| 1 | =head1 NAME |
| 2 | |
| 3 | perltodo - Perl TO-DO List |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 7 | This is a list of wishes for Perl. The most up to date version of this file |
| 8 | is at http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod |
| 9 | |
| 10 | The tasks we think are smaller or easier are listed first. Anyone is welcome |
| 11 | to work on any of these, but it's a good idea to first contact |
| 12 | I<perl5-porters@perl.org> to avoid duplication of effort, and to learn from |
| 13 | any previous attempts. By all means contact a pumpking privately first if you |
| 14 | prefer. |
| 15 | |
| 16 | Whilst patches to make the list shorter are most welcome, ideas to add to |
| 17 | the list are also encouraged. Check the perl5-porters archives for past |
| 18 | ideas, and any discussion about them. One set of archives may be found at: |
| 19 | |
| 20 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ |
| 21 | |
| 22 | What can we offer you in return? Fame, fortune, and everlasting glory? Maybe |
| 23 | not, but if your patch is incorporated, then we'll add your name to the |
| 24 | F<AUTHORS> file, which ships in the official distribution. How many other |
| 25 | programming languages offer you 1 line of immortality? |
| 26 | |
| 27 | =head1 Tasks that only need Perl knowledge |
| 28 | |
| 29 | =head2 Smartmatch design issues |
| 30 | |
| 31 | In 5.10.0 the smartmatch operator C<~~> isn't working quite "right". But |
| 32 | before we can fix the implementation, we need to define what "right" is. |
| 33 | The first problem is that Robin Houston implemented the Perl 6 smart match |
| 34 | spec as of February 2006, when smart match was axiomatically symmetrical: |
| 35 | L<http://groups.google.com/group/perl.perl6.language/msg/bf2b486f089ad021> |
| 36 | |
| 37 | Since then the Perl 6 target moved, but the Perl 5 implementation did not. |
| 38 | |
| 39 | So it would be useful for someone to compare the Perl 6 smartmatch table |
| 40 | as of February 2006 L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=markup&pathrev=7615> |
| 41 | and the current table L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?revision=14556&view=markup> |
| 42 | and tabulate the differences in Perl 6. The annotated view of changes is |
| 43 | L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=annotate> and the diff is |
| 44 | C<svn diff -r7615:14556 http://svn.perl.org/perl6/doc/trunk/design/syn/S03.pod> |
| 45 | -- search for C<=head1 Smart matching>. (In theory F<viewvc> can generate that, |
| 46 | but in practice when I tried it hung forever, I assume "thinking") |
| 47 | |
| 48 | With that done and published, someone (else) can then map any changed Perl 6 |
| 49 | semantics back to Perl 5, based on how the existing semantics map to Perl 5: |
| 50 | L<http://search.cpan.org/~rgarcia/perl-5.10.0/pod/perlsyn.pod#Smart_matching_in_detail> |
| 51 | |
| 52 | |
| 53 | There are also some questions that need answering: |
| 54 | |
| 55 | =over 4 |
| 56 | |
| 57 | =item * |
| 58 | |
| 59 | How do you negate one? (documentation issue) |
| 60 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-01/msg00071.html |
| 61 | |
| 62 | =item * |
| 63 | |
| 64 | Array behaviors |
| 65 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00799.html |
| 66 | |
| 67 | * Should smart matches be symmetrical? (Perl 6 says no) |
| 68 | |
| 69 | * Other differences between Perl 5 and Perl 6 smart match? |
| 70 | |
| 71 | =item * |
| 72 | |
| 73 | Objects and smart match |
| 74 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00865.html |
| 75 | |
| 76 | =back |
| 77 | |
| 78 | =head2 Remove duplication of test setup. |
| 79 | |
| 80 | Schwern notes, that there's duplication of code - lots and lots of tests have |
| 81 | some variation on the big block of C<$Is_Foo> checks. We can safely put this |
| 82 | into a file, change it to build an C<%Is> hash and require it. Maybe just put |
| 83 | it into F<test.pl>. Throw in the handy tainting subroutines. |
| 84 | |
| 85 | =head2 POD -E<gt> HTML conversion in the core still sucks |
| 86 | |
| 87 | Which is crazy given just how simple POD purports to be, and how simple HTML |
| 88 | can be. It's not actually I<as> simple as it sounds, particularly with the |
| 89 | flexibility POD allows for C<=item>, but it would be good to improve the |
| 90 | visual appeal of the HTML generated, and to avoid it having any validation |
| 91 | errors. See also L</make HTML install work>, as the layout of installation tree |
| 92 | is needed to improve the cross-linking. |
| 93 | |
| 94 | The addition of C<Pod::Simple> and its related modules may make this task |
| 95 | easier to complete. |
| 96 | |
| 97 | =head2 Parallel testing |
| 98 | |
| 99 | (This probably impacts much more than the core: also the Test::Harness |
| 100 | and TAP::* modules on CPAN.) |
| 101 | |
| 102 | All of the tests in F<t/> can now be run in parallel, if C<$ENV{TEST_JOBS}> |
| 103 | is set. However, tests within each directory in F<ext> and F<lib> are still |
| 104 | run in series, with directories run in parallel. This is an adequate |
| 105 | heuristic, but it might be possible to relax it further, and get more |
| 106 | throughput. Specifically, it would be good to audit all of F<lib/*.t>, and |
| 107 | make them use C<File::Temp>. |
| 108 | |
| 109 | =head2 Make Schwern poorer |
| 110 | |
| 111 | We should have tests for everything. When all the core's modules are tested, |
| 112 | Schwern has promised to donate to $500 to TPF. We may need volunteers to |
| 113 | hold him upside down and shake vigorously in order to actually extract the |
| 114 | cash. |
| 115 | |
| 116 | =head2 Improve the coverage of the core tests |
| 117 | |
| 118 | Use Devel::Cover to ascertain the core modules's test coverage, then add |
| 119 | tests that are currently missing. |
| 120 | |
| 121 | =head2 test B |
| 122 | |
| 123 | A full test suite for the B module would be nice. |
| 124 | |
| 125 | =head2 A decent benchmark |
| 126 | |
| 127 | C<perlbench> seems impervious to any recent changes made to the perl core. It |
| 128 | would be useful to have a reasonable general benchmarking suite that roughly |
| 129 | represented what current perl programs do, and measurably reported whether |
| 130 | tweaks to the core improve, degrade or don't really affect performance, to |
| 131 | guide people attempting to optimise the guts of perl. Gisle would welcome |
| 132 | new tests for perlbench. |
| 133 | |
| 134 | =head2 fix tainting bugs |
| 135 | |
| 136 | Fix the bugs revealed by running the test suite with the C<-t> switch (via |
| 137 | C<make test.taintwarn>). |
| 138 | |
| 139 | =head2 Dual life everything |
| 140 | |
| 141 | As part of the "dists" plan, anything that doesn't belong in the smallest perl |
| 142 | distribution needs to be dual lifed. Anything else can be too. Figure out what |
| 143 | changes would be needed to package that module and its tests up for CPAN, and |
| 144 | do so. Test it with older perl releases, and fix the problems you find. |
| 145 | |
| 146 | To make a minimal perl distribution, it's useful to look at |
| 147 | F<t/lib/commonsense.t>. |
| 148 | |
| 149 | =head2 Bundle dual life modules in ext/ |
| 150 | |
| 151 | For maintenance (and branch merging) reasons, it would be useful to move |
| 152 | some architecture-independent dual-life modules from lib/ to ext/, if this |
| 153 | has no negative impact on the build of perl itself. |
| 154 | |
| 155 | =head2 POSIX memory footprint |
| 156 | |
| 157 | Ilya observed that use POSIX; eats memory like there's no tomorrow, and at |
| 158 | various times worked to cut it down. There is probably still fat to cut out - |
| 159 | for example POSIX passes Exporter some very memory hungry data structures. |
| 160 | |
| 161 | =head2 embed.pl/makedef.pl |
| 162 | |
| 163 | There is a script F<embed.pl> that generates several header files to prefix |
| 164 | all of Perl's symbols in a consistent way, to provide some semblance of |
| 165 | namespace support in C<C>. Functions are declared in F<embed.fnc>, variables |
| 166 | in F<interpvar.h>. Quite a few of the functions and variables |
| 167 | are conditionally declared there, using C<#ifdef>. However, F<embed.pl> |
| 168 | doesn't understand the C macros, so the rules about which symbols are present |
| 169 | when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay. |
| 170 | It would be good to teach C<embed.pl> to understand the conditional |
| 171 | compilation, and hence remove the duplication, and the mistakes it has caused. |
| 172 | |
| 173 | =head2 use strict; and AutoLoad |
| 174 | |
| 175 | Currently if you write |
| 176 | |
| 177 | package Whack; |
| 178 | use AutoLoader 'AUTOLOAD'; |
| 179 | use strict; |
| 180 | 1; |
| 181 | __END__ |
| 182 | sub bloop { |
| 183 | print join (' ', No, strict, here), "!\n"; |
| 184 | } |
| 185 | |
| 186 | then C<use strict;> isn't in force within the autoloaded subroutines. It would |
| 187 | be more consistent (and less surprising) to arrange for all lexical pragmas |
| 188 | in force at the __END__ block to be in force within each autoloaded subroutine. |
| 189 | |
| 190 | There's a similar problem with SelfLoader. |
| 191 | |
| 192 | =head2 profile installman |
| 193 | |
| 194 | The F<installman> script is slow. All it is doing text processing, which we're |
| 195 | told is something Perl is good at. So it would be nice to know what it is doing |
| 196 | that is taking so much CPU, and where possible address it. |
| 197 | |
| 198 | |
| 199 | =head1 Tasks that need a little sysadmin-type knowledge |
| 200 | |
| 201 | Or if you prefer, tasks that you would learn from, and broaden your skills |
| 202 | base... |
| 203 | |
| 204 | =head2 make HTML install work |
| 205 | |
| 206 | There is an C<installhtml> target in the Makefile. It's marked as |
| 207 | "experimental". It would be good to get this tested, make it work reliably, and |
| 208 | remove the "experimental" tag. This would include |
| 209 | |
| 210 | =over 4 |
| 211 | |
| 212 | =item 1 |
| 213 | |
| 214 | Checking that cross linking between various parts of the documentation works. |
| 215 | In particular that links work between the modules (files with POD in F<lib/>) |
| 216 | and the core documentation (files in F<pod/>) |
| 217 | |
| 218 | =item 2 |
| 219 | |
| 220 | Work out how to split C<perlfunc> into chunks, preferably one per function |
| 221 | group, preferably with general case code that could be used elsewhere. |
| 222 | Challenges here are correctly identifying the groups of functions that go |
| 223 | together, and making the right named external cross-links point to the right |
| 224 | page. Things to be aware of are C<-X>, groups such as C<getpwnam> to |
| 225 | C<endservent>, two or more C<=items> giving the different parameter lists, such |
| 226 | as |
| 227 | |
| 228 | =item substr EXPR,OFFSET,LENGTH,REPLACEMENT |
| 229 | =item substr EXPR,OFFSET,LENGTH |
| 230 | =item substr EXPR,OFFSET |
| 231 | |
| 232 | and different parameter lists having different meanings. (eg C<select>) |
| 233 | |
| 234 | =back |
| 235 | |
| 236 | =head2 compressed man pages |
| 237 | |
| 238 | Be able to install them. This would probably need a configure test to see how |
| 239 | the system does compressed man pages (same directory/different directory? |
| 240 | same filename/different filename), as well as tweaking the F<installman> script |
| 241 | to compress as necessary. |
| 242 | |
| 243 | =head2 Add a code coverage target to the Makefile |
| 244 | |
| 245 | Make it easy for anyone to run Devel::Cover on the core's tests. The steps |
| 246 | to do this manually are roughly |
| 247 | |
| 248 | =over 4 |
| 249 | |
| 250 | =item * |
| 251 | |
| 252 | do a normal C<Configure>, but include Devel::Cover as a module to install |
| 253 | (see F<INSTALL> for how to do this) |
| 254 | |
| 255 | =item * |
| 256 | |
| 257 | make perl |
| 258 | |
| 259 | =item * |
| 260 | |
| 261 | cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness |
| 262 | |
| 263 | =item * |
| 264 | |
| 265 | Process the resulting Devel::Cover database |
| 266 | |
| 267 | =back |
| 268 | |
| 269 | This just give you the coverage of the F<.pm>s. To also get the C level |
| 270 | coverage you need to |
| 271 | |
| 272 | =over 4 |
| 273 | |
| 274 | =item * |
| 275 | |
| 276 | Additionally tell C<Configure> to use the appropriate C compiler flags for |
| 277 | C<gcov> |
| 278 | |
| 279 | =item * |
| 280 | |
| 281 | make perl.gcov |
| 282 | |
| 283 | (instead of C<make perl>) |
| 284 | |
| 285 | =item * |
| 286 | |
| 287 | After running the tests run C<gcov> to generate all the F<.gcov> files. |
| 288 | (Including down in the subdirectories of F<ext/> |
| 289 | |
| 290 | =item * |
| 291 | |
| 292 | (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files |
| 293 | to get their stats into the cover_db directory. |
| 294 | |
| 295 | =item * |
| 296 | |
| 297 | Then process the Devel::Cover database |
| 298 | |
| 299 | =back |
| 300 | |
| 301 | It would be good to add a single switch to C<Configure> to specify that you |
| 302 | wanted to perform perl level coverage, and another to specify C level |
| 303 | coverage, and have C<Configure> and the F<Makefile> do all the right things |
| 304 | automatically. |
| 305 | |
| 306 | =head2 Make Config.pm cope with differences between built and installed perl |
| 307 | |
| 308 | Quite often vendors ship a perl binary compiled with their (pay-for) |
| 309 | compilers. People install a free compiler, such as gcc. To work out how to |
| 310 | build extensions, Perl interrogates C<%Config>, so in this situation |
| 311 | C<%Config> describes compilers that aren't there, and extension building |
| 312 | fails. This forces people into choosing between re-compiling perl themselves |
| 313 | using the compiler they have, or only using modules that the vendor ships. |
| 314 | |
| 315 | It would be good to find a way teach C<Config.pm> about the installation setup, |
| 316 | possibly involving probing at install time or later, so that the C<%Config> in |
| 317 | a binary distribution better describes the installed machine, when the |
| 318 | installed machine differs from the build machine in some significant way. |
| 319 | |
| 320 | =head2 linker specification files |
| 321 | |
| 322 | Some platforms mandate that you provide a list of a shared library's external |
| 323 | symbols to the linker, so the core already has the infrastructure in place to |
| 324 | do this for generating shared perl libraries. My understanding is that the |
| 325 | GNU toolchain can accept an optional linker specification file, and restrict |
| 326 | visibility just to symbols declared in that file. It would be good to extend |
| 327 | F<makedef.pl> to support this format, and to provide a means within |
| 328 | C<Configure> to enable it. This would allow Unix users to test that the |
| 329 | export list is correct, and to build a perl that does not pollute the global |
| 330 | namespace with private symbols. |
| 331 | |
| 332 | =head2 Cross-compile support |
| 333 | |
| 334 | Currently C<Configure> understands C<-Dusecrosscompile> option. This option |
| 335 | arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is |
| 336 | assumed then to be copied to TARGET machine and used as a replacement of full |
| 337 | C<perl> executable. |
| 338 | |
| 339 | This could be done little differently. Namely C<miniperl> should be built for |
| 340 | HOST and then full C<perl> with extensions should be compiled for TARGET. |
| 341 | This, however, might require extra trickery for %Config: we have one config |
| 342 | first for HOST and then another for TARGET. Tools like MakeMaker will be |
| 343 | mightily confused. Having around two different types of executables and |
| 344 | libraries (HOST and TARGET) makes life interesting for Makefiles and |
| 345 | shell (and Perl) scripts. There is $Config{run}, normally empty, which |
| 346 | can be used as an execution wrapper. Also note that in some |
| 347 | cross-compilation/execution environments the HOST and the TARGET do |
| 348 | not see the same filesystem(s), the $Config{run} may need to do some |
| 349 | file/directory copying back and forth. |
| 350 | |
| 351 | =head2 roffitall |
| 352 | |
| 353 | Make F<pod/roffitall> be updated by F<pod/buildtoc>. |
| 354 | |
| 355 | =head2 Split "linker" from "compiler" |
| 356 | |
| 357 | Right now, Configure probes for two commands, and sets two variables: |
| 358 | |
| 359 | =over 4 |
| 360 | |
| 361 | =item * C<cc> (in F<cc.U>) |
| 362 | |
| 363 | This variable holds the name of a command to execute a C compiler which |
| 364 | can resolve multiple global references that happen to have the same |
| 365 | name. Usual values are F<cc> and F<gcc>. |
| 366 | Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>. |
| 367 | |
| 368 | =item * C<ld> (in F<dlsrc.U>) |
| 369 | |
| 370 | This variable indicates the program to be used to link |
| 371 | libraries for dynamic loading. On some systems, it is F<ld>. |
| 372 | On ELF systems, it should be C<$cc>. Mostly, we'll try to respect |
| 373 | the hint file setting. |
| 374 | |
| 375 | =back |
| 376 | |
| 377 | There is an implicit historical assumption from around Perl5.000alpha |
| 378 | something, that C<$cc> is also the correct command for linking object files |
| 379 | together to make an executable. This may be true on Unix, but it's not true |
| 380 | on other platforms, and there are a maze of work arounds in other places (such |
| 381 | as F<Makefile.SH>) to cope with this. |
| 382 | |
| 383 | Ideally, we should create a new variable to hold the name of the executable |
| 384 | linker program, probe for it in F<Configure>, and centralise all the special |
| 385 | case logic there or in hints files. |
| 386 | |
| 387 | A small bikeshed issue remains - what to call it, given that C<$ld> is already |
| 388 | taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command |
| 389 | for creating dynamically-loadable modules) and C<$link> could be confused with |
| 390 | the Unix command line executable of the same name, which does something |
| 391 | completely different. Andy Dougherty makes the counter argument "In parrot, I |
| 392 | tried to call the command used to link object files and libraries into an |
| 393 | executable F<link>, since that's what my vaguely-remembered DOS and VMS |
| 394 | experience suggested. I don't think any real confusion has ensued, so it's |
| 395 | probably a reasonable name for perl5 to use." |
| 396 | |
| 397 | "Alas, I've always worried that introducing it would make things worse, |
| 398 | since now the module building utilities would have to look for |
| 399 | C<$Config{link}> and institute a fall-back plan if it weren't found." |
| 400 | Although I can see that as confusing, given that C<$Config{d_link}> is true |
| 401 | when (hard) links are available. |
| 402 | |
| 403 | =head1 Tasks that need a little C knowledge |
| 404 | |
| 405 | These tasks would need a little C knowledge, but don't need any specific |
| 406 | background or experience with XS, or how the Perl interpreter works |
| 407 | |
| 408 | =head2 Weed out needless PERL_UNUSED_ARG |
| 409 | |
| 410 | The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about |
| 411 | unused arguments. Often the arguments can't be removed, as there is an |
| 412 | external constraint that determines the prototype of the function, so this |
| 413 | approach is valid. However, there are some cases where C<PERL_UNUSED_ARG> |
| 414 | could be removed. Specifically |
| 415 | |
| 416 | =over 4 |
| 417 | |
| 418 | =item * |
| 419 | |
| 420 | The prototypes of (nearly all) static functions can be changed |
| 421 | |
| 422 | =item * |
| 423 | |
| 424 | Unused arguments generated by short cut macros are wasteful - the short cut |
| 425 | macro used can be changed. |
| 426 | |
| 427 | =back |
| 428 | |
| 429 | =head2 Modernize the order of directories in @INC |
| 430 | |
| 431 | The way @INC is laid out by default, one cannot upgrade core (dual-life) |
| 432 | modules without overwriting files. This causes problems for binary |
| 433 | package builders. One possible proposal is laid out in this |
| 434 | message: |
| 435 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>. |
| 436 | |
| 437 | =head2 -Duse32bit* |
| 438 | |
| 439 | Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall. |
| 440 | On these systems, it might be the default compilation mode, and there |
| 441 | is currently no guarantee that passing no use64bitall option to the |
| 442 | Configure process will build a 32bit perl. Implementing -Duse32bit* |
| 443 | options would be nice for perl 5.12. |
| 444 | |
| 445 | =head2 Profile Perl - am I hot or not? |
| 446 | |
| 447 | The Perl source code is stable enough that it makes sense to profile it, |
| 448 | identify and optimise the hotspots. It would be good to measure the |
| 449 | performance of the Perl interpreter using free tools such as cachegrind, |
| 450 | gprof, and dtrace, and work to reduce the bottlenecks they reveal. |
| 451 | |
| 452 | As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops, |
| 453 | the ops that are most commonly used. The idea is that by grouping them, their |
| 454 | object code will be adjacent in the executable, so they have a greater chance |
| 455 | of already being in the CPU cache (or swapped in) due to being near another op |
| 456 | already in use. |
| 457 | |
| 458 | Except that it's not clear if these really are the most commonly used ops. So |
| 459 | as part of exercising your skills with coverage and profiling tools you might |
| 460 | want to determine what ops I<really> are the most commonly used. And in turn |
| 461 | suggest evictions and promotions to achieve a better F<pp_hot.c>. |
| 462 | |
| 463 | One piece of Perl code that might make a good testbed is F<installman>. |
| 464 | |
| 465 | =head2 Allocate OPs from arenas |
| 466 | |
| 467 | Currently all new OP structures are individually malloc()ed and free()d. |
| 468 | All C<malloc> implementations have space overheads, and are now as fast as |
| 469 | custom allocates so it would both use less memory and less CPU to allocate |
| 470 | the various OP structures from arenas. The SV arena code can probably be |
| 471 | re-used for this. |
| 472 | |
| 473 | Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use |
| 474 | Perl_Slab_alloc() to pack optrees into a contiguous block, which is |
| 475 | probably superior to the use of OP arenas, esp. from a cache locality |
| 476 | standpoint. See L<Profile Perl - am I hot or not?>. |
| 477 | |
| 478 | =head2 Improve win32/wince.c |
| 479 | |
| 480 | Currently, numerous functions look virtually, if not completely, |
| 481 | identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't |
| 482 | be good. |
| 483 | |
| 484 | =head2 Use secure CRT functions when building with VC8 on Win32 |
| 485 | |
| 486 | Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis |
| 487 | that they were "unsafe" and introduced differently named secure versions of |
| 488 | them as replacements, e.g. instead of writing |
| 489 | |
| 490 | FILE* f = fopen(__FILE__, "r"); |
| 491 | |
| 492 | one should now write |
| 493 | |
| 494 | FILE* f; |
| 495 | errno_t err = fopen_s(&f, __FILE__, "r"); |
| 496 | |
| 497 | Currently, the warnings about these deprecations have been disabled by adding |
| 498 | -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that |
| 499 | warning suppressant and actually make use of the new secure CRT functions. |
| 500 | |
| 501 | There is also a similar issue with POSIX CRT function names like fileno having |
| 502 | been deprecated in favour of ISO C++ conformant names like _fileno. These |
| 503 | warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It |
| 504 | might be nice to do as Microsoft suggest here too, although, unlike the secure |
| 505 | functions issue, there is presumably little or no benefit in this case. |
| 506 | |
| 507 | =head2 Fix POSIX::access() and chdir() on Win32 |
| 508 | |
| 509 | These functions currently take no account of DACLs and therefore do not behave |
| 510 | correctly in situations where access is restricted by DACLs (as opposed to the |
| 511 | read-only attribute). |
| 512 | |
| 513 | Furthermore, POSIX::access() behaves differently for directories having the |
| 514 | read-only attribute set depending on what CRT library is being used. For |
| 515 | example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that |
| 516 | such directories are not writable, whereas in fact all directories are writable |
| 517 | unless access is denied by DACLs. (In the case of directories, the read-only |
| 518 | attribute actually only means that the directory cannot be deleted.) This CRT |
| 519 | bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still |
| 520 | not actually be writable if access is indeed denied by DACLs). |
| 521 | |
| 522 | For the chdir() issue, see ActiveState bug #74552: |
| 523 | http://bugs.activestate.com/show_bug.cgi?id=74552 |
| 524 | |
| 525 | Therefore, DACLs should be checked both for consistency across CRTs and for |
| 526 | the correct answer. |
| 527 | |
| 528 | (Note that perl's -w operator should not be modified to check DACLs. It has |
| 529 | been written so that it reflects the state of the read-only attribute, even |
| 530 | for directories (whatever CRT is being used), for symmetry with chmod().) |
| 531 | |
| 532 | =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf() |
| 533 | |
| 534 | Maybe create a utility that checks after each libperl.a creation that |
| 535 | none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets()) |
| 536 | ever creep back to libperl.a. |
| 537 | |
| 538 | nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/' |
| 539 | |
| 540 | Note, of course, that this will only tell whether B<your> platform |
| 541 | is using those naughty interfaces. |
| 542 | |
| 543 | =head2 -D_FORTIFY_SOURCE=2, -fstack-protector |
| 544 | |
| 545 | Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc |
| 546 | (4.1 onwards?) supports C<-fstack-protector>, both of which give |
| 547 | protection against various kinds of buffer overflow problems. |
| 548 | These should probably be used for compiling Perl whenever available, |
| 549 | Configure and/or hints files should be adjusted to probe for the |
| 550 | availability of these features and enable them as appropriate. |
| 551 | |
| 552 | =head2 Arenas for GPs? For MAGIC? |
| 553 | |
| 554 | C<struct gp> and C<struct magic> are both currently allocated by C<malloc>. |
| 555 | It might be a speed or memory saving to change to using arenas. Or it might |
| 556 | not. It would need some suitable benchmarking first. In particular, C<GP>s |
| 557 | can probably be changed with minimal compatibility impact (probably nothing |
| 558 | outside of the core, or even outside of F<gv.c> allocates them), but they |
| 559 | probably aren't allocated/deallocated often enough for a speed saving. Whereas |
| 560 | C<MAGIC> is allocated/deallocated more often, but in turn, is also something |
| 561 | more externally visible, so changing the rules here may bite external code. |
| 562 | |
| 563 | =head2 Shared arenas |
| 564 | |
| 565 | Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and |
| 566 | PVHV, and PVCV and PVFM. It should be possible to allocate and return same |
| 567 | sized bodies from the same actual arena, rather than maintaining one arena for |
| 568 | each. This could save 4-6K per thread, of memory no longer tied up in the |
| 569 | not-yet-allocated part of an arena. |
| 570 | |
| 571 | |
| 572 | =head1 Tasks that need a knowledge of XS |
| 573 | |
| 574 | These tasks would need C knowledge, and roughly the level of knowledge of |
| 575 | the perl API that comes from writing modules that use XS to interface to |
| 576 | C. |
| 577 | |
| 578 | =head2 safely supporting POSIX SA_SIGINFO |
| 579 | |
| 580 | Some years ago Jarkko supplied patches to provide support for the POSIX |
| 581 | SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler. |
| 582 | |
| 583 | Unfortunately, it only works with "unsafe" signals, because under safe |
| 584 | signals, by the time Perl gets to run the signal handler, the extra |
| 585 | information has been lost. Moreover, it's not easy to store it somewhere, |
| 586 | as you can't call mutexs, or do anything else fancy, from inside a signal |
| 587 | handler. |
| 588 | |
| 589 | So it strikes me that we could provide safe SA_SIGINFO support |
| 590 | |
| 591 | =over 4 |
| 592 | |
| 593 | =item 1 |
| 594 | |
| 595 | Provide global variables for two file descriptors |
| 596 | |
| 597 | =item 2 |
| 598 | |
| 599 | When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a |
| 600 | pipe, store the reader in one, the writer in the other |
| 601 | |
| 602 | =item 3 |
| 603 | |
| 604 | In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if |
| 605 | the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open, |
| 606 | |
| 607 | =over 8 |
| 608 | |
| 609 | =item 1 |
| 610 | |
| 611 | serialise signal number, C<struct siginfo_t> (or at least the parts we care |
| 612 | about) into a small auto char buff |
| 613 | |
| 614 | =item 2 |
| 615 | |
| 616 | C<write()> that (non-blocking) to the writer fd |
| 617 | |
| 618 | =over 12 |
| 619 | |
| 620 | =item 1 |
| 621 | |
| 622 | if it writes 100%, flag the signal in a counter of "signals on the pipe" akin |
| 623 | to the current per-signal-number counts |
| 624 | |
| 625 | =item 2 |
| 626 | |
| 627 | if it writes 0%, assume the pipe is full. Flag the data as lost? |
| 628 | |
| 629 | =item 3 |
| 630 | |
| 631 | if it writes partially, croak a panic, as your OS is broken. |
| 632 | |
| 633 | =back |
| 634 | |
| 635 | =back |
| 636 | |
| 637 | =item 4 |
| 638 | |
| 639 | in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on |
| 640 | the pipe", read the data out, deserialise, build the Perl structures on |
| 641 | the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as |
| 642 | usual. |
| 643 | |
| 644 | =back |
| 645 | |
| 646 | I think that this gets us decent C<SA_SIGINFO> support, without the current risk |
| 647 | of running Perl code inside the signal handler context. (With all the dangers |
| 648 | of things like C<malloc> corruption that that currently offers us) |
| 649 | |
| 650 | For more information see the thread starting with this message: |
| 651 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html |
| 652 | |
| 653 | =head2 autovivification |
| 654 | |
| 655 | Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict; |
| 656 | |
| 657 | This task is incremental - even a little bit of work on it will help. |
| 658 | |
| 659 | =head2 Unicode in Filenames |
| 660 | |
| 661 | chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open, |
| 662 | opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen, |
| 663 | system, truncate, unlink, utime, -X. All these could potentially accept |
| 664 | Unicode filenames either as input or output (and in the case of system |
| 665 | and qx Unicode in general, as input or output to/from the shell). |
| 666 | Whether a filesystem - an operating system pair understands Unicode in |
| 667 | filenames varies. |
| 668 | |
| 669 | Known combinations that have some level of understanding include |
| 670 | Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac |
| 671 | OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to |
| 672 | create Unicode filenames, what forms of Unicode are accepted and used |
| 673 | (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used, |
| 674 | and so on, varies. Finding the right level of interfacing to Perl |
| 675 | requires some thought. Remember that an OS does not implicate a |
| 676 | filesystem. |
| 677 | |
| 678 | (The Windows -C command flag "wide API support" has been at least |
| 679 | temporarily retired in 5.8.1, and the -C has been repurposed, see |
| 680 | L<perlrun>.) |
| 681 | |
| 682 | Most probably the right way to do this would be this: |
| 683 | L</"Virtualize operating system access">. |
| 684 | |
| 685 | =head2 Unicode in %ENV |
| 686 | |
| 687 | Currently the %ENV entries are always byte strings. |
| 688 | See L</"Virtualize operating system access">. |
| 689 | |
| 690 | =head2 Unicode and glob() |
| 691 | |
| 692 | Currently glob patterns and filenames returned from File::Glob::glob() |
| 693 | are always byte strings. See L</"Virtualize operating system access">. |
| 694 | |
| 695 | =head2 Unicode and lc/uc operators |
| 696 | |
| 697 | Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on |
| 698 | what the internal encoding of their argument is. That should not be the |
| 699 | case. Maybe add a pragma to switch behaviour. |
| 700 | |
| 701 | =head2 use less 'memory' |
| 702 | |
| 703 | Investigate trade offs to switch out perl's choices on memory usage. |
| 704 | Particularly perl should be able to give memory back. |
| 705 | |
| 706 | This task is incremental - even a little bit of work on it will help. |
| 707 | |
| 708 | =head2 Re-implement C<:unique> in a way that is actually thread-safe |
| 709 | |
| 710 | The old implementation made bad assumptions on several levels. A good 90% |
| 711 | solution might be just to make C<:unique> work to share the string buffer |
| 712 | of SvPVs. That way large constant strings can be shared between ithreads, |
| 713 | such as the configuration information in F<Config>. |
| 714 | |
| 715 | =head2 Make tainting consistent |
| 716 | |
| 717 | Tainting would be easier to use if it didn't take documented shortcuts and |
| 718 | allow taint to "leak" everywhere within an expression. |
| 719 | |
| 720 | =head2 readpipe(LIST) |
| 721 | |
| 722 | system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid |
| 723 | running a shell. readpipe() (the function behind qx//) could be similarly |
| 724 | extended. |
| 725 | |
| 726 | =head2 Audit the code for destruction ordering assumptions |
| 727 | |
| 728 | Change 25773 notes |
| 729 | |
| 730 | /* Need to check SvMAGICAL, as during global destruction it may be that |
| 731 | AvARYLEN(av) has been freed before av, and hence the SvANY() pointer |
| 732 | is now part of the linked list of SV heads, rather than pointing to |
| 733 | the original body. */ |
| 734 | /* FIXME - audit the code for other bugs like this one. */ |
| 735 | |
| 736 | adding the C<SvMAGICAL> check to |
| 737 | |
| 738 | if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) { |
| 739 | MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen); |
| 740 | |
| 741 | Go through the core and look for similar assumptions that SVs have particular |
| 742 | types, as all bets are off during global destruction. |
| 743 | |
| 744 | =head2 Extend PerlIO and PerlIO::Scalar |
| 745 | |
| 746 | PerlIO::Scalar doesn't know how to truncate(). Implementing this |
| 747 | would require extending the PerlIO vtable. |
| 748 | |
| 749 | Similarly the PerlIO vtable doesn't know about formats (write()), or |
| 750 | about stat(), or chmod()/chown(), utime(), or flock(). |
| 751 | |
| 752 | (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership |
| 753 | would mean.) |
| 754 | |
| 755 | PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(), |
| 756 | opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(), |
| 757 | readlink(). |
| 758 | |
| 759 | See also L</"Virtualize operating system access">. |
| 760 | |
| 761 | =head2 -C on the #! line |
| 762 | |
| 763 | It should be possible to make -C work correctly if found on the #! line, |
| 764 | given that all perl command line options are strict ASCII, and -C changes |
| 765 | only the interpretation of non-ASCII characters, and not for the script file |
| 766 | handle. To make it work needs some investigation of the ordering of function |
| 767 | calls during startup, and (by implication) a bit of tweaking of that order. |
| 768 | |
| 769 | =head2 Organize error messages |
| 770 | |
| 771 | Perl's diagnostics (error messages, see L<perldiag>) could use |
| 772 | reorganizing and formalizing so that each error message has its |
| 773 | stable-for-all-eternity unique id, categorized by severity, type, and |
| 774 | subsystem. (The error messages would be listed in a datafile outside |
| 775 | of the Perl source code, and the source code would only refer to the |
| 776 | messages by the id.) This clean-up and regularizing should apply |
| 777 | for all croak() messages. |
| 778 | |
| 779 | This would enable all sorts of things: easier translation/localization |
| 780 | of the messages (though please do keep in mind the caveats of |
| 781 | L<Locale::Maketext> about too straightforward approaches to |
| 782 | translation), filtering by severity, and instead of grepping for a |
| 783 | particular error message one could look for a stable error id. (Of |
| 784 | course, changing the error messages by default would break all the |
| 785 | existing software depending on some particular error message...) |
| 786 | |
| 787 | This kind of functionality is known as I<message catalogs>. Look for |
| 788 | inspiration for example in the catgets() system, possibly even use it |
| 789 | if available-- but B<only> if available, all platforms will B<not> |
| 790 | have catgets(). |
| 791 | |
| 792 | For the really pure at heart, consider extending this item to cover |
| 793 | also the warning messages (see L<perllexwarn>, C<warnings.pl>). |
| 794 | |
| 795 | =head1 Tasks that need a knowledge of the interpreter |
| 796 | |
| 797 | These tasks would need C knowledge, and knowledge of how the interpreter works, |
| 798 | or a willingness to learn. |
| 799 | |
| 800 | =head2 error reporting of [$a ; $b] |
| 801 | |
| 802 | Using C<;> inside brackets is a syntax error, and we don't propose to change |
| 803 | that by giving it any meaning. However, it's not reported very helpfully: |
| 804 | |
| 805 | $ perl -e '$a = [$b; $c];' |
| 806 | syntax error at -e line 1, near "$b;" |
| 807 | syntax error at -e line 1, near "$c]" |
| 808 | Execution of -e aborted due to compilation errors. |
| 809 | |
| 810 | It should be possible to hook into the tokeniser or the lexer, so that when a |
| 811 | C<;> is parsed where it is not legal as a statement terminator (ie inside |
| 812 | C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like |
| 813 | I<';' isn't legal inside an expression - if you need multiple statements use a |
| 814 | do {...} block>. See the thread starting at |
| 815 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html |
| 816 | |
| 817 | =head2 lexicals used only once |
| 818 | |
| 819 | This warns: |
| 820 | |
| 821 | $ perl -we '$pie = 42' |
| 822 | Name "main::pie" used only once: possible typo at -e line 1. |
| 823 | |
| 824 | This does not: |
| 825 | |
| 826 | $ perl -we 'my $pie = 42' |
| 827 | |
| 828 | Logically all lexicals used only once should warn, if the user asks for |
| 829 | warnings. An unworked RT ticket (#5087) has been open for almost seven |
| 830 | years for this discrepancy. |
| 831 | |
| 832 | =head2 UTF-8 revamp |
| 833 | |
| 834 | The handling of Unicode is unclean in many places. For example, the regexp |
| 835 | engine matches in Unicode semantics whenever the string or the pattern is |
| 836 | flagged as UTF-8, but that should not be dependent on an internal storage |
| 837 | detail of the string. Likewise, case folding behaviour is dependent on the |
| 838 | UTF8 internal flag being on or off. |
| 839 | |
| 840 | =head2 Properly Unicode safe tokeniser and pads. |
| 841 | |
| 842 | The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack - |
| 843 | variable names are stored in stashes as raw bytes, without the utf-8 flag |
| 844 | set. The pad API only takes a C<char *> pointer, so that's all bytes too. The |
| 845 | tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from |
| 846 | source filters. All this could be fixed. |
| 847 | |
| 848 | =head2 state variable initialization in list context |
| 849 | |
| 850 | Currently this is illegal: |
| 851 | |
| 852 | state ($a, $b) = foo(); |
| 853 | |
| 854 | In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different |
| 855 | semantics, which is tricky to implement in Perl 5 as currently they produce |
| 856 | the same opcode trees. The Perl 6 design is firm, so it would be good to |
| 857 | implement the necessary code in Perl 5. There are comments in |
| 858 | C<Perl_newASSIGNOP()> that show the code paths taken by various assignment |
| 859 | constructions involving state variables. |
| 860 | |
| 861 | =head2 Implement $value ~~ 0 .. $range |
| 862 | |
| 863 | It would be nice to extend the syntax of the C<~~> operator to also |
| 864 | understand numeric (and maybe alphanumeric) ranges. |
| 865 | |
| 866 | =head2 A does() built-in |
| 867 | |
| 868 | Like ref(), only useful. It would call the C<DOES> method on objects; it |
| 869 | would also tell whether something can be dereferenced as an |
| 870 | array/hash/etc., or used as a regexp, etc. |
| 871 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html> |
| 872 | |
| 873 | =head2 Tied filehandles and write() don't mix |
| 874 | |
| 875 | There is no method on tied filehandles to allow them to be called back by |
| 876 | formats. |
| 877 | |
| 878 | =head2 Attach/detach debugger from running program |
| 879 | |
| 880 | The old perltodo notes "With C<gdb>, you can attach the debugger to a running |
| 881 | program if you pass the process ID. It would be good to do this with the Perl |
| 882 | debugger on a running Perl program, although I'm not sure how it would be |
| 883 | done." ssh and screen do this with named pipes in /tmp. Maybe we can too. |
| 884 | |
| 885 | =head2 LVALUE functions for lists |
| 886 | |
| 887 | The old perltodo notes that lvalue functions don't work for list or hash |
| 888 | slices. This would be good to fix. |
| 889 | |
| 890 | =head2 regexp optimiser optional |
| 891 | |
| 892 | The regexp optimiser is not optional. It should configurable to be, to allow |
| 893 | its performance to be measured, and its bugs to be easily demonstrated. |
| 894 | |
| 895 | =head2 delete &function |
| 896 | |
| 897 | Allow to delete functions. One can already undef them, but they're still |
| 898 | in the stash. |
| 899 | |
| 900 | =head2 C</w> regex modifier |
| 901 | |
| 902 | That flag would enable to match whole words, and also to interpolate |
| 903 | arrays as alternations. With it, C</P/w> would be roughly equivalent to: |
| 904 | |
| 905 | do { local $"='|'; /\b(?:P)\b/ } |
| 906 | |
| 907 | See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html> |
| 908 | for the discussion. |
| 909 | |
| 910 | =head2 optional optimizer |
| 911 | |
| 912 | Make the peephole optimizer optional. Currently it performs two tasks as |
| 913 | it walks the optree - genuine peephole optimisations, and necessary fixups of |
| 914 | ops. It would be good to find an efficient way to switch out the |
| 915 | optimisations whilst keeping the fixups. |
| 916 | |
| 917 | =head2 You WANT *how* many |
| 918 | |
| 919 | Currently contexts are void, scalar and list. split has a special mechanism in |
| 920 | place to pass in the number of return values wanted. It would be useful to |
| 921 | have a general mechanism for this, backwards compatible and little speed hit. |
| 922 | This would allow proposals such as short circuiting sort to be implemented |
| 923 | as a module on CPAN. |
| 924 | |
| 925 | =head2 lexical aliases |
| 926 | |
| 927 | Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>. |
| 928 | |
| 929 | =head2 entersub XS vs Perl |
| 930 | |
| 931 | At the moment pp_entersub is huge, and has code to deal with entering both |
| 932 | perl and XS subroutines. Subroutine implementations rarely change between |
| 933 | perl and XS at run time, so investigate using 2 ops to enter subs (one for |
| 934 | XS, one for perl) and swap between if a sub is redefined. |
| 935 | |
| 936 | =head2 Self-ties |
| 937 | |
| 938 | Self-ties are currently illegal because they caused too many segfaults. Maybe |
| 939 | the causes of these could be tracked down and self-ties on all types |
| 940 | reinstated. |
| 941 | |
| 942 | =head2 Optimize away @_ |
| 943 | |
| 944 | The old perltodo notes "Look at the "reification" code in C<av.c>". |
| 945 | |
| 946 | =head2 Virtualize operating system access |
| 947 | |
| 948 | Implement a set of "vtables" that virtualizes operating system access |
| 949 | (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very |
| 950 | least these interfaces should take SVs as "name" arguments instead of |
| 951 | bare char pointers; probably the most flexible and extensible way |
| 952 | would be for the Perl-facing interfaces to accept HVs. The system |
| 953 | needs to be per-operating-system and per-file-system |
| 954 | hookable/filterable, preferably both from XS and Perl level |
| 955 | (L<perlport/"Files and Filesystems"> is good reading at this point, |
| 956 | in fact, all of L<perlport> is.) |
| 957 | |
| 958 | This has actually already been implemented (but only for Win32), |
| 959 | take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32 |
| 960 | variants go through a set of "vtables" for operating system access, |
| 961 | non-Win32 systems currently go straight for the POSIX/UNIX-style |
| 962 | system/library call. Similar system as for Win32 should be |
| 963 | implemented for all platforms. The existing Win32 implementation |
| 964 | probably does not need to survive alongside this proposed new |
| 965 | implementation, the approaches could be merged. |
| 966 | |
| 967 | What would this give us? One often-asked-for feature this would |
| 968 | enable is using Unicode for filenames, and other "names" like %ENV, |
| 969 | usernames, hostnames, and so forth. |
| 970 | (See L<perlunicode/"When Unicode Does Not Happen">.) |
| 971 | |
| 972 | But this kind of virtualization would also allow for things like |
| 973 | virtual filesystems, virtual networks, and "sandboxes" (though as long |
| 974 | as dynamic loading of random object code is allowed, not very safe |
| 975 | sandboxes since external code of course know not of Perl's vtables). |
| 976 | An example of a smaller "sandbox" is that this feature can be used to |
| 977 | implement per-thread working directories: Win32 already does this. |
| 978 | |
| 979 | See also L</"Extend PerlIO and PerlIO::Scalar">. |
| 980 | |
| 981 | =head2 Investigate PADTMP hash pessimisation |
| 982 | |
| 983 | The peephole optimiser converts constants used for hash key lookups to shared |
| 984 | hash key scalars. Under ithreads, something is undoing this work. |
| 985 | See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html |
| 986 | |
| 987 | =head2 Store the current pad in the OP slab allocator |
| 988 | |
| 989 | =for clarification |
| 990 | I hope that I got that "current pad" part correct |
| 991 | |
| 992 | Currently we leak ops in various cases of parse failure. I suggested that we |
| 993 | could solve this by always using the op slab allocator, and walking it to |
| 994 | free ops. Dave comments that as some ops are already freed during optree |
| 995 | creation one would have to mark which ops are freed, and not double free them |
| 996 | when walking the slab. He notes that one problem with this is that for some ops |
| 997 | you have to know which pad was current at the time of allocation, which does |
| 998 | change. I suggested storing a pointer to the current pad in the memory allocated |
| 999 | for the slab, and swapping to a new slab each time the pad changes. Dave thinks |
| 1000 | that this would work. |
| 1001 | |
| 1002 | =head2 repack the optree |
| 1003 | |
| 1004 | Repacking the optree after execution order is determined could allow |
| 1005 | removal of NULL ops, and optimal ordering of OPs with respect to cache-line |
| 1006 | filling. The slab allocator could be reused for this purpose. I think that |
| 1007 | the best way to do this is to make it an optional step just before the |
| 1008 | completed optree is attached to anything else, and to use the slab allocator |
| 1009 | unchanged, so that freeing ops is identical whether or not this step runs. |
| 1010 | Note that the slab allocator allocates ops downwards in memory, so one would |
| 1011 | have to actually "allocate" the ops in reverse-execution order to get them |
| 1012 | contiguous in memory in execution order. |
| 1013 | |
| 1014 | See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html |
| 1015 | |
| 1016 | Note that running this copy, and then freeing all the old location ops would |
| 1017 | cause their slabs to be freed, which would eliminate possible memory wastage if |
| 1018 | the previous suggestion is implemented, and we swap slabs more frequently. |
| 1019 | |
| 1020 | =head2 eliminate incorrect line numbers in warnings |
| 1021 | |
| 1022 | This code |
| 1023 | |
| 1024 | use warnings; |
| 1025 | my $undef; |
| 1026 | |
| 1027 | if ($undef == 3) { |
| 1028 | } elsif ($undef == 0) { |
| 1029 | } |
| 1030 | |
| 1031 | used to produce this output: |
| 1032 | |
| 1033 | Use of uninitialized value in numeric eq (==) at wrong.pl line 4. |
| 1034 | Use of uninitialized value in numeric eq (==) at wrong.pl line 4. |
| 1035 | |
| 1036 | where the line of the second warning was misreported - it should be line 5. |
| 1037 | Rafael fixed this - the problem arose because there was no nextstate OP |
| 1038 | between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still |
| 1039 | reports that the currently executing line is line 4. The solution was to inject |
| 1040 | a nextstate OPs for each C<elsif>, although it turned out that the nextstate |
| 1041 | OP needed to be a nulled OP, rather than a live nextstate OP, else other line |
| 1042 | numbers became misreported. (Jenga!) |
| 1043 | |
| 1044 | The problem is more general than C<elsif> (although the C<elsif> case is the |
| 1045 | most common and the most confusing). Ideally this code |
| 1046 | |
| 1047 | use warnings; |
| 1048 | my $undef; |
| 1049 | |
| 1050 | my $a = $undef + 1; |
| 1051 | my $b |
| 1052 | = $undef |
| 1053 | + 1; |
| 1054 | |
| 1055 | would produce this output |
| 1056 | |
| 1057 | Use of uninitialized value $undef in addition (+) at wrong.pl line 4. |
| 1058 | Use of uninitialized value $undef in addition (+) at wrong.pl line 7. |
| 1059 | |
| 1060 | (rather than lines 4 and 5), but this would seem to require every OP to carry |
| 1061 | (at least) line number information. |
| 1062 | |
| 1063 | What might work is to have an optional line number in memory just before the |
| 1064 | BASEOP structure, with a flag bit in the op to say whether it's present. |
| 1065 | Initially during compile every OP would carry its line number. Then add a late |
| 1066 | pass to the optimiser (potentially combined with L</repack the optree>) which |
| 1067 | looks at the two ops on every edge of the graph of the execution path. If |
| 1068 | the line number changes, flags the destination OP with this information. |
| 1069 | Once all paths are traced, replace every op with the flag with a |
| 1070 | nextstate-light op (that just updates C<PL_curcop>), which in turn then passes |
| 1071 | control on to the true op. All ops would then be replaced by variants that |
| 1072 | do not store the line number. (Which, logically, why it would work best in |
| 1073 | conjunction with L</repack the optree>, as that is already copying/reallocating |
| 1074 | all the OPs) |
| 1075 | |
| 1076 | (Although I should note that we're not certain that doing this for the general |
| 1077 | case is worth it) |
| 1078 | |
| 1079 | =head2 optimize tail-calls |
| 1080 | |
| 1081 | Tail-calls present an opportunity for broadly applicable optimization; |
| 1082 | anywhere that C<< return foo(...) >> is called, the outer return can |
| 1083 | be replaced by a goto, and foo will return directly to the outer |
| 1084 | caller, saving (conservatively) 25% of perl's call&return cost, which |
| 1085 | is relatively higher than in C. The scheme language is known to do |
| 1086 | this heavily. B::Concise provides good insight into where this |
| 1087 | optimization is possible, ie anywhere entersub,leavesub op-sequence |
| 1088 | occurs. |
| 1089 | |
| 1090 | perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)' |
| 1091 | |
| 1092 | Bottom line on this is probably a new pp_tailcall function which |
| 1093 | combines the code in pp_entersub, pp_leavesub. This should probably |
| 1094 | be done 1st in XS, and using B::Generate to patch the new OP into the |
| 1095 | optrees. |
| 1096 | |
| 1097 | =head1 Big projects |
| 1098 | |
| 1099 | Tasks that will get your name mentioned in the description of the "Highlights |
| 1100 | of 5.12" |
| 1101 | |
| 1102 | =head2 make ithreads more robust |
| 1103 | |
| 1104 | Generally make ithreads more robust. See also L</iCOW> |
| 1105 | |
| 1106 | This task is incremental - even a little bit of work on it will help, and |
| 1107 | will be greatly appreciated. |
| 1108 | |
| 1109 | One bit would be to write the missing code in sv.c:Perl_dirp_dup. |
| 1110 | |
| 1111 | Fix Perl_sv_dup, et al so that threads can return objects. |
| 1112 | |
| 1113 | =head2 iCOW |
| 1114 | |
| 1115 | Sarathy and Arthur have a proposal for an improved Copy On Write which |
| 1116 | specifically will be able to COW new ithreads. If this can be implemented |
| 1117 | it would be a good thing. |
| 1118 | |
| 1119 | =head2 (?{...}) closures in regexps |
| 1120 | |
| 1121 | Fix (or rewrite) the implementation of the C</(?{...})/> closures. |
| 1122 | |
| 1123 | =head2 A re-entrant regexp engine |
| 1124 | |
| 1125 | This will allow the use of a regex from inside (?{ }), (??{ }) and |
| 1126 | (?(?{ })|) constructs. |
| 1127 | |
| 1128 | =head2 Add class set operations to regexp engine |
| 1129 | |
| 1130 | Apparently these are quite useful. Anyway, Jeffery Friedl wants them. |
| 1131 | |
| 1132 | demerphq has this on his todo list, but right at the bottom. |