MirBSD manpage: perltodo(1)

PERLTODO(1)     Perl Programmers Reference Guide      PERLTODO(1)


     perltodo - Perl TO-DO List


     This is a list of wishes for Perl. 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
     perl5-porters@perl.org to avoid duplication of effort. 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:


     What can we offer you in return? Fame, fortune, and ever-
     lasting glory? Maybe not, but if your patch is incorporated,
     then we'll add your name to the AUTHORS file, which ships in
     the official distribution. How many other programming
     languages offer you 1 line of immortality?

The roadmap to 5.10
     The roadmap to 5.10 envisages feature based releases, as
     various items in this TODO are completed.

     Needed for a 5.9.4 release

     +   Review assertions. Review syntax to combine assertions.
         Assertions could take advantage of the lexical pragmas
         work. "What hooks would assertions need?"

     Needed for a 5.9.5 release

     * Implement "_ prototype character"
     * Implement "state variables"

     Needed for a 5.9.6 release

     Stabilisation. If all goes well, this will be the equivalent
     of a 5.10-beta.

Tasks that only need Perl knowledge

     common test code for timed bail out

     Write portable self destruct code for tests to stop them
     burning CPU in infinite loops. This needs to avoid using
     alarm, as some of the tests are testing alarm/sleep or

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     POD -> 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 as simple as it
     sounds, particularly with the flexibility POD allows for
     "=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 "make HTML install work", as the layout of
     installation tree is needed to improve the cross-linking.

     The addition of "Pod::Simple" and its related modules may
     make this task easier to complete.

     Parallel testing

     The core regression test suite is getting ever more
     comprehensive, which has the side effect that it takes
     longer to run. This isn't so good. Investigate whether it
     would be feasible to give the harness script the option of
     running sets of tests in parallel. This would be useful for
     tests in t/op/*.t and t/uni/*.t and maybe some sets of tests
     in lib/.

     Questions to answer

     1   How does screen layout work when you're running more
         than one test?

     2   How does the caller of test specify how many tests to
         run in parallel?

     3   How do setup/teardown tests identify themselves?

     Pugs already does parallel testing - can their approach be

     Make Schwern poorer

     We should have 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.

     See t/lib/1_compile.t for the 3 remaining modules that need

     Improve the coverage of the core tests

     Use Devel::Cover to ascertain the core's test coverage, then
     add tests that are currently missing.

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     test B

     A full test suite for the B module would be nice.

     A decent benchmark

     "perlbench" seems impervious to any recent changes made to
     the perl core. It would be useful to have a reasonable gen-
     eral 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.

     fix tainting bugs

     Fix the bugs revealed by running the test suite with the
     "-t" switch (via "make test.taintwarn").

     Dual life everything

     As part of the "dists" plan, anything that doesn't belong in
     the smallest perl distribution needs to be dual lifed. Any-
     thing 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 prob-
     lems you find.

     Improving "threads::shared"

     Investigate whether "threads::shared" could share aggregates
     properly with only Perl level changes to shared.pm

     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.

Tasks that need a little sysadmin-type knowledge
     Or if you prefer, tasks that you would learn from, and
     broaden your skills base...

     Relocatable perl

     The C level patches needed to create a relocatable perl
     binary are done, as is the work on Config.pm. All that's
     left to do is the "Configure" tweaking to let people specify
     how they want to do the install.

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     make HTML install work

     There is an "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

     1   Checking that cross linking between various parts of the
         documentation works. In particular that links work
         between the modules (files with POD in lib/) and the
         core documentation (files in pod/)

     2   Work out how to split "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
         "-X", groups such as "getpwnam" to "endservent", two or
         more "=items" giving the different parameter lists, such

             =item substr EXPR,OFFSET,LENGTH,REPLACEMENT

             =item substr EXPR,OFFSET,LENGTH

             =item substr EXPR,OFFSET

         and different parameter lists having different meanings.
         (eg "select")

     compressed man pages

     Be able to install them. This would probably need a config-
     ure test to see how the system does compressed man pages
     (same directory/different directory? same filename/different
     filename), as well as tweaking the installman script to
     compress as necessary.

     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

     +   do a normal "Configure", but include Devel::Cover as a
         module to install (see INSTALL for how to do this)

             make perl

             cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness

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     +   Process the resulting Devel::Cover database

     This just give you the coverage of the .pms. To also get the
     C level coverage you need to

     +   Additionally tell "Configure" to use the appropriate C
         compiler flags for "gcov"

             make perl.gcov

         (instead of "make perl")

     +   After running the tests run "gcov" to generate all the
         .gcov files. (Including down in the subdirectories of

     +   (From the top level perl directory) run "gcov2perl" on
         all the ".gcov" files to get their stats into the
         cover_db directory.

     +   Then process the Devel::Cover database

     It would be good to add a single switch to "Configure" to
     specify that you wanted to perform perl level coverage, and
     another to specify C level coverage, and have "Configure"
     and the Makefile do all the right things automatically.

     Make Config.pm cope with differences between build 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 interro-
     gates %Config, so in this situation %Config describes com-
     pilers that aren't there, and extension building fails. This
     forces people into choosing between re-compiling perl them-
     selves using the compiler they have, or only using modules
     that the vendor ships.

     It would be good to find a way teach "Config.pm" about the
     installation setup, possibly involving probing at install
     time or later, so that the %Config in a binary distribution
     better describes the installed machine, when the installed
     machine differs from the build machine in some significant

     make parallel builds work

     Currently parallel builds (such as "make -j3") don't work
     reliably. We believe that this is due to incomplete depen-
     dency specification in the Makefile. It would be good if

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     someone were able to track down the causes of these prob-
     lems, so that parallel builds worked properly.

     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 gen-
     erating 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 makedef.pl to support
     this format, and to provide a means within "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.

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

     Make it clear from -v if this is the exact official release

     Currently perl from "p4"/"rsync" ships with a patchlevel.h
     file that usually defines one local patch, of the form
     "MAINT12345" or "RC1". The output of perl -v doesn't report
     that a perl isn't an official release, and this information
     can get lost in bugs reports. Because of this, the minor
     version isn't bumped up until RC time, to minimise the pos-
     sibility of versions of perl escaping that believe them-
     selves to be newer than they actually are.

     It would be useful to find an elegant way to have the "this
     is an interim maintenance release" or "this is a release
     candidate" in the terse -v output, and have it so that it's
     easy for the pumpking to remove this just as the release
     tarball is rolled up. This way the version pulled out of
     rsync would always say "I'm a development release" and it
     would be safe to bump the reported minor version as soon as
     a release ships, which would aid perl developers.

     This task is really about thinking of an elegant way to
     arrange the C source such that it's trivial for the Pumpking
     to flag "this is an official release" when making a tarball,
     yet leave the default source saying "I'm not the official

     Tidy up global variables

     There's a note in intrpvar.h

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       /* These two variables are needed to preserve 5.8.x bincompat because
          we can't change function prototypes of two exported functions.
          Probably should be taken out of blead soon, and relevant prototypes
          changed.  */

     So doing this, and removing any of the unused variables
     still present would be good.

     Ordering of "global" variables.

     thrdvar.h and intrpvarh define the "global" variables that
     need to be per-thread under ithreads, where the variables
     are actually elements in a structure. As C dictates, the
     variables must be laid out in order of declaration. There is
     a comment "/* Important ones in the first cache line (if
     alignment is done right) */" which implies that at some
     point in the past the ordering was carefully chosen (at
     least in part). However, it's clear that the ordering is
     less than perfect, as currently there are things such as 7
     "bool"s in a row, then something typically requiring 4 byte
     alignment, and then an odd "bool" later on. ("bool"s are
     typically defined as "char"s). So it would be good for some-
     one to review the ordering of the variables, to see how much
     alignment padding can be removed.

     bincompat functions

     There are lots of functions which are retained for binary
     compatibility. Clean these up. Move them to mathom.c, and
     don't compile for blead?

     am I hot or not?

     The idea of pp_hot.c is that it contains the hot ops, the
     ops that are most commonly used. The idea is that by group-
     ing them, their object code will be adjacent in the execut-
     able, 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 com-
     monly used ops. So anyone feeling like exercising their
     skill with coverage and profiling tools might want to deter-
     mine what ops really are the most commonly used. And in turn
     suggest evictions and promotions to achieve a better

     emulate the per-thread memory pool on Unix

     For Windows, ithreads allocates memory for each thread from
     a separate pool, which it discards at thread exit. It also
     checks that memory is free()d to the correct pool. Neither

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     check is done on Unix, so code developed there won't be sub-
     ject to such strictures, so can harbour bugs that only show
     up when the code reaches Windows.

     It would be good to be able to optionally emulate the Window
     pool system on Unix, to let developers who only have access
     to Unix, or want to use Unix-specific debugging tools, check
     for these problems. To do this would involve figuring out
     how the "PerlMem_*" macros wrap "malloc()" access, and pro-
     viding a layer that records/checks the identity of the
     thread making the call, and recording all the memory allo-
     cated by each thread via this API so that it can be sum-
     marily free()d at thread exit. One implementation idea would
     be to increase the size of allocation, and store the
     "my_perl" pointer (to identify the thread) at the start,
     along with pointers to make a linked list of blocks for this
     thread. To avoid alignment problems it would be necessary to
     do something like

       union memory_header_padded {
         struct memory_header {
           void *thread_id;   /* For my_perl */
           void *next;        /* Pointer to next block for this thread */
         } data;
         long double padding; /* whatever type has maximal alignment constraint */

     although "long double" might not be the only type to add to
     the padding union.

     reduce duplication in sv_setsv_flags

     "Perl_sv_setsv_flags" has a comment "/* There's a lot of
     redundancy below but we're going for speed here */"

     Whilst this was true 10 years ago, the growing disparity
     between RAM and CPU speeds mean that the trade offs have
     changed. In addition, the duplicate code adds to the mainte-
     nance burden. It would be good to see how much of the redun-
     dancy can be pruned, particular in the less common paths.
     (Profiling tools at the ready...). For example, why does the
     test for "Can't redefine active sort subroutine" need to
     occur in two places?

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.

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     Clean this up. Check everything in core works

     shrink "GV"s, "CV"s

     By removing unused elements and careful re-ordering, the
     structures for "AV"s and "HV"s have recently been shrunk
     considerably. It's probable that the same approach would
     find savings in "GV"s and "CV"s, if not all the other
     larger-than-"PVMG" types.

     merge Perl_sv_2[inpu]v

     There's a lot of code shared between "Perl_sv_2iv_flags",
     "Perl_sv_2uv_flags", "Perl_sv_2nv", and "Perl_sv_2pv_flags".
     It would be interesting to see if some of it can be merged
     into common shared static functions. In particular,
     "Perl_sv_2uv_flags" started out as a cut&paste from
     "Perl_sv_2iv_flags" around 5.005_50 time, and it may be pos-
     sible to replace both with a single function that returns a
     value or union which is split out by the macros in sv.h

     UTF8 caching code

     The string position/offset cache is not optional. It should

     Implicit Latin 1 => Unicode translation

     Conversions from byte strings to UTF-8 currently map high
     bit characters to Unicode without translation (or, depending
     on how you look at it, by implicitly assuming that the byte
     strings are in Latin-1). As perl assumes the C locale by
     default, upgrading a string to UTF-8 may change the meaning
     of its contents regarding character classes, case mapping,
     etc. This should probably emit a warning (at least).

     This task is incremental - even a little bit of work on it
     will help.


     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.

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     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 impli-
     cate 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 perlrun.)

     Unicode in %ENV

     Currently the %ENV entries are always byte strings.

     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.

     Re-implement ":unique" in a way that is actually thread-safe

     The old implementation made bad assumptions on several lev-
     els. A good 90% solution might be just to make ":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 Config.

     Make tainting consistent

     Tainting would be easier to use if it didn't take documented
     shortcuts and allow taint to "leak" everywhere within an

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     system() accepts a LIST syntax (and a PROGRAM LIST syntax)
     to avoid running a shell. readpipe() (the function behind
     qx//) could be similarly extended.

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.

     lexical pragmas

     Document the new support for lexical pragmas in 5.9.3 and
     how %^H works. Maybe "re", "encoding", maybe other pragmas
     could be made lexical.

     Attach/detach debugger from running program

     The old perltodo notes "With "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.

     Constant folding

     The peephole optimiser should trap errors during constant
     folding, and give up on the folding, rather than bailing out
     at compile time.  It is quite possible that the unfoldable
     constant is in unreachable code, eg something akin to "$a =
     0/0 if 0;"

     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.

     LVALUE functions in the debugger

     The old perltodo notes that lvalue functions don't work in
     the debugger. This would be good to fix.

     _ prototype character

     Study the possibility of adding a new prototype character,
     "_", meaning "this argument defaults to $_".

     state variables

     "my $foo if 0;" is deprecated, and should be replaced with
     "state $x = "initial value\n";" the syntax from Perl 6.

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     @INC source filter to Filter::Simple

     The second return value from a sub in @INC can be a source
     filter. This isn't documented. It should be changed to use
     Filter::Simple, tested and documented.

     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.


     Introduce a new special block, UNITCHECK, which is run at
     the end of a compilation unit (module, file, eval(STRING)
     block). This will correspond to the Perl 6 CHECK. Perl 5's
     CHECK cannot be changed or removed because the O.pm/B.pm
     backend framework depends on it.

     optional optimizer

     Make the peephole optimizer optional. Currently it performs
     two tasks as it walks the optree - genuine peephole optimi-
     sations, and necessary fixups of ops. It would be good to
     find an efficient way to switch out the optimisations whilst
     keeping the fixups.

     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 mechan-
     ism 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.

     lexical aliases

     Allow lexical aliases (maybe via the syntax "my \$alias =

     entersub XS vs Perl

     At the moment pp_entersub is huge, and has code to deal with
     entering both perl and XS subroutines. Subroutine implemen-
     tations 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.

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     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 re- instated.

     Optimize away @_

     The old perltodo notes "Look at the "reification" code in

     What hooks would assertions need?

     Assertions are in the core, and work. However, assertions
     needed to be added as a core patch, rather than an XS module
     in ext, or a CPAN module, because the core has no hooks in
     the necessary places. It would be useful to investigate what
     hooks would need to be added to make it possible to provide
     the full assertion support from a CPAN module, so that we
     aren't constraining the imagination of future CPAN authors.

Big projects

     Tasks that will get your name mentioned in the description
     of the "Highlights of 5.10"

     make ithreads more robust

     Generally make ithreads more robust. See also "iCOW"

     This task is incremental - even a little bit of work on it
     will help, and will be greatly appreciated.


     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.

     (?{...}) closures in regexps

     Fix (or rewrite) the implementation of the "/(?{...})/" clo-

     A re-entrant regexp engine

     This will allow the use of a regex from inside (?{ }), (??{
     }) and (?(?{ })|) constructs.

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