| =head1 NAME |
| |
| todo - 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:/Porting/todo.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 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. Steffen Schwingon would welcome help with |
| L<Benchmark::Perl::Formance> |
| |
| =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 makedef.pl and conditional compilation |
| |
| The script F<makedef.pl> that generates the list of exported symbols on |
| platforms which need this. Functions are declared in F<embed.fnc>, variables |
| in F<intrpvar.h>. Quite a few of the functions and variables are conditionally |
| declared there, using C<#ifdef>. However, F<makedef.pl> doesn't understand the |
| C macros, so the rules about which symbols are present when is duplicated in |
| the Perl code. Writing things twice is bad, m'kay. It would be good to teach |
| F<.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. |
| |
| =head2 document diagnostics |
| |
| Many diagnostic messages are not currently documented. The list is at the end |
| of t/porting/diag.t. |
| |
| =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<install.html> 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 |
| |
| Improving the code that split C<perlfunc> into chunks, preferably with |
| general case code added to L<Pod::Functions> 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. Currently this works reasonably well in the general case, and correctly |
| parses two or more C<=items> giving the different parameter lists for the |
| same function, such used by C<substr>. However it fails completely where |
| I<different> functions are listed as a sequence of C<=items> but share the |
| same description. All the functions from C<getpwnam> to C<endprotoent> have |
| individual stub pages, with only the page for C<endservent> holding the |
| description common to all. Likewise C<q>, C<qq> and C<qw> have stub pages, |
| instead of sharing the body of C<qx>. |
| |
| Note also the current code isn't ideal with the two forms of C<select>, mushing |
| them both into one F<select.html> with the two descriptions run together. |
| Fixing this may well be a special case. |
| |
| =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. Florian Ragwitz has been working |
| to offer this for the GNU toolchain, to 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. See the branch smoke-me/rafl/ld_export |
| |
| =head2 Cross-compile support |
| |
| We get requests for "how to cross compile Perl". The vast majority of these |
| seem to be for a couple of scenarios: |
| |
| =over 4 |
| |
| =item * |
| |
| Platforms that could build natively using F<./Configure> (I<e.g.> Linux or |
| NetBSD on MIPS or ARM) but people want to use a beefier machine (and on the |
| same OS) to build more easily. |
| |
| =item * |
| |
| Platforms that can't build natively, but no (significant) porting changes |
| are needed to our current source code. Prime example of this is Android. |
| |
| =back |
| |
| There are several scripts and tools for cross-compiling perl for other |
| platforms. However, these are somewhat inconsistent and scattered across the |
| codebase, none are documented well, none are clearly flexible enough to |
| be confident that they can support any TARGET/HOST plaform pair other than |
| that which they were developed on, and it's not clear how bitrotted they are. |
| |
| For example, 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 code is almost 10 years old. Meanwhile, the |
| F<Cross/> directory contains two different approaches for cross compiling to |
| ARM Linux targets, relying on hand curated F<config.sh> files, but that code |
| is getting on for 5 years old, and requires insider knowledge of perl's |
| build system to draft a F<config.sh> for a new platform. |
| |
| Jess Robinson has sumbitted a grant to TPF to work on cleaning this up. |
| |
| =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. |
| |
| =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 -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 5.18.0. |
| |
| =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 F<win32/wince.c> and F<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 |
| |
| Recent glibcs support C<-D_FORTIFY_SOURCE=2> which gives |
| protection against various kinds of buffer overflow problems. |
| It should probably be used for compiling Perl whenever available, |
| Configure and/or hints files should be adjusted to probe for the |
| availability of these feature and enable it 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 Document how XSUBs can use C<cv_set_call_checker> to inline themselves as OPs |
| |
| For a simple XSUB, often the subroutine dispatch takes more time than the |
| XSUB itself. v5.14.0 now allows XSUBs to register a function which will be |
| called when the parser is finished building an C<entersub> op which calls |
| them. |
| |
| Registration is done with C<Perl_cv_set_call_checker>, is documented at the |
| API level in L<perlapi>, and L<perl5140delta/Custom per-subroutine check hooks> |
| notes that it can be used to inline a subroutine, by replacing it with a |
| custom op. However there is no further detail of the code needed to do this. |
| It would be useful to add one or more annotated examples of how to create |
| XSUBs that inline. |
| |
| This 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 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<*$> instead. (This is changed in F<opcode.pl>) |
| |
| =head2 error reporting of [$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 $pie = 42' |
| |
| Logically all lexicals used only once should warn, if the user asks for |
| warnings. An unworked RT ticket (#5087) has been open for almost seven |
| years for this discrepancy. |
| |
| =head2 UTF-8 revamp |
| |
| The handling of Unicode is unclean in many places. In the regex engine |
| there are especially many problems. The swash data structure could be |
| replaced my something better. Inversion lists and maps are likely |
| candidates. The whole Unicode database could be placed in-core for a |
| huge speed-up. Only minimal work was done on the optimizer when utf8 |
| was added, with the result that the synthetic start class often will |
| fail to narrow down the possible choices when given non-Latin1 input. |
| Karl Williamson has been working on this - talk to him. |
| |
| =begin todo |
| |
| Many things are fixed, but is these still true? |
| |
| The tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs |
| returned from source filters. |
| |
| =end |
| |
| =head2 state variable initialization in list context |
| |
| Currently this is illegal: |
| |
| state ($a, $b) = foo(); |
| |
| In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different |
| semantics, which is tricky to implement in Perl 5 as currently they produce |
| the same opcode trees. The Perl 6 design is firm, so it would be good to |
| implement the necessary code in Perl 5. There are comments in |
| C<Perl_newASSIGNOP()> that show the code paths taken by various assignment |
| constructions involving state variables. |
| |
| =head2 A does() built-in |
| |
| Like ref(), only useful. It would call the C<DOES> method on objects; it |
| would also tell whether something can be dereferenced as an |
| array/hash/etc., or used as a regexp, etc. |
| L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html> |
| |
| =head2 Tied filehandles and write() don't mix |
| |
| There is no method on tied filehandles to allow them to be called back by |
| formats. |
| |
| =head2 Propagate compilation hints to the debugger |
| |
| Currently a debugger started with -dE on the command-line doesn't see the |
| features enabled by -E. More generally hints (C<$^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 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 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<0odddd> |
| |
| 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 5.18.0" |
| |
| =head2 make ithreads more robust |
| |
| Generally make ithreads more robust. |
| |
| 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 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 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 |
| |