X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperltodo.pod;h=a16cf0d604adff14905f09dfc0f43ed39d2aacd2;hb=e706c0cd31a70bd2c97d4510f261613278a7e1f5;hp=f4f9f59aba7e289f74d5b4b6ecc68d66a2acc565;hpb=35b64ab6316ff2abf98a24e9ac2da58ed5dd1894;p=p5sagit%2Fp5-mst-13.2.git
diff --git a/pod/perltodo.pod b/pod/perltodo.pod
index f4f9f59..a16cf0d 100644
--- a/pod/perltodo.pod
+++ b/pod/perltodo.pod
@@ -4,10 +4,14 @@ perltodo - 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 to avoid duplication of
-effort. By all means contact a pumpking privately first if you prefer.
+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
+I 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
@@ -20,52 +24,69 @@ not, but if your patch is incorporated, then we'll add your name to the
F file, which ships in the official distribution. How many other
programming languages offer you 1 line of immortality?
-=head1 The roadmap to 5.10
+=head1 Tasks that only need Perl knowledge
-The roadmap to 5.10 envisages feature based releases, as various items in this
-TODO are completed.
+=head2 Improve Porting/cmpVERSION.pl to work from git tags
-=head2 Needed for a 5.9.4 release
+See F for a bit more detail.
-=over
+=head2 Migrate t/ from custom TAP generation
-=item *
+Many tests below F still generate TAP by "hand", rather than using library
+functions. As explained in L, tests in F are
+written in a particular way to test that more complex constructions actually
+work before using them routinely. Hence they don't use C, but
+instead there is an intentionally simpler library, F. However,
+quite a few tests in F have not been refactored to use it. Refactoring
+any of these tests, one at a time, is a useful thing TODO.
-Review assertions. Review syntax to combine assertions. Assertions could take
-advantage of the lexical pragmas work. L
+The subdirectories F, F and F, that contain the most
+basic tests, should be excluded from this task.
-=item *
+=head2 Test that regen.pl was run
-C should be turned into a lexical pragma.
-C should, too (probably).
+There are various generated files shipped with the perl distribution, for
+things like header files generate from data. The generation scripts are
+written in perl, and all can be run by F. However, because they're
+written in perl, we can't run them before we've built perl. We can't run them
+as part of the F, because changing files underneath F confuses
+it completely, and we don't want to run them automatically anyway, as they
+change files shipped by the distribution, something we seek not do to.
-=back
+If someone changes the data, but forgets to re-run F then the
+generated files are out of sync. It would be good to have a test in
+F that checks that the generated files are in sync, and fails
+otherwise, to alert someone before they make a poor commit. I suspect that this
+would require adapting the scripts run from F to have dry-run
+options, and invoking them with these, or by refactoring them into a library
+that does the generation, which can be called by the scripts, and by the test.
-=head2 Needed for a 5.9.5 release
+=head2 Automate perldelta generation
-=over
+The perldelta file accompanying each release summaries the major changes.
+It's mostly manually generated currently, but some of that could be
+automated with a bit of perl, specifically the generation of
-=item *
-Implement L
+=over
-=item *
-Implement L
+=item Modules and Pragmata
-=back
+=item New Documentation
-=head2 Needed for a 5.9.6 release
+=item New Tests
-Stabilisation. If all goes well, this will be the equivalent of a 5.10-beta.
+=back
-=head1 Tasks that only need Perl knowledge
+See F for details.
-=head2 common test code for timed bail out
+=head2 Remove duplication of test setup.
-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.
+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. Throw in the handy tainting subroutines.
-=head2 POD -> HTML conversion in the core still sucks
+=head2 POD -E 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 simple as it sounds, particularly with the
@@ -77,47 +98,29 @@ is needed to improve the cross-linking.
The addition of C and its related modules may make this task
easier to complete.
-=head2 Parallel testing
+=head2 Make ExtUtils::ParseXS use strict;
-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
would be roughly equivalent to:
+
+ do { local $"='|'; /\b(?:P)\b/ }
-Introduce a new special block, UNITCHECK, which is run at the end of a
-compilation unit (module, file, eval(STRING) block). This will correspond to
-the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
-O.pm/B.pm backend framework depends on it.
+See L
+for the discussion.
=head2 optional optimizer
@@ -555,33 +1087,171 @@ 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
+=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 re-
-instated.
+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".
-=head2 What hooks would assertions need?
+=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 is good reading at this point,
+in fact, all of L is.)
+
+This has actually already been implemented (but only for Win32),
+take a look at F and F. 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.)
+
+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 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/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) {
+ }
-Assertions are in the core, and work. However, assertions needed to be added
-as a core patch, rather than an XS module in ext, or a CPAN module, because
-the core has no hooks in the necessary places. It would be useful to
-investigate what hooks would need to be added to make it possible to provide
-the full assertion support from a CPAN module, so that we aren't constraining
-the imagination of future CPAN authors.
+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 and the C, hence C still
+reports that the currently executing line is line 4. The solution was to inject
+a nextstate OPs for each C, 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 (although the C 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) 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), 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, 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 5.10"
+of 5.12"
=head2 make ithreads more robust
@@ -592,6 +1262,8 @@ 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
@@ -606,3 +1278,30 @@ Fix (or rewrite) the implementation of the C(?{...})/> closures.
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.
+
+
+=head1 Tasks for microperl
+
+
+[ Each and every one of these may be obsolete, but they were listed
+ in the old Todo.micro file]
+
+
+=head2 make creating uconfig.sh automatic
+
+=head2 make creating Makefile.micro automatic
+
+=head2 do away with fork/exec/wait?
+
+(system, popen should be enough?)
+
+=head2 some of the uconfig.sh really needs to be probed (using cc) in buildtime:
+
+(uConfigure? :-) native datatype widths and endianness come to mind
+