frequently.
1102 =head2 eliminate incorrect line numbers in warnings
1110 } elsif ($undef == 0) {
1113 used to produce this output:
1115 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1116 Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
1118 where the line of the second warning was misreported - it should be line 5.
1119 Rafael fixed this - the problem arose because there was no nextstate OP
1120 between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still
1121 reports that the currently executing line is line 4. The solution was to inject
1122 a nextstate OPs for each C<elsif>, although it turned out that the nextstate
1123 OP needed to be a nulled OP, rather than a live nextstate OP, else other line
1124 numbers became misreported. (Jenga!)
1126 The problem is more general than C<elsif> (although the C<elsif> case is the
1127 most common and the most confusing). Ideally this code
1137 would produce this output
1139 Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
1140 Use of uninitialized value $undef in addition (+) at wrong.pl line 7.
1142 (rather than lines 4 and 5), but this would seem to require every OP to carry
1143 (at least) line number information.
1145 What might work is to have an optional line number in memory just before the
1146 BASEOP structure, with a flag bit in the op to say whether it's present.
1147 Initially during compile every OP would carry its line number. Then add a late
1148 pass to the optimiser (potentially combined with L</repack the optree>) which
1149 looks at the two ops on every edge of the graph of the execution path. If
1150 the line number changes, flags the destination OP with this information.
1151 Once all paths are traced, replace every op with the flag with a
1152 nextstate-light op (that just updates C<PL_curcop>), which in turn then passes
1153 control on to the true op. All ops would then be replaced by variants that
1154 do not store the line number. (Which, logically, why it would work best in
1155 conjunction with L</repack the optree>, as that is already copying/reallocating
1158 (Although I should note that we're not certain that doing this for the general
1161 =head2 optimize tail-calls
1163 Tail-calls present an opportunity for broadly applicable optimization;
1164 anywhere that C<< return foo(...) >> is called, the outer return can
1165 be replaced by a goto, and foo will return directly to the outer
1166 caller, saving (conservatively) 25% of perl's call&return cost, which
1167 is relatively higher than in C. The scheme language is known to do
1168 this heavily. B::Concise provides good insight into where this
1169 optimization is possible, ie anywhere entersub,leavesub op-sequence
1172 perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'
1174 Bottom line on this is probably a new pp_tailcall function which
1175 combines the code in pp_entersub, pp_leavesub. This should probably
1176 be done 1st in XS, and using B::Generate to patch the new OP into the
1181 Tasks that will get your name mentioned in the description of the "Highlights
1184 =head2 make ithreads more robust
1186 Generally make ithreads more robust. See also L</iCOW>
1188 This task is incremental - even a little bit of work on it will help, and
1189 will be greatly appreciated.
1191 One bit would be to write the missing code in sv.c:Perl_dirp_dup.
1193 Fix Perl_sv_dup, et al so that threads can return objects.
1197 Sarathy and Arthur have a proposal for an improved Copy On Write which
1198 specifically will be able to COW new ithreads. If this can be implemented
1199 it would be a good thing.
1201 =head2 (?{...}) closures in regexps
1203 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
1205 =head2 A re-entrant regexp engine
1207 This will allow the use of a regex from inside (?{ }), (??{ }) and
1208 (?(?{ })|) constructs.
1210 =head2 Add class set operations to regexp engine
1212 Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
1214 demerphq has this on his todo list, but right at the bottom.
1217 =head1 Tasks for microperl
1220 [ Each and every one of these may be obsolete, but they were listed
1221 in the old Todo.micro file]
1224 =head2 make creating uconfig.sh automatic
1226 =head2 make creating Makefile.micro automatic
1228 =head2 do away with fork/exec/wait?
1230 (system, popen should be enough?)
1232 =head2 some of the uconfig.sh really needs to be probed (using cc) in buildtime:
1234 (uConfigure? :-) native datatype widths and endianness come to mind