X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperltodo.pod;h=7b10f5fa3a397f6b7819963e78fcf41d7501e456;hb=f71d6157c7933c0d3df645f0411d97d7e2b66b2f;hp=3f1593902f342dd637b0e3cab4985592b778874c;hpb=256d1bb207447524e8a478707a9d2a73dc679170;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/pod/perltodo.pod b/pod/perltodo.pod
index 3f15939..7b10f5f 100644
--- a/pod/perltodo.pod
+++ b/pod/perltodo.pod
@@ -4,11 +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<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.
+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<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
@@ -30,21 +33,6 @@ 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 merge common code in installperl and installman
-
-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.
-
-=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
@@ -57,49 +45,29 @@ 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
+=head2 Make ExtUtils::ParseXS use strict;
+
+F<lib/ExtUtils/ParseXS.pm> contains this line
 
-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.
+    # use strict;  # One of these days...
 
-=head2 perlmodlib.PL rewrite
+Simply uncomment it, and fix all the resulting issues :-)
 
-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).
+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 C<{ ... }> blocks, and turning on strict within them.
 
 =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?
+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
 
@@ -117,28 +85,6 @@ tests that are currently missing.
 
 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
@@ -163,10 +109,11 @@ 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 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
 
@@ -205,6 +152,13 @@ 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
@@ -361,6 +315,77 @@ file/directory copying back and forth.
 
 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.
+
+=head2 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.
+
+=head2 decouple -g and -DDEBUGGING
+
+Currently F<Configure> automatically adds C<-DDEBUGGING> to the C compiler
+flags if it spots C<-g> in the optimiser flags. The pre-processor directive
+C<DEBUGGING> enables F<perl>'s command line <-D> options, but in the process
+makes F<perl> slower. It would be good to disentangle this logic, so that
+C-level debugging with C<-g> and Perl level debugging with C<-D> can easily
+be enabled independently.
+
 =head1 Tasks that need a little C knowledge
 
 These tasks would need a little C knowledge, but don't need any specific
@@ -403,28 +428,6 @@ 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,
@@ -443,6 +446,8 @@ 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.
@@ -541,6 +546,14 @@ 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.
 
+=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
 
@@ -548,6 +561,102 @@ 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 Remove the use of SVs as temporaries in dump.c
+
+F<dump.c> contains debugging routines to dump out the contains of perl data
+structures, such as C<SV>s, C<AV>s and C<HV>s. Currently, the dumping code
+B<uses> C<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 F<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 C<malloc>. The F<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 C<SV>s for
+B<its> buffers, use of which can cause problems similar to those of F<dump.c>,
+at similar times.
+
+=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;
@@ -695,6 +804,35 @@ also the warning messages (see L<perllexwarn>, C<warnings.pl>).
 These tasks would need C knowledge, and knowledge of how the interpreter works,
 or a willingness to learn.
 
+=head2 truncate() prototype
+
+The prototype of truncate() is currently C<$$>. It should probably
+be C<*$> instead. (This is changed in F<opcode.pl>)
+
+=head2 decapsulation of smart match argument
+
+Currently C<$foo ~~ $object> will die with the message "Smart matching a
+non-overloaded object breaks encapsulation". It would be nice to allow
+to bypass this by using explictly the syntax C<$foo ~~ %$object> or
+C<$foo ~~ @$object>.
+
+=head2 error reporting of [$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:
@@ -763,22 +901,11 @@ 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
@@ -835,16 +962,6 @@ reinstated.
 
 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
@@ -882,17 +999,101 @@ 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
+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 wrt cache-line
-filling.  The slab allocator could be reused for this purpose.
+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) {
+    }
 
-http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html
+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