PERLTODO(1) Perl Programmers Reference Guide PERLTODO(1)NAMEperltodo - 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 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:
http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
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
timers.
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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
re-used?
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
tests.
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
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 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
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 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
way.
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
release".
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
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
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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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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. 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
be.
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.
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.
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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
expression.
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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.
UNITCHECK
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 =
\$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 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
"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 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.
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 "/(?{...})/" clo-
sures.
A re-entrant regexp engine
This will allow the use of a regex from inside (?{ }), (??{
}) and (?(?{ })|) constructs.
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