| 1 | =head1 NAME |
| 2 | |
| 3 | todo - 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 L<http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/Porting/todo.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 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/> |
| 20 | |
| 21 | What can we offer you in return? Fame, fortune, and everlasting glory? Maybe |
| 22 | not, but if your patch is incorporated, then we'll add your name to the |
| 23 | F<AUTHORS> file, which ships in the official distribution. How many other |
| 24 | programming languages offer you 1 line of immortality? |
| 25 | |
| 26 | =head1 Tasks that need only a little Perl knowledge |
| 27 | |
| 28 | =head2 Fix POD errors in Perl documentation |
| 29 | |
| 30 | Perl documentation is furnished in POD (Plain Old Documentation); see |
| 31 | L<perlpod>. We also have a utility that checks for various errors in |
| 32 | this documentation: F<t/porting/podcheck.t>. Unfortunately many files |
| 33 | have errors in them, and there is a database of known problems, kept in |
| 34 | F<t/porting/known_pod_issues.dat>. The most prevalent errors are lines |
| 35 | too wide to fit in a standard terminal window, but there are more |
| 36 | serious problems as well; and there are items listed there that are not |
| 37 | in fact errors. The task would be to go through and clean up the |
| 38 | documentation. This would be a good way to learn more about Perl. |
| 39 | |
| 40 | =head1 Tasks that only need Perl knowledge |
| 41 | |
| 42 | =head2 Classify bug tickets by type |
| 43 | |
| 44 | Known bugs in Perl are tracked by L<https://rt.perl.org/rt3> (which also |
| 45 | includes Perl 6). A summary can be found at |
| 46 | L<https://rt.perl.org/rt3/NoAuth/perl5/Overview.html>. |
| 47 | It shows bugs classified by "type". However, the type of many of the |
| 48 | bugs is "unknown". This greatly lowers the chances of them getting |
| 49 | fixed, as the number of open bugs is overwhelming -- too many to wade |
| 50 | through for someone to try to find the bugs in the parts of |
| 51 | Perl that s/he knows well enough to try to fix. This task involves |
| 52 | going through these bugs and classifying them into one or more types. |
| 53 | |
| 54 | =head2 Ongoing: investigate new bug reports |
| 55 | |
| 56 | When a bug report is filed, it would be very helpful to have someone do |
| 57 | a quick investigation to see if it is a real problem, and to reply to |
| 58 | the poster about it, asking for example code that reproduces the |
| 59 | problem. Such code should be added to the test suite as TODO tests, and |
| 60 | the ticket should be classified by type. To get started on this task, |
| 61 | look at the tickets that are marked as "New Issues" in |
| 62 | L<https://rt.perl.org/rt3/NoAuth/perl5/Overview.html>. |
| 63 | |
| 64 | =head2 Migrate t/ from custom TAP generation |
| 65 | |
| 66 | Many tests below F<t/> still generate TAP by "hand", rather than using library |
| 67 | functions. As explained in L<perlhack/TESTING>, tests in F<t/> are |
| 68 | written in a particular way to test that more complex constructions actually |
| 69 | work before using them routinely. Hence they don't use C<Test::More>, but |
| 70 | instead there is an intentionally simpler library, F<t/test.pl>. However, |
| 71 | quite a few tests in F<t/> have not been refactored to use it. Refactoring |
| 72 | any of these tests, one at a time, is a useful thing TODO. |
| 73 | |
| 74 | The subdirectories F<base>, F<cmd> and F<comp>, that contain the most |
| 75 | basic tests, should be excluded from this task. |
| 76 | |
| 77 | =head2 Automate perldelta generation |
| 78 | |
| 79 | The perldelta file accompanying each release summaries the major changes. |
| 80 | It's mostly manually generated currently, but some of that could be |
| 81 | automated with a bit of perl, specifically the generation of |
| 82 | |
| 83 | =over |
| 84 | |
| 85 | =item Modules and Pragmata |
| 86 | |
| 87 | =item New Documentation |
| 88 | |
| 89 | =item New Tests |
| 90 | |
| 91 | =back |
| 92 | |
| 93 | See F<Porting/how_to_write_a_perldelta.pod> for details. |
| 94 | |
| 95 | =head2 Make Schwern poorer |
| 96 | |
| 97 | We should have tests for everything. When all the core's modules are tested, |
| 98 | Schwern has promised to donate to $500 to TPF. We may need volunteers to |
| 99 | hold him upside down and shake vigorously in order to actually extract the |
| 100 | cash. |
| 101 | |
| 102 | =head2 Write descriptions for all tests |
| 103 | |
| 104 | Many individual tests in the test suite lack descriptions (or names, or labels |
| 105 | -- call them what you will). Many files completely lack descriptions, meaning |
| 106 | that the only output you get is the test numbers. If all tests had |
| 107 | descriptions, understanding what the tests are testing and why they sometimes |
| 108 | fail would both get a whole lot easier. |
| 109 | |
| 110 | =head2 Improve the coverage of the core tests |
| 111 | |
| 112 | Use Devel::Cover to ascertain the core modules' test coverage, then add |
| 113 | tests that are currently missing. |
| 114 | |
| 115 | =head2 test B |
| 116 | |
| 117 | A full test suite for the B module would be nice. |
| 118 | |
| 119 | =head2 A decent benchmark |
| 120 | |
| 121 | C<perlbench> seems impervious to any recent changes made to the perl core. It |
| 122 | would be useful to have a reasonable general benchmarking suite that roughly |
| 123 | represented what current perl programs do, and measurably reported whether |
| 124 | tweaks to the core improve, degrade or don't really affect performance, to |
| 125 | guide people attempting to optimise the guts of perl. Gisle would welcome |
| 126 | new tests for perlbench. Steffen Schwingon would welcome help with |
| 127 | L<Benchmark::Perl::Formance> |
| 128 | |
| 129 | =head2 fix tainting bugs |
| 130 | |
| 131 | Fix the bugs revealed by running the test suite with the C<-t> switch (via |
| 132 | C<make test.taintwarn>). |
| 133 | |
| 134 | =head2 Dual life everything |
| 135 | |
| 136 | As part of the "dists" plan, anything that doesn't belong in the smallest perl |
| 137 | distribution needs to be dual lifed. Anything else can be too. Figure out what |
| 138 | changes would be needed to package that module and its tests up for CPAN, and |
| 139 | do so. Test it with older perl releases, and fix the problems you find. |
| 140 | |
| 141 | To make a minimal perl distribution, it's useful to look at |
| 142 | F<t/lib/commonsense.t>. |
| 143 | |
| 144 | =head2 POSIX memory footprint |
| 145 | |
| 146 | Ilya observed that use POSIX; eats memory like there's no tomorrow, and at |
| 147 | various times worked to cut it down. There is probably still fat to cut out - |
| 148 | for example POSIX passes Exporter some very memory hungry data structures. |
| 149 | |
| 150 | =head2 makedef.pl and conditional compilation |
| 151 | |
| 152 | The script F<makedef.pl> that generates the list of exported symbols on |
| 153 | platforms which need this. Functions are declared in F<embed.fnc>, variables |
| 154 | in F<intrpvar.h>. Quite a few of the functions and variables are conditionally |
| 155 | declared there, using C<#ifdef>. However, F<makedef.pl> doesn't understand the |
| 156 | C macros, so the rules about which symbols are present when is duplicated in |
| 157 | the Perl code. Writing things twice is bad, m'kay. It would be good to teach |
| 158 | F<.pl> to understand the conditional compilation, and hence remove the |
| 159 | duplication, and the mistakes it has caused. |
| 160 | |
| 161 | =head2 use strict; and AutoLoad |
| 162 | |
| 163 | Currently if you write |
| 164 | |
| 165 | package Whack; |
| 166 | use AutoLoader 'AUTOLOAD'; |
| 167 | use strict; |
| 168 | 1; |
| 169 | __END__ |
| 170 | sub bloop { |
| 171 | print join (' ', No, strict, here), "!\n"; |
| 172 | } |
| 173 | |
| 174 | then C<use strict;> isn't in force within the autoloaded subroutines. It would |
| 175 | be more consistent (and less surprising) to arrange for all lexical pragmas |
| 176 | in force at the __END__ block to be in force within each autoloaded subroutine. |
| 177 | |
| 178 | There's a similar problem with SelfLoader. |
| 179 | |
| 180 | =head2 profile installman |
| 181 | |
| 182 | The F<installman> script is slow. All it is doing text processing, which we're |
| 183 | told is something Perl is good at. So it would be nice to know what it is doing |
| 184 | that is taking so much CPU, and where possible address it. |
| 185 | |
| 186 | =head2 enable lexical enabling/disabling of individual warnings |
| 187 | |
| 188 | Currently, warnings can only be enabled or disabled by category. There |
| 189 | are times when it would be useful to quash a single warning, not a |
| 190 | whole category. |
| 191 | |
| 192 | =head2 document diagnostics |
| 193 | |
| 194 | Many diagnostic messages are not currently documented. The list is at the end |
| 195 | of t/porting/diag.t. |
| 196 | |
| 197 | =head2 Write TODO tests for open bugs |
| 198 | |
| 199 | Sometimes bugs get fixed as a side effect of something else, and |
| 200 | the bug remains open because no one realizes that it has been fixed. |
| 201 | Ideally, every open bug should have a TODO test in the core test suite. |
| 202 | |
| 203 | =head1 Tasks that need a little sysadmin-type knowledge |
| 204 | |
| 205 | Or if you prefer, tasks that you would learn from, and broaden your skills |
| 206 | base... |
| 207 | |
| 208 | =head2 make HTML install work |
| 209 | |
| 210 | There is an C<install.html> target in the Makefile. It's marked as |
| 211 | "experimental". It would be good to get this tested, make it work reliably, and |
| 212 | remove the "experimental" tag. This would include |
| 213 | |
| 214 | =over 4 |
| 215 | |
| 216 | =item 1 |
| 217 | |
| 218 | Checking that cross linking between various parts of the documentation works. |
| 219 | In particular that links work between the modules (files with POD in F<lib/>) |
| 220 | and the core documentation (files in F<pod/>) |
| 221 | |
| 222 | =item 2 |
| 223 | |
| 224 | Improving the code that split C<perlfunc> into chunks, preferably with |
| 225 | general case code added to L<Pod::Functions> that could be used elsewhere. |
| 226 | |
| 227 | Challenges here are correctly identifying the groups of functions that go |
| 228 | together, and making the right named external cross-links point to the right |
| 229 | page. Currently this works reasonably well in the general case, and correctly |
| 230 | parses two or more C<=items> giving the different parameter lists for the |
| 231 | same function, such used by C<substr>. However it fails completely where |
| 232 | I<different> functions are listed as a sequence of C<=items> but share the |
| 233 | same description. All the functions from C<getpwnam> to C<endprotoent> have |
| 234 | individual stub pages, with only the page for C<endservent> holding the |
| 235 | description common to all. Likewise C<q>, C<qq> and C<qw> have stub pages, |
| 236 | instead of sharing the body of C<qx>. |
| 237 | |
| 238 | Note also the current code isn't ideal with the two forms of C<select>, mushing |
| 239 | them both into one F<select.html> with the two descriptions run together. |
| 240 | Fixing this may well be a special case. |
| 241 | |
| 242 | =back |
| 243 | |
| 244 | =head2 compressed man pages |
| 245 | |
| 246 | Be able to install them. This would probably need a configure test to see how |
| 247 | the system does compressed man pages (same directory/different directory? |
| 248 | same filename/different filename), as well as tweaking the F<installman> script |
| 249 | to compress as necessary. |
| 250 | |
| 251 | =head2 Add a code coverage target to the Makefile |
| 252 | |
| 253 | Make it easy for anyone to run Devel::Cover on the core's tests. The steps |
| 254 | to do this manually are roughly |
| 255 | |
| 256 | =over 4 |
| 257 | |
| 258 | =item * |
| 259 | |
| 260 | do a normal C<Configure>, but include Devel::Cover as a module to install |
| 261 | (see L<INSTALL> for how to do this) |
| 262 | |
| 263 | =item * |
| 264 | |
| 265 | make perl |
| 266 | |
| 267 | =item * |
| 268 | |
| 269 | cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness |
| 270 | |
| 271 | =item * |
| 272 | |
| 273 | Process the resulting Devel::Cover database |
| 274 | |
| 275 | =back |
| 276 | |
| 277 | This just give you the coverage of the F<.pm>s. To also get the C level |
| 278 | coverage you need to |
| 279 | |
| 280 | =over 4 |
| 281 | |
| 282 | =item * |
| 283 | |
| 284 | Additionally tell C<Configure> to use the appropriate C compiler flags for |
| 285 | C<gcov> |
| 286 | |
| 287 | =item * |
| 288 | |
| 289 | make perl.gcov |
| 290 | |
| 291 | (instead of C<make perl>) |
| 292 | |
| 293 | =item * |
| 294 | |
| 295 | After running the tests run C<gcov> to generate all the F<.gcov> files. |
| 296 | (Including down in the subdirectories of F<ext/> |
| 297 | |
| 298 | =item * |
| 299 | |
| 300 | (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files |
| 301 | to get their stats into the cover_db directory. |
| 302 | |
| 303 | =item * |
| 304 | |
| 305 | Then process the Devel::Cover database |
| 306 | |
| 307 | =back |
| 308 | |
| 309 | It would be good to add a single switch to C<Configure> to specify that you |
| 310 | wanted to perform perl level coverage, and another to specify C level |
| 311 | coverage, and have C<Configure> and the F<Makefile> do all the right things |
| 312 | automatically. |
| 313 | |
| 314 | =head2 Make Config.pm cope with differences between built and installed perl |
| 315 | |
| 316 | Quite often vendors ship a perl binary compiled with their (pay-for) |
| 317 | compilers. People install a free compiler, such as gcc. To work out how to |
| 318 | build extensions, Perl interrogates C<%Config>, so in this situation |
| 319 | C<%Config> describes compilers that aren't there, and extension building |
| 320 | fails. This forces people into choosing between re-compiling perl themselves |
| 321 | using the compiler they have, or only using modules that the vendor ships. |
| 322 | |
| 323 | It would be good to find a way teach C<Config.pm> about the installation setup, |
| 324 | possibly involving probing at install time or later, so that the C<%Config> in |
| 325 | a binary distribution better describes the installed machine, when the |
| 326 | installed machine differs from the build machine in some significant way. |
| 327 | |
| 328 | =head2 linker specification files |
| 329 | |
| 330 | Some platforms mandate that you provide a list of a shared library's external |
| 331 | symbols to the linker, so the core already has the infrastructure in place to |
| 332 | do this for generating shared perl libraries. Florian Ragwitz has been working |
| 333 | to offer this for the GNU toolchain, to allow Unix users to test that the |
| 334 | export list is correct, and to build a perl that does not pollute the global |
| 335 | namespace with private symbols, and will fail in the same way as msvc or mingw |
| 336 | builds or when using PERL_DL_NONLAZY=1. See the branch smoke-me/rafl/ld_export |
| 337 | |
| 338 | =head2 Cross-compile support |
| 339 | |
| 340 | We get requests for "how to cross compile Perl". The vast majority of these |
| 341 | seem to be for a couple of scenarios: |
| 342 | |
| 343 | =over 4 |
| 344 | |
| 345 | =item * |
| 346 | |
| 347 | Platforms that could build natively using F<./Configure> (I<e.g.> Linux or |
| 348 | NetBSD on MIPS or ARM) but people want to use a beefier machine (and on the |
| 349 | same OS) to build more easily. |
| 350 | |
| 351 | =item * |
| 352 | |
| 353 | Platforms that can't build natively, but no (significant) porting changes |
| 354 | are needed to our current source code. Prime example of this is Android. |
| 355 | |
| 356 | =back |
| 357 | |
| 358 | There are several scripts and tools for cross-compiling perl for other |
| 359 | platforms. However, these are somewhat inconsistent and scattered across the |
| 360 | codebase, none are documented well, none are clearly flexible enough to |
| 361 | be confident that they can support any TARGET/HOST plaform pair other than |
| 362 | that which they were developed on, and it's not clear how bitrotted they are. |
| 363 | |
| 364 | For example, C<Configure> understands C<-Dusecrosscompile> option. This option |
| 365 | arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is |
| 366 | assumed then to be copied to TARGET machine and used as a replacement of |
| 367 | full C<perl> executable. This code is almost 10 years old. Meanwhile, the |
| 368 | F<Cross/> directory contains two different approaches for cross compiling to |
| 369 | ARM Linux targets, relying on hand curated F<config.sh> files, but that code |
| 370 | is getting on for 5 years old, and requires insider knowledge of perl's |
| 371 | build system to draft a F<config.sh> for a new platform. |
| 372 | |
| 373 | Jess Robinson has sumbitted a grant to TPF to work on cleaning this up. |
| 374 | |
| 375 | =head2 Split "linker" from "compiler" |
| 376 | |
| 377 | Right now, Configure probes for two commands, and sets two variables: |
| 378 | |
| 379 | =over 4 |
| 380 | |
| 381 | =item * C<cc> (in F<cc.U>) |
| 382 | |
| 383 | This variable holds the name of a command to execute a C compiler which |
| 384 | can resolve multiple global references that happen to have the same |
| 385 | name. Usual values are F<cc> and F<gcc>. |
| 386 | Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>. |
| 387 | |
| 388 | =item * C<ld> (in F<dlsrc.U>) |
| 389 | |
| 390 | This variable indicates the program to be used to link |
| 391 | libraries for dynamic loading. On some systems, it is F<ld>. |
| 392 | On ELF systems, it should be C<$cc>. Mostly, we'll try to respect |
| 393 | the hint file setting. |
| 394 | |
| 395 | =back |
| 396 | |
| 397 | There is an implicit historical assumption from around Perl5.000alpha |
| 398 | something, that C<$cc> is also the correct command for linking object files |
| 399 | together to make an executable. This may be true on Unix, but it's not true |
| 400 | on other platforms, and there are a maze of work arounds in other places (such |
| 401 | as F<Makefile.SH>) to cope with this. |
| 402 | |
| 403 | Ideally, we should create a new variable to hold the name of the executable |
| 404 | linker program, probe for it in F<Configure>, and centralise all the special |
| 405 | case logic there or in hints files. |
| 406 | |
| 407 | A small bikeshed issue remains - what to call it, given that C<$ld> is already |
| 408 | taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command |
| 409 | for creating dynamically-loadable modules) and C<$link> could be confused with |
| 410 | the Unix command line executable of the same name, which does something |
| 411 | completely different. Andy Dougherty makes the counter argument "In parrot, I |
| 412 | tried to call the command used to link object files and libraries into an |
| 413 | executable F<link>, since that's what my vaguely-remembered DOS and VMS |
| 414 | experience suggested. I don't think any real confusion has ensued, so it's |
| 415 | probably a reasonable name for perl5 to use." |
| 416 | |
| 417 | "Alas, I've always worried that introducing it would make things worse, |
| 418 | since now the module building utilities would have to look for |
| 419 | C<$Config{link}> and institute a fall-back plan if it weren't found." |
| 420 | Although I can see that as confusing, given that C<$Config{d_link}> is true |
| 421 | when (hard) links are available. |
| 422 | |
| 423 | =head2 Configure Windows using PowerShell |
| 424 | |
| 425 | Currently, Windows uses hard-coded config files based to build the |
| 426 | config.h for compiling Perl. Makefiles are also hard-coded and need to be |
| 427 | hand edited prior to building Perl. While this makes it easy to create a perl.exe |
| 428 | that works across multiple Windows versions, being able to accurately |
| 429 | configure a perl.exe for a specific Windows versions and VS C++ would be |
| 430 | a nice enhancement. With PowerShell available on Windows XP and up, this |
| 431 | may now be possible. Step 1 might be to investigate whether this is possible |
| 432 | and use this to clean up our current makefile situation. Step 2 would be to |
| 433 | see if there would be a way to use our existing metaconfig units to configure a |
| 434 | Windows Perl or whether we go in a separate direction and make it so. Of |
| 435 | course, we all know what step 3 is. |
| 436 | |
| 437 | =head1 Tasks that need a little C knowledge |
| 438 | |
| 439 | These tasks would need a little C knowledge, but don't need any specific |
| 440 | background or experience with XS, or how the Perl interpreter works |
| 441 | |
| 442 | =head2 Weed out needless PERL_UNUSED_ARG |
| 443 | |
| 444 | The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about |
| 445 | unused arguments. Often the arguments can't be removed, as there is an |
| 446 | external constraint that determines the prototype of the function, so this |
| 447 | approach is valid. However, there are some cases where C<PERL_UNUSED_ARG> |
| 448 | could be removed. Specifically |
| 449 | |
| 450 | =over 4 |
| 451 | |
| 452 | =item * |
| 453 | |
| 454 | The prototypes of (nearly all) static functions can be changed |
| 455 | |
| 456 | =item * |
| 457 | |
| 458 | Unused arguments generated by short cut macros are wasteful - the short cut |
| 459 | macro used can be changed. |
| 460 | |
| 461 | =back |
| 462 | |
| 463 | =head2 -Duse32bit* |
| 464 | |
| 465 | Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall. |
| 466 | On these systems, it might be the default compilation mode, and there |
| 467 | is currently no guarantee that passing no use64bitall option to the |
| 468 | Configure process will build a 32bit perl. Implementing -Duse32bit* |
| 469 | options would be nice for perl 5.18.0. |
| 470 | |
| 471 | =head2 Profile Perl - am I hot or not? |
| 472 | |
| 473 | The Perl source code is stable enough that it makes sense to profile it, |
| 474 | identify and optimise the hotspots. It would be good to measure the |
| 475 | performance of the Perl interpreter using free tools such as cachegrind, |
| 476 | gprof, and dtrace, and work to reduce the bottlenecks they reveal. |
| 477 | |
| 478 | As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops, |
| 479 | the ops that are most commonly used. The idea is that by grouping them, their |
| 480 | object code will be adjacent in the executable, so they have a greater chance |
| 481 | of already being in the CPU cache (or swapped in) due to being near another op |
| 482 | already in use. |
| 483 | |
| 484 | Except that it's not clear if these really are the most commonly used ops. So |
| 485 | as part of exercising your skills with coverage and profiling tools you might |
| 486 | want to determine what ops I<really> are the most commonly used. And in turn |
| 487 | suggest evictions and promotions to achieve a better F<pp_hot.c>. |
| 488 | |
| 489 | One piece of Perl code that might make a good testbed is F<installman>. |
| 490 | |
| 491 | =head2 Improve win32/wince.c |
| 492 | |
| 493 | Currently, numerous functions look virtually, if not completely, |
| 494 | identical in both F<win32/wince.c> and F<win32/win32.c> files, which can't |
| 495 | be good. |
| 496 | |
| 497 | =head2 Use secure CRT functions when building with VC8 on Win32 |
| 498 | |
| 499 | Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis |
| 500 | that they were "unsafe" and introduced differently named secure versions of |
| 501 | them as replacements, e.g. instead of writing |
| 502 | |
| 503 | FILE* f = fopen(__FILE__, "r"); |
| 504 | |
| 505 | one should now write |
| 506 | |
| 507 | FILE* f; |
| 508 | errno_t err = fopen_s(&f, __FILE__, "r"); |
| 509 | |
| 510 | Currently, the warnings about these deprecations have been disabled by adding |
| 511 | -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that |
| 512 | warning suppressant and actually make use of the new secure CRT functions. |
| 513 | |
| 514 | There is also a similar issue with POSIX CRT function names like fileno having |
| 515 | been deprecated in favour of ISO C++ conformant names like _fileno. These |
| 516 | warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It |
| 517 | might be nice to do as Microsoft suggest here too, although, unlike the secure |
| 518 | functions issue, there is presumably little or no benefit in this case. |
| 519 | |
| 520 | =head2 Fix POSIX::access() and chdir() on Win32 |
| 521 | |
| 522 | These functions currently take no account of DACLs and therefore do not behave |
| 523 | correctly in situations where access is restricted by DACLs (as opposed to the |
| 524 | read-only attribute). |
| 525 | |
| 526 | Furthermore, POSIX::access() behaves differently for directories having the |
| 527 | read-only attribute set depending on what CRT library is being used. For |
| 528 | example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that |
| 529 | such directories are not writable, whereas in fact all directories are writable |
| 530 | unless access is denied by DACLs. (In the case of directories, the read-only |
| 531 | attribute actually only means that the directory cannot be deleted.) This CRT |
| 532 | bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still |
| 533 | not actually be writable if access is indeed denied by DACLs). |
| 534 | |
| 535 | For the chdir() issue, see ActiveState bug #74552: |
| 536 | L<http://bugs.activestate.com/show_bug.cgi?id=74552> |
| 537 | |
| 538 | Therefore, DACLs should be checked both for consistency across CRTs and for |
| 539 | the correct answer. |
| 540 | |
| 541 | (Note that perl's -w operator should not be modified to check DACLs. It has |
| 542 | been written so that it reflects the state of the read-only attribute, even |
| 543 | for directories (whatever CRT is being used), for symmetry with chmod().) |
| 544 | |
| 545 | =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf() |
| 546 | |
| 547 | Maybe create a utility that checks after each libperl.a creation that |
| 548 | none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets()) |
| 549 | ever creep back to libperl.a. |
| 550 | |
| 551 | nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/' |
| 552 | |
| 553 | Note, of course, that this will only tell whether B<your> platform |
| 554 | is using those naughty interfaces. |
| 555 | |
| 556 | =head2 -D_FORTIFY_SOURCE=2 |
| 557 | |
| 558 | Recent glibcs support C<-D_FORTIFY_SOURCE=2> which gives |
| 559 | protection against various kinds of buffer overflow problems. |
| 560 | It should probably be used for compiling Perl whenever available, |
| 561 | Configure and/or hints files should be adjusted to probe for the |
| 562 | availability of these feature and enable it as appropriate. |
| 563 | |
| 564 | =head2 Arenas for GPs? For MAGIC? |
| 565 | |
| 566 | C<struct gp> and C<struct magic> are both currently allocated by C<malloc>. |
| 567 | It might be a speed or memory saving to change to using arenas. Or it might |
| 568 | not. It would need some suitable benchmarking first. In particular, C<GP>s |
| 569 | can probably be changed with minimal compatibility impact (probably nothing |
| 570 | outside of the core, or even outside of F<gv.c> allocates them), but they |
| 571 | probably aren't allocated/deallocated often enough for a speed saving. Whereas |
| 572 | C<MAGIC> is allocated/deallocated more often, but in turn, is also something |
| 573 | more externally visible, so changing the rules here may bite external code. |
| 574 | |
| 575 | =head2 Shared arenas |
| 576 | |
| 577 | Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and |
| 578 | PVHV, and PVCV and PVFM. It should be possible to allocate and return same |
| 579 | sized bodies from the same actual arena, rather than maintaining one arena for |
| 580 | each. This could save 4-6K per thread, of memory no longer tied up in the |
| 581 | not-yet-allocated part of an arena. |
| 582 | |
| 583 | |
| 584 | =head1 Tasks that need a knowledge of XS |
| 585 | |
| 586 | These tasks would need C knowledge, and roughly the level of knowledge of |
| 587 | the perl API that comes from writing modules that use XS to interface to |
| 588 | C. |
| 589 | |
| 590 | =head2 Write an XS cookbook |
| 591 | |
| 592 | Create pod/perlxscookbook.pod with short, task-focused 'recipes' in XS that |
| 593 | demonstrate common tasks and good practices. (Some of these might be |
| 594 | extracted from perlguts.) The target audience should be XS novices, who need |
| 595 | more examples than perlguts but something less overwhelming than perlapi. |
| 596 | Recipes should provide "one pretty good way to do it" instead of TIMTOWTDI. |
| 597 | |
| 598 | Rather than focusing on interfacing Perl to C libraries, such a cookbook |
| 599 | should probably focus on how to optimize Perl routines by re-writing them |
| 600 | in XS. This will likely be more motivating to those who mostly work in |
| 601 | Perl but are looking to take the next step into XS. |
| 602 | |
| 603 | Deconstructing and explaining some simpler XS modules could be one way to |
| 604 | bootstrap a cookbook. (List::Util? Class::XSAccessor? Tree::Ternary_XS?) |
| 605 | Another option could be deconstructing the implementation of some simpler |
| 606 | functions in op.c. |
| 607 | |
| 608 | =head2 Document how XSUBs can use C<cv_set_call_checker> to inline themselves as OPs |
| 609 | |
| 610 | For a simple XSUB, often the subroutine dispatch takes more time than the |
| 611 | XSUB itself. v5.14.0 now allows XSUBs to register a function which will be |
| 612 | called when the parser is finished building an C<entersub> op which calls |
| 613 | them. |
| 614 | |
| 615 | Registration is done with C<Perl_cv_set_call_checker>, is documented at the |
| 616 | API level in L<perlapi>, and L<perl5140delta/Custom per-subroutine check hooks> |
| 617 | notes that it can be used to inline a subroutine, by replacing it with a |
| 618 | custom op. However there is no further detail of the code needed to do this. |
| 619 | It would be useful to add one or more annotated examples of how to create |
| 620 | XSUBs that inline. |
| 621 | |
| 622 | This should provide a measurable speed up to simple XSUBs inside |
| 623 | tight loops. Initially one would have to write the OP alternative |
| 624 | implementation by hand, but it's likely that this should be reasonably |
| 625 | straightforward for the type of XSUB that would benefit the most. Longer |
| 626 | term, once the run-time implementation is proven, it should be possible to |
| 627 | progressively update ExtUtils::ParseXS to generate OP implementations for |
| 628 | some XSUBs. |
| 629 | |
| 630 | =head2 Remove the use of SVs as temporaries in dump.c |
| 631 | |
| 632 | F<dump.c> contains debugging routines to dump out the contains of perl data |
| 633 | structures, such as C<SV>s, C<AV>s and C<HV>s. Currently, the dumping code |
| 634 | B<uses> C<SV>s for its temporary buffers, which was a logical initial |
| 635 | implementation choice, as they provide ready made memory handling. |
| 636 | |
| 637 | However, they also lead to a lot of confusion when it happens that what you're |
| 638 | trying to debug is seen by the code in F<dump.c>, correctly or incorrectly, as |
| 639 | a temporary scalar it can use for a temporary buffer. It's also not possible |
| 640 | to dump scalars before the interpreter is properly set up, such as during |
| 641 | ithreads cloning. It would be good to progressively replace the use of scalars |
| 642 | as string accumulation buffers with something much simpler, directly allocated |
| 643 | by C<malloc>. The F<dump.c> code is (or should be) only producing 7 bit |
| 644 | US-ASCII, so output character sets are not an issue. |
| 645 | |
| 646 | Producing and proving an internal simple buffer allocation would make it easier |
| 647 | to re-write the internals of the PerlIO subsystem to avoid using C<SV>s for |
| 648 | B<its> buffers, use of which can cause problems similar to those of F<dump.c>, |
| 649 | at similar times. |
| 650 | |
| 651 | =head2 safely supporting POSIX SA_SIGINFO |
| 652 | |
| 653 | Some years ago Jarkko supplied patches to provide support for the POSIX |
| 654 | SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler. |
| 655 | |
| 656 | Unfortunately, it only works with "unsafe" signals, because under safe |
| 657 | signals, by the time Perl gets to run the signal handler, the extra |
| 658 | information has been lost. Moreover, it's not easy to store it somewhere, |
| 659 | as you can't call mutexs, or do anything else fancy, from inside a signal |
| 660 | handler. |
| 661 | |
| 662 | So it strikes me that we could provide safe SA_SIGINFO support |
| 663 | |
| 664 | =over 4 |
| 665 | |
| 666 | =item 1 |
| 667 | |
| 668 | Provide global variables for two file descriptors |
| 669 | |
| 670 | =item 2 |
| 671 | |
| 672 | When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a |
| 673 | pipe, store the reader in one, the writer in the other |
| 674 | |
| 675 | =item 3 |
| 676 | |
| 677 | In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if |
| 678 | the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open, |
| 679 | |
| 680 | =over 8 |
| 681 | |
| 682 | =item 1 |
| 683 | |
| 684 | serialise signal number, C<struct siginfo_t> (or at least the parts we care |
| 685 | about) into a small auto char buff |
| 686 | |
| 687 | =item 2 |
| 688 | |
| 689 | C<write()> that (non-blocking) to the writer fd |
| 690 | |
| 691 | =over 12 |
| 692 | |
| 693 | =item 1 |
| 694 | |
| 695 | if it writes 100%, flag the signal in a counter of "signals on the pipe" akin |
| 696 | to the current per-signal-number counts |
| 697 | |
| 698 | =item 2 |
| 699 | |
| 700 | if it writes 0%, assume the pipe is full. Flag the data as lost? |
| 701 | |
| 702 | =item 3 |
| 703 | |
| 704 | if it writes partially, croak a panic, as your OS is broken. |
| 705 | |
| 706 | =back |
| 707 | |
| 708 | =back |
| 709 | |
| 710 | =item 4 |
| 711 | |
| 712 | in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on |
| 713 | the pipe", read the data out, deserialise, build the Perl structures on |
| 714 | the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as |
| 715 | usual. |
| 716 | |
| 717 | =back |
| 718 | |
| 719 | I think that this gets us decent C<SA_SIGINFO> support, without the current risk |
| 720 | of running Perl code inside the signal handler context. (With all the dangers |
| 721 | of things like C<malloc> corruption that that currently offers us) |
| 722 | |
| 723 | For more information see the thread starting with this message: |
| 724 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html> |
| 725 | |
| 726 | =head2 autovivification |
| 727 | |
| 728 | Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict; |
| 729 | |
| 730 | This task is incremental - even a little bit of work on it will help. |
| 731 | |
| 732 | =head2 Unicode in Filenames |
| 733 | |
| 734 | chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open, |
| 735 | opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen, |
| 736 | system, truncate, unlink, utime, -X. All these could potentially accept |
| 737 | Unicode filenames either as input or output (and in the case of system |
| 738 | and qx Unicode in general, as input or output to/from the shell). |
| 739 | Whether a filesystem - an operating system pair understands Unicode in |
| 740 | filenames varies. |
| 741 | |
| 742 | Known combinations that have some level of understanding include |
| 743 | Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac |
| 744 | OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to |
| 745 | create Unicode filenames, what forms of Unicode are accepted and used |
| 746 | (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used, |
| 747 | and so on, varies. Finding the right level of interfacing to Perl |
| 748 | requires some thought. Remember that an OS does not implicate a |
| 749 | filesystem. |
| 750 | |
| 751 | (The Windows -C command flag "wide API support" has been at least |
| 752 | temporarily retired in 5.8.1, and the -C has been repurposed, see |
| 753 | L<perlrun>.) |
| 754 | |
| 755 | Most probably the right way to do this would be this: |
| 756 | L</"Virtualize operating system access">. |
| 757 | |
| 758 | =head2 Unicode in %ENV |
| 759 | |
| 760 | Currently the %ENV entries are always byte strings. |
| 761 | See L</"Virtualize operating system access">. |
| 762 | |
| 763 | (See RT ticket #113536 for information on Win32's handling of %ENV, |
| 764 | which was fixed to work with native ANSI codepage characters in the |
| 765 | environment, but still doesn't work with other characters outside of |
| 766 | that codepage present in the environment.) |
| 767 | |
| 768 | =head2 Unicode and glob() |
| 769 | |
| 770 | Currently glob patterns and filenames returned from File::Glob::glob() |
| 771 | are always byte strings. See L</"Virtualize operating system access">. |
| 772 | |
| 773 | =head2 use less 'memory' |
| 774 | |
| 775 | Investigate trade offs to switch out perl's choices on memory usage. |
| 776 | Particularly perl should be able to give memory back. |
| 777 | |
| 778 | This task is incremental - even a little bit of work on it will help. |
| 779 | |
| 780 | =head2 Re-implement C<:unique> in a way that is actually thread-safe |
| 781 | |
| 782 | The old implementation made bad assumptions on several levels. A good 90% |
| 783 | solution might be just to make C<:unique> work to share the string buffer |
| 784 | of SvPVs. That way large constant strings can be shared between ithreads, |
| 785 | such as the configuration information in F<Config>. |
| 786 | |
| 787 | =head2 Make tainting consistent |
| 788 | |
| 789 | Tainting would be easier to use if it didn't take documented shortcuts and |
| 790 | allow taint to "leak" everywhere within an expression. |
| 791 | |
| 792 | =head2 readpipe(LIST) |
| 793 | |
| 794 | system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid |
| 795 | running a shell. readpipe() (the function behind qx//) could be similarly |
| 796 | extended. |
| 797 | |
| 798 | =head2 Audit the code for destruction ordering assumptions |
| 799 | |
| 800 | Change 25773 notes |
| 801 | |
| 802 | /* Need to check SvMAGICAL, as during global destruction it may be that |
| 803 | AvARYLEN(av) has been freed before av, and hence the SvANY() pointer |
| 804 | is now part of the linked list of SV heads, rather than pointing to |
| 805 | the original body. */ |
| 806 | /* FIXME - audit the code for other bugs like this one. */ |
| 807 | |
| 808 | adding the C<SvMAGICAL> check to |
| 809 | |
| 810 | if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) { |
| 811 | MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen); |
| 812 | |
| 813 | Go through the core and look for similar assumptions that SVs have particular |
| 814 | types, as all bets are off during global destruction. |
| 815 | |
| 816 | =head2 Extend PerlIO and PerlIO::Scalar |
| 817 | |
| 818 | PerlIO::Scalar doesn't know how to truncate(). Implementing this |
| 819 | would require extending the PerlIO vtable. |
| 820 | |
| 821 | Similarly the PerlIO vtable doesn't know about formats (write()), or |
| 822 | about stat(), or chmod()/chown(), utime(), or flock(). |
| 823 | |
| 824 | (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership |
| 825 | would mean.) |
| 826 | |
| 827 | PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(), |
| 828 | opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(), |
| 829 | readlink(). |
| 830 | |
| 831 | See also L</"Virtualize operating system access">. |
| 832 | |
| 833 | =head2 Organize error messages |
| 834 | |
| 835 | Perl's diagnostics (error messages, see L<perldiag>) could use |
| 836 | reorganizing and formalizing so that each error message has its |
| 837 | stable-for-all-eternity unique id, categorized by severity, type, and |
| 838 | subsystem. (The error messages would be listed in a datafile outside |
| 839 | of the Perl source code, and the source code would only refer to the |
| 840 | messages by the id.) This clean-up and regularizing should apply |
| 841 | for all croak() messages. |
| 842 | |
| 843 | This would enable all sorts of things: easier translation/localization |
| 844 | of the messages (though please do keep in mind the caveats of |
| 845 | L<Locale::Maketext> about too straightforward approaches to |
| 846 | translation), filtering by severity, and instead of grepping for a |
| 847 | particular error message one could look for a stable error id. (Of |
| 848 | course, changing the error messages by default would break all the |
| 849 | existing software depending on some particular error message...) |
| 850 | |
| 851 | This kind of functionality is known as I<message catalogs>. Look for |
| 852 | inspiration for example in the catgets() system, possibly even use it |
| 853 | if available-- but B<only> if available, all platforms will B<not> |
| 854 | have catgets(). |
| 855 | |
| 856 | For the really pure at heart, consider extending this item to cover |
| 857 | also the warning messages (see L<perllexwarn>, C<warnings.pl>). |
| 858 | |
| 859 | =head1 Tasks that need a knowledge of the interpreter |
| 860 | |
| 861 | These tasks would need C knowledge, and knowledge of how the interpreter works, |
| 862 | or a willingness to learn. |
| 863 | |
| 864 | =head2 forbid labels with keyword names |
| 865 | |
| 866 | Currently C<goto keyword> "computes" the label value: |
| 867 | |
| 868 | $ perl -e 'goto print' |
| 869 | Can't find label 1 at -e line 1. |
| 870 | |
| 871 | It is controversial if the right way to avoid the confusion is to forbid |
| 872 | labels with keyword names, or if it would be better to always treat |
| 873 | bareword expressions after a "goto" as a label and never as a keyword. |
| 874 | |
| 875 | =head2 truncate() prototype |
| 876 | |
| 877 | The prototype of truncate() is currently C<$$>. It should probably |
| 878 | be C<*$> instead. (This is changed in F<opcode.pl>) |
| 879 | |
| 880 | =head2 error reporting of [$a ; $b] |
| 881 | |
| 882 | Using C<;> inside brackets is a syntax error, and we don't propose to change |
| 883 | that by giving it any meaning. However, it's not reported very helpfully: |
| 884 | |
| 885 | $ perl -e '$a = [$b; $c];' |
| 886 | syntax error at -e line 1, near "$b;" |
| 887 | syntax error at -e line 1, near "$c]" |
| 888 | Execution of -e aborted due to compilation errors. |
| 889 | |
| 890 | It should be possible to hook into the tokeniser or the lexer, so that when a |
| 891 | C<;> is parsed where it is not legal as a statement terminator (ie inside |
| 892 | C<{}> used as a hashref, C<[]> or C<()>) it issues an error something like |
| 893 | I<';' isn't legal inside an expression - if you need multiple statements use a |
| 894 | do {...} block>. See the thread starting at |
| 895 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html> |
| 896 | |
| 897 | =head2 strict as warnings |
| 898 | |
| 899 | See L<http://markmail.org/message/vbrupaslr3bybmvk>, where Josua ben Jore |
| 900 | writes: I've been of the opinion that everything strict.pm does ought to be |
| 901 | able to considered just warnings that have been promoted to 'FATAL'. |
| 902 | |
| 903 | =head2 lexicals used only once |
| 904 | |
| 905 | This warns: |
| 906 | |
| 907 | $ perl -we '$pie = 42' |
| 908 | Name "main::pie" used only once: possible typo at -e line 1. |
| 909 | |
| 910 | This does not: |
| 911 | |
| 912 | $ perl -we 'my $pie = 42' |
| 913 | |
| 914 | Logically all lexicals used only once should warn, if the user asks for |
| 915 | warnings. An unworked RT ticket (#5087) has been open for almost seven |
| 916 | years for this discrepancy. |
| 917 | |
| 918 | =head2 UTF-8 revamp |
| 919 | |
| 920 | The handling of Unicode is unclean in many places. In the regex engine |
| 921 | there are especially many problems. The swash data structure could be |
| 922 | replaced my something better. Inversion lists and maps are likely |
| 923 | candidates. The whole Unicode database could be placed in-core for a |
| 924 | huge speed-up. Only minimal work was done on the optimizer when utf8 |
| 925 | was added, with the result that the synthetic start class often will |
| 926 | fail to narrow down the possible choices when given non-Latin1 input. |
| 927 | Karl Williamson has been working on this - talk to him. |
| 928 | |
| 929 | =head2 state variable initialization in list context |
| 930 | |
| 931 | Currently this is illegal: |
| 932 | |
| 933 | state ($a, $b) = foo(); |
| 934 | |
| 935 | In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different |
| 936 | semantics, which is tricky to implement in Perl 5 as currently they produce |
| 937 | the same opcode trees. The Perl 6 design is firm, so it would be good to |
| 938 | implement the necessary code in Perl 5. There are comments in |
| 939 | C<Perl_newASSIGNOP()> that show the code paths taken by various assignment |
| 940 | constructions involving state variables. |
| 941 | |
| 942 | =head2 A does() built-in |
| 943 | |
| 944 | Like ref(), only useful. It would call the C<DOES> method on objects; it |
| 945 | would also tell whether something can be dereferenced as an |
| 946 | array/hash/etc., or used as a regexp, etc. |
| 947 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html> |
| 948 | |
| 949 | =head2 Tied filehandles and write() don't mix |
| 950 | |
| 951 | There is no method on tied filehandles to allow them to be called back by |
| 952 | formats. |
| 953 | |
| 954 | =head2 Propagate compilation hints to the debugger |
| 955 | |
| 956 | Currently a debugger started with -dE on the command-line doesn't see the |
| 957 | features enabled by -E. More generally hints (C<$^H> and C<%^H>) aren't |
| 958 | propagated to the debugger. Probably it would be a good thing to propagate |
| 959 | hints from the innermost non-C<DB::> scope: this would make code eval'ed |
| 960 | in the debugger see the features (and strictures, etc.) currently in |
| 961 | scope. |
| 962 | |
| 963 | =head2 Attach/detach debugger from running program |
| 964 | |
| 965 | The old perltodo notes "With C<gdb>, you can attach the debugger to a running |
| 966 | program if you pass the process ID. It would be good to do this with the Perl |
| 967 | debugger on a running Perl program, although I'm not sure how it would be |
| 968 | done." ssh and screen do this with named pipes in /tmp. Maybe we can too. |
| 969 | |
| 970 | =head2 LVALUE functions for lists |
| 971 | |
| 972 | The old perltodo notes that lvalue functions don't work for list or hash |
| 973 | slices. This would be good to fix. |
| 974 | |
| 975 | =head2 regexp optimiser optional |
| 976 | |
| 977 | The regexp optimiser is not optional. It should configurable to be, to allow |
| 978 | its performance to be measured, and its bugs to be easily demonstrated. |
| 979 | |
| 980 | =head2 C</w> regex modifier |
| 981 | |
| 982 | That flag would enable to match whole words, and also to interpolate |
| 983 | arrays as alternations. With it, C</P/w> would be roughly equivalent to: |
| 984 | |
| 985 | do { local $"='|'; /\b(?:P)\b/ } |
| 986 | |
| 987 | See |
| 988 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html> |
| 989 | for the discussion. |
| 990 | |
| 991 | =head2 optional optimizer |
| 992 | |
| 993 | Make the peephole optimizer optional. Currently it performs two tasks as |
| 994 | it walks the optree - genuine peephole optimisations, and necessary fixups of |
| 995 | ops. It would be good to find an efficient way to switch out the |
| 996 | optimisations whilst keeping the fixups. |
| 997 | |
| 998 | =head2 You WANT *how* many |
| 999 | |
| 1000 | Currently contexts are void, scalar and list. split has a special mechanism in |
| 1001 | place to pass in the number of return values wanted. It would be useful to |
| 1002 | have a general mechanism for this, backwards compatible and little speed hit. |
| 1003 | This would allow proposals such as short circuiting sort to be implemented |
| 1004 | as a module on CPAN. |
| 1005 | |
| 1006 | =head2 lexical aliases |
| 1007 | |
| 1008 | Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>). |
| 1009 | |
| 1010 | =head2 Self-ties |
| 1011 | |
| 1012 | Self-ties are currently illegal because they caused too many segfaults. Maybe |
| 1013 | the causes of these could be tracked down and self-ties on all types |
| 1014 | reinstated. |
| 1015 | |
| 1016 | =head2 Optimize away @_ |
| 1017 | |
| 1018 | The old perltodo notes "Look at the "reification" code in C<av.c>". |
| 1019 | |
| 1020 | =head2 Virtualize operating system access |
| 1021 | |
| 1022 | Implement a set of "vtables" that virtualizes operating system access |
| 1023 | (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very |
| 1024 | least these interfaces should take SVs as "name" arguments instead of |
| 1025 | bare char pointers; probably the most flexible and extensible way |
| 1026 | would be for the Perl-facing interfaces to accept HVs. The system |
| 1027 | needs to be per-operating-system and per-file-system |
| 1028 | hookable/filterable, preferably both from XS and Perl level |
| 1029 | (L<perlport/"Files and Filesystems"> is good reading at this point, |
| 1030 | in fact, all of L<perlport> is.) |
| 1031 | |
| 1032 | This has actually already been implemented (but only for Win32), |
| 1033 | take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32 |
| 1034 | variants go through a set of "vtables" for operating system access, |
| 1035 | non-Win32 systems currently go straight for the POSIX/Unix-style |
| 1036 | system/library call. Similar system as for Win32 should be |
| 1037 | implemented for all platforms. The existing Win32 implementation |
| 1038 | probably does not need to survive alongside this proposed new |
| 1039 | implementation, the approaches could be merged. |
| 1040 | |
| 1041 | What would this give us? One often-asked-for feature this would |
| 1042 | enable is using Unicode for filenames, and other "names" like %ENV, |
| 1043 | usernames, hostnames, and so forth. |
| 1044 | (See L<perlunicode/"When Unicode Does Not Happen">.) |
| 1045 | |
| 1046 | But this kind of virtualization would also allow for things like |
| 1047 | virtual filesystems, virtual networks, and "sandboxes" (though as long |
| 1048 | as dynamic loading of random object code is allowed, not very safe |
| 1049 | sandboxes since external code of course know not of Perl's vtables). |
| 1050 | An example of a smaller "sandbox" is that this feature can be used to |
| 1051 | implement per-thread working directories: Win32 already does this. |
| 1052 | |
| 1053 | See also L</"Extend PerlIO and PerlIO::Scalar">. |
| 1054 | |
| 1055 | =head2 repack the optree |
| 1056 | |
| 1057 | Repacking the optree after execution order is determined could allow |
| 1058 | removal of NULL ops, and optimal ordering of OPs with respect to cache-line |
| 1059 | filling. I think that |
| 1060 | the best way to do this is to make it an optional step just before the |
| 1061 | completed optree is attached to anything else, and to use the slab allocator |
| 1062 | unchanged--but allocate a single slab the right size, avoiding partial |
| 1063 | slabs--, so that freeing ops is identical whether or not this step runs. |
| 1064 | Note that the slab allocator allocates ops downwards in memory, so one would |
| 1065 | have to actually "allocate" the ops in reverse-execution order to get them |
| 1066 | contiguous in memory in execution order. |
| 1067 | |
| 1068 | See |
| 1069 | L<http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html> |
| 1070 | |
| 1071 | Note that running this copy, and then freeing all the old location ops would |
| 1072 | cause their slabs to be freed, which would eliminate possible memory wastage if |
| 1073 | the previous suggestion is implemented, and we swap slabs more frequently. |
| 1074 | |
| 1075 | =head2 eliminate incorrect line numbers in warnings |
| 1076 | |
| 1077 | This code |
| 1078 | |
| 1079 | use warnings; |
| 1080 | my $undef; |
| 1081 | |
| 1082 | if ($undef == 3) { |
| 1083 | } elsif ($undef == 0) { |
| 1084 | } |
| 1085 | |
| 1086 | used to produce this output: |
| 1087 | |
| 1088 | Use of uninitialized value in numeric eq (==) at wrong.pl line 4. |
| 1089 | Use of uninitialized value in numeric eq (==) at wrong.pl line 4. |
| 1090 | |
| 1091 | where the line of the second warning was misreported - it should be line 5. |
| 1092 | Rafael fixed this - the problem arose because there was no nextstate OP |
| 1093 | between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still |
| 1094 | reports that the currently executing line is line 4. The solution was to inject |
| 1095 | a nextstate OPs for each C<elsif>, although it turned out that the nextstate |
| 1096 | OP needed to be a nulled OP, rather than a live nextstate OP, else other line |
| 1097 | numbers became misreported. (Jenga!) |
| 1098 | |
| 1099 | The problem is more general than C<elsif> (although the C<elsif> case is the |
| 1100 | most common and the most confusing). Ideally this code |
| 1101 | |
| 1102 | use warnings; |
| 1103 | my $undef; |
| 1104 | |
| 1105 | my $a = $undef + 1; |
| 1106 | my $b |
| 1107 | = $undef |
| 1108 | + 1; |
| 1109 | |
| 1110 | would produce this output |
| 1111 | |
| 1112 | Use of uninitialized value $undef in addition (+) at wrong.pl line 4. |
| 1113 | Use of uninitialized value $undef in addition (+) at wrong.pl line 7. |
| 1114 | |
| 1115 | (rather than lines 4 and 5), but this would seem to require every OP to carry |
| 1116 | (at least) line number information. |
| 1117 | |
| 1118 | What might work is to have an optional line number in memory just before the |
| 1119 | BASEOP structure, with a flag bit in the op to say whether it's present. |
| 1120 | Initially during compile every OP would carry its line number. Then add a late |
| 1121 | pass to the optimiser (potentially combined with L</repack the optree>) which |
| 1122 | looks at the two ops on every edge of the graph of the execution path. If |
| 1123 | the line number changes, flags the destination OP with this information. |
| 1124 | Once all paths are traced, replace every op with the flag with a |
| 1125 | nextstate-light op (that just updates C<PL_curcop>), which in turn then passes |
| 1126 | control on to the true op. All ops would then be replaced by variants that |
| 1127 | do not store the line number. (Which, logically, why it would work best in |
| 1128 | conjunction with L</repack the optree>, as that is already copying/reallocating |
| 1129 | all the OPs) |
| 1130 | |
| 1131 | (Although I should note that we're not certain that doing this for the general |
| 1132 | case is worth it) |
| 1133 | |
| 1134 | =head2 optimize tail-calls |
| 1135 | |
| 1136 | Tail-calls present an opportunity for broadly applicable optimization; |
| 1137 | anywhere that C<< return foo(...) >> is called, the outer return can |
| 1138 | be replaced by a goto, and foo will return directly to the outer |
| 1139 | caller, saving (conservatively) 25% of perl's call&return cost, which |
| 1140 | is relatively higher than in C. The scheme language is known to do |
| 1141 | this heavily. B::Concise provides good insight into where this |
| 1142 | optimization is possible, ie anywhere entersub,leavesub op-sequence |
| 1143 | occurs. |
| 1144 | |
| 1145 | perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)' |
| 1146 | |
| 1147 | Bottom line on this is probably a new pp_tailcall function which |
| 1148 | combines the code in pp_entersub, pp_leavesub. This should probably |
| 1149 | be done 1st in XS, and using B::Generate to patch the new OP into the |
| 1150 | optrees. |
| 1151 | |
| 1152 | =head2 Add C<0odddd> |
| 1153 | |
| 1154 | It has been proposed that octal constants be specifiable through the syntax |
| 1155 | C<0oddddd>, parallel to the existing construct to specify hex constants |
| 1156 | C<0xddddd> |
| 1157 | |
| 1158 | =head2 Revisit the regex super-linear cache code |
| 1159 | |
| 1160 | Perl executes regexes using the traditional backtracking algorithm, which |
| 1161 | makes it possible to implement a variety of powerful pattern-matching |
| 1162 | features (like embedded code blocks), at the cost of taking exponential time |
| 1163 | to run on some pathological patterns. The exponential-time problem is |
| 1164 | mitigated by the I<super-linear cache>, which detects when we're processing |
| 1165 | such a pathological pattern, and does some additional bookkeeping to avoid |
| 1166 | much of the work. However, that code has bit-rotted a little; some patterns |
| 1167 | don't make as much use of it as they should. The proposal is to analyse |
| 1168 | where the current cache code has problems, and extend it to cover those cases. |
| 1169 | |
| 1170 | See also |
| 1171 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2013-01/msg00339.html> |
| 1172 | |
| 1173 | =head1 Big projects |
| 1174 | |
| 1175 | Tasks that will get your name mentioned in the description of the "Highlights |
| 1176 | of 5.18.0" |
| 1177 | |
| 1178 | =head2 make ithreads more robust |
| 1179 | |
| 1180 | Generally make ithreads more robust. |
| 1181 | |
| 1182 | This task is incremental - even a little bit of work on it will help, and |
| 1183 | will be greatly appreciated. |
| 1184 | |
| 1185 | One bit would be to determine how to clone directory handles on systems |
| 1186 | without a C<fchdir> function (in sv.c:Perl_dirp_dup). |
| 1187 | |
| 1188 | Fix Perl_sv_dup, et al so that threads can return objects. |
| 1189 | |
| 1190 | =head2 Add class set operations to regexp engine |
| 1191 | |
| 1192 | Apparently these are quite useful. Anyway, Jeffery Friedl wants them. |
| 1193 | |
| 1194 | demerphq has this on his todo list, but right at the bottom. |
| 1195 | |
| 1196 | |
| 1197 | =head1 Tasks for microperl |
| 1198 | |
| 1199 | |
| 1200 | [ Each and every one of these may be obsolete, but they were listed |
| 1201 | in the old Todo.micro file] |
| 1202 | |
| 1203 | =head2 do away with fork/exec/wait? |
| 1204 | |
| 1205 | (system, popen should be enough?) |
| 1206 | |
| 1207 | =head2 some of the uconfig.sh really needs to be probed (using cc) in buildtime: |
| 1208 | |
| 1209 | (uConfigure? :-) native datatype widths and endianness come to mind |
| 1210 | |