=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 Smartmatch design issues
-=head2 merge common code in installperl and installman
+In 5.10.0 the smartmatch operator C<~~> isn't working quite "right". But
+before we can fix the implementation, we need to define what "right" is.
+The first problem is that Robin Houston implemented the Perl 6 smart match
+spec as of February 2006, when smart match was axiomatically symmetrical:
+L<http://groups.google.com/group/perl.perl6.language/msg/bf2b486f089ad021>
-There are some common subroutines and a common C<BEGIN> block in F<installperl>
-and F<installman>. These should probably be merged. It would also be good to
-check for duplication in all the utility scripts supplied in the source
-tarball. It might be good to move them all to a subdirectory, but this would
-require careful checking to find all places that call them, and change those
-correctly.
+Since then the Perl 6 target moved, but the Perl 5 implementation did not.
-=head2 common test code for timed bail out
+So it would be useful for someone to compare the Perl 6 smartmatch table
+as of February 2006 L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=markup&pathrev=7615>
+and the current table L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?revision=14556&view=markup>
+and tabulate the differences in Perl 6. The annotated view of changes is
+L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=annotate> and the diff is
+C<svn diff -r7615:14556 http://svn.perl.org/perl6/doc/trunk/design/syn/S03.pod>
+-- search for C<=head1 Smart matching>. (In theory F<viewvc> can generate that,
+but in practice when I tried it hung forever, I assume "thinking")
-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.
+With that done and published, someone (else) can then map any changed Perl 6
+semantics back to Perl 5, based on how the existing semantics map to Perl 5:
+L<http://search.cpan.org/~rgarcia/perl-5.10.0/pod/perlsyn.pod#Smart_matching_in_detail>
-=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.
+There are also some questions that need answering:
-The addition of C<Pod::Simple> and its related modules may make this task
-easier to complete.
+=over 4
-=head2 merge checkpods and podchecker
+=item *
-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.
+How do you negate one? (documentation issue)
+http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-01/msg00071.html
-=head2 perlmodlib.PL rewrite
+=item *
-Currently perlmodlib.PL needs to be run from a source directory where perl
-has been built, or some modules won't be found, and others will be
-skipped. Make it run from a clean perl source tree (so it's reproducible).
+Array behaviors
+http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00799.html
-=head2 Parallel testing
+* Should smart matches be symmetrical? (Perl 6 says no)
-(This probably impacts much more than the core: also the Test::Harness
-and TAP::* modules on CPAN.)
+* Other differences between Perl 5 and Perl 6 smart match?
-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/>.
+=item *
-Questions to answer
+Objects and smart match
+http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00865.html
-=over 4
+=back
-=item 1
+=head2 Remove duplication of test setup.
-How does screen layout work when you're running more than one test?
+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.
-=item 2
+=head2 POD -E<gt> HTML conversion in the core still sucks
-How does the caller of test specify how many tests to run in parallel?
+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.
-=item 3
+The addition of C<Pod::Simple> and its related modules may make this task
+easier to complete.
-How do setup/teardown tests identify themselves?
+=head2 Parallel testing
-=back
+(This probably impacts much more than the core: also the Test::Harness
+and TAP::* modules on CPAN.)
-Pugs already does parallel testing - can their approach be re-used?
+All of the tests in F<t/> can now be run in parallel, if C<$ENV{TEST_JOBS}>
+is set. However, tests within each directory in F<ext> and F<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 F<lib/*.t>, and
+make them use C<File::Temp>.
=head2 Make Schwern poorer
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
To make a minimal perl distribution, it's useful to look at
F<t/lib/commonsense.t>.
-=head2 Improving C<threads::shared>
+=head2 Bundle dual life modules in ext/
-Investigate whether C<threads::shared> could share aggregates properly with
-only Perl level changes to shared.pm
+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.
=head2 POSIX memory footprint
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
Make F<pod/roffitall> be updated by F<pod/buildtoc>.
+=head2 Split "linker" from "compiler"
+
+Right now, Configure probes for two commands, and sets two variables:
+
+=over 4
+
+=item * C<cc> (in F<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 F<cc> and F<gcc>.
+Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>.
+
+=item * C<ld> (in F<dlsrc.U>)
+
+This variable indicates the program to be used to link
+libraries for dynamic loading. On some systems, it is F<ld>.
+On ELF systems, it should be C<$cc>. Mostly, we'll try to respect
+the hint file setting.
+
+=back
+
+There is an implicit historical assumption from around Perl5.000alpha
+something, that C<$cc> is also the correct command for linking object files
+together to make an executable. This may be true on Unix, but it's not true
+on other platforms, and there are a maze of work arounds in other places (such
+as F<Makefile.SH>) to cope with this.
+
+Ideally, we should create a new variable to hold the name of the executable
+linker program, probe for it in F<Configure>, and centralise all the special
+case logic there or in hints files.
+
+A small bikeshed issue remains - what to call it, given that C<$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 C<$link> could be confused with
+the Unix command line executable of the same name, which does something
+completely different. Andy Dougherty makes the counter argument "In parrot, I
+tried to call the command used to link object files and libraries into an
+executable F<link>, since that's what my vaguely-remembered DOS and VMS
+experience suggested. I don't think any real confusion has ensued, so it's
+probably a reasonable name for perl5 to use."
+
+"Alas, I've always worried that introducing it would make things worse,
+since now the module building utilities would have to look for
+C<$Config{link}> and institute a fall-back plan if it weren't found."
+Although I can see that as confusing, given that C<$Config{d_link}> is true
+when (hard) links are available.
+
=head1 Tasks that need a little C knowledge
These tasks would need a little C knowledge, but don't need any specific
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.
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.
+=head2 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.
+
=head1 Tasks that need a knowledge of XS
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;
These tasks would need C knowledge, and knowledge of how the interpreter works,
or a willingness to learn.
+=head2 error reporting of [$a ; $b]
+
+Using C<;> 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
+C<;> is parsed where it is not legal as a statement terminator (ie inside
+C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like
+I<';' isn't 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/msg00573.html
+
=head2 lexicals used only once
This warns:
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
The old perltodo notes "Look at the "reification" code in C<av.c>".
-=head2 The yada yada yada operators
-
-Perl 6's Synopsis 3 says:
-
-I<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.
-
=head2 Virtualize operating system access
Implement a set of "vtables" that virtualizes operating system access
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;
projects / p5sagit/p5-mst-13.2.git / blobdiff