X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperltodo.pod;h=53158e7848e2ef7a3453dba9c2808eeadfe15047;hb=e99d581a4aaa3c92d0b0dda6799157fe7a569f31;hp=a1ebcb5d48ee6886ea5582c22ab0473445e6d746;hpb=a8d0aeb90259a19deb4d329326cf295d4f6d468f;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perltodo.pod b/pod/perltodo.pod index a1ebcb5..53158e7 100644 --- a/pod/perltodo.pod +++ b/pod/perltodo.pod @@ -4,10 +4,11 @@ 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 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 @@ -29,15 +30,6 @@ 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. Throw in the handy tainting subroutines. -=head2 merge common code in installperl and installman - -There are some common subroutines and a common C block in F -and F. 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 @@ -63,12 +55,6 @@ 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 use podchecker. -=head2 perlmodlib.PL rewrite - -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). - =head2 Parallel testing (This probably impacts much more than the core: also the Test::Harness @@ -162,6 +148,15 @@ 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. +=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. + =head2 Improving C Investigate whether C could share aggregates properly with @@ -204,6 +199,13 @@ 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 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 @@ -365,10 +367,26 @@ Make F be updated by F. 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 Exterminate PL_na! +=head2 Weed out needless PERL_UNUSED_ARG + +The C code uses the macro C 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 +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. -C festers still in the darkest corners of various typemap files. -It needs to be exterminated, replaced by a local variable of type C. +=back =head2 Modernize the order of directories in @INC @@ -426,6 +444,8 @@ as part of exercising your skills with coverage and profiling tools you might want to determine what ops I are the most commonly used. And in turn suggest evictions and promotions to achieve a better F. +One piece of Perl code that might make a good testbed is F. + =head2 Allocate OPs from arenas Currently all new OP structures are individually malloc()ed and free()d. @@ -468,6 +488,31 @@ 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 @@ -488,12 +533,99 @@ 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 and C are both currently allocated by C. +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, Cs +can probably be changed with minimal compatibility impact (probably nothing +outside of the core, or even outside of F allocates them), but they +probably aren't allocated/deallocated often enough for a speed saving. Whereas +C 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 for C, create a +pipe, store the reader in one, the writer in the other + +=item 3 + +In the "safe" signal handler (C/C), if +the C pointer non-C, and the writer file handle is open, + +=over 8 + +=item 1 + +serialise signal number, C (or at least the parts we care +about) into a small auto char buff + +=item 2 + +C 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 processing, if there are "signals on +the pipe", read the data out, deserialise, build the Perl structures on +the stack (code in C, the "unsafe" handler), and call as +usual. + +=back + +I think that this gets us decent C support, without the current risk +of running Perl code inside the signal handler context. (With all the dangers +of things like C 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; @@ -610,32 +742,6 @@ 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 Propagate const outwards from Perl_moreswitches() - -Change 32057 changed the parameter and return value of C -from to . It should now be possible to propagate -const-correctness outwards to C, C -and C. - -=head2 Duplicate logic in S_method_common() and Perl_gv_fetchmethod_autoload() - -A comment in C notes - - /* This code tries to figure out just what went wrong with - gv_fetchmethod. It therefore needs to duplicate a lot of - the internals of that function. We can't move it inside - Perl_gv_fetchmethod_autoload(), however, since that would - cause UNIVERSAL->can("NoSuchPackage::foo") to croak, and we - don't want that. - */ - -If C gets rewritten to take (more) flag bits, -then it ought to be possible to move the logic from C to -the "right" place. When making this change it would probably be good to also -pass in at least the method name length, if not also pre-computed hash values -when known. (I'm contemplating a plan to pre-compute hash values for common -fixed strings such as C and pass them in to functions.) - =head2 Organize error messages Perl's diagnostics (error messages, see L) could use @@ -667,6 +773,37 @@ also the warning messages (see L, C). 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 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 pointer, so that's all bytes too. The +tokeniser ignores the UTF-8-ness of C, or any SVs returned from +source filters. All this could be fixed. + =head2 state variable initialization in list context Currently this is illegal: @@ -766,34 +903,16 @@ 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 +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. +reinstated. =head2 Optimize away @_ The old perltodo notes "Look at the "reification" code in C". -=head2 Properly Unicode safe tokeniser and pads. - -The tokeniser isn't actually very UTF-8 clean. C 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 pointer, so that's all bytes too. The -tokeniser ignores the UTF-8-ness of C, or any SVs returned from -source filters. All this could be fixed. - -=head2 The yada yada yada operators - -Perl 6's Synopsis 3 says: - -I - -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 @@ -832,9 +951,119 @@ See also L. =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 +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 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