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Diffstat (limited to 'Master/tlpkg/tlperl/lib/pods/perltodo.pod')
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1 files changed, 4 insertions, 1274 deletions
diff --git a/Master/tlpkg/tlperl/lib/pods/perltodo.pod b/Master/tlpkg/tlperl/lib/pods/perltodo.pod index de0e373b468..524a501681f 100644 --- a/Master/tlpkg/tlperl/lib/pods/perltodo.pod +++ b/Master/tlpkg/tlperl/lib/pods/perltodo.pod @@ -4,1277 +4,7 @@ perltodo - Perl TO-DO List =head1 DESCRIPTION -This is a list of wishes for Perl. The most up to date version of this file -is at L<http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod> - -The tasks we think are smaller or easier are listed first. Anyone is welcome -to work on any of these, but it's a good idea to first contact -I<perl5-porters@perl.org> to avoid duplication of effort, and to learn from -any previous attempts. By all means contact a pumpking privately first if you -prefer. - -Whilst patches to make the list shorter are most welcome, ideas to add to -the list are also encouraged. Check the perl5-porters archives for past -ideas, and any discussion about them. One set of archives may be found at -L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/> - -What can we offer you in return? Fame, fortune, and everlasting glory? Maybe -not, but if your patch is incorporated, then we'll add your name to the -F<AUTHORS> file, which ships in the official distribution. How many other -programming languages offer you 1 line of immortality? - -=head1 Tasks that only need Perl knowledge - -=head2 Migrate t/ from custom TAP generation - -Many tests below F<t/> still generate TAP by "hand", rather than using library -functions. As explained in L<perlhack/TESTING>, tests in F<t/> are -written in a particular way to test that more complex constructions actually -work before using them routinely. Hence they don't use C<Test::More>, but -instead there is an intentionally simpler library, F<t/test.pl>. However, -quite a few tests in F<t/> have not been refactored to use it. Refactoring -any of these tests, one at a time, is a useful thing TODO. - -The subdirectories F<base>, F<cmd> and F<comp>, that contain the most -basic tests, should be excluded from this task. - -=head2 Automate perldelta generation - -The perldelta file accompanying each release summaries the major changes. -It's mostly manually generated currently, but some of that could be -automated with a bit of perl, specifically the generation of - -=over - -=item Modules and Pragmata - -=item New Documentation - -=item New Tests - -=back - -See F<Porting/how_to_write_a_perldelta.pod> for details. - -=head2 Remove duplication of test setup. - -Schwern notes, that there's duplication of code - lots and lots of tests have -some variation on the big block of C<$Is_Foo> checks. We can safely put this -into a file, change it to build an C<%Is> hash and require it. Maybe just put -it into F<test.pl>. Throw in the handy tainting subroutines. - -=head2 POD -E<gt> HTML conversion in the core still sucks - -Which is crazy given just how simple POD purports to be, and how simple HTML -can be. It's not actually I<as> simple as it sounds, particularly with the -flexibility POD allows for C<=item>, but it would be good to improve the -visual appeal of the HTML generated, and to avoid it having any validation -errors. See also L</make HTML install work>, as the layout of installation tree -is needed to improve the cross-linking. - -The addition of C<Pod::Simple> and its related modules may make this task -easier to complete. - -=head2 Make ExtUtils::ParseXS use strict; - -F<lib/ExtUtils/ParseXS.pm> contains this line - - # use strict; # One of these days... - -Simply uncomment it, and fix all the resulting issues :-) - -The more practical approach, to break the task down into manageable chunks, is -to work your way though the code from bottom to top, or if necessary adding -extra C<{ ... }> blocks, and turning on strict within them. - -=head2 Make Schwern poorer - -We should have tests for everything. When all the core's modules are tested, -Schwern has promised to donate to $500 to TPF. We may need volunteers to -hold him upside down and shake vigorously in order to actually extract the -cash. - -=head2 Improve the coverage of the core tests - -Use Devel::Cover to ascertain the core modules' test coverage, then add -tests that are currently missing. - -=head2 test B - -A full test suite for the B module would be nice. - -=head2 A decent benchmark - -C<perlbench> seems impervious to any recent changes made to the perl core. It -would be useful to have a reasonable general benchmarking suite that roughly -represented what current perl programs do, and measurably reported whether -tweaks to the core improve, degrade or don't really affect performance, to -guide people attempting to optimise the guts of perl. Gisle would welcome -new tests for perlbench. - -=head2 fix tainting bugs - -Fix the bugs revealed by running the test suite with the C<-t> switch (via -C<make test.taintwarn>). - -=head2 Dual life everything - -As part of the "dists" plan, anything that doesn't belong in the smallest perl -distribution needs to be dual lifed. Anything else can be too. Figure out what -changes would be needed to package that module and its tests up for CPAN, and -do so. Test it with older perl releases, and fix the problems you find. - -To make a minimal perl distribution, it's useful to look at -F<t/lib/commonsense.t>. - -=head2 POSIX memory footprint - -Ilya observed that use POSIX; eats memory like there's no tomorrow, and at -various times worked to cut it down. There is probably still fat to cut out - -for example POSIX passes Exporter some very memory hungry data structures. - -=head2 embed.pl/makedef.pl - -There is a script F<embed.pl> that generates several header files to prefix -all of Perl's symbols in a consistent way, to provide some semblance of -namespace support in C<C>. Functions are declared in F<embed.fnc>, variables -in F<interpvar.h>. Quite a few of the functions and variables -are conditionally declared there, using C<#ifdef>. However, F<embed.pl> -doesn't understand the C macros, so the rules about which symbols are present -when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay. -It would be good to teach C<embed.pl> to understand the conditional -compilation, and hence remove the duplication, and the mistakes it has caused. - -=head2 use strict; and AutoLoad - -Currently if you write - - package Whack; - use AutoLoader 'AUTOLOAD'; - use strict; - 1; - __END__ - sub bloop { - print join (' ', No, strict, here), "!\n"; - } - -then C<use strict;> isn't in force within the autoloaded subroutines. It would -be more consistent (and less surprising) to arrange for all lexical pragmas -in force at the __END__ block to be in force within each autoloaded subroutine. - -There's a similar problem with SelfLoader. - -=head2 profile installman - -The F<installman> script is slow. All it is doing text processing, which we're -told is something Perl is good at. So it would be nice to know what it is doing -that is taking so much CPU, and where possible address it. - -=head2 enable lexical enabling/disabling of individual warnings - -Currently, warnings can only be enabled or disabled by category. There -are times when it would be useful to quash a single warning, not a -whole category. - -=head1 Tasks that need a little sysadmin-type knowledge - -Or if you prefer, tasks that you would learn from, and broaden your skills -base... - -=head2 make HTML install work - -There is an C<installhtml> target in the Makefile. It's marked as -"experimental". It would be good to get this tested, make it work reliably, and -remove the "experimental" tag. This would include - -=over 4 - -=item 1 - -Checking that cross linking between various parts of the documentation works. -In particular that links work between the modules (files with POD in F<lib/>) -and the core documentation (files in F<pod/>) - -=item 2 - -Work out how to split C<perlfunc> into chunks, preferably one per function -group, preferably with general case code that could be used elsewhere. -Challenges here are correctly identifying the groups of functions that go -together, and making the right named external cross-links point to the right -page. Things to be aware of are C<-X>, groups such as C<getpwnam> to -C<endservent>, two or more C<=items> giving the different parameter lists, such -as - - =item substr EXPR,OFFSET,LENGTH,REPLACEMENT - =item substr EXPR,OFFSET,LENGTH - =item substr EXPR,OFFSET - -and different parameter lists having different meanings. (eg C<select>) - -=back - -=head2 compressed man pages - -Be able to install them. This would probably need a configure test to see how -the system does compressed man pages (same directory/different directory? -same filename/different filename), as well as tweaking the F<installman> script -to compress as necessary. - -=head2 Add a code coverage target to the Makefile - -Make it easy for anyone to run Devel::Cover on the core's tests. The steps -to do this manually are roughly - -=over 4 - -=item * - -do a normal C<Configure>, but include Devel::Cover as a module to install -(see L<INSTALL> for how to do this) - -=item * - - make perl - -=item * - - cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness - -=item * - -Process the resulting Devel::Cover database - -=back - -This just give you the coverage of the F<.pm>s. To also get the C level -coverage you need to - -=over 4 - -=item * - -Additionally tell C<Configure> to use the appropriate C compiler flags for -C<gcov> - -=item * - - make perl.gcov - -(instead of C<make perl>) - -=item * - -After running the tests run C<gcov> to generate all the F<.gcov> files. -(Including down in the subdirectories of F<ext/> - -=item * - -(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files -to get their stats into the cover_db directory. - -=item * - -Then process the Devel::Cover database - -=back - -It would be good to add a single switch to C<Configure> to specify that you -wanted to perform perl level coverage, and another to specify C level -coverage, and have C<Configure> and the F<Makefile> do all the right things -automatically. - -=head2 Make Config.pm cope with differences between built and installed perl - -Quite often vendors ship a perl binary compiled with their (pay-for) -compilers. People install a free compiler, such as gcc. To work out how to -build extensions, Perl interrogates C<%Config>, so in this situation -C<%Config> describes compilers that aren't there, and extension building -fails. This forces people into choosing between re-compiling perl themselves -using the compiler they have, or only using modules that the vendor ships. - -It would be good to find a way teach C<Config.pm> about the installation setup, -possibly involving probing at install time or later, so that the C<%Config> in -a binary distribution better describes the installed machine, when the -installed machine differs from the build machine in some significant way. - -=head2 linker specification files - -Some platforms mandate that you provide a list of a shared library's external -symbols to the linker, so the core already has the infrastructure in place to -do this for generating shared perl libraries. My understanding is that the -GNU toolchain can accept an optional linker specification file, and restrict -visibility just to symbols declared in that file. It would be good to extend -F<makedef.pl> to support this format, and to provide a means within -C<Configure> to enable it. This would allow Unix users to test that the -export list is correct, and to build a perl that does not pollute the global -namespace with private symbols, and will fail in the same way as msvc or mingw -builds or when using PERL_DL_NONLAZY=1. - -=head2 Cross-compile support - -Currently C<Configure> understands C<-Dusecrosscompile> option. This option -arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is -assumed then to be copied to TARGET machine and used as a replacement of full -C<perl> executable. - -This could be done little differently. Namely C<miniperl> should be built for -HOST and then full C<perl> with extensions should be compiled for TARGET. -This, however, might require extra trickery for %Config: we have one config -first for HOST and then another for TARGET. Tools like MakeMaker will be -mightily confused. Having around two different types of executables and -libraries (HOST and TARGET) makes life interesting for Makefiles and -shell (and Perl) scripts. There is $Config{run}, normally empty, which -can be used as an execution wrapper. Also note that in some -cross-compilation/execution environments the HOST and the TARGET do -not see the same filesystem(s), the $Config{run} may need to do some -file/directory copying back and forth. - -=head2 roffitall - -Make F<pod/roffitall> be updated by F<pod/buildtoc>. - -=head2 Split "linker" from "compiler" - -Right now, Configure probes for two commands, and sets two variables: - -=over 4 - -=item * C<cc> (in F<cc.U>) - -This variable holds the name of a command to execute a C compiler which -can resolve multiple global references that happen to have the same -name. Usual values are F<cc> and F<gcc>. -Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>. - -=item * C<ld> (in F<dlsrc.U>) - -This variable indicates the program to be used to link -libraries for dynamic loading. On some systems, it is F<ld>. -On ELF systems, it should be C<$cc>. Mostly, we'll try to respect -the hint file setting. - -=back - -There is an implicit historical assumption from around Perl5.000alpha -something, that C<$cc> is also the correct command for linking object files -together to make an executable. This may be true on Unix, but it's not true -on other platforms, and there are a maze of work arounds in other places (such -as F<Makefile.SH>) to cope with this. - -Ideally, we should create a new variable to hold the name of the executable -linker program, probe for it in F<Configure>, and centralise all the special -case logic there or in hints files. - -A small bikeshed issue remains - what to call it, given that C<$ld> is already -taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command -for creating dynamically-loadable modules) and C<$link> could be confused with -the Unix command line executable of the same name, which does something -completely different. Andy Dougherty makes the counter argument "In parrot, I -tried to call the command used to link object files and libraries into an -executable F<link>, since that's what my vaguely-remembered DOS and VMS -experience suggested. I don't think any real confusion has ensued, so it's -probably a reasonable name for perl5 to use." - -"Alas, I've always worried that introducing it would make things worse, -since now the module building utilities would have to look for -C<$Config{link}> and institute a fall-back plan if it weren't found." -Although I can see that as confusing, given that C<$Config{d_link}> is true -when (hard) links are available. - -=head2 Configure Windows using PowerShell - -Currently, Windows uses hard-coded config files based to build the -config.h for compiling Perl. Makefiles are also hard-coded and need to be -hand edited prior to building Perl. While this makes it easy to create a perl.exe -that works across multiple Windows versions, being able to accurately -configure a perl.exe for a specific Windows versions and VS C++ would be -a nice enhancement. With PowerShell available on Windows XP and up, this -may now be possible. Step 1 might be to investigate whether this is possible -and use this to clean up our current makefile situation. Step 2 would be to -see if there would be a way to use our existing metaconfig units to configure a -Windows Perl or whether we go in a separate direction and make it so. Of -course, we all know what step 3 is. - -=head2 decouple -g and -DDEBUGGING - -Currently F<Configure> automatically adds C<-DDEBUGGING> to the C compiler -flags if it spots C<-g> in the optimiser flags. The pre-processor directive -C<DEBUGGING> enables F<perl>'s command line C<-D> options, but in the process -makes F<perl> slower. It would be good to disentangle this logic, so that -C-level debugging with C<-g> and Perl level debugging with C<-D> can easily -be enabled independently. - -=head1 Tasks that need a little C knowledge - -These tasks would need a little C knowledge, but don't need any specific -background or experience with XS, or how the Perl interpreter works - -=head2 Weed out needless PERL_UNUSED_ARG - -The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about -unused arguments. Often the arguments can't be removed, as there is an -external constraint that determines the prototype of the function, so this -approach is valid. However, there are some cases where C<PERL_UNUSED_ARG> -could be removed. Specifically - -=over 4 - -=item * - -The prototypes of (nearly all) static functions can be changed - -=item * - -Unused arguments generated by short cut macros are wasteful - the short cut -macro used can be changed. - -=back - -=head2 Modernize the order of directories in @INC - -The way @INC is laid out by default, one cannot upgrade core (dual-life) -modules without overwriting files. This causes problems for binary -package builders. One possible proposal is laid out in this -message: -L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html> - -=head2 -Duse32bit* - -Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall. -On these systems, it might be the default compilation mode, and there -is currently no guarantee that passing no use64bitall option to the -Configure process will build a 32bit perl. Implementing -Duse32bit* -options would be nice for perl 5.14. - -=head2 Profile Perl - am I hot or not? - -The Perl source code is stable enough that it makes sense to profile it, -identify and optimise the hotspots. It would be good to measure the -performance of the Perl interpreter using free tools such as cachegrind, -gprof, and dtrace, and work to reduce the bottlenecks they reveal. - -As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops, -the ops that are most commonly used. The idea is that by grouping them, their -object code will be adjacent in the executable, so they have a greater chance -of already being in the CPU cache (or swapped in) due to being near another op -already in use. - -Except that it's not clear if these really are the most commonly used ops. So -as part of exercising your skills with coverage and profiling tools you might -want to determine what ops I<really> are the most commonly used. And in turn -suggest evictions and promotions to achieve a better F<pp_hot.c>. - -One piece of Perl code that might make a good testbed is F<installman>. - -=head2 Allocate OPs from arenas - -Currently all new OP structures are individually malloc()ed and free()d. -All C<malloc> implementations have space overheads, and are now as fast as -custom allocates so it would both use less memory and less CPU to allocate -the various OP structures from arenas. The SV arena code can probably be -re-used for this. - -Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use -Perl_Slab_alloc() to pack optrees into a contiguous block, which is -probably superior to the use of OP arenas, esp. from a cache locality -standpoint. See L<Profile Perl - am I hot or not?>. - -=head2 Improve win32/wince.c - -Currently, numerous functions look virtually, if not completely, -identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't -be good. - -=head2 Use secure CRT functions when building with VC8 on Win32 - -Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis -that they were "unsafe" and introduced differently named secure versions of -them as replacements, e.g. instead of writing - - FILE* f = fopen(__FILE__, "r"); - -one should now write - - FILE* f; - errno_t err = fopen_s(&f, __FILE__, "r"); - -Currently, the warnings about these deprecations have been disabled by adding --D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that -warning suppressant and actually make use of the new secure CRT functions. - -There is also a similar issue with POSIX CRT function names like fileno having -been deprecated in favour of ISO C++ conformant names like _fileno. These -warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It -might be nice to do as Microsoft suggest here too, although, unlike the secure -functions issue, there is presumably little or no benefit in this case. - -=head2 Fix POSIX::access() and chdir() on Win32 - -These functions currently take no account of DACLs and therefore do not behave -correctly in situations where access is restricted by DACLs (as opposed to the -read-only attribute). - -Furthermore, POSIX::access() behaves differently for directories having the -read-only attribute set depending on what CRT library is being used. For -example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that -such directories are not writable, whereas in fact all directories are writable -unless access is denied by DACLs. (In the case of directories, the read-only -attribute actually only means that the directory cannot be deleted.) This CRT -bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still -not actually be writable if access is indeed denied by DACLs). - -For the chdir() issue, see ActiveState bug #74552: -L<http://bugs.activestate.com/show_bug.cgi?id=74552> - -Therefore, DACLs should be checked both for consistency across CRTs and for -the correct answer. - -(Note that perl's -w operator should not be modified to check DACLs. It has -been written so that it reflects the state of the read-only attribute, even -for directories (whatever CRT is being used), for symmetry with chmod().) - -=head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf() - -Maybe create a utility that checks after each libperl.a creation that -none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets()) -ever creep back to libperl.a. - - nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/' - -Note, of course, that this will only tell whether B<your> platform -is using those naughty interfaces. - -=head2 -D_FORTIFY_SOURCE=2, -fstack-protector - -Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc -(4.1 onwards?) supports C<-fstack-protector>, both of which give -protection against various kinds of buffer overflow problems. -These should probably be used for compiling Perl whenever available, -Configure and/or hints files should be adjusted to probe for the -availability of these features and enable them as appropriate. - -=head2 Arenas for GPs? For MAGIC? - -C<struct gp> and C<struct magic> are both currently allocated by C<malloc>. -It might be a speed or memory saving to change to using arenas. Or it might -not. It would need some suitable benchmarking first. In particular, C<GP>s -can probably be changed with minimal compatibility impact (probably nothing -outside of the core, or even outside of F<gv.c> allocates them), but they -probably aren't allocated/deallocated often enough for a speed saving. Whereas -C<MAGIC> is allocated/deallocated more often, but in turn, is also something -more externally visible, so changing the rules here may bite external code. - -=head2 Shared arenas - -Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and -PVHV, and PVCV and PVFM. It should be possible to allocate and return same -sized bodies from the same actual arena, rather than maintaining one arena for -each. This could save 4-6K per thread, of memory no longer tied up in the -not-yet-allocated part of an arena. - - -=head1 Tasks that need a knowledge of XS - -These tasks would need C knowledge, and roughly the level of knowledge of -the perl API that comes from writing modules that use XS to interface to -C. - -=head2 Write an XS cookbook - -Create pod/perlxscookbook.pod with short, task-focused 'recipes' in XS that -demonstrate common tasks and good practices. (Some of these might be -extracted from perlguts.) The target audience should be XS novices, who need -more examples than perlguts but something less overwhelming than perlapi. -Recipes should provide "one pretty good way to do it" instead of TIMTOWTDI. - -Rather than focusing on interfacing Perl to C libraries, such a cookbook -should probably focus on how to optimize Perl routines by re-writing them -in XS. This will likely be more motivating to those who mostly work in -Perl but are looking to take the next step into XS. - -Deconstructing and explaining some simpler XS modules could be one way to -bootstrap a cookbook. (List::Util? Class::XSAccessor? Tree::Ternary_XS?) -Another option could be deconstructing the implementation of some simpler -functions in op.c. - -=head2 Allow XSUBs to inline themselves as OPs - -For a simple XSUB, often the subroutine dispatch takes more time than the -XSUB itself. The tokeniser already has the ability to inline constant -subroutines - it would be good to provide a way to inline other subroutines. - -Specifically, simplest approach looks to be to allow an XSUB to provide an -alternative implementation of itself as a custom OP. A new flag bit in -C<CvFLAGS()> would signal to the peephole optimiser to take an optree -such as this: - - b <@> leave[1 ref] vKP/REFC ->(end) - 1 <0> enter ->2 - 2 <;> nextstate(main 1 -e:1) v:{ ->3 - a <2> sassign vKS/2 ->b - 8 <1> entersub[t2] sKS/TARG,1 ->9 - - <1> ex-list sK ->8 - 3 <0> pushmark s ->4 - 4 <$> const(IV 1) sM ->5 - 6 <1> rv2av[t1] lKM/1 ->7 - 5 <$> gv(*a) s ->6 - - <1> ex-rv2cv sK ->- - 7 <$> gv(*x) s/EARLYCV ->8 - - <1> ex-rv2sv sKRM*/1 ->a - 9 <$> gvsv(*b) s ->a - -perform the symbol table lookup of C<rv2cv> and C<gv(*x)>, locate the -pointer to the custom OP that provides the direct implementation, and re- -write the optree something like: - - b <@> leave[1 ref] vKP/REFC ->(end) - 1 <0> enter ->2 - 2 <;> nextstate(main 1 -e:1) v:{ ->3 - a <2> sassign vKS/2 ->b - 7 <1> custom_x -> 8 - - <1> ex-list sK ->7 - 3 <0> pushmark s ->4 - 4 <$> const(IV 1) sM ->5 - 6 <1> rv2av[t1] lKM/1 ->7 - 5 <$> gv(*a) s ->6 - - <1> ex-rv2cv sK ->- - - <$> ex-gv(*x) s/EARLYCV ->7 - - <1> ex-rv2sv sKRM*/1 ->a - 8 <$> gvsv(*b) s ->a - -I<i.e.> the C<gv(*)> OP has been nulled and spliced out of the execution -path, and the C<entersub> OP has been replaced by the custom op. - -This approach should provide a measurable speed up to simple XSUBs inside -tight loops. Initially one would have to write the OP alternative -implementation by hand, but it's likely that this should be reasonably -straightforward for the type of XSUB that would benefit the most. Longer -term, once the run-time implementation is proven, it should be possible to -progressively update ExtUtils::ParseXS to generate OP implementations for -some XSUBs. - -=head2 Remove the use of SVs as temporaries in dump.c - -F<dump.c> contains debugging routines to dump out the contains of perl data -structures, such as C<SV>s, C<AV>s and C<HV>s. Currently, the dumping code -B<uses> C<SV>s for its temporary buffers, which was a logical initial -implementation choice, as they provide ready made memory handling. - -However, they also lead to a lot of confusion when it happens that what you're -trying to debug is seen by the code in F<dump.c>, correctly or incorrectly, as -a temporary scalar it can use for a temporary buffer. It's also not possible -to dump scalars before the interpreter is properly set up, such as during -ithreads cloning. It would be good to progressively replace the use of scalars -as string accumulation buffers with something much simpler, directly allocated -by C<malloc>. The F<dump.c> code is (or should be) only producing 7 bit -US-ASCII, so output character sets are not an issue. - -Producing and proving an internal simple buffer allocation would make it easier -to re-write the internals of the PerlIO subsystem to avoid using C<SV>s for -B<its> buffers, use of which can cause problems similar to those of F<dump.c>, -at similar times. - -=head2 safely supporting POSIX SA_SIGINFO - -Some years ago Jarkko supplied patches to provide support for the POSIX -SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler. - -Unfortunately, it only works with "unsafe" signals, because under safe -signals, by the time Perl gets to run the signal handler, the extra -information has been lost. Moreover, it's not easy to store it somewhere, -as you can't call mutexs, or do anything else fancy, from inside a signal -handler. - -So it strikes me that we could provide safe SA_SIGINFO support - -=over 4 - -=item 1 - -Provide global variables for two file descriptors - -=item 2 - -When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a -pipe, store the reader in one, the writer in the other - -=item 3 - -In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if -the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open, - -=over 8 - -=item 1 - -serialise signal number, C<struct siginfo_t> (or at least the parts we care -about) into a small auto char buff - -=item 2 - -C<write()> that (non-blocking) to the writer fd - -=over 12 - -=item 1 - -if it writes 100%, flag the signal in a counter of "signals on the pipe" akin -to the current per-signal-number counts - -=item 2 - -if it writes 0%, assume the pipe is full. Flag the data as lost? - -=item 3 - -if it writes partially, croak a panic, as your OS is broken. - -=back - -=back - -=item 4 - -in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on -the pipe", read the data out, deserialise, build the Perl structures on -the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as -usual. - -=back - -I think that this gets us decent C<SA_SIGINFO> support, without the current risk -of running Perl code inside the signal handler context. (With all the dangers -of things like C<malloc> corruption that that currently offers us) - -For more information see the thread starting with this message: -L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html> - -=head2 autovivification - -Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict; - -This task is incremental - even a little bit of work on it will help. - -=head2 Unicode in Filenames - -chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open, -opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen, -system, truncate, unlink, utime, -X. All these could potentially accept -Unicode filenames either as input or output (and in the case of system -and qx Unicode in general, as input or output to/from the shell). -Whether a filesystem - an operating system pair understands Unicode in -filenames varies. - -Known combinations that have some level of understanding include -Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac -OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to -create Unicode filenames, what forms of Unicode are accepted and used -(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used, -and so on, varies. Finding the right level of interfacing to Perl -requires some thought. Remember that an OS does not implicate a -filesystem. - -(The Windows -C command flag "wide API support" has been at least -temporarily retired in 5.8.1, and the -C has been repurposed, see -L<perlrun>.) - -Most probably the right way to do this would be this: -L</"Virtualize operating system access">. - -=head2 Unicode in %ENV - -Currently the %ENV entries are always byte strings. -See L</"Virtualize operating system access">. - -=head2 Unicode and glob() - -Currently glob patterns and filenames returned from File::Glob::glob() -are always byte strings. See L</"Virtualize operating system access">. - -=head2 use less 'memory' - -Investigate trade offs to switch out perl's choices on memory usage. -Particularly perl should be able to give memory back. - -This task is incremental - even a little bit of work on it will help. - -=head2 Re-implement C<:unique> in a way that is actually thread-safe - -The old implementation made bad assumptions on several levels. A good 90% -solution might be just to make C<:unique> work to share the string buffer -of SvPVs. That way large constant strings can be shared between ithreads, -such as the configuration information in F<Config>. - -=head2 Make tainting consistent - -Tainting would be easier to use if it didn't take documented shortcuts and -allow taint to "leak" everywhere within an expression. - -=head2 readpipe(LIST) - -system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid -running a shell. readpipe() (the function behind qx//) could be similarly -extended. - -=head2 Audit the code for destruction ordering assumptions - -Change 25773 notes - - /* Need to check SvMAGICAL, as during global destruction it may be that - AvARYLEN(av) has been freed before av, and hence the SvANY() pointer - is now part of the linked list of SV heads, rather than pointing to - the original body. */ - /* FIXME - audit the code for other bugs like this one. */ - -adding the C<SvMAGICAL> check to - - if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) { - MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen); - -Go through the core and look for similar assumptions that SVs have particular -types, as all bets are off during global destruction. - -=head2 Extend PerlIO and PerlIO::Scalar - -PerlIO::Scalar doesn't know how to truncate(). Implementing this -would require extending the PerlIO vtable. - -Similarly the PerlIO vtable doesn't know about formats (write()), or -about stat(), or chmod()/chown(), utime(), or flock(). - -(For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership -would mean.) - -PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(), -opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(), -readlink(). - -See also L</"Virtualize operating system access">. - -=head2 -C on the #! line - -It should be possible to make -C work correctly if found on the #! line, -given that all perl command line options are strict ASCII, and -C changes -only the interpretation of non-ASCII characters, and not for the script file -handle. To make it work needs some investigation of the ordering of function -calls during startup, and (by implication) a bit of tweaking of that order. - -=head2 Organize error messages - -Perl's diagnostics (error messages, see L<perldiag>) could use -reorganizing and formalizing so that each error message has its -stable-for-all-eternity unique id, categorized by severity, type, and -subsystem. (The error messages would be listed in a datafile outside -of the Perl source code, and the source code would only refer to the -messages by the id.) This clean-up and regularizing should apply -for all croak() messages. - -This would enable all sorts of things: easier translation/localization -of the messages (though please do keep in mind the caveats of -L<Locale::Maketext> about too straightforward approaches to -translation), filtering by severity, and instead of grepping for a -particular error message one could look for a stable error id. (Of -course, changing the error messages by default would break all the -existing software depending on some particular error message...) - -This kind of functionality is known as I<message catalogs>. Look for -inspiration for example in the catgets() system, possibly even use it -if available-- but B<only> if available, all platforms will B<not> -have catgets(). - -For the really pure at heart, consider extending this item to cover -also the warning messages (see L<perllexwarn>, C<warnings.pl>). - -=head1 Tasks that need a knowledge of the interpreter - -These tasks would need C knowledge, and knowledge of how the interpreter works, -or a willingness to learn. - -=head2 forbid labels with keyword names - -Currently C<goto keyword> "computes" the label value: - - $ perl -e 'goto print' - Can't find label 1 at -e line 1. - -It is controversial if the right way to avoid the confusion is to forbid -labels with keyword names, or if it would be better to always treat -bareword expressions after a "goto" as a label and never as a keyword. - -=head2 truncate() prototype - -The prototype of truncate() is currently C<$$>. It should probably -be C<*$> instead. (This is changed in F<opcode.pl>) - -=head2 decapsulation of smart match argument - -Currently C<$foo ~~ $object> will die with the message "Smart matching a -non-overloaded object breaks encapsulation". It would be nice to allow -to bypass this by using explicitly the syntax C<$foo ~~ %$object> or -C<$foo ~~ @$object>. - -=head2 error reporting of [$a ; $b] - -Using C<;> inside brackets is a syntax error, and we don't propose to change -that by giving it any meaning. However, it's not reported very helpfully: - - $ perl -e '$a = [$b; $c];' - syntax error at -e line 1, near "$b;" - syntax error at -e line 1, near "$c]" - Execution of -e aborted due to compilation errors. - -It should be possible to hook into the tokeniser or the lexer, so that when a -C<;> is parsed where it is not legal as a statement terminator (ie inside -C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like -I<';' isn't legal inside an expression - if you need multiple statements use a -do {...} block>. See the thread starting at -L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html> - -=head2 lexicals used only once - -This warns: - - $ perl -we '$pie = 42' - Name "main::pie" used only once: possible typo at -e line 1. - -This does not: - - $ perl -we 'my $pie = 42' - -Logically all lexicals used only once should warn, if the user asks for -warnings. An unworked RT ticket (#5087) has been open for almost seven -years for this discrepancy. - -=head2 UTF-8 revamp - -The handling of Unicode is unclean in many places. In the regex engine -there are especially many problems. The swash data structure could be -replaced my something better. Inversion lists and maps are likely -candidates. The whole Unicode database could be placed in-core for a -huge speed-up. Only minimal work was done on the optimizer when utf8 -was added, with the result that the synthetic start class often will -fail to narrow down the possible choices when given non-Latin1 input. - -=head2 Properly Unicode safe tokeniser and pads. - -The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack - -variable names are stored in stashes as raw bytes, without the utf-8 flag -set. The pad API only takes a C<char *> pointer, so that's all bytes too. The -tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from -source filters. All this could be fixed. - -=head2 state variable initialization in list context - -Currently this is illegal: - - state ($a, $b) = foo(); - -In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different -semantics, which is tricky to implement in Perl 5 as currently they produce -the same opcode trees. The Perl 6 design is firm, so it would be good to -implement the necessary code in Perl 5. There are comments in -C<Perl_newASSIGNOP()> that show the code paths taken by various assignment -constructions involving state variables. - -=head2 Implement $value ~~ 0 .. $range - -It would be nice to extend the syntax of the C<~~> operator to also -understand numeric (and maybe alphanumeric) ranges. - -=head2 A does() built-in - -Like ref(), only useful. It would call the C<DOES> method on objects; it -would also tell whether something can be dereferenced as an -array/hash/etc., or used as a regexp, etc. -L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html> - -=head2 Tied filehandles and write() don't mix - -There is no method on tied filehandles to allow them to be called back by -formats. - -=head2 Propagate compilation hints to the debugger - -Currently a debugger started with -dE on the command-line doesn't see the -features enabled by -E. More generally hints (C<$^H> and C<%^H>) aren't -propagated to the debugger. Probably it would be a good thing to propagate -hints from the innermost non-C<DB::> scope: this would make code eval'ed -in the debugger see the features (and strictures, etc.) currently in -scope. - -=head2 Attach/detach debugger from running program - -The old perltodo notes "With C<gdb>, you can attach the debugger to a running -program if you pass the process ID. It would be good to do this with the Perl -debugger on a running Perl program, although I'm not sure how it would be -done." ssh and screen do this with named pipes in /tmp. Maybe we can too. - -=head2 LVALUE functions for lists - -The old perltodo notes that lvalue functions don't work for list or hash -slices. This would be good to fix. - -=head2 regexp optimiser optional - -The regexp optimiser is not optional. It should configurable to be, to allow -its performance to be measured, and its bugs to be easily demonstrated. - -=head2 C</w> regex modifier - -That flag would enable to match whole words, and also to interpolate -arrays as alternations. With it, C</P/w> would be roughly equivalent to: - - do { local $"='|'; /\b(?:P)\b/ } - -See -L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html> -for the discussion. - -=head2 optional optimizer - -Make the peephole optimizer optional. Currently it performs two tasks as -it walks the optree - genuine peephole optimisations, and necessary fixups of -ops. It would be good to find an efficient way to switch out the -optimisations whilst keeping the fixups. - -=head2 You WANT *how* many - -Currently contexts are void, scalar and list. split has a special mechanism in -place to pass in the number of return values wanted. It would be useful to -have a general mechanism for this, backwards compatible and little speed hit. -This would allow proposals such as short circuiting sort to be implemented -as a module on CPAN. - -=head2 lexical aliases - -Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>. - -=head2 entersub XS vs Perl - -At the moment pp_entersub is huge, and has code to deal with entering both -perl and XS subroutines. Subroutine implementations rarely change between -perl and XS at run time, so investigate using 2 ops to enter subs (one for -XS, one for perl) and swap between if a sub is redefined. - -=head2 Self-ties - -Self-ties are currently illegal because they caused too many segfaults. Maybe -the causes of these could be tracked down and self-ties on all types -reinstated. - -=head2 Optimize away @_ - -The old perltodo notes "Look at the "reification" code in C<av.c>". - -=head2 Virtualize operating system access - -Implement a set of "vtables" that virtualizes operating system access -(open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very -least these interfaces should take SVs as "name" arguments instead of -bare char pointers; probably the most flexible and extensible way -would be for the Perl-facing interfaces to accept HVs. The system -needs to be per-operating-system and per-file-system -hookable/filterable, preferably both from XS and Perl level -(L<perlport/"Files and Filesystems"> is good reading at this point, -in fact, all of L<perlport> is.) - -This has actually already been implemented (but only for Win32), -take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32 -variants go through a set of "vtables" for operating system access, -non-Win32 systems currently go straight for the POSIX/Unix-style -system/library call. Similar system as for Win32 should be -implemented for all platforms. The existing Win32 implementation -probably does not need to survive alongside this proposed new -implementation, the approaches could be merged. - -What would this give us? One often-asked-for feature this would -enable is using Unicode for filenames, and other "names" like %ENV, -usernames, hostnames, and so forth. -(See L<perlunicode/"When Unicode Does Not Happen">.) - -But this kind of virtualization would also allow for things like -virtual filesystems, virtual networks, and "sandboxes" (though as long -as dynamic loading of random object code is allowed, not very safe -sandboxes since external code of course know not of Perl's vtables). -An example of a smaller "sandbox" is that this feature can be used to -implement per-thread working directories: Win32 already does this. - -See also L</"Extend PerlIO and PerlIO::Scalar">. - -=head2 Investigate PADTMP hash pessimisation - -The peephole optimiser converts constants used for hash key lookups to shared -hash key scalars. Under ithreads, something is undoing this work. -See -L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html> - -=head2 Store the current pad in the OP slab allocator - -=for clarification -I hope that I got that "current pad" part correct - -Currently we leak ops in various cases of parse failure. I suggested that we -could solve this by always using the op slab allocator, and walking it to -free ops. Dave comments that as some ops are already freed during optree -creation one would have to mark which ops are freed, and not double free them -when walking the slab. He notes that one problem with this is that for some ops -you have to know which pad was current at the time of allocation, which does -change. I suggested storing a pointer to the current pad in the memory allocated -for the slab, and swapping to a new slab each time the pad changes. Dave thinks -that this would work. - -=head2 repack the optree - -Repacking the optree after execution order is determined could allow -removal of NULL ops, and optimal ordering of OPs with respect to cache-line -filling. The slab allocator could be reused for this purpose. I think that -the best way to do this is to make it an optional step just before the -completed optree is attached to anything else, and to use the slab allocator -unchanged, so that freeing ops is identical whether or not this step runs. -Note that the slab allocator allocates ops downwards in memory, so one would -have to actually "allocate" the ops in reverse-execution order to get them -contiguous in memory in execution order. - -See -L<http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html> - -Note that running this copy, and then freeing all the old location ops would -cause their slabs to be freed, which would eliminate possible memory wastage if -the previous suggestion is implemented, and we swap slabs more frequently. - -=head2 eliminate incorrect line numbers in warnings - -This code - - use warnings; - my $undef; - - if ($undef == 3) { - } elsif ($undef == 0) { - } - -used to produce this output: - - Use of uninitialized value in numeric eq (==) at wrong.pl line 4. - Use of uninitialized value in numeric eq (==) at wrong.pl line 4. - -where the line of the second warning was misreported - it should be line 5. -Rafael fixed this - the problem arose because there was no nextstate OP -between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still -reports that the currently executing line is line 4. The solution was to inject -a nextstate OPs for each C<elsif>, although it turned out that the nextstate -OP needed to be a nulled OP, rather than a live nextstate OP, else other line -numbers became misreported. (Jenga!) - -The problem is more general than C<elsif> (although the C<elsif> case is the -most common and the most confusing). Ideally this code - - use warnings; - my $undef; - - my $a = $undef + 1; - my $b - = $undef - + 1; - -would produce this output - - Use of uninitialized value $undef in addition (+) at wrong.pl line 4. - Use of uninitialized value $undef in addition (+) at wrong.pl line 7. - -(rather than lines 4 and 5), but this would seem to require every OP to carry -(at least) line number information. - -What might work is to have an optional line number in memory just before the -BASEOP structure, with a flag bit in the op to say whether it's present. -Initially during compile every OP would carry its line number. Then add a late -pass to the optimiser (potentially combined with L</repack the optree>) which -looks at the two ops on every edge of the graph of the execution path. If -the line number changes, flags the destination OP with this information. -Once all paths are traced, replace every op with the flag with a -nextstate-light op (that just updates C<PL_curcop>), which in turn then passes -control on to the true op. All ops would then be replaced by variants that -do not store the line number. (Which, logically, why it would work best in -conjunction with L</repack the optree>, as that is already copying/reallocating -all the OPs) - -(Although I should note that we're not certain that doing this for the general -case is worth it) - -=head2 optimize tail-calls - -Tail-calls present an opportunity for broadly applicable optimization; -anywhere that C<< return foo(...) >> is called, the outer return can -be replaced by a goto, and foo will return directly to the outer -caller, saving (conservatively) 25% of perl's call&return cost, which -is relatively higher than in C. The scheme language is known to do -this heavily. B::Concise provides good insight into where this -optimization is possible, ie anywhere entersub,leavesub op-sequence -occurs. - - perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)' - -Bottom line on this is probably a new pp_tailcall function which -combines the code in pp_entersub, pp_leavesub. This should probably -be done 1st in XS, and using B::Generate to patch the new OP into the -optrees. - -=head2 Add C<00dddd> - -It has been proposed that octal constants be specifiable through the syntax -C<0oddddd>, parallel to the existing construct to specify hex constants -C<0xddddd> - -=head1 Big projects - -Tasks that will get your name mentioned in the description of the "Highlights -of 5.14" - -=head2 make ithreads more robust - -Generally make ithreads more robust. See also L</iCOW> - -This task is incremental - even a little bit of work on it will help, and -will be greatly appreciated. - -One bit would be to determine how to clone directory handles on systems -without a C<fchdir> function (in sv.c:Perl_dirp_dup). - -Fix Perl_sv_dup, et al so that threads can return objects. - -=head2 iCOW - -Sarathy and Arthur have a proposal for an improved Copy On Write which -specifically will be able to COW new ithreads. If this can be implemented -it would be a good thing. - -=head2 (?{...}) closures in regexps - -Fix (or rewrite) the implementation of the C</(?{...})/> closures. - -=head2 Add class set operations to regexp engine - -Apparently these are quite useful. Anyway, Jeffery Friedl wants them. - -demerphq has this on his todo list, but right at the bottom. - - -=head1 Tasks for microperl - - -[ Each and every one of these may be obsolete, but they were listed - in the old Todo.micro file] - - -=head2 make creating uconfig.sh automatic - -=head2 make creating Makefile.micro automatic - -=head2 do away with fork/exec/wait? - -(system, popen should be enough?) - -=head2 some of the uconfig.sh really needs to be probed (using cc) in buildtime: - -(uConfigure? :-) native datatype widths and endianness come to mind - +We no longer install the Perl 5 to-do list as a manpage, as installing +snapshot that becomes increasingly out of date isn't that useful to anyone. +The current Perl 5 to-do list is maintained in the git repository, and can +be viewed at L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod> |