X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/e99d581a4aaa3c92d0b0dda6799157fe7a569f31..370c71c555fdc393b7abe16f74b496061898b884:/pod/perltodo.pod

diff --git a/pod/perltodo.pod b/pod/perltodo.pod
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--- a/pod/perltodo.pod
+++ b/pod/perltodo.pod
@@ -1,1102 +1,11 @@
 =head1 NAME
 
-perltodo - Perl TO-DO List
+perltodo - Link to the Perl to-do list
 
 =head1 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 I<perl5-porters@perl.org> to
-avoid duplication of effort, and to learn from any previous attempts.
-By all means contact a pumpking privately first if you prefer.
+The Perl 5 to-do list is maintained in the git repository, and can
+be viewed at L<http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>
 
-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
-F<AUTHORS> file, which ships in the official distribution. How many other
-programming languages offer you 1 line of immortality?
-
-=head1 Tasks that only need Perl knowledge
-
-=head2 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 C<$Is_Foo> checks.  We can safely put this
-into a file, change it to build an C<%Is> hash and require it.  Maybe just put
-it into F<test.pl>. Throw in the handy tainting subroutines.
-
-=head2 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.
-
-=head2 POD -E<gt> 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 I<as> simple as it sounds, particularly with the
-flexibility POD allows for C<=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 L</make HTML install work>, as the layout of installation tree
-is needed to improve the cross-linking.
-
-The addition of C<Pod::Simple> and its related modules may make this task
-easier to complete.
-
-=head2 merge checkpods and podchecker
-
-F<pod/checkpods.PL> (and C<make check> in the F<pod/> subdirectory)
-implements a very basic check for pod files, but the errors it discovers
-aren't found by podchecker. Add this check to podchecker, get rid of
-checkpods and have C<make check> use podchecker.
-
-=head2 Parallel testing
-
-(This probably impacts much more than the core: also the Test::Harness
-and TAP::* modules on CPAN.)
-
-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 B<option> of
-running sets of tests in parallel. This would be useful for tests in
-F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
-
-Questions to answer
-
-=over 4
-
-=item 1
-
-How does screen layout work when you're running more than one test?
-
-=item 2
-
-How does the caller of test specify how many tests to run in parallel?
-
-=item 3
-
-How do setup/teardown tests identify themselves?
-
-=back
-
-Pugs already does parallel testing - can their approach be re-used?
-
-=head2 Make Schwern poorer
-
-We should have tests for everything. When all the core's modules are tested,
-Schwern has promised to donate to $500 to TPF. We may need volunteers to
-hold him upside down and shake vigorously in order to actually extract the
-cash.
-
-=head2 Improve the coverage of the core tests
-
-Use Devel::Cover to ascertain the core modules's test coverage, then add
-tests that are currently missing.
-
-=head2 test B
-
-A full test suite for the B module would be nice.
-
-=head2 Deparse inlined constants
-
-Code such as this
-
-    use constant PI => 4;
-    warn PI
-
-will currently deparse as
-
-    use constant ('PI', 4);
-    warn 4;
-
-because the tokenizer inlines the value of the constant subroutine C<PI>.
-This allows various compile time optimisations, such as constant folding
-and dead code elimination. Where these haven't happened (such as the example
-above) it ought be possible to make B::Deparse work out the name of the
-original constant, because just enough information survives in the symbol
-table to do this. Specifically, the same scalar is used for the constant in
-the optree as is used for the constant subroutine, so by iterating over all
-symbol tables and generating a mapping of SV address to constant name, it
-would be possible to provide B::Deparse with this functionality.
-
-=head2 A decent benchmark
-
-C<perlbench> seems impervious to any recent changes made to the perl core. It
-would be useful to have a reasonable general benchmarking suite that roughly
-represented what current perl programs do, and measurably reported whether
-tweaks to the core improve, degrade or don't really affect performance, to
-guide people attempting to optimise the guts of perl. Gisle would welcome
-new tests for perlbench.
-
-=head2 fix tainting bugs
-
-Fix the bugs revealed by running the test suite with the C<-t> switch (via
-C<make test.taintwarn>).
-
-=head2 Dual life everything
-
-As part of the "dists" plan, anything that doesn't belong in the smallest perl
-distribution needs to be dual lifed. Anything else can be too. Figure out what
-changes would be needed to package that module and its tests up for CPAN, and
-do so. Test it with older perl releases, and fix the problems you find.
-
-To make a minimal perl distribution, it's useful to look at
-F<t/lib/commonsense.t>.
-
-=head2 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.
-
-However, we need to make sure that they are still installed in
-architecture-independent directories by C<make install>.
-
-=head2 Improving C<threads::shared>
-
-Investigate whether C<threads::shared> could share aggregates properly with
-only Perl level changes to shared.pm
-
-=head2 POSIX memory footprint
-
-Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
-various times worked to cut it down. There is probably still fat to cut out -
-for example POSIX passes Exporter some very memory hungry data structures.
-
-=head2 embed.pl/makedef.pl
-
-There is a script F<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<C>. Functions are declared in F<embed.fnc>, variables
-in F<interpvar.h>. Quite a few of the functions and variables
-are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
-doesn't understand the C macros, so the rules about which symbols are present
-when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
-It would be good to teach C<embed.pl> to understand the conditional
-compilation, and hence remove the duplication, and the mistakes it has caused.
-
-=head2 use strict; and AutoLoad
-
-Currently if you write
-
-    package Whack;
-    use AutoLoader 'AUTOLOAD';
-    use strict;
-    1;
-    __END__
-    sub bloop {
-        print join (' ', No, strict, here), "!\n";
-    }
-
-then C<use strict;> isn't in force within the autoloaded subroutines. It would
-be more consistent (and less surprising) to arrange for all lexical pragmas
-in force at the __END__ block to be in force within each autoloaded subroutine.
-
-There's a similar problem with SelfLoader.
-
-=head2 profile installman
-
-The F<installman> script is slow. All it is doing text processing, which we're
-told is something Perl is good at. So it would be nice to know what it is doing
-that is taking so much CPU, and where possible address it.
-
-
-=head1 Tasks that need a little sysadmin-type knowledge
-
-Or if you prefer, tasks that you would learn from, and broaden your skills
-base...
-
-=head2 make HTML install work
-
-There is an C<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
-
-=over 4
-
-=item 1
-
-Checking that cross linking between various parts of the documentation works.
-In particular that links work between the modules (files with POD in F<lib/>)
-and the core documentation (files in F<pod/>)
-
-=item 2
-
-Work out how to split C<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 C<-X>, groups such as C<getpwnam> to
-C<endservent>, two or more C<=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 C<select>)
-
-=back
-
-=head2 compressed man pages
-
-Be able to install them. This would probably need a configure test to see how
-the system does compressed man pages (same directory/different directory?
-same filename/different filename), as well as tweaking the F<installman> script
-to compress as necessary.
-
-=head2 Add a code coverage target to the Makefile
-
-Make it easy for anyone to run Devel::Cover on the core's tests. The steps
-to do this manually are roughly
-
-=over 4
-
-=item *
-
-do a normal C<Configure>, but include Devel::Cover as a module to install
-(see F<INSTALL> for how to do this)
-
-=item *
-
-    make perl
-
-=item *
-
-    cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
-
-=item *
-
-Process the resulting Devel::Cover database
-
-=back
-
-This just give you the coverage of the F<.pm>s. To also get the C level
-coverage you need to
-
-=over 4
-
-=item *
-
-Additionally tell C<Configure> to use the appropriate C compiler flags for
-C<gcov>
-
-=item *
-
-    make perl.gcov
-
-(instead of C<make perl>)
-
-=item *
-
-After running the tests run C<gcov> to generate all the F<.gcov> files.
-(Including down in the subdirectories of F<ext/>
-
-=item *
-
-(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
-to get their stats into the cover_db directory.
-
-=item *
-
-Then process the Devel::Cover database
-
-=back
-
-It would be good to add a single switch to C<Configure> to specify that you
-wanted to perform perl level coverage, and another to specify C level
-coverage, and have C<Configure> and the F<Makefile> do all the right things
-automatically.
-
-=head2 Make Config.pm cope with differences between built and installed perl
-
-Quite often vendors ship a perl binary compiled with their (pay-for)
-compilers.  People install a free compiler, such as gcc. To work out how to
-build extensions, Perl interrogates C<%Config>, so in this situation
-C<%Config> describes compilers that aren't there, and extension building
-fails. This forces people into choosing between re-compiling perl themselves
-using the compiler they have, or only using modules that the vendor ships.
-
-It would be good to find a way teach C<Config.pm> about the installation setup,
-possibly involving probing at install time or later, so that the C<%Config> in
-a binary distribution better describes the installed machine, when the
-installed machine differs from the build machine in some significant way.
-
-=head2 linker specification files
-
-Some platforms mandate that you provide a list of a shared library's external
-symbols to the linker, so the core already has the infrastructure in place to
-do this for generating shared perl libraries. 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
-F<makedef.pl> to support this format, and to provide a means within
-C<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.
-
-=head2 Cross-compile support
-
-Currently C<Configure> understands C<-Dusecrosscompile> option. This option
-arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
-assumed then to be copied to TARGET machine and used as a replacement of full
-C<perl> executable.
-
-This could be done little differently. Namely C<miniperl> should be built for
-HOST and then full C<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.
-
-=head2 roffitall
-
-Make F<pod/roffitall> be updated by F<pod/buildtoc>.
-
-=head1 Tasks that need a little C knowledge
-
-These tasks would need a little C knowledge, but don't need any specific
-background or experience with XS, or how the Perl interpreter works
-
-=head2 Weed out needless PERL_UNUSED_ARG
-
-The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about
-unused arguments. Often the arguments can't be removed, as there is an
-external constraint that determines the prototype of the function, so this
-approach is valid. However, there are some cases where C<PERL_UNUSED_ARG>
-could be removed. Specifically
-
-=over 4
-
-=item *
-
-The prototypes of (nearly all) static functions can be changed
-
-=item *
-
-Unused arguments generated by short cut macros are wasteful - the short cut
-macro used can be changed.
-
-=back
-
-=head2 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:
-L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.
-
-=head2 -Duse32bit*
-
-Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
-On these systems, it might be the default compilation mode, and there
-is currently no guarantee that passing no use64bitall option to the
-Configure process will build a 32bit perl. Implementing -Duse32bit*
-options would be nice for perl 5.12.
-
-=head2 Make it clear from -v if this is the exact official release
-
-Currently perl from C<p4>/C<rsync> ships with a F<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 possibility 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 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".
-
-=head2 Profile Perl - am I hot or not?
-
-The Perl source code is stable enough that it makes sense to profile it,
-identify and optimise the hotspots. It would be good to measure the
-performance of the Perl interpreter using free tools such as cachegrind,
-gprof, and dtrace, and work to reduce the bottlenecks they reveal.
-
-As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
-the ops that are most commonly used. The idea is that by grouping them, their
-object code will be adjacent in the executable, so they have a greater chance
-of already being in the CPU cache (or swapped in) due to being near another op
-already in use.
-
-Except that it's not clear if these really are the most commonly used ops. So
-as part of exercising your skills with coverage and profiling tools you might
-want to determine what ops I<really> are the most commonly used. And in turn
-suggest evictions and promotions to achieve a better F<pp_hot.c>.
-
-One piece of Perl code that might make a good testbed is F<installman>.
-
-=head2 Allocate OPs from arenas
-
-Currently all new OP structures are individually malloc()ed and free()d.
-All C<malloc> implementations have space overheads, and are now as fast as
-custom allocates so it would both use less memory and less CPU to allocate
-the various OP structures from arenas. The SV arena code can probably be
-re-used for this.
-
-Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use
-Perl_Slab_alloc() to pack optrees into a contiguous block, which is
-probably superior to the use of OP arenas, esp. from a cache locality
-standpoint.  See L<Profile Perl - am I hot or not?>.
-
-=head2 Improve win32/wince.c
-
-Currently, numerous functions look virtually, if not completely,
-identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
-be good.
-
-=head2 Use secure CRT functions when building with VC8 on Win32
-
-Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis
-that they were "unsafe" and introduced differently named secure versions of
-them as replacements, e.g. instead of writing
-
-    FILE* f = fopen(__FILE__, "r");
-
-one should now write
-
-    FILE* f;
-    errno_t err = fopen_s(&f, __FILE__, "r"); 
-
-Currently, the warnings about these deprecations have been disabled by adding
--D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that
-warning suppressant and actually make use of the new secure CRT functions.
-
-There is also a similar issue with POSIX CRT function names like fileno having
-been deprecated in favour of ISO C++ conformant names like _fileno. These
-warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It
-might be nice to do as Microsoft suggest here too, although, unlike the secure
-functions issue, there is presumably little or no benefit in this case.
-
-=head2 Fix POSIX::access() and chdir() on Win32
-
-These functions currently take no account of DACLs and therefore do not behave
-correctly in situations where access is restricted by DACLs (as opposed to the
-read-only attribute).
-
-Furthermore, POSIX::access() behaves differently for directories having the
-read-only attribute set depending on what CRT library is being used. For
-example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that
-such directories are not writable, whereas in fact all directories are writable
-unless access is denied by DACLs. (In the case of directories, the read-only
-attribute actually only means that the directory cannot be deleted.) This CRT
-bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still
-not actually be writable if access is indeed denied by DACLs).
-
-For the chdir() issue, see ActiveState bug #74552:
-http://bugs.activestate.com/show_bug.cgi?id=74552
-
-Therefore, DACLs should be checked both for consistency across CRTs and for
-the correct answer.
-
-(Note that perl's -w operator should not be modified to check DACLs. It has
-been written so that it reflects the state of the read-only attribute, even
-for directories (whatever CRT is being used), for symmetry with chmod().)
-
-=head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
-
-Maybe create a utility that checks after each libperl.a creation that
-none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
-ever creep back to libperl.a.
-
-  nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
-
-Note, of course, that this will only tell whether B<your> platform
-is using those naughty interfaces.
-
-=head2 -D_FORTIFY_SOURCE=2, -fstack-protector
-
-Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc
-(4.1 onwards?) supports C<-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.
-
-=head2 Arenas for GPs? For MAGIC?
-
-C<struct gp> and C<struct magic> are both currently allocated by C<malloc>.
-It might be a speed or memory saving to change to using arenas. Or it might
-not. It would need some suitable benchmarking first. In particular, C<GP>s
-can probably be changed with minimal compatibility impact (probably nothing
-outside of the core, or even outside of F<gv.c> allocates them), but they
-probably aren't allocated/deallocated often enough for a speed saving. Whereas
-C<MAGIC> is allocated/deallocated more often, but in turn, is also something
-more externally visible, so changing the rules here may bite external code.
-
-
-=head1 Tasks that need a knowledge of XS
-
-These tasks would need C knowledge, and roughly the level of knowledge of
-the perl API that comes from writing modules that use XS to interface to
-C.
-
-=head2 safely supporting POSIX SA_SIGINFO
-
-Some years ago Jarkko supplied patches to provide support for the POSIX
-SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler.
-
-Unfortunately, it only works with "unsafe" signals, because under safe
-signals, by the time Perl gets to run the signal handler, the extra
-information has been lost. Moreover, it's not easy to store it somewhere,
-as you can't call mutexs, or do anything else fancy, from inside a signal
-handler.
-
-So it strikes me that we could provide safe SA_SIGINFO support
-
-=over 4
-
-=item 1
-
-Provide global variables for two file descriptors
-
-=item 2
-
-When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a
-pipe, store the reader in one, the writer in the other
-
-=item 3
-
-In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if
-the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open,
-
-=over 8
-
-=item 1
-
-serialise signal number, C<struct siginfo_t> (or at least the parts we care
-about) into a small auto char buff
-
-=item 2
-
-C<write()> that (non-blocking) to the writer fd
-
-=over 12
-
-=item 1
-
-if it writes 100%, flag the signal in a counter of "signals on the pipe" akin
-to the current per-signal-number counts
-
-=item 2
-
-if it writes 0%, assume the pipe is full. Flag the data as lost?
-
-=item 3
-
-if it writes partially, croak a panic, as your OS is broken.
-
-=back
-
-=back
-
-=item 4
-
-in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on
-the pipe", read the data out, deserialise, build the Perl structures on
-the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as
-usual.
-
-=back
-
-I think that this gets us decent C<SA_SIGINFO> support, without the current risk
-of running Perl code inside the signal handler context. (With all the dangers
-of things like C<malloc> corruption that that currently offers us)
-
-For more information see the thread starting with this message:
-http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html
-
-=head2 autovivification
-
-Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
-
-This task is incremental - even a little bit of work on it will help.
-
-=head2 Unicode in Filenames
-
-chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
-opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
-system, truncate, unlink, utime, -X.  All these could potentially accept
-Unicode filenames either as input or output (and in the case of system
-and qx Unicode in general, as input or output to/from the shell).
-Whether a filesystem - an operating system pair understands Unicode in
-filenames varies.
-
-Known combinations that have some level of understanding include
-Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
-OS X), NFS v4 is rumored to be Unicode, and of course Plan 9.  How to
-create Unicode filenames, what forms of Unicode are accepted and used
-(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
-and so on, varies.  Finding the right level of interfacing to Perl
-requires some thought.  Remember that an OS does not implicate a
-filesystem.
-
-(The Windows -C command flag "wide API support" has been at least
-temporarily retired in 5.8.1, and the -C has been repurposed, see
-L<perlrun>.)
-
-Most probably the right way to do this would be this:
-L</"Virtualize operating system access">.
-
-=head2 Unicode in %ENV
-
-Currently the %ENV entries are always byte strings.
-See L</"Virtualize operating system access">.
-
-=head2 Unicode and glob()
-
-Currently glob patterns and filenames returned from File::Glob::glob()
-are always byte strings.  See L</"Virtualize operating system access">.
-
-=head2 Unicode and lc/uc operators
-
-Some built-in operators (C<lc>, C<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.
-
-=head2 use less 'memory'
-
-Investigate trade offs to switch out perl's choices on memory usage.
-Particularly perl should be able to give memory back.
-
-This task is incremental - even a little bit of work on it will help.
-
-=head2 Re-implement C<:unique> in a way that is actually thread-safe
-
-The old implementation made bad assumptions on several levels. A good 90%
-solution might be just to make C<:unique> work to share the string buffer
-of SvPVs. That way large constant strings can be shared between ithreads,
-such as the configuration information in F<Config>.
-
-=head2 Make tainting consistent
-
-Tainting would be easier to use if it didn't take documented shortcuts and
-allow taint to "leak" everywhere within an expression.
-
-=head2 readpipe(LIST)
-
-system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
-running a shell. readpipe() (the function behind qx//) could be similarly
-extended.
-
-=head2 Audit the code for destruction ordering assumptions
-
-Change 25773 notes
-
-    /* Need to check SvMAGICAL, as during global destruction it may be that
-       AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
-       is now part of the linked list of SV heads, rather than pointing to
-       the original body.  */
-    /* FIXME - audit the code for other bugs like this one.  */
-
-adding the C<SvMAGICAL> check to
-
-    if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
-        MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);
-
-Go through the core and look for similar assumptions that SVs have particular
-types, as all bets are off during global destruction.
-
-=head2 Extend PerlIO and PerlIO::Scalar
-
-PerlIO::Scalar doesn't know how to truncate().  Implementing this
-would require extending the PerlIO vtable.
-
-Similarly the PerlIO vtable doesn't know about formats (write()), or
-about stat(), or chmod()/chown(), utime(), or flock().
-
-(For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership
-would mean.)
-
-PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(),
-opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(),
-readlink().
-
-See also L</"Virtualize operating system access">.
-
-=head2 -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.
-
-=head2 Organize error messages
-
-Perl's diagnostics (error messages, see L<perldiag>) could use
-reorganizing and formalizing so that each error message has its
-stable-for-all-eternity unique id, categorized by severity, type, and
-subsystem.  (The error messages would be listed in a datafile outside
-of the Perl source code, and the source code would only refer to the
-messages by the id.)  This clean-up and regularizing should apply
-for all croak() messages.
-
-This would enable all sorts of things: easier translation/localization
-of the messages (though please do keep in mind the caveats of
-L<Locale::Maketext> about too straightforward approaches to
-translation), filtering by severity, and instead of grepping for a
-particular error message one could look for a stable error id.  (Of
-course, changing the error messages by default would break all the
-existing software depending on some particular error message...)
-
-This kind of functionality is known as I<message catalogs>.  Look for
-inspiration for example in the catgets() system, possibly even use it
-if available-- but B<only> if available, all platforms will B<not>
-have catgets().
-
-For the really pure at heart, consider extending this item to cover
-also the warning messages (see L<perllexwarn>, C<warnings.pl>).
-
-=head1 Tasks that need a knowledge of the interpreter
-
-These tasks would need C knowledge, and knowledge of how the interpreter works,
-or a willingness to learn.
-
-=head2 lexicals used only once
-
-This warns:
-
-    $ perl -we '$pie = 42'
-    Name "main::pie" used only once: possible typo at -e line 1.
-
-This does not:
-
-    $ perl -we 'my $pie = 42'
-
-Logically all lexicals used only once should warn, if the user asks for
-warnings.  An unworked RT ticket (#5087) has been open for almost seven
-years for this discrepancy.
-
-=head2 UTF-8 revamp
-
-The handling of Unicode is unclean in many places. For example, the regexp
-engine matches in Unicode semantics whenever the string or the pattern is
-flagged as UTF-8, but that should not be dependent on an internal storage
-detail of the string. Likewise, case folding behaviour is dependent on the
-UTF8 internal flag being on or off.
-
-=head2 Properly Unicode safe tokeniser and pads.
-
-The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
-variable names are stored in stashes as raw bytes, without the utf-8 flag
-set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
-tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
-source filters.  All this could be fixed.
-
-=head2 state variable initialization in list context
-
-Currently this is illegal:
-
-    state ($a, $b) = foo(); 
-
-In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different
-semantics, which is tricky to implement in Perl 5 as currently they produce
-the same opcode trees. The Perl 6 design is firm, so it would be good to
-implement the necessary code in Perl 5. There are comments in
-C<Perl_newASSIGNOP()> that show the code paths taken by various assignment
-constructions involving state variables.
-
-=head2 Implement $value ~~ 0 .. $range
-
-It would be nice to extend the syntax of the C<~~> operator to also
-understand numeric (and maybe alphanumeric) ranges.
-
-=head2 A does() built-in
-
-Like ref(), only useful. It would call the C<DOES> method on objects; it
-would also tell whether something can be dereferenced as an
-array/hash/etc., or used as a regexp, etc.
-L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>
-
-=head2 Tied filehandles and write() don't mix
-
-There is no method on tied filehandles to allow them to be called back by
-formats.
-
-=head2 Attach/detach debugger from running program
-
-The old perltodo notes "With C<gdb>, you can attach the debugger to a running
-program if you pass the process ID. It would be good to do this with the Perl
-debugger on a running Perl program, although I'm not sure how it would be
-done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
-
-=head2 Optimize away empty destructors
-
-Defining an empty DESTROY method might be useful (notably in
-AUTOLOAD-enabled classes), but it's still a bit expensive to call. That
-could probably be optimized.
-
-=head2 LVALUE functions for lists
-
-The old perltodo notes that lvalue functions don't work for list or hash
-slices. This would be good to fix.
-
-=head2 LVALUE functions in the debugger
-
-The old perltodo notes that lvalue functions don't work in the debugger. This
-would be good to fix.
-
-=head2 regexp optimiser optional
-
-The regexp optimiser is not optional. It should configurable to be, to allow
-its performance to be measured, and its bugs to be easily demonstrated.
-
-=head2 delete &function
-
-Allow to delete functions. One can already undef them, but they're still
-in the stash.
-
-=head2 C</w> regex modifier
-
-That flag would enable to match whole words, and also to interpolate
-arrays as alternations. With it, C</P/w> would be roughly equivalent to:
-
-    do { local $"='|'; /\b(?:P)\b/ }
-
-See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html>
-for the discussion.
-
-=head2 optional optimizer
-
-Make the peephole optimizer optional. Currently it performs two tasks as
-it walks the optree - genuine peephole optimisations, and necessary fixups of
-ops. It would be good to find an efficient way to switch out the
-optimisations whilst keeping the fixups.
-
-=head2 You WANT *how* many
-
-Currently contexts are void, scalar and list. split has a special mechanism in
-place to pass in the number of return values wanted. It would be useful to
-have a general mechanism for this, backwards compatible and little speed hit.
-This would allow proposals such as short circuiting sort to be implemented
-as a module on CPAN.
-
-=head2 lexical aliases
-
-Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
-
-=head2 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.
-
-=head2 Self-ties
-
-Self-ties are currently illegal because they caused too many segfaults. Maybe
-the causes of these could be tracked down and self-ties on all types
-reinstated.
-
-=head2 Optimize away @_
-
-The old perltodo notes "Look at the "reification" code in C<av.c>".
-
-=head2 Virtualize operating system access
-
-Implement a set of "vtables" that virtualizes operating system access
-(open(), mkdir(), unlink(), readdir(), getenv(), etc.)  At the very
-least these interfaces should take SVs as "name" arguments instead of
-bare char pointers; probably the most flexible and extensible way
-would be for the Perl-facing interfaces to accept HVs.  The system
-needs to be per-operating-system and per-file-system
-hookable/filterable, preferably both from XS and Perl level
-(L<perlport/"Files and Filesystems"> is good reading at this point,
-in fact, all of L<perlport> is.)
-
-This has actually already been implemented (but only for Win32),
-take a look at F<iperlsys.h> and F<win32/perlhost.h>.  While all Win32
-variants go through a set of "vtables" for operating system access,
-non-Win32 systems currently go straight for the POSIX/UNIX-style
-system/library call.  Similar system as for Win32 should be
-implemented for all platforms.  The existing Win32 implementation
-probably does not need to survive alongside this proposed new
-implementation, the approaches could be merged.
-
-What would this give us?  One often-asked-for feature this would
-enable is using Unicode for filenames, and other "names" like %ENV,
-usernames, hostnames, and so forth.
-(See L<perlunicode/"When Unicode Does Not Happen">.)
-
-But this kind of virtualization would also allow for things like
-virtual filesystems, virtual networks, and "sandboxes" (though as long
-as dynamic loading of random object code is allowed, not very safe
-sandboxes since external code of course know not of Perl's vtables).
-An example of a smaller "sandbox" is that this feature can be used to
-implement per-thread working directories: Win32 already does this.
-
-See also L</"Extend PerlIO and PerlIO::Scalar">.
-
-=head2 Investigate PADTMP hash pessimisation
-
-The peephole optimier 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/msg00793.html
-
-=head2 Store the current pad in the OP slab allocator
-
-=for clarification
-I hope that I got that "current pad" part correct
-
-Currently we leak ops in various cases of parse failure. I suggested that we
-could solve this by always using the op slab allocator, and walking it to
-free ops. Dave comments that as some ops are already freed during optree
-creation one would have to mark which ops are freed, and not double free them
-when walking the slab. He notes that one problem with this is that for some ops
-you have to know which pad was current at the time of allocation, which does
-change. I suggested storing a pointer to the current pad in the memory allocated
-for the slab, and swapping to a new slab each time the pad changes. Dave thinks
-that this would work.
-
-=head2 repack the optree
-
-Repacking the optree after execution order is determined could allow
-removal of NULL ops, and optimal ordering of OPs with respect to cache-line
-filling.  The slab allocator could be reused for this purpose.  I think that
-the best way to do this is to make it an optional step just before the
-completed optree is attached to anything else, and to use the slab allocator
-unchanged, so that freeing ops is identical whether or not this step runs.
-Note that the slab allocator allocates ops downwards in memory, so one would
-have to actually "allocate" the ops in reverse-execution order to get them
-contiguous in memory in execution order.
-
-See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html
-
-Note that running this copy, and then freeing all the old location ops would
-cause their slabs to be freed, which would eliminate possible memory wastage if
-the previous suggestion is implemented, and we swap slabs more frequently.
-
-=head2 eliminate incorrect line numbers in warnings
-
-This code
-
-    use warnings;
-    my $undef;
-    
-    if ($undef == 3) {
-    } elsif ($undef == 0) {
-    }
-
-used to produce this output:
-
-    Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
-    Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
-
-where the line of the second warning was misreported - it should be line 5.
-Rafael fixed this - the problem arose because there was no nextstate OP
-between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still
-reports that the currently executing line is line 4. The solution was to inject
-a nextstate OPs for each C<elsif>, although it turned out that the nextstate
-OP needed to be a nulled OP, rather than a live nextstate OP, else other line
-numbers became misreported. (Jenga!)
-
-The problem is more general than C<elsif> (although the C<elsif> case is the
-most common and the most confusing). Ideally this code
-
-    use warnings;
-    my $undef;
-    
-    my $a = $undef + 1;
-    my $b
-      = $undef
-      + 1;
-
-would produce this output
-
-    Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
-    Use of uninitialized value $undef in addition (+) at wrong.pl line 7.
-
-(rather than lines 4 and 5), but this would seem to require every OP to carry
-(at least) line number information.
-
-What might work is to have an optional line number in memory just before the
-BASEOP structure, with a flag bit in the op to say whether it's present.
-Initially during compile every OP would carry its line number. Then add a late
-pass to the optimiser (potentially combined with L</repack the optree>) which
-looks at the two ops on every edge of the graph of the execution path. If
-the line number changes, flags the destination OP with this information.
-Once all paths are traced, replace every op with the flag with a
-nextstate-light op (that just updates C<PL_curcop>), which in turn then passes
-control on to the true op. All ops would then be replaced by variants that
-do not store the line number. (Which, logically, why it would work best in
-conjunction with L</repack the optree>, as that is already copying/reallocating
-all the OPs)
-
-(Although I should note that we're not certain that doing this for the general
-case is worth it)
-
-=head2 optimize tail-calls
-
-Tail-calls present an opportunity for broadly applicable optimization;
-anywhere that C<< return foo(...) >> is called, the outer return can
-be replaced by a goto, and foo will return directly to the outer
-caller, saving (conservatively) 25% of perl's call&return cost, which
-is relatively higher than in C.  The scheme language is known to do
-this heavily.  B::Concise provides good insight into where this
-optimization is possible, ie anywhere entersub,leavesub op-sequence
-occurs.
-
- perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'
-
-Bottom line on this is probably a new pp_tailcall function which
-combines the code in pp_entersub, pp_leavesub.  This should probably
-be done 1st in XS, and using B::Generate to patch the new OP into the
-optrees.
-
-=head1 Big projects
-
-Tasks that will get your name mentioned in the description of the "Highlights
-of 5.12"
-
-=head2 make ithreads more robust
-
-Generally make ithreads more robust. See also L</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.
-
-=head2 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.
-
-=head2 (?{...}) closures in regexps
-
-Fix (or rewrite) the implementation of the C</(?{...})/> closures.
-
-=head2 A re-entrant regexp engine
-
-This will allow the use of a regex from inside (?{ }), (??{ }) and
-(?(?{ })|) constructs.
-
-=head2 Add class set operations to regexp engine
-
-Apparently these are quite useful. Anyway, Jeffery Friedl wants them.
-
-demerphq has this on his todo list, but right at the bottom.  
+(The to-do list used to be here in perltodo. That has stopped, as installing a
+snapshot that becomes increasingly out of date isn't that useful to anyone.)