NAME
perltodo - Perl TO-DO List
DESCRIPTION
This is a list of wishes for Perl. The most up to date version of this
file is at
http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod
The tasks we think are smaller or easier are listed first. Anyone is
welcome to work on any of these, but it’s a good idea to first contact
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:
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 AUTHORS file, which ships in the official distribution. How many
other programming languages offer you 1 line of immortality?
Tasks that only need Perl knowledge
Remove macperl references from tests
MacPerl is gone. The tests don’t need to be there.
Remove duplication of test setup.
Schwern notes, that there’s duplication of code - lots and lots of
tests have some variation on the big block of $Is_Foo checks. We can
safely put this into a file, change it to build an %Is hash and require
it. Maybe just put it into test.pl. Throw in the handy tainting
subroutines.
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.
Make ExtUtils::ParseXS use strict;
lib/ExtUtils/ParseXS.pm contains this line
# use strict; # One of these days...
Simply uncomment it, and fix all the resulting issues :-)
The more practical approach, to break the task down into manageable
chunks, is to work your way though the code from bottom to top, or if
necessary adding extra "{ ... }" blocks, and turning on strict within
them.
Parallel testing
(This probably impacts much more than the core: also the Test::Harness
and TAP::* modules on CPAN.)
All of the tests in t/ can now be run in parallel, if $ENV{TEST_JOBS}
is set. However, tests within each directory in ext and lib are still
run in series, with directories run in parallel. This is an adequate
heuristic, but it might be possible to relax it further, and get more
throughput. Specifically, it would be good to audit all of lib/*.t, and
make them use "File::Temp".
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.
Improve the coverage of the core tests
Use Devel::Cover to ascertain the core modules’s 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
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. 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
t/lib/commonsense.t.
Bundle dual life modules in ext/
For maintenance (and branch merging) reasons, it would be useful to
move some architecture-independent dual-life modules from lib/ to ext/,
if this has no negative impact on the build of perl itself.
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.
embed.pl/makedef.pl
There is a script embed.pl that generates several header files to
prefix all of Perl’s symbols in a consistent way, to provide some
semblance of namespace support in "C". Functions are declared in
embed.fnc, variables in interpvar.h. Quite a few of the functions and
variables are conditionally declared there, using "#ifdef". However,
embed.pl doesn’t understand the C macros, so the rules about which
symbols are present when is duplicated in makedef.pl. Writing things
twice is bad, m’kay. It would be good to teach "embed.pl" to
understand the conditional compilation, and hence remove the
duplication, and the mistakes it has caused.
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 "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.
profile installman
The 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.
Tasks that need a little sysadmin-type knowledge
Or if you prefer, tasks that you would learn from, and broaden your
skills base...
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 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 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
· 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 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 %Config, so in this
situation %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 "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.
linker specification files
Some platforms mandate that you provide a list of a shared library’s
external symbols to the linker, so the core already has the
infrastructure in place to do this for generating shared perl
libraries. My understanding is that the GNU toolchain can accept an
optional linker specification file, and restrict visibility just to
symbols declared in that file. It would be good to extend 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.
Cross-compile support
Currently "Configure" understands "-Dusecrosscompile" option. This
option arranges for building "miniperl" for TARGET machine, so this
"miniperl" is assumed then to be copied to TARGET machine and used as a
replacement of full "perl" executable.
This could be done little differently. Namely "miniperl" should be
built for HOST and then full "perl" with extensions should be compiled
for TARGET. This, however, might require extra trickery for %Config:
we have one config first for HOST and then another for TARGET. Tools
like MakeMaker will be mightily confused. Having around two different
types of executables and libraries (HOST and TARGET) makes life
interesting for Makefiles and shell (and Perl) scripts. There is
$Config{run}, normally empty, which can be used as an execution
wrapper. Also note that in some cross-compilation/execution
environments the HOST and the TARGET do not see the same filesystem(s),
the $Config{run} may need to do some file/directory copying back and
forth.
roffitall
Make pod/roffitall be updated by pod/buildtoc.
Split "linker" from "compiler"
Right now, Configure probes for two commands, and sets two variables:
· "cc" (in 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 cc and gcc. Fervent ANSI
compilers may be called c89. AIX has xlc.
· "ld" (in dlsrc.U)
This variable indicates the program to be used to link libraries
for dynamic loading. On some systems, it is ld. On ELF systems,
it should be $cc. Mostly, we’ll try to respect the hint file
setting.
There is an implicit historical assumption from around Perl5.000alpha
something, that $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 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 Configure, and centralise
all the special case logic there or in hints files.
A small bikeshed issue remains - what to call it, given that $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 $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 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
$Config{link} and institute a fall-back plan if it weren’t found."
Although I can see that as confusing, given that $Config{d_link} is
true when (hard) links are available.
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.
decouple -g and -DDEBUGGING
Currently Configure automatically adds "-DDEBUGGING" to the C compiler
flags if it spots "-g" in the optimiser flags. The pre-processor
directive "DEBUGGING" enables perl’s command line <-D> options, but in
the process makes perl slower. It would be good to disentangle this
logic, so that C-level debugging with "-g" and Perl level debugging
with "-D" can easily be enabled independently.
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
Weed out needless PERL_UNUSED_ARG
The C code uses the macro "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 "PERL_UNUSED_ARG" could be removed. Specifically
· The prototypes of (nearly all) static functions can be changed
· Unused arguments generated by short cut macros are wasteful - the
short cut macro used can be changed.
Modernize the order of directories in @INC
The way @INC is laid out by default, one cannot upgrade core (dual-
life) modules without overwriting files. This causes problems for
binary package builders. One possible proposal is laid out in this
message:
<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.
-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 5.12.
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 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 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 really are the most commonly
used. And in turn suggest evictions and promotions to achieve a better
pp_hot.c.
One piece of Perl code that might make a good testbed is installman.
Allocate OPs from arenas
Currently all new OP structures are individually malloc()ed and
free()d. All "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 "-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 "Profile Perl - am I hot or not?".
Improve win32/wince.c
Currently, numerous functions look virtually, if not completely,
identical in both "win32/wince.c" and "win32/win32.c" files, which
can’t be good.
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.
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:
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().)
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 your platform is
using those naughty interfaces.
-D_FORTIFY_SOURCE=2, -fstack-protector
Recent glibcs support "-D_FORTIFY_SOURCE=2" and recent gcc (4.1
onwards?) supports "-fstack-protector", both of which give protection
against various kinds of buffer overflow problems. These should
probably be used for compiling Perl whenever available, Configure
and/or hints files should be adjusted to probe for the availability of
these features and enable them as appropriate.
Arenas for GPs? For MAGIC?
"struct gp" and "struct magic" are both currently allocated by
"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, "GP"s can probably be changed with minimal
compatibility impact (probably nothing outside of the core, or even
outside of gv.c allocates them), but they probably aren’t
allocated/deallocated often enough for a speed saving. Whereas "MAGIC"
is allocated/deallocated more often, but in turn, is also something
more externally visible, so changing the rules here may bite external
code.
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.
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.
Remove the use of SVs as temporaries in dump.c
dump.c contains debugging routines to dump out the contains of perl
data structures, such as "SV"s, "AV"s and "HV"s. Currently, the dumping
code uses "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 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 "malloc". The 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 "SV"s for its buffers, use of which can cause problems similar to
those of dump.c, at similar times.
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
1. Provide global variables for two file descriptors
2. When the first request is made via "sigaction" for "SA_SIGINFO",
create a pipe, store the reader in one, the writer in the other
3. In the "safe" signal handler
("Perl_csighandler()"/"S_raise_signal()"), if the "siginfo_t"
pointer non-"NULL", and the writer file handle is open,
1. serialise signal number, "struct siginfo_t" (or at least
the parts we care about) into a small auto char buff
2. "write()" that (non-blocking) to the writer fd
1. if it writes 100%, flag the signal in a counter
of "signals on the pipe" akin to the current
per-signal-number counts
2. if it writes 0%, assume the pipe is full. Flag
the data as lost?
3. if it writes partially, croak a panic, as your
OS is broken.
4. in the regular "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 "Perl_sighandler()", the
"unsafe" handler), and call as usual.
I think that this gets us decent "SA_SIGINFO" support, without the
current risk of running Perl code inside the signal handler context.
(With all the dangers of things like "malloc" corruption that that
currently offers us)
For more information see the thread starting with this message:
http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg003.html
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
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
perlrun.)
Most probably the right way to do this would be this: "Virtualize
operating system access".
Unicode in %ENV
Currently the %ENV entries are always byte strings. See "Virtualize
operating system access".
Unicode and glob()
Currently glob patterns and filenames returned from File::Glob::glob()
are always byte strings. See "Virtualize operating system access".
Unicode and lc/uc operators
Some built-in operators ("lc", "uc", etc.) behave differently, based on
what the internal encoding of their argument is. That should not be the
case. Maybe add a pragma to switch behaviour.
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 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 didn’t 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
similarly extended.
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 "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.
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 "Virtualize operating system access".
-C on the #! line
It should be possible to make -C work correctly if found on the #!
line, given that all perl command line options are strict ASCII, and -C
changes only the interpretation of non-ASCII characters, and not for
the script file handle. To make it work needs some investigation of the
ordering of function calls during startup, and (by implication) a bit
of tweaking of that order.
Duplicate logic in S_method_common() and Perl_gv_fetchmethod_autoload()
A comment in "S_method_common" notes
/* This code tries to figure out just what went wrong with
gv_fetchmethod. It therefore needs to duplicate a lot of
the internals of that function. We can't move it inside
Perl_gv_fetchmethod_autoload(), however, since that would
cause UNIVERSAL->can("NoSuchPackage::foo") to croak, and we
don't want that.
*/
If "Perl_gv_fetchmethod_autoload" gets rewritten to take (more) flag
bits, then it ought to be possible to move the logic from
"S_method_common" to the "right" place. When making this change it
would probably be good to also pass in at least the method name length,
if not also pre-computed hash values when known. (I’m contemplating a
plan to pre-compute hash values for common fixed strings such as "ISA"
and pass them in to functions.)
Organize error messages
Perl’s diagnostics (error messages, see 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
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 message catalogs. Look for
inspiration for example in the catgets() system, possibly even use it
if available-- but only if available, all platforms will not have
catgets().
For the really pure at heart, consider extending this item to cover
also the warning messages (see perllexwarn, "warnings.pl").
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.
forbid labels with keyword names
Currently "goto keyword" "computes" the label value:
$ perl -e 'goto print'
Can't find label 1 at -e line 1.
It would be nice to forbid labels with keyword names, to avoid
confusion.
truncate() prototype
The prototype of truncate() is currently $$. It should probably be "*$"
instead. (This is changed in opcode.pl)
decapsulation of smart match argument
Currently "$foo ~~ $object" will die with the message "Smart matching a
non-overloaded object breaks encapsulation". It would be nice to allow
to bypass this by using explictly the syntax "$foo ~~ %$object" or
"$foo ~~ @$object".
error reporting of [$a ; $b]
Using ";" 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 ";" is parsed where it is not legal as a statement terminator
(ie inside "{}" used as a hashref, "[]" or "()") it issues an error
something like ; isnt legal inside an expression - if you need
multiple statements use a do {...} block. See the thread starting at
http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg0.html
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 $pie = 42'
Logically all lexicals used only once should warn, if the user asks for
warnings. An unworked RT ticket (#5087) has been open for almost seven
years for this discrepancy.
UTF-8 revamp
The handling of Unicode is unclean in many places. For example, the
regexp engine matches in Unicode semantics whenever the string or the
pattern is flagged as UTF-8, but that should not be dependent on an
internal storage detail of the string. Likewise, case folding behaviour
is dependent on the UTF8 internal flag being on or off.
Properly Unicode safe tokeniser and pads.
The tokeniser isn’t actually very UTF-8 clean. "use utf8;" is a hack -
variable names are stored in stashes as raw bytes, without the utf-8
flag set. The pad API only takes a "char *" pointer, so that’s all
bytes too. The tokeniser ignores the UTF-8-ness of "PL_rsfp", or any
SVs returned from source filters. All this could be fixed.
state variable initialization in list context
Currently this is illegal:
state ($a, $b) = foo();
In Perl 6, "state ($a) = foo();" and "(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 "Perl_newASSIGNOP()" that show the code paths
taken by various assignment constructions involving state variables.
Implement $value ~~ 0 .. $range
It would be nice to extend the syntax of the "~~" operator to also
understand numeric (and maybe alphanumeric) ranges.
A does() built-in
Like ref(), only useful. It would call the "DOES" method on objects; it
would also tell whether something can be dereferenced as an
array/hash/etc., or used as a regexp, etc.
<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg0.html>
Tied filehandles and write() don’t mix
There is no method on tied filehandles to allow them to be called back
by formats.
Propagate compilation hints to the debugger
Currently a debugger started with -dE on the command-line doesn’t see
the features enabled by -E. More generally hints ($^H and "%^H") aren’t
propagated to the debugger. Probably it would be a good thing to
propagate hints from the innermost non-"DB::" scope: this would make
code eval’ed in the debugger see the features (and strictures, etc.)
currently in scope.
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.
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.
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.
delete &function
Allow to delete functions. One can already undef them, but they’re
still in the stash.
"/w" regex modifier
That flag would enable to match whole words, and also to interpolate
arrays as alternations. With it, "/P/w" would be roughly equivalent to:
do { local $"='|'; /\b(?:P)\b/ }
See
<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
for the discussion.
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
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.
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 reinstated.
Optimize away @_
The old perltodo notes "Look at the "reification" code in "av.c"".
The yada yada yada operators
Perl 6’s Synopsis 3 says:
The ... operator is the "yada, yada, yada" list operator, which is used
as the body in function prototypes. It complains bitterly (by calling
fail) if it is ever executed. Variant ??? calls warn, and !!! calls
die.
Those would be nice to add to Perl 5. That could be done without new
ops.
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 ("Files and Filesystems" in
perlport is good reading at this point, in fact, all of perlport is.)
This has actually already been implemented (but only for Win32), take a
look at iperlsys.h and 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 "When Unicode Does Not Happen" in
perlunicode.)
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 "Extend PerlIO and PerlIO::Scalar".
Investigate PADTMP hash pessimisation
The peephole optimiser converts constants used for hash key lookups to
shared hash key scalars. Under ithreads, something is undoing this
work. See
http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg0.html
Store the current pad in the OP slab allocator
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.
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
http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg13.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.
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 "if" and the "elsif", hence
"PL_curcop" still reports that the currently executing line is line 4.
The solution was to inject a nextstate OPs for each "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 "elsif" (although the "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 "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 "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 "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)
optimize tail-calls
Tail-calls present an opportunity for broadly applicable optimization;
anywhere that "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.
"\N"
It should be possible to add a "\N" regex assertion, meaning "every
character except "\n"AX independently of the context. That would of
course imply that "\N" couldn’t be followed by an opening "{".
Big projects
Tasks that will get your name mentioned in the description of the
"Highlights of 5.12"
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.
One bit would be to write the missing code in sv.c:Perl_dirp_dup.
Fix Perl_sv_dup, et al so that threads can return objects.
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.
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.
Tasks for microperl
[ Each and every one of these may be obsolete, but they were listed
in the old Todo.micro file]
make creating uconfig.sh automatic
make creating Makefile.micro automatic
do away with fork/exec/wait?
(system, popen should be enough?)
some of the uconfig.sh really needs to be probed (using cc) in buildtime:
(uConfigure? :-) native datatype widths and endianness come to mind