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1 | =head1 NAME |
2 | |
3 | perltodo - Perl TO-DO List |
4 | |
5 | =head1 DESCRIPTION |
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6 | |
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7 | This is a list of wishes for Perl. The tasks we think are smaller or |
8 | easier are listed first. Anyone is welcome to work on any of these, |
9 | but it's a good idea to first contact I<perl5-porters@perl.org> to |
10 | avoid duplication of effort, and to learn from any previous attempts. |
11 | By all means contact a pumpking privately first if you prefer. |
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12 | |
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13 | Whilst patches to make the list shorter are most welcome, ideas to add to |
14 | the list are also encouraged. Check the perl5-porters archives for past |
15 | ideas, and any discussion about them. One set of archives may be found at: |
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16 | |
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17 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ |
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18 | |
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19 | What can we offer you in return? Fame, fortune, and everlasting glory? Maybe |
20 | not, but if your patch is incorporated, then we'll add your name to the |
21 | F<AUTHORS> file, which ships in the official distribution. How many other |
22 | programming languages offer you 1 line of immortality? |
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23 | |
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24 | =head1 Tasks that only need Perl knowledge |
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25 | |
162f8c67 |
26 | =head2 Smartmatch design issues |
27 | |
28 | In 5.10.0 the smartmatch operator C<~~> isn't working quite "right". But |
29 | before we can fix the implementation, we need to define what "right" is. |
30 | The first problem is that Robin Houston implemented the Perl 6 smart match |
31 | spec as of February 2006, when smart match was axiomatically symmetrical: |
32 | L<http://groups.google.com/group/perl.perl6.language/msg/bf2b486f089ad021> |
33 | |
34 | Since then the Perl 6 target moved, but the Perl 5 implementation did not. |
35 | |
36 | So it would be useful for someone to compare the Perl 6 smartmatch table |
37 | as of February 2006 L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=markup&pathrev=7615> |
38 | and the current table L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?revision=14556&view=markup> |
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39 | and tabulate the differences in Perl 6. The annotated view of changes is |
40 | L<http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=annotate> and the diff is |
162f8c67 |
41 | C<svn diff -r7615:14556 http://svn.perl.org/perl6/doc/trunk/design/syn/S03.pod> |
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42 | -- search for C<=head1 Smart matching>. (In theory F<viewvc> can generate that, |
43 | but in practice when I tried it hung forever, I assume "thinking") |
162f8c67 |
44 | |
45 | With that done and published, someone (else) can then map any changed Perl 6 |
46 | semantics back to Perl 5, based on how the existing semantics map to Perl 5: |
47 | L<http://search.cpan.org/~rgarcia/perl-5.10.0/pod/perlsyn.pod#Smart_matching_in_detail> |
48 | |
49 | |
50 | There are also some questions that need answering: |
51 | |
52 | =over 4 |
53 | |
54 | =item * |
55 | |
56 | How do you negate one? (documentation issue) |
57 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-01/msg00071.html |
58 | |
59 | =item * |
60 | |
61 | Array behaviors |
62 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00799.html |
63 | |
64 | * Should smart matches be symmetrical? (Perl 6 says no) |
65 | |
66 | * Other differences between Perl 5 and Perl 6 smart match? |
67 | |
68 | =item * |
69 | |
70 | Objects and smart match |
71 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-12/msg00865.html |
72 | |
73 | =back |
74 | |
5a176cbc |
75 | =head2 Remove duplication of test setup. |
76 | |
77 | Schwern notes, that there's duplication of code - lots and lots of tests have |
78 | some variation on the big block of C<$Is_Foo> checks. We can safely put this |
79 | into a file, change it to build an C<%Is> hash and require it. Maybe just put |
80 | it into F<test.pl>. Throw in the handy tainting subroutines. |
81 | |
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82 | =head2 POD -E<gt> HTML conversion in the core still sucks |
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83 | |
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84 | Which is crazy given just how simple POD purports to be, and how simple HTML |
adebf063 |
85 | can be. It's not actually I<as> simple as it sounds, particularly with the |
86 | flexibility POD allows for C<=item>, but it would be good to improve the |
87 | visual appeal of the HTML generated, and to avoid it having any validation |
88 | errors. See also L</make HTML install work>, as the layout of installation tree |
89 | is needed to improve the cross-linking. |
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90 | |
dc0fb092 |
91 | The addition of C<Pod::Simple> and its related modules may make this task |
92 | easier to complete. |
93 | |
8537f021 |
94 | =head2 merge checkpods and podchecker |
95 | |
96 | F<pod/checkpods.PL> (and C<make check> in the F<pod/> subdirectory) |
97 | implements a very basic check for pod files, but the errors it discovers |
98 | aren't found by podchecker. Add this check to podchecker, get rid of |
99 | checkpods and have C<make check> use podchecker. |
100 | |
aa237293 |
101 | =head2 Parallel testing |
102 | |
b2e2905c |
103 | (This probably impacts much more than the core: also the Test::Harness |
02f21748 |
104 | and TAP::* modules on CPAN.) |
105 | |
c707cc00 |
106 | All of the tests in F<t/> can now be run in parallel, if C<$ENV{TEST_JOBS}> |
107 | is set. However, tests within each directory in F<ext> and F<lib> are still |
108 | run in series, with directories run in parallel. This is an adequate |
109 | heuristic, but it might be possible to relax it further, and get more |
110 | throughput. Specifically, it would be good to audit all of F<lib/*.t>, and |
111 | make them use C<File::Temp>. |
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112 | |
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113 | =head2 Make Schwern poorer |
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114 | |
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115 | We should have tests for everything. When all the core's modules are tested, |
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116 | Schwern has promised to donate to $500 to TPF. We may need volunteers to |
117 | hold him upside down and shake vigorously in order to actually extract the |
118 | cash. |
3958b146 |
119 | |
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120 | =head2 Improve the coverage of the core tests |
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121 | |
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122 | Use Devel::Cover to ascertain the core modules's test coverage, then add |
123 | tests that are currently missing. |
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124 | |
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125 | =head2 test B |
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126 | |
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127 | A full test suite for the B module would be nice. |
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128 | |
636e63cb |
129 | =head2 Deparse inlined constants |
130 | |
131 | Code such as this |
132 | |
133 | use constant PI => 4; |
134 | warn PI |
135 | |
136 | will currently deparse as |
137 | |
138 | use constant ('PI', 4); |
139 | warn 4; |
140 | |
141 | because the tokenizer inlines the value of the constant subroutine C<PI>. |
142 | This allows various compile time optimisations, such as constant folding |
143 | and dead code elimination. Where these haven't happened (such as the example |
144 | above) it ought be possible to make B::Deparse work out the name of the |
145 | original constant, because just enough information survives in the symbol |
146 | table to do this. Specifically, the same scalar is used for the constant in |
147 | the optree as is used for the constant subroutine, so by iterating over all |
148 | symbol tables and generating a mapping of SV address to constant name, it |
149 | would be possible to provide B::Deparse with this functionality. |
150 | |
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151 | =head2 A decent benchmark |
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152 | |
617eabfa |
153 | C<perlbench> seems impervious to any recent changes made to the perl core. It |
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154 | would be useful to have a reasonable general benchmarking suite that roughly |
155 | represented what current perl programs do, and measurably reported whether |
156 | tweaks to the core improve, degrade or don't really affect performance, to |
157 | guide people attempting to optimise the guts of perl. Gisle would welcome |
158 | new tests for perlbench. |
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159 | |
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160 | =head2 fix tainting bugs |
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161 | |
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162 | Fix the bugs revealed by running the test suite with the C<-t> switch (via |
163 | C<make test.taintwarn>). |
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164 | |
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165 | =head2 Dual life everything |
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166 | |
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167 | As part of the "dists" plan, anything that doesn't belong in the smallest perl |
168 | distribution needs to be dual lifed. Anything else can be too. Figure out what |
169 | changes would be needed to package that module and its tests up for CPAN, and |
170 | do so. Test it with older perl releases, and fix the problems you find. |
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171 | |
a393eb28 |
172 | To make a minimal perl distribution, it's useful to look at |
173 | F<t/lib/commonsense.t>. |
174 | |
c2aba5b8 |
175 | =head2 Bundle dual life modules in ext/ |
176 | |
177 | For maintenance (and branch merging) reasons, it would be useful to move |
178 | some architecture-independent dual-life modules from lib/ to ext/, if this |
179 | has no negative impact on the build of perl itself. |
180 | |
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181 | =head2 POSIX memory footprint |
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182 | |
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183 | Ilya observed that use POSIX; eats memory like there's no tomorrow, and at |
184 | various times worked to cut it down. There is probably still fat to cut out - |
185 | for example POSIX passes Exporter some very memory hungry data structures. |
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186 | |
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187 | =head2 embed.pl/makedef.pl |
188 | |
189 | There is a script F<embed.pl> that generates several header files to prefix |
190 | all of Perl's symbols in a consistent way, to provide some semblance of |
191 | namespace support in C<C>. Functions are declared in F<embed.fnc>, variables |
907b3e23 |
192 | in F<interpvar.h>. Quite a few of the functions and variables |
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193 | are conditionally declared there, using C<#ifdef>. However, F<embed.pl> |
194 | doesn't understand the C macros, so the rules about which symbols are present |
195 | when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay. |
196 | It would be good to teach C<embed.pl> to understand the conditional |
197 | compilation, and hence remove the duplication, and the mistakes it has caused. |
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198 | |
801de10e |
199 | =head2 use strict; and AutoLoad |
200 | |
201 | Currently if you write |
202 | |
203 | package Whack; |
204 | use AutoLoader 'AUTOLOAD'; |
205 | use strict; |
206 | 1; |
207 | __END__ |
208 | sub bloop { |
209 | print join (' ', No, strict, here), "!\n"; |
210 | } |
211 | |
212 | then C<use strict;> isn't in force within the autoloaded subroutines. It would |
213 | be more consistent (and less surprising) to arrange for all lexical pragmas |
214 | in force at the __END__ block to be in force within each autoloaded subroutine. |
215 | |
773b3597 |
216 | There's a similar problem with SelfLoader. |
217 | |
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218 | =head2 profile installman |
219 | |
220 | The F<installman> script is slow. All it is doing text processing, which we're |
221 | told is something Perl is good at. So it would be nice to know what it is doing |
222 | that is taking so much CPU, and where possible address it. |
223 | |
224 | |
0bdfc961 |
225 | =head1 Tasks that need a little sysadmin-type knowledge |
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226 | |
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227 | Or if you prefer, tasks that you would learn from, and broaden your skills |
228 | base... |
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229 | |
cd793d32 |
230 | =head2 make HTML install work |
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231 | |
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232 | There is an C<installhtml> target in the Makefile. It's marked as |
233 | "experimental". It would be good to get this tested, make it work reliably, and |
234 | remove the "experimental" tag. This would include |
235 | |
236 | =over 4 |
237 | |
238 | =item 1 |
239 | |
240 | Checking that cross linking between various parts of the documentation works. |
241 | In particular that links work between the modules (files with POD in F<lib/>) |
242 | and the core documentation (files in F<pod/>) |
243 | |
244 | =item 2 |
245 | |
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246 | Work out how to split C<perlfunc> into chunks, preferably one per function |
247 | group, preferably with general case code that could be used elsewhere. |
248 | Challenges here are correctly identifying the groups of functions that go |
249 | together, and making the right named external cross-links point to the right |
250 | page. Things to be aware of are C<-X>, groups such as C<getpwnam> to |
251 | C<endservent>, two or more C<=items> giving the different parameter lists, such |
252 | as |
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253 | |
254 | =item substr EXPR,OFFSET,LENGTH,REPLACEMENT |
adebf063 |
255 | =item substr EXPR,OFFSET,LENGTH |
adebf063 |
256 | =item substr EXPR,OFFSET |
257 | |
258 | and different parameter lists having different meanings. (eg C<select>) |
259 | |
260 | =back |
3a89a73c |
261 | |
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262 | =head2 compressed man pages |
263 | |
264 | Be able to install them. This would probably need a configure test to see how |
265 | the system does compressed man pages (same directory/different directory? |
266 | same filename/different filename), as well as tweaking the F<installman> script |
267 | to compress as necessary. |
268 | |
30222c0f |
269 | =head2 Add a code coverage target to the Makefile |
270 | |
271 | Make it easy for anyone to run Devel::Cover on the core's tests. The steps |
272 | to do this manually are roughly |
273 | |
274 | =over 4 |
275 | |
276 | =item * |
277 | |
278 | do a normal C<Configure>, but include Devel::Cover as a module to install |
279 | (see F<INSTALL> for how to do this) |
280 | |
281 | =item * |
282 | |
283 | make perl |
284 | |
285 | =item * |
286 | |
287 | cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness |
288 | |
289 | =item * |
290 | |
291 | Process the resulting Devel::Cover database |
292 | |
293 | =back |
294 | |
295 | This just give you the coverage of the F<.pm>s. To also get the C level |
296 | coverage you need to |
297 | |
298 | =over 4 |
299 | |
300 | =item * |
301 | |
302 | Additionally tell C<Configure> to use the appropriate C compiler flags for |
303 | C<gcov> |
304 | |
305 | =item * |
306 | |
307 | make perl.gcov |
308 | |
309 | (instead of C<make perl>) |
310 | |
311 | =item * |
312 | |
313 | After running the tests run C<gcov> to generate all the F<.gcov> files. |
314 | (Including down in the subdirectories of F<ext/> |
315 | |
316 | =item * |
317 | |
318 | (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files |
319 | to get their stats into the cover_db directory. |
320 | |
321 | =item * |
322 | |
323 | Then process the Devel::Cover database |
324 | |
325 | =back |
326 | |
327 | It would be good to add a single switch to C<Configure> to specify that you |
328 | wanted to perform perl level coverage, and another to specify C level |
329 | coverage, and have C<Configure> and the F<Makefile> do all the right things |
330 | automatically. |
331 | |
02f21748 |
332 | =head2 Make Config.pm cope with differences between built and installed perl |
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333 | |
334 | Quite often vendors ship a perl binary compiled with their (pay-for) |
335 | compilers. People install a free compiler, such as gcc. To work out how to |
336 | build extensions, Perl interrogates C<%Config>, so in this situation |
337 | C<%Config> describes compilers that aren't there, and extension building |
338 | fails. This forces people into choosing between re-compiling perl themselves |
339 | using the compiler they have, or only using modules that the vendor ships. |
340 | |
341 | It would be good to find a way teach C<Config.pm> about the installation setup, |
342 | possibly involving probing at install time or later, so that the C<%Config> in |
343 | a binary distribution better describes the installed machine, when the |
344 | installed machine differs from the build machine in some significant way. |
345 | |
728f4ecd |
346 | =head2 linker specification files |
347 | |
348 | Some platforms mandate that you provide a list of a shared library's external |
349 | symbols to the linker, so the core already has the infrastructure in place to |
350 | do this for generating shared perl libraries. My understanding is that the |
351 | GNU toolchain can accept an optional linker specification file, and restrict |
352 | visibility just to symbols declared in that file. It would be good to extend |
353 | F<makedef.pl> to support this format, and to provide a means within |
354 | C<Configure> to enable it. This would allow Unix users to test that the |
355 | export list is correct, and to build a perl that does not pollute the global |
356 | namespace with private symbols. |
357 | |
a229ae3b |
358 | =head2 Cross-compile support |
359 | |
360 | Currently C<Configure> understands C<-Dusecrosscompile> option. This option |
361 | arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is |
362 | assumed then to be copied to TARGET machine and used as a replacement of full |
363 | C<perl> executable. |
364 | |
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365 | This could be done little differently. Namely C<miniperl> should be built for |
a229ae3b |
366 | HOST and then full C<perl> with extensions should be compiled for TARGET. |
d1307786 |
367 | This, however, might require extra trickery for %Config: we have one config |
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368 | first for HOST and then another for TARGET. Tools like MakeMaker will be |
369 | mightily confused. Having around two different types of executables and |
370 | libraries (HOST and TARGET) makes life interesting for Makefiles and |
371 | shell (and Perl) scripts. There is $Config{run}, normally empty, which |
372 | can be used as an execution wrapper. Also note that in some |
373 | cross-compilation/execution environments the HOST and the TARGET do |
374 | not see the same filesystem(s), the $Config{run} may need to do some |
375 | file/directory copying back and forth. |
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376 | |
8537f021 |
377 | =head2 roffitall |
378 | |
379 | Make F<pod/roffitall> be updated by F<pod/buildtoc>. |
380 | |
98fca0e8 |
381 | =head2 Split "linker" from "compiler" |
382 | |
383 | Right now, Configure probes for two commands, and sets two variables: |
384 | |
385 | =over 4 |
386 | |
b91dd380 |
387 | =item * C<cc> (in F<cc.U>) |
98fca0e8 |
388 | |
389 | This variable holds the name of a command to execute a C compiler which |
390 | can resolve multiple global references that happen to have the same |
391 | name. Usual values are F<cc> and F<gcc>. |
392 | Fervent ANSI compilers may be called F<c89>. AIX has F<xlc>. |
393 | |
b91dd380 |
394 | =item * C<ld> (in F<dlsrc.U>) |
98fca0e8 |
395 | |
396 | This variable indicates the program to be used to link |
397 | libraries for dynamic loading. On some systems, it is F<ld>. |
398 | On ELF systems, it should be C<$cc>. Mostly, we'll try to respect |
399 | the hint file setting. |
400 | |
401 | =back |
402 | |
8d159ec1 |
403 | There is an implicit historical assumption from around Perl5.000alpha |
404 | something, that C<$cc> is also the correct command for linking object files |
405 | together to make an executable. This may be true on Unix, but it's not true |
406 | on other platforms, and there are a maze of work arounds in other places (such |
407 | as F<Makefile.SH>) to cope with this. |
98fca0e8 |
408 | |
409 | Ideally, we should create a new variable to hold the name of the executable |
410 | linker program, probe for it in F<Configure>, and centralise all the special |
411 | case logic there or in hints files. |
412 | |
413 | A small bikeshed issue remains - what to call it, given that C<$ld> is already |
8d159ec1 |
414 | taken (arguably for the wrong thing now, but on SunOS 4.1 it is the command |
415 | for creating dynamically-loadable modules) and C<$link> could be confused with |
416 | the Unix command line executable of the same name, which does something |
417 | completely different. Andy Dougherty makes the counter argument "In parrot, I |
418 | tried to call the command used to link object files and libraries into an |
419 | executable F<link>, since that's what my vaguely-remembered DOS and VMS |
420 | experience suggested. I don't think any real confusion has ensued, so it's |
421 | probably a reasonable name for perl5 to use." |
98fca0e8 |
422 | |
423 | "Alas, I've always worried that introducing it would make things worse, |
424 | since now the module building utilities would have to look for |
425 | C<$Config{link}> and institute a fall-back plan if it weren't found." |
8d159ec1 |
426 | Although I can see that as confusing, given that C<$Config{d_link}> is true |
427 | when (hard) links are available. |
98fca0e8 |
428 | |
0bdfc961 |
429 | =head1 Tasks that need a little C knowledge |
430 | |
431 | These tasks would need a little C knowledge, but don't need any specific |
432 | background or experience with XS, or how the Perl interpreter works |
433 | |
3d826b29 |
434 | =head2 Weed out needless PERL_UNUSED_ARG |
435 | |
436 | The C code uses the macro C<PERL_UNUSED_ARG> to stop compilers warning about |
437 | unused arguments. Often the arguments can't be removed, as there is an |
438 | external constraint that determines the prototype of the function, so this |
439 | approach is valid. However, there are some cases where C<PERL_UNUSED_ARG> |
440 | could be removed. Specifically |
441 | |
442 | =over 4 |
443 | |
444 | =item * |
445 | |
446 | The prototypes of (nearly all) static functions can be changed |
447 | |
448 | =item * |
449 | |
450 | Unused arguments generated by short cut macros are wasteful - the short cut |
451 | macro used can be changed. |
452 | |
453 | =back |
454 | |
fbf638cb |
455 | =head2 Modernize the order of directories in @INC |
456 | |
457 | The way @INC is laid out by default, one cannot upgrade core (dual-life) |
458 | modules without overwriting files. This causes problems for binary |
3d14fd97 |
459 | package builders. One possible proposal is laid out in this |
460 | message: |
461 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>. |
fbf638cb |
462 | |
bcbaa2d5 |
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 5.12. |
470 | |
0bdfc961 |
471 | =head2 Make it clear from -v if this is the exact official release |
89007cb3 |
472 | |
617eabfa |
473 | Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that |
474 | usually defines one local patch, of the form "MAINT12345" or "RC1". The output |
475 | of perl -v doesn't report that a perl isn't an official release, and this |
89007cb3 |
476 | information can get lost in bugs reports. Because of this, the minor version |
fa11829f |
477 | isn't bumped up until RC time, to minimise the possibility of versions of perl |
89007cb3 |
478 | escaping that believe themselves to be newer than they actually are. |
479 | |
480 | It would be useful to find an elegant way to have the "this is an interim |
481 | maintenance release" or "this is a release candidate" in the terse -v output, |
482 | and have it so that it's easy for the pumpking to remove this just as the |
483 | release tarball is rolled up. This way the version pulled out of rsync would |
484 | always say "I'm a development release" and it would be safe to bump the |
485 | reported minor version as soon as a release ships, which would aid perl |
486 | developers. |
487 | |
0bdfc961 |
488 | This task is really about thinking of an elegant way to arrange the C source |
489 | such that it's trivial for the Pumpking to flag "this is an official release" |
490 | when making a tarball, yet leave the default source saying "I'm not the |
491 | official release". |
492 | |
fee0a0f7 |
493 | =head2 Profile Perl - am I hot or not? |
62403a3c |
494 | |
fee0a0f7 |
495 | The Perl source code is stable enough that it makes sense to profile it, |
496 | identify and optimise the hotspots. It would be good to measure the |
497 | performance of the Perl interpreter using free tools such as cachegrind, |
498 | gprof, and dtrace, and work to reduce the bottlenecks they reveal. |
499 | |
500 | As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops, |
501 | the ops that are most commonly used. The idea is that by grouping them, their |
502 | object code will be adjacent in the executable, so they have a greater chance |
503 | of already being in the CPU cache (or swapped in) due to being near another op |
504 | already in use. |
62403a3c |
505 | |
506 | Except that it's not clear if these really are the most commonly used ops. So |
fee0a0f7 |
507 | as part of exercising your skills with coverage and profiling tools you might |
508 | want to determine what ops I<really> are the most commonly used. And in turn |
509 | suggest evictions and promotions to achieve a better F<pp_hot.c>. |
62403a3c |
510 | |
91d0cbf6 |
511 | One piece of Perl code that might make a good testbed is F<installman>. |
512 | |
98fed0ad |
513 | =head2 Allocate OPs from arenas |
514 | |
515 | Currently all new OP structures are individually malloc()ed and free()d. |
516 | All C<malloc> implementations have space overheads, and are now as fast as |
517 | custom allocates so it would both use less memory and less CPU to allocate |
518 | the various OP structures from arenas. The SV arena code can probably be |
519 | re-used for this. |
520 | |
539f2c54 |
521 | Note that Configuring perl with C<-Accflags=-DPL_OP_SLAB_ALLOC> will use |
522 | Perl_Slab_alloc() to pack optrees into a contiguous block, which is |
523 | probably superior to the use of OP arenas, esp. from a cache locality |
524 | standpoint. See L<Profile Perl - am I hot or not?>. |
525 | |
a229ae3b |
526 | =head2 Improve win32/wince.c |
0bdfc961 |
527 | |
a229ae3b |
528 | Currently, numerous functions look virtually, if not completely, |
02f21748 |
529 | identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't |
6d71adcd |
530 | be good. |
531 | |
c5b31784 |
532 | =head2 Use secure CRT functions when building with VC8 on Win32 |
533 | |
534 | Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis |
535 | that they were "unsafe" and introduced differently named secure versions of |
536 | them as replacements, e.g. instead of writing |
537 | |
538 | FILE* f = fopen(__FILE__, "r"); |
539 | |
540 | one should now write |
541 | |
542 | FILE* f; |
543 | errno_t err = fopen_s(&f, __FILE__, "r"); |
544 | |
545 | Currently, the warnings about these deprecations have been disabled by adding |
546 | -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that |
547 | warning suppressant and actually make use of the new secure CRT functions. |
548 | |
549 | There is also a similar issue with POSIX CRT function names like fileno having |
550 | been deprecated in favour of ISO C++ conformant names like _fileno. These |
26a6faa8 |
551 | warnings are also currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It |
c5b31784 |
552 | might be nice to do as Microsoft suggest here too, although, unlike the secure |
553 | functions issue, there is presumably little or no benefit in this case. |
554 | |
038ae9a4 |
555 | =head2 Fix POSIX::access() and chdir() on Win32 |
556 | |
557 | These functions currently take no account of DACLs and therefore do not behave |
558 | correctly in situations where access is restricted by DACLs (as opposed to the |
559 | read-only attribute). |
560 | |
561 | Furthermore, POSIX::access() behaves differently for directories having the |
562 | read-only attribute set depending on what CRT library is being used. For |
563 | example, the _access() function in the VC6 and VC7 CRTs (wrongly) claim that |
564 | such directories are not writable, whereas in fact all directories are writable |
565 | unless access is denied by DACLs. (In the case of directories, the read-only |
566 | attribute actually only means that the directory cannot be deleted.) This CRT |
567 | bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory may still |
568 | not actually be writable if access is indeed denied by DACLs). |
569 | |
570 | For the chdir() issue, see ActiveState bug #74552: |
571 | http://bugs.activestate.com/show_bug.cgi?id=74552 |
572 | |
573 | Therefore, DACLs should be checked both for consistency across CRTs and for |
574 | the correct answer. |
575 | |
576 | (Note that perl's -w operator should not be modified to check DACLs. It has |
577 | been written so that it reflects the state of the read-only attribute, even |
578 | for directories (whatever CRT is being used), for symmetry with chmod().) |
579 | |
16815324 |
580 | =head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf() |
581 | |
582 | Maybe create a utility that checks after each libperl.a creation that |
583 | none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets()) |
584 | ever creep back to libperl.a. |
585 | |
586 | nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/' |
587 | |
588 | Note, of course, that this will only tell whether B<your> platform |
589 | is using those naughty interfaces. |
590 | |
de96509d |
591 | =head2 -D_FORTIFY_SOURCE=2, -fstack-protector |
592 | |
593 | Recent glibcs support C<-D_FORTIFY_SOURCE=2> and recent gcc |
594 | (4.1 onwards?) supports C<-fstack-protector>, both of which give |
595 | protection against various kinds of buffer overflow problems. |
596 | These should probably be used for compiling Perl whenever available, |
597 | Configure and/or hints files should be adjusted to probe for the |
598 | availability of these features and enable them as appropriate. |
16815324 |
599 | |
8964cfe0 |
600 | =head2 Arenas for GPs? For MAGIC? |
601 | |
602 | C<struct gp> and C<struct magic> are both currently allocated by C<malloc>. |
603 | It might be a speed or memory saving to change to using arenas. Or it might |
604 | not. It would need some suitable benchmarking first. In particular, C<GP>s |
605 | can probably be changed with minimal compatibility impact (probably nothing |
606 | outside of the core, or even outside of F<gv.c> allocates them), but they |
607 | probably aren't allocated/deallocated often enough for a speed saving. Whereas |
608 | C<MAGIC> is allocated/deallocated more often, but in turn, is also something |
609 | more externally visible, so changing the rules here may bite external code. |
610 | |
3880c8ec |
611 | =head2 Shared arenas |
612 | |
613 | Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and |
614 | PVHV, and PVCV and PVFM. It should be possible to allocate and return same |
615 | sized bodies from the same actual arena, rather than maintaining one arena for |
616 | each. This could save 4-6K per thread, of memory no longer tied up in the |
617 | not-yet-allocated part of an arena. |
618 | |
8964cfe0 |
619 | |
6d71adcd |
620 | =head1 Tasks that need a knowledge of XS |
621 | |
622 | These tasks would need C knowledge, and roughly the level of knowledge of |
623 | the perl API that comes from writing modules that use XS to interface to |
624 | C. |
625 | |
5d96f598 |
626 | =head2 safely supporting POSIX SA_SIGINFO |
627 | |
628 | Some years ago Jarkko supplied patches to provide support for the POSIX |
629 | SA_SIGINFO feature in Perl, passing the extra data to the Perl signal handler. |
630 | |
631 | Unfortunately, it only works with "unsafe" signals, because under safe |
632 | signals, by the time Perl gets to run the signal handler, the extra |
633 | information has been lost. Moreover, it's not easy to store it somewhere, |
634 | as you can't call mutexs, or do anything else fancy, from inside a signal |
635 | handler. |
636 | |
637 | So it strikes me that we could provide safe SA_SIGINFO support |
638 | |
639 | =over 4 |
640 | |
641 | =item 1 |
642 | |
643 | Provide global variables for two file descriptors |
644 | |
645 | =item 2 |
646 | |
647 | When the first request is made via C<sigaction> for C<SA_SIGINFO>, create a |
648 | pipe, store the reader in one, the writer in the other |
649 | |
650 | =item 3 |
651 | |
652 | In the "safe" signal handler (C<Perl_csighandler()>/C<S_raise_signal()>), if |
653 | the C<siginfo_t> pointer non-C<NULL>, and the writer file handle is open, |
654 | |
655 | =over 8 |
656 | |
657 | =item 1 |
658 | |
659 | serialise signal number, C<struct siginfo_t> (or at least the parts we care |
660 | about) into a small auto char buff |
661 | |
662 | =item 2 |
663 | |
664 | C<write()> that (non-blocking) to the writer fd |
665 | |
666 | =over 12 |
667 | |
668 | =item 1 |
669 | |
670 | if it writes 100%, flag the signal in a counter of "signals on the pipe" akin |
671 | to the current per-signal-number counts |
672 | |
673 | =item 2 |
674 | |
675 | if it writes 0%, assume the pipe is full. Flag the data as lost? |
676 | |
677 | =item 3 |
678 | |
679 | if it writes partially, croak a panic, as your OS is broken. |
680 | |
681 | =back |
682 | |
683 | =back |
684 | |
685 | =item 4 |
686 | |
687 | in the regular C<PERL_ASYNC_CHECK()> processing, if there are "signals on |
688 | the pipe", read the data out, deserialise, build the Perl structures on |
689 | the stack (code in C<Perl_sighandler()>, the "unsafe" handler), and call as |
690 | usual. |
691 | |
692 | =back |
693 | |
694 | I think that this gets us decent C<SA_SIGINFO> support, without the current risk |
695 | of running Perl code inside the signal handler context. (With all the dangers |
696 | of things like C<malloc> corruption that that currently offers us) |
697 | |
698 | For more information see the thread starting with this message: |
699 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html |
700 | |
6d71adcd |
701 | =head2 autovivification |
702 | |
703 | Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict; |
704 | |
705 | This task is incremental - even a little bit of work on it will help. |
706 | |
707 | =head2 Unicode in Filenames |
708 | |
709 | chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open, |
710 | opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen, |
711 | system, truncate, unlink, utime, -X. All these could potentially accept |
712 | Unicode filenames either as input or output (and in the case of system |
713 | and qx Unicode in general, as input or output to/from the shell). |
714 | Whether a filesystem - an operating system pair understands Unicode in |
715 | filenames varies. |
716 | |
717 | Known combinations that have some level of understanding include |
718 | Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac |
719 | OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to |
720 | create Unicode filenames, what forms of Unicode are accepted and used |
721 | (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used, |
722 | and so on, varies. Finding the right level of interfacing to Perl |
723 | requires some thought. Remember that an OS does not implicate a |
724 | filesystem. |
725 | |
726 | (The Windows -C command flag "wide API support" has been at least |
727 | temporarily retired in 5.8.1, and the -C has been repurposed, see |
728 | L<perlrun>.) |
729 | |
87a942b1 |
730 | Most probably the right way to do this would be this: |
731 | L</"Virtualize operating system access">. |
732 | |
6d71adcd |
733 | =head2 Unicode in %ENV |
734 | |
735 | Currently the %ENV entries are always byte strings. |
87a942b1 |
736 | See L</"Virtualize operating system access">. |
6d71adcd |
737 | |
1f2e7916 |
738 | =head2 Unicode and glob() |
739 | |
740 | Currently glob patterns and filenames returned from File::Glob::glob() |
87a942b1 |
741 | are always byte strings. See L</"Virtualize operating system access">. |
1f2e7916 |
742 | |
dbb0c492 |
743 | =head2 Unicode and lc/uc operators |
744 | |
745 | Some built-in operators (C<lc>, C<uc>, etc.) behave differently, based on |
746 | what the internal encoding of their argument is. That should not be the |
747 | case. Maybe add a pragma to switch behaviour. |
748 | |
6d71adcd |
749 | =head2 use less 'memory' |
750 | |
751 | Investigate trade offs to switch out perl's choices on memory usage. |
752 | Particularly perl should be able to give memory back. |
753 | |
754 | This task is incremental - even a little bit of work on it will help. |
755 | |
756 | =head2 Re-implement C<:unique> in a way that is actually thread-safe |
757 | |
758 | The old implementation made bad assumptions on several levels. A good 90% |
759 | solution might be just to make C<:unique> work to share the string buffer |
760 | of SvPVs. That way large constant strings can be shared between ithreads, |
761 | such as the configuration information in F<Config>. |
762 | |
763 | =head2 Make tainting consistent |
764 | |
765 | Tainting would be easier to use if it didn't take documented shortcuts and |
766 | allow taint to "leak" everywhere within an expression. |
767 | |
768 | =head2 readpipe(LIST) |
769 | |
770 | system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid |
771 | running a shell. readpipe() (the function behind qx//) could be similarly |
772 | extended. |
773 | |
6d71adcd |
774 | =head2 Audit the code for destruction ordering assumptions |
775 | |
776 | Change 25773 notes |
777 | |
778 | /* Need to check SvMAGICAL, as during global destruction it may be that |
779 | AvARYLEN(av) has been freed before av, and hence the SvANY() pointer |
780 | is now part of the linked list of SV heads, rather than pointing to |
781 | the original body. */ |
782 | /* FIXME - audit the code for other bugs like this one. */ |
783 | |
784 | adding the C<SvMAGICAL> check to |
785 | |
786 | if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) { |
787 | MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen); |
788 | |
789 | Go through the core and look for similar assumptions that SVs have particular |
790 | types, as all bets are off during global destruction. |
791 | |
749904bf |
792 | =head2 Extend PerlIO and PerlIO::Scalar |
793 | |
794 | PerlIO::Scalar doesn't know how to truncate(). Implementing this |
795 | would require extending the PerlIO vtable. |
796 | |
797 | Similarly the PerlIO vtable doesn't know about formats (write()), or |
798 | about stat(), or chmod()/chown(), utime(), or flock(). |
799 | |
800 | (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership |
801 | would mean.) |
802 | |
803 | PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(), |
804 | opendir(), closedir(), seekdir(), rewinddir(), glob(); symlink(), |
805 | readlink(). |
806 | |
94da6c29 |
807 | See also L</"Virtualize operating system access">. |
808 | |
3236f110 |
809 | =head2 -C on the #! line |
810 | |
811 | It should be possible to make -C work correctly if found on the #! line, |
812 | given that all perl command line options are strict ASCII, and -C changes |
813 | only the interpretation of non-ASCII characters, and not for the script file |
814 | handle. To make it work needs some investigation of the ordering of function |
815 | calls during startup, and (by implication) a bit of tweaking of that order. |
816 | |
d6c1e11f |
817 | =head2 Organize error messages |
818 | |
819 | Perl's diagnostics (error messages, see L<perldiag>) could use |
a8d0aeb9 |
820 | reorganizing and formalizing so that each error message has its |
d6c1e11f |
821 | stable-for-all-eternity unique id, categorized by severity, type, and |
822 | subsystem. (The error messages would be listed in a datafile outside |
c4bd451b |
823 | of the Perl source code, and the source code would only refer to the |
824 | messages by the id.) This clean-up and regularizing should apply |
d6c1e11f |
825 | for all croak() messages. |
826 | |
827 | This would enable all sorts of things: easier translation/localization |
828 | of the messages (though please do keep in mind the caveats of |
829 | L<Locale::Maketext> about too straightforward approaches to |
830 | translation), filtering by severity, and instead of grepping for a |
831 | particular error message one could look for a stable error id. (Of |
832 | course, changing the error messages by default would break all the |
833 | existing software depending on some particular error message...) |
834 | |
835 | This kind of functionality is known as I<message catalogs>. Look for |
836 | inspiration for example in the catgets() system, possibly even use it |
837 | if available-- but B<only> if available, all platforms will B<not> |
de96509d |
838 | have catgets(). |
d6c1e11f |
839 | |
840 | For the really pure at heart, consider extending this item to cover |
841 | also the warning messages (see L<perllexwarn>, C<warnings.pl>). |
3236f110 |
842 | |
0bdfc961 |
843 | =head1 Tasks that need a knowledge of the interpreter |
3298bd4d |
844 | |
0bdfc961 |
845 | These tasks would need C knowledge, and knowledge of how the interpreter works, |
846 | or a willingness to learn. |
3298bd4d |
847 | |
718140ec |
848 | =head2 lexicals used only once |
849 | |
850 | This warns: |
851 | |
852 | $ perl -we '$pie = 42' |
853 | Name "main::pie" used only once: possible typo at -e line 1. |
854 | |
855 | This does not: |
856 | |
857 | $ perl -we 'my $pie = 42' |
858 | |
859 | Logically all lexicals used only once should warn, if the user asks for |
d6f4ea2e |
860 | warnings. An unworked RT ticket (#5087) has been open for almost seven |
861 | years for this discrepancy. |
718140ec |
862 | |
a3d15f9a |
863 | =head2 UTF-8 revamp |
864 | |
865 | The handling of Unicode is unclean in many places. For example, the regexp |
866 | engine matches in Unicode semantics whenever the string or the pattern is |
867 | flagged as UTF-8, but that should not be dependent on an internal storage |
868 | detail of the string. Likewise, case folding behaviour is dependent on the |
869 | UTF8 internal flag being on or off. |
870 | |
871 | =head2 Properly Unicode safe tokeniser and pads. |
872 | |
873 | The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack - |
874 | variable names are stored in stashes as raw bytes, without the utf-8 flag |
875 | set. The pad API only takes a C<char *> pointer, so that's all bytes too. The |
876 | tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from |
877 | source filters. All this could be fixed. |
878 | |
636e63cb |
879 | =head2 state variable initialization in list context |
880 | |
881 | Currently this is illegal: |
882 | |
883 | state ($a, $b) = foo(); |
884 | |
a2874905 |
885 | In Perl 6, C<state ($a) = foo();> and C<(state $a) = foo();> have different |
a8d0aeb9 |
886 | semantics, which is tricky to implement in Perl 5 as currently they produce |
a2874905 |
887 | the same opcode trees. The Perl 6 design is firm, so it would be good to |
a8d0aeb9 |
888 | implement the necessary code in Perl 5. There are comments in |
a2874905 |
889 | C<Perl_newASSIGNOP()> that show the code paths taken by various assignment |
890 | constructions involving state variables. |
636e63cb |
891 | |
4fedb12c |
892 | =head2 Implement $value ~~ 0 .. $range |
893 | |
894 | It would be nice to extend the syntax of the C<~~> operator to also |
895 | understand numeric (and maybe alphanumeric) ranges. |
a393eb28 |
896 | |
897 | =head2 A does() built-in |
898 | |
899 | Like ref(), only useful. It would call the C<DOES> method on objects; it |
900 | would also tell whether something can be dereferenced as an |
901 | array/hash/etc., or used as a regexp, etc. |
902 | L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html> |
903 | |
904 | =head2 Tied filehandles and write() don't mix |
905 | |
906 | There is no method on tied filehandles to allow them to be called back by |
907 | formats. |
4fedb12c |
908 | |
d10fc472 |
909 | =head2 Attach/detach debugger from running program |
1626a787 |
910 | |
cd793d32 |
911 | The old perltodo notes "With C<gdb>, you can attach the debugger to a running |
912 | program if you pass the process ID. It would be good to do this with the Perl |
0bdfc961 |
913 | debugger on a running Perl program, although I'm not sure how it would be |
914 | done." ssh and screen do this with named pipes in /tmp. Maybe we can too. |
1626a787 |
915 | |
a8cb5b9e |
916 | =head2 Optimize away empty destructors |
917 | |
918 | Defining an empty DESTROY method might be useful (notably in |
919 | AUTOLOAD-enabled classes), but it's still a bit expensive to call. That |
920 | could probably be optimized. |
921 | |
0bdfc961 |
922 | =head2 LVALUE functions for lists |
923 | |
924 | The old perltodo notes that lvalue functions don't work for list or hash |
925 | slices. This would be good to fix. |
926 | |
927 | =head2 LVALUE functions in the debugger |
928 | |
929 | The old perltodo notes that lvalue functions don't work in the debugger. This |
930 | would be good to fix. |
931 | |
0bdfc961 |
932 | =head2 regexp optimiser optional |
933 | |
934 | The regexp optimiser is not optional. It should configurable to be, to allow |
935 | its performance to be measured, and its bugs to be easily demonstrated. |
936 | |
02f21748 |
937 | =head2 delete &function |
938 | |
939 | Allow to delete functions. One can already undef them, but they're still |
940 | in the stash. |
941 | |
ef36c6a7 |
942 | =head2 C</w> regex modifier |
943 | |
944 | That flag would enable to match whole words, and also to interpolate |
945 | arrays as alternations. With it, C</P/w> would be roughly equivalent to: |
946 | |
947 | do { local $"='|'; /\b(?:P)\b/ } |
948 | |
949 | See L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html> |
950 | for the discussion. |
951 | |
0bdfc961 |
952 | =head2 optional optimizer |
953 | |
954 | Make the peephole optimizer optional. Currently it performs two tasks as |
955 | it walks the optree - genuine peephole optimisations, and necessary fixups of |
956 | ops. It would be good to find an efficient way to switch out the |
957 | optimisations whilst keeping the fixups. |
958 | |
959 | =head2 You WANT *how* many |
960 | |
961 | Currently contexts are void, scalar and list. split has a special mechanism in |
962 | place to pass in the number of return values wanted. It would be useful to |
963 | have a general mechanism for this, backwards compatible and little speed hit. |
964 | This would allow proposals such as short circuiting sort to be implemented |
965 | as a module on CPAN. |
966 | |
967 | =head2 lexical aliases |
968 | |
969 | Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>. |
970 | |
971 | =head2 entersub XS vs Perl |
972 | |
973 | At the moment pp_entersub is huge, and has code to deal with entering both |
974 | perl and XS subroutines. Subroutine implementations rarely change between |
975 | perl and XS at run time, so investigate using 2 ops to enter subs (one for |
976 | XS, one for perl) and swap between if a sub is redefined. |
2810d901 |
977 | |
de535794 |
978 | =head2 Self-ties |
2810d901 |
979 | |
de535794 |
980 | Self-ties are currently illegal because they caused too many segfaults. Maybe |
a8d0aeb9 |
981 | the causes of these could be tracked down and self-ties on all types |
de535794 |
982 | reinstated. |
0bdfc961 |
983 | |
984 | =head2 Optimize away @_ |
985 | |
986 | The old perltodo notes "Look at the "reification" code in C<av.c>". |
987 | |
87a942b1 |
988 | =head2 Virtualize operating system access |
989 | |
990 | Implement a set of "vtables" that virtualizes operating system access |
991 | (open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very |
992 | least these interfaces should take SVs as "name" arguments instead of |
993 | bare char pointers; probably the most flexible and extensible way |
e1a3d5d1 |
994 | would be for the Perl-facing interfaces to accept HVs. The system |
995 | needs to be per-operating-system and per-file-system |
996 | hookable/filterable, preferably both from XS and Perl level |
87a942b1 |
997 | (L<perlport/"Files and Filesystems"> is good reading at this point, |
998 | in fact, all of L<perlport> is.) |
999 | |
e1a3d5d1 |
1000 | This has actually already been implemented (but only for Win32), |
1001 | take a look at F<iperlsys.h> and F<win32/perlhost.h>. While all Win32 |
1002 | variants go through a set of "vtables" for operating system access, |
1003 | non-Win32 systems currently go straight for the POSIX/UNIX-style |
1004 | system/library call. Similar system as for Win32 should be |
1005 | implemented for all platforms. The existing Win32 implementation |
1006 | probably does not need to survive alongside this proposed new |
1007 | implementation, the approaches could be merged. |
87a942b1 |
1008 | |
1009 | What would this give us? One often-asked-for feature this would |
94da6c29 |
1010 | enable is using Unicode for filenames, and other "names" like %ENV, |
1011 | usernames, hostnames, and so forth. |
1012 | (See L<perlunicode/"When Unicode Does Not Happen">.) |
1013 | |
1014 | But this kind of virtualization would also allow for things like |
1015 | virtual filesystems, virtual networks, and "sandboxes" (though as long |
1016 | as dynamic loading of random object code is allowed, not very safe |
1017 | sandboxes since external code of course know not of Perl's vtables). |
1018 | An example of a smaller "sandbox" is that this feature can be used to |
1019 | implement per-thread working directories: Win32 already does this. |
1020 | |
1021 | See also L</"Extend PerlIO and PerlIO::Scalar">. |
87a942b1 |
1022 | |
ac6197af |
1023 | =head2 Investigate PADTMP hash pessimisation |
1024 | |
1025 | The peephole optimier converts constants used for hash key lookups to shared |
057163d7 |
1026 | hash key scalars. Under ithreads, something is undoing this work. |
ac6197af |
1027 | See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html |
1028 | |
057163d7 |
1029 | =head2 Store the current pad in the OP slab allocator |
1030 | |
1031 | =for clarification |
1032 | I hope that I got that "current pad" part correct |
1033 | |
1034 | Currently we leak ops in various cases of parse failure. I suggested that we |
1035 | could solve this by always using the op slab allocator, and walking it to |
1036 | free ops. Dave comments that as some ops are already freed during optree |
1037 | creation one would have to mark which ops are freed, and not double free them |
1038 | when walking the slab. He notes that one problem with this is that for some ops |
1039 | you have to know which pad was current at the time of allocation, which does |
1040 | change. I suggested storing a pointer to the current pad in the memory allocated |
1041 | for the slab, and swapping to a new slab each time the pad changes. Dave thinks |
1042 | that this would work. |
1043 | |
52960e22 |
1044 | =head2 repack the optree |
1045 | |
1046 | Repacking the optree after execution order is determined could allow |
057163d7 |
1047 | removal of NULL ops, and optimal ordering of OPs with respect to cache-line |
1048 | filling. The slab allocator could be reused for this purpose. I think that |
1049 | the best way to do this is to make it an optional step just before the |
1050 | completed optree is attached to anything else, and to use the slab allocator |
1051 | unchanged, so that freeing ops is identical whether or not this step runs. |
1052 | Note that the slab allocator allocates ops downwards in memory, so one would |
1053 | have to actually "allocate" the ops in reverse-execution order to get them |
1054 | contiguous in memory in execution order. |
1055 | |
1056 | See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html |
1057 | |
1058 | Note that running this copy, and then freeing all the old location ops would |
1059 | cause their slabs to be freed, which would eliminate possible memory wastage if |
1060 | the previous suggestion is implemented, and we swap slabs more frequently. |
52960e22 |
1061 | |
12e06b6f |
1062 | =head2 eliminate incorrect line numbers in warnings |
1063 | |
1064 | This code |
1065 | |
1066 | use warnings; |
1067 | my $undef; |
1068 | |
1069 | if ($undef == 3) { |
1070 | } elsif ($undef == 0) { |
1071 | } |
1072 | |
18a16cc5 |
1073 | used to produce this output: |
12e06b6f |
1074 | |
1075 | Use of uninitialized value in numeric eq (==) at wrong.pl line 4. |
1076 | Use of uninitialized value in numeric eq (==) at wrong.pl line 4. |
1077 | |
18a16cc5 |
1078 | where the line of the second warning was misreported - it should be line 5. |
1079 | Rafael fixed this - the problem arose because there was no nextstate OP |
1080 | between the execution of the C<if> and the C<elsif>, hence C<PL_curcop> still |
1081 | reports that the currently executing line is line 4. The solution was to inject |
1082 | a nextstate OPs for each C<elsif>, although it turned out that the nextstate |
1083 | OP needed to be a nulled OP, rather than a live nextstate OP, else other line |
1084 | numbers became misreported. (Jenga!) |
12e06b6f |
1085 | |
1086 | The problem is more general than C<elsif> (although the C<elsif> case is the |
1087 | most common and the most confusing). Ideally this code |
1088 | |
1089 | use warnings; |
1090 | my $undef; |
1091 | |
1092 | my $a = $undef + 1; |
1093 | my $b |
1094 | = $undef |
1095 | + 1; |
1096 | |
1097 | would produce this output |
1098 | |
1099 | Use of uninitialized value $undef in addition (+) at wrong.pl line 4. |
1100 | Use of uninitialized value $undef in addition (+) at wrong.pl line 7. |
1101 | |
1102 | (rather than lines 4 and 5), but this would seem to require every OP to carry |
1103 | (at least) line number information. |
1104 | |
1105 | What might work is to have an optional line number in memory just before the |
1106 | BASEOP structure, with a flag bit in the op to say whether it's present. |
1107 | Initially during compile every OP would carry its line number. Then add a late |
1108 | pass to the optimiser (potentially combined with L</repack the optree>) which |
1109 | looks at the two ops on every edge of the graph of the execution path. If |
1110 | the line number changes, flags the destination OP with this information. |
1111 | Once all paths are traced, replace every op with the flag with a |
1112 | nextstate-light op (that just updates C<PL_curcop>), which in turn then passes |
1113 | control on to the true op. All ops would then be replaced by variants that |
1114 | do not store the line number. (Which, logically, why it would work best in |
1115 | conjunction with L</repack the optree>, as that is already copying/reallocating |
1116 | all the OPs) |
1117 | |
18a16cc5 |
1118 | (Although I should note that we're not certain that doing this for the general |
1119 | case is worth it) |
1120 | |
52960e22 |
1121 | =head2 optimize tail-calls |
1122 | |
1123 | Tail-calls present an opportunity for broadly applicable optimization; |
1124 | anywhere that C<< return foo(...) >> is called, the outer return can |
1125 | be replaced by a goto, and foo will return directly to the outer |
1126 | caller, saving (conservatively) 25% of perl's call&return cost, which |
1127 | is relatively higher than in C. The scheme language is known to do |
1128 | this heavily. B::Concise provides good insight into where this |
1129 | optimization is possible, ie anywhere entersub,leavesub op-sequence |
1130 | occurs. |
1131 | |
1132 | perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)' |
1133 | |
1134 | Bottom line on this is probably a new pp_tailcall function which |
1135 | combines the code in pp_entersub, pp_leavesub. This should probably |
1136 | be done 1st in XS, and using B::Generate to patch the new OP into the |
1137 | optrees. |
1138 | |
0bdfc961 |
1139 | =head1 Big projects |
1140 | |
1141 | Tasks that will get your name mentioned in the description of the "Highlights |
87a942b1 |
1142 | of 5.12" |
0bdfc961 |
1143 | |
1144 | =head2 make ithreads more robust |
1145 | |
4e577f8b |
1146 | Generally make ithreads more robust. See also L</iCOW> |
0bdfc961 |
1147 | |
1148 | This task is incremental - even a little bit of work on it will help, and |
1149 | will be greatly appreciated. |
1150 | |
6c047da7 |
1151 | One bit would be to write the missing code in sv.c:Perl_dirp_dup. |
1152 | |
59c7f7d5 |
1153 | Fix Perl_sv_dup, et al so that threads can return objects. |
1154 | |
0bdfc961 |
1155 | =head2 iCOW |
1156 | |
1157 | Sarathy and Arthur have a proposal for an improved Copy On Write which |
1158 | specifically will be able to COW new ithreads. If this can be implemented |
1159 | it would be a good thing. |
1160 | |
1161 | =head2 (?{...}) closures in regexps |
1162 | |
1163 | Fix (or rewrite) the implementation of the C</(?{...})/> closures. |
1164 | |
1165 | =head2 A re-entrant regexp engine |
1166 | |
1167 | This will allow the use of a regex from inside (?{ }), (??{ }) and |
1168 | (?(?{ })|) constructs. |
6bda09f9 |
1169 | |
6bda09f9 |
1170 | =head2 Add class set operations to regexp engine |
1171 | |
1172 | Apparently these are quite useful. Anyway, Jeffery Friedl wants them. |
1173 | |
1174 | demerphq has this on his todo list, but right at the bottom. |