PERLTODO(1) Perl Programmers Reference Guide PERLTODO(1)
NAME
perltodo - Perl TO-DO List
DESCRIPTION
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
its 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:
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 well 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 timers.
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. Its 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 isnt 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 youre running more than one test?
2 How does the caller of test specify how many tests to run in paral
lel?
3 How do setup/teardown tests identify themselves?
Pugs already does parallel testing - can their approach be re-used?
Make Schwern poorer
We should have for everything. When all the cores 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 tests.
Improve the coverage of the core tests
Use Devel::Cover to ascertain the cores test coverage, then add tests
that are currently missing.
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 general benchmarking
suite that roughly represented what current perl programs do, and mea
surably reported whether tweaks to the core improve, degrade or dont
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 doesnt belong in the small
est 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.
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 theres 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 thats left to do is the "Con
figure" tweaking to let people specify how they want to do the install.
make HTML install work
There is an "installhtml" target in the Makefile. Its marked as
"experimental". It would be good to get this tested, make it work reli
ably, and remove the "experimental" tag. This would include
1 Checking that cross linking between various parts of the documenta
tion 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 as
=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 configure 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 cores 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
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 ext/
(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 interrogates %Config, so in this situa
tion %Config describes compilers that arent 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 "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 way.
make parallel builds work
Currently parallel builds (such as "make -j3") dont work reliably. We
believe that this is due to incomplete dependency specification in the
Makefile. It would be good if someone were able to track down the
causes of these problems, so that parallel builds worked properly.
linker specification files
Some platforms mandate that you provide a list of a shared librarys
external symbols to the linker, so the core already has the infrastruc
ture 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 makedef.pl to support this for
mat, 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 dont need any spe
cific 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 doesnt report that a perl isnt an official release,
and this information can get lost in bugs reports. Because of this, the
minor version isnt bumped up until RC time, to minimise the possibil
ity of versions of perl escaping that believe themselves 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 its easy for the pumpking to
remove this just as the release tarball is rolled up. This way the ver
sion pulled out of rsync would always say "Im 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 its trivial for the Pumpking to flag "this is an
official release" when making a tarball, yet leave the default source
saying "Im not the official release".
Tidy up global variables
Theres a note in intrpvar.h
/* These two variables are needed to preserve 5.8.x bincompat because
we cant 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). How
ever, its 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 someone 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 compatibil
ity. Clean these up. Move them to mathom.c, and dont 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 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 its not clear if these really are the most commonly used
ops. So anyone feeling like exercising their skill with coverage and
profiling tools might want to determine what ops really are the most
commonly used. And in turn suggest evictions and promotions to achieve
a better pp_hot.c.
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 check is done on Unix, so code
developed there wont be subject 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 sys
tem 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 providing a layer that records/checks the identity of the
thread making the call, and recording all the memory allocated by each
thread via this API so that it can be summarily 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 "/* Theres a lot of redundancy
below but were 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 maintenance burden. It would be good to see
how much of the redundancy can be pruned, particular in the less common
paths. (Profiling tools at the ready...). For example, why does the
test for "Cant 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 inter
face to C.
IPv6
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. Its 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
Theres 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
possible 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 be.
Implicit Latin 1 => Unicode translation
Conversions from byte strings to UTF-8 currently map high bit charac
ters 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.
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.
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 cre
ate 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 tem
porarily retired in 5.8.1, and the -C has been repurposed, see perl
run.)
Unicode in %ENV
Currently the %ENV entries are always byte strings.
use less memory
Investigate trade offs to switch out perls 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 levels. 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 didnt take documented shortcuts
and allow taint to "leak" everywhere within an expression.
readpipe(LIST)
system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
running a shell. readpipe() (the function behind qx//) could be simi
larly extended.
Tasks that need a knowledge of the interpreter
These tasks would need C knowledge, and knowledge of how the inter
preter 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 lexi
cal.
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 Im 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 dont work for list or
hash slices. This would be good to fix.
LVALUE functions in the debugger
The old perltodo notes that lvalue functions dont work in the debug
ger. 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.
@INC source filter to Filter::Simple
The second return value from a sub in @INC can be a source filter. This
isnt 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 demon
strated.
UNITCHECK
Introduce a new special block, UNITCHECK, which is run at the end of a
compilation unit (module, file, eval(STRING) block). This will corre
spond to the Perl 6 CHECK. Perl 5s 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 optimisations, 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 mech
anism 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 cir
cuiting sort to be implemented as a module on CPAN.
lexical aliases
Allow lexical aliases (maybe via the syntax "my \$alias = \$foo".
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.
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 "av.c"".
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 mod
ule, 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 pos
sible to provide the full assertion support from a CPAN module, so that
we arent 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.
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.
(?{...}) closures in regexps
Fix (or rewrite) the implementation of the "/(?{...})/" closures.
A re-entrant regexp engine
This will allow the use of a regex from inside (?{ }), (??{ }) and
(?(?{ })|) constructs.
perl v5.8.8 2008-04-25 PERLTODO(1)
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