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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 easier |
8 | are listed first. Anyone is welcome to work on any of these, but it's a good |
9 | idea to first contact I<perl5-porters@perl.org> to avoid duplication of |
10 | effort. By all means contact a pumpking privately first if you prefer. |
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11 | |
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12 | Whilst patches to make the list shorter are most welcome, ideas to add to |
13 | the list are also encouraged. Check the perl5-porters archives for past |
14 | ideas, and any discussion about them. One set of archives may be found at: |
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15 | |
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16 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ |
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17 | |
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18 | |
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19 | |
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20 | |
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21 | |
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22 | =head1 Tasks that only need Perl knowledge |
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23 | |
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24 | =head2 common test code for timed bail out |
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25 | |
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26 | Write portable self destruct code for tests to stop them burning CPU in |
27 | infinite loops. This needs to avoid using alarm, as some of the tests are |
28 | testing alarm/sleep or timers. |
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29 | |
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30 | =head2 POD -> HTML conversion in the core still sucks |
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31 | |
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32 | Which is crazy given just how simple POD purports to be, and how simple HTML |
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33 | can be. It's not actually I<as> simple as it sounds, particularly with the |
34 | flexibility POD allows for C<=item>, but it would be good to improve the |
35 | visual appeal of the HTML generated, and to avoid it having any validation |
36 | errors. See also L</make HTML install work>, as the layout of installation tree |
37 | is needed to improve the cross-linking. |
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38 | |
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39 | =head2 Make Schwern poorer |
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40 | |
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41 | We should have for everything. When all the core's modules are tested, |
42 | Schwern has promised to donate to $500 to TPF. We may need volunteers to |
43 | hold him upside down and shake vigorously in order to actually extract the |
44 | cash. |
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45 | |
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46 | See F<t/lib/1_compile.t> for the 3 remaining modules that need tests. |
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47 | |
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48 | =head2 Improve the coverage of the core tests |
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49 | |
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50 | Use Devel::Cover to ascertain the core's test coverage, then add tests that |
51 | are currently missing. |
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52 | |
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53 | =head2 test B |
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54 | |
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55 | A full test suite for the B module would be nice. |
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56 | |
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57 | =head2 A decent benchmark |
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58 | |
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59 | perlbench seems impervious to any recent changes made to the perl core. It |
60 | would be useful to have a reasonable general benchmarking suite that roughly |
61 | represented what current perl programs do, and measurably reported whether |
62 | tweaks to the core improve, degrade or don't really affect performance, to |
63 | guide people attempting to optimise the guts of perl. Gisle would welcome |
64 | new tests for perlbench. |
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65 | |
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66 | =head2 fix tainting bugs |
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67 | |
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68 | Fix the bugs revealed by running the test suite with the C<-t> switch (via |
69 | C<make test.taintwarn>). |
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70 | |
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71 | =head2 Dual life everything |
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72 | |
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73 | As part of the "dists" plan, anything that doesn't belong in the smallest perl |
74 | distribution needs to be dual lifed. Anything else can be too. Figure out what |
75 | changes would be needed to package that module and its tests up for CPAN, and |
76 | do so. Test it with older perl releases, and fix the problems you find. |
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77 | |
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78 | =head2 Improving C<threads::shared> |
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79 | |
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80 | Investigate whether C<threads::shared> could share aggregates properly with |
81 | only Perl level changes to shared.pm |
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82 | |
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83 | =head2 POSIX memory footprint |
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84 | |
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85 | Ilya observed that use POSIX; eats memory like there's no tomorrow, and at |
86 | various times worked to cut it down. There is probably still fat to cut out - |
87 | for example POSIX passes Exporter some very memory hungry data structures. |
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88 | |
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89 | |
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90 | |
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91 | |
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92 | |
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93 | |
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94 | |
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95 | =head1 Tasks that need a little sysadmin-type knowledge |
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96 | |
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97 | Or if you prefer, tasks that you would learn from, and broaden your skills |
98 | base... |
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99 | |
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100 | =head2 make HTML install work |
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101 | |
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102 | There is an C<installhtml> target in the Makefile. It's marked as |
103 | "experimental". It would be good to get this tested, make it work reliably, and |
104 | remove the "experimental" tag. This would include |
105 | |
106 | =over 4 |
107 | |
108 | =item 1 |
109 | |
110 | Checking that cross linking between various parts of the documentation works. |
111 | In particular that links work between the modules (files with POD in F<lib/>) |
112 | and the core documentation (files in F<pod/>) |
113 | |
114 | =item 2 |
115 | |
116 | Work out how to split perlfunc into chunks, preferably one per function group, |
117 | preferably with general case code that could be used elsewhere. Challenges |
118 | here are correctly identifying the groups of functions that go together, and |
119 | making the right named external cross-links point to the right page. Things to |
120 | be aware of are C<-X>, groups such as C<getpwnam> to C<endservent>, two or |
121 | more C<=items> giving the different parameter lists, such as |
122 | |
123 | =item substr EXPR,OFFSET,LENGTH,REPLACEMENT |
124 | |
125 | =item substr EXPR,OFFSET,LENGTH |
126 | |
127 | =item substr EXPR,OFFSET |
128 | |
129 | and different parameter lists having different meanings. (eg C<select>) |
130 | |
131 | =back |
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132 | |
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133 | =head2 compressed man pages |
134 | |
135 | Be able to install them. This would probably need a configure test to see how |
136 | the system does compressed man pages (same directory/different directory? |
137 | same filename/different filename), as well as tweaking the F<installman> script |
138 | to compress as necessary. |
139 | |
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140 | =head2 Add a code coverage target to the Makefile |
141 | |
142 | Make it easy for anyone to run Devel::Cover on the core's tests. The steps |
143 | to do this manually are roughly |
144 | |
145 | =over 4 |
146 | |
147 | =item * |
148 | |
149 | do a normal C<Configure>, but include Devel::Cover as a module to install |
150 | (see F<INSTALL> for how to do this) |
151 | |
152 | =item * |
153 | |
154 | make perl |
155 | |
156 | =item * |
157 | |
158 | cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness |
159 | |
160 | =item * |
161 | |
162 | Process the resulting Devel::Cover database |
163 | |
164 | =back |
165 | |
166 | This just give you the coverage of the F<.pm>s. To also get the C level |
167 | coverage you need to |
168 | |
169 | =over 4 |
170 | |
171 | =item * |
172 | |
173 | Additionally tell C<Configure> to use the appropriate C compiler flags for |
174 | C<gcov> |
175 | |
176 | =item * |
177 | |
178 | make perl.gcov |
179 | |
180 | (instead of C<make perl>) |
181 | |
182 | =item * |
183 | |
184 | After running the tests run C<gcov> to generate all the F<.gcov> files. |
185 | (Including down in the subdirectories of F<ext/> |
186 | |
187 | =item * |
188 | |
189 | (From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files |
190 | to get their stats into the cover_db directory. |
191 | |
192 | =item * |
193 | |
194 | Then process the Devel::Cover database |
195 | |
196 | =back |
197 | |
198 | It would be good to add a single switch to C<Configure> to specify that you |
199 | wanted to perform perl level coverage, and another to specify C level |
200 | coverage, and have C<Configure> and the F<Makefile> do all the right things |
201 | automatically. |
202 | |
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203 | =head2 Make Config.pm cope with differences between build and installed perl |
204 | |
205 | Quite often vendors ship a perl binary compiled with their (pay-for) |
206 | compilers. People install a free compiler, such as gcc. To work out how to |
207 | build extensions, Perl interrogates C<%Config>, so in this situation |
208 | C<%Config> describes compilers that aren't there, and extension building |
209 | fails. This forces people into choosing between re-compiling perl themselves |
210 | using the compiler they have, or only using modules that the vendor ships. |
211 | |
212 | It would be good to find a way teach C<Config.pm> about the installation setup, |
213 | possibly involving probing at install time or later, so that the C<%Config> in |
214 | a binary distribution better describes the installed machine, when the |
215 | installed machine differs from the build machine in some significant way. |
216 | |
217 | =head2 Relocatable perl |
218 | |
219 | The C level patches needed to create a relocatable perl binary are done, as |
220 | is the work on Config.pm. All that's left to do is the C<Configure> tweaking |
221 | to let people specify how they want to do the install. |
222 | |
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223 | =head2 make parallel builds work |
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224 | |
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225 | Currently parallel builds (such as C<make -j3>) don't work reliably. We believe |
226 | that this is due to incomplete dependency specification in the F<Makefile>. |
227 | It would be good if someone were able to track down the causes of these |
228 | problems, so that parallel builds worked properly. |
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229 | |
230 | |
231 | |
232 | =head1 Tasks that need a little C knowledge |
233 | |
234 | These tasks would need a little C knowledge, but don't need any specific |
235 | background or experience with XS, or how the Perl interpreter works |
236 | |
237 | =head2 Make it clear from -v if this is the exact official release |
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238 | |
239 | Currently perl from p4/rsync ships with a patchlevel.h file that usually |
240 | defines one local patch, of the form "MAINT12345" or "RC1". The output of |
241 | perl -v doesn't report that a perl isn't an official release, and this |
242 | information can get lost in bugs reports. Because of this, the minor version |
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243 | isn't bumped up until RC time, to minimise the possibility of versions of perl |
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244 | escaping that believe themselves to be newer than they actually are. |
245 | |
246 | It would be useful to find an elegant way to have the "this is an interim |
247 | maintenance release" or "this is a release candidate" in the terse -v output, |
248 | and have it so that it's easy for the pumpking to remove this just as the |
249 | release tarball is rolled up. This way the version pulled out of rsync would |
250 | always say "I'm a development release" and it would be safe to bump the |
251 | reported minor version as soon as a release ships, which would aid perl |
252 | developers. |
253 | |
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254 | This task is really about thinking of an elegant way to arrange the C source |
255 | such that it's trivial for the Pumpking to flag "this is an official release" |
256 | when making a tarball, yet leave the default source saying "I'm not the |
257 | official release". |
258 | |
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259 | =head2 Ordering of "global" variables. |
260 | |
261 | F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be |
262 | per-thread under ithreads, where the variables are actually elements in a |
263 | structure. As C dictates, the variables must be laid out in order of |
264 | declaration. There is a comment |
265 | C</* Important ones in the first cache line (if alignment is done right) */> |
266 | which implies that at some point in the past the ordering was carefully chosen |
267 | (at least in part). However, it's clear that the ordering is less than perfect, |
268 | as currently there are things such as 7 C<bool>s in a row, then something |
269 | typically requiring 4 byte alignment, and then an odd C<bool> later on. |
270 | (C<bool>s are typically defined as C<char>s). So it would be good for someone |
271 | to review the ordering of the variables, to see how much alignment padding can |
272 | be removed. |
273 | |
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274 | =head2 bincompat functions |
275 | |
276 | There are lots of functions which are retained for binary compatibility. |
277 | Clean these up. Move them to mathom.c, and don't compile for blead? |
278 | |
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279 | =head2 am I hot or not? |
280 | |
281 | The idea of F<pp_hot.c> is that it contains the I<hot> ops, the ops that are |
282 | most commonly used. The idea is that by grouping them, their object code will |
283 | be adjacent in the executable, so they have a greater chance of already being |
284 | in the CPU cache (or swapped in) due to being near another op already in use. |
285 | |
286 | Except that it's not clear if these really are the most commonly used ops. So |
287 | anyone feeling like exercising their skill with coverage and profiling tools |
288 | might want to determine what ops I<really> are the most commonly used. And in |
289 | turn suggest evictions and promotions to achieve a better F<pp_hot.c>. |
290 | |
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291 | =head2 emulate the per-thread memory pool on Unix |
292 | |
293 | For Windows, ithreads allocates memory for each thread from a separate pool, |
294 | which it discards at thread exit. It also checks that memory is free()d to |
295 | the correct pool. Neither check is done on Unix, so code developed there won't |
296 | be subject to such strictures, so can harbour bugs that only show up when the |
297 | code reaches Windows. |
298 | |
299 | It would be good to be able to optionally emulate the Window pool system on |
300 | Unix, to let developers who only have access to Unix, or want to use |
301 | Unix-specific debugging tools, check for these problems. To do this would |
302 | involve figuring out how the C<PerlMem_*> macros wrap C<malloc()> access, and |
303 | providing a layer that records/checks the identity of the thread making the |
304 | call, and recording all the memory allocated by each thread via this API so |
305 | that it can be summarily free()d at thread exit. One implementation idea |
306 | would be to increase the size of allocation, and store the C<my_perl> pointer |
307 | (to identify the thread) at the start, along with pointers to make a linked |
308 | list of blocks for this thread. To avoid alignment problems it would be |
309 | necessary to do something like |
310 | |
311 | union memory_header_padded { |
312 | struct memory_header { |
313 | void *thread_id; /* For my_perl */ |
314 | void *next; /* Pointer to next block for this thread */ |
315 | } data; |
316 | long double padding; /* whatever type has maximal alignment constraint */ |
317 | }; |
318 | |
319 | |
320 | although C<long double> might not be the only type to add to the padding |
321 | union. |
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322 | |
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323 | |
324 | |
325 | |
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326 | =head1 Tasks that need a knowledge of XS |
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327 | |
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328 | These tasks would need C knowledge, and roughly the level of knowledge of |
329 | the perl API that comes from writing modules that use XS to interface to |
330 | C. |
331 | |
332 | =head2 IPv6 |
333 | |
334 | Clean this up. Check everything in core works |
335 | |
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336 | =head2 merge Perl_sv_2[inpu]v |
337 | |
338 | There's a lot of code shared between C<Perl_sv_2iv_flags>, |
339 | C<Perl_sv_2uv_flags>, C<Perl_sv_2nv>, and C<Perl_sv_2pv_flags>. It would be |
340 | interesting to see if some of it can be merged into common shared static |
341 | functions. In particular, C<Perl_sv_2uv_flags> started out as a cut&paste |
342 | from C<Perl_sv_2iv_flags> around 5.005_50 time, and it may be possible to |
343 | replace both with a single function that returns a value or union which is |
344 | split out by the macros in F<sv.h> |
345 | |
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346 | =head2 UTF8 caching code |
347 | |
348 | The string position/offset cache is not optional. It should be. |
349 | |
350 | =head2 Implicit Latin 1 => Unicode translation |
351 | |
352 | Conversions from byte strings to UTF-8 currently map high bit characters |
353 | to Unicode without translation (or, depending on how you look at it, by |
354 | implicitly assuming that the byte strings are in Latin-1). As perl assumes |
355 | the C locale by default, upgrading a string to UTF-8 may change the |
356 | meaning of its contents regarding character classes, case mapping, etc. |
357 | This should probably emit a warning (at least). |
358 | |
359 | This task is incremental - even a little bit of work on it will help. |
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360 | |
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361 | =head2 autovivification |
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362 | |
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363 | Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict; |
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364 | |
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365 | This task is incremental - even a little bit of work on it will help. |
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366 | |
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367 | =head2 Unicode in Filenames |
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368 | |
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369 | chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open, |
370 | opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen, |
371 | system, truncate, unlink, utime, -X. All these could potentially accept |
372 | Unicode filenames either as input or output (and in the case of system |
373 | and qx Unicode in general, as input or output to/from the shell). |
374 | Whether a filesystem - an operating system pair understands Unicode in |
375 | filenames varies. |
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376 | |
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377 | Known combinations that have some level of understanding include |
378 | Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac |
379 | OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to |
380 | create Unicode filenames, what forms of Unicode are accepted and used |
381 | (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used, |
382 | and so on, varies. Finding the right level of interfacing to Perl |
383 | requires some thought. Remember that an OS does not implicate a |
384 | filesystem. |
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385 | |
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386 | (The Windows -C command flag "wide API support" has been at least |
387 | temporarily retired in 5.8.1, and the -C has been repurposed, see |
388 | L<perlrun>.) |
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389 | |
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390 | =head2 Unicode in %ENV |
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391 | |
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392 | Currently the %ENV entries are always byte strings. |
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393 | |
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394 | =head2 use less 'memory' |
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395 | |
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396 | Investigate trade offs to switch out perl's choices on memory usage. |
397 | Particularly perl should be able to give memory back. |
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398 | |
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399 | This task is incremental - even a little bit of work on it will help. |
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400 | |
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401 | =head2 Re-implement C<:unique> in a way that is actually thread-safe |
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402 | |
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403 | The old implementation made bad assumptions on several levels. A good 90% |
404 | solution might be just to make C<:unique> work to share the string buffer |
405 | of SvPVs. That way large constant strings can be shared between ithreads, |
406 | such as the configuration information in F<Config>. |
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407 | |
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408 | =head2 Make tainting consistent |
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409 | |
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410 | Tainting would be easier to use if it didn't take documented shortcuts and |
411 | allow taint to "leak" everywhere within an expression. |
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412 | |
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413 | =head2 readpipe(LIST) |
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414 | |
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415 | system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid |
416 | running a shell. readpipe() (the function behind qx//) could be similarly |
417 | extended. |
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418 | |
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419 | |
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420 | |
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421 | |
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422 | |
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423 | =head1 Tasks that need a knowledge of the interpreter |
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424 | |
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425 | These tasks would need C knowledge, and knowledge of how the interpreter works, |
426 | or a willingness to learn. |
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427 | |
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428 | =head2 lexical pragmas |
429 | |
430 | Reimplement the mechanism of lexical pragmas to be more extensible. Fix |
431 | current pragmas that don't work well (or at all) with lexical scopes or in |
432 | run-time eval(STRING) (C<sort>, C<re>, C<encoding> for example). MJD has a |
433 | preliminary patch that implements this. |
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434 | |
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435 | =head2 Attach/detach debugger from running program |
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436 | |
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437 | The old perltodo notes "With C<gdb>, you can attach the debugger to a running |
438 | program if you pass the process ID. It would be good to do this with the Perl |
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439 | debugger on a running Perl program, although I'm not sure how it would be |
440 | done." ssh and screen do this with named pipes in /tmp. Maybe we can too. |
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441 | |
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442 | =head2 inlining autoloaded constants |
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443 | |
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444 | Currently the optimiser can inline constants when expressed as subroutines |
445 | with prototype ($) that return a constant. Likewise, many packages wrapping |
446 | C libraries export lots of constants as subroutines which are AUTOLOADed on |
447 | demand. However, these have no prototypes, so can't be seen as constants by |
448 | the optimiser. Some way of cheaply (low syntax, low memory overhead) to the |
449 | perl compiler that a name is a constant would be great, so that it knows to |
450 | call the AUTOLOAD routine at compile time, and then inline the constant. |
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451 | |
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452 | =head2 Constant folding |
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453 | |
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454 | The peephole optimiser should trap errors during constant folding, and give |
455 | up on the folding, rather than bailing out at compile time. It is quite |
456 | possible that the unfoldable constant is in unreachable code, eg something |
457 | akin to C<$a = 0/0 if 0;> |
458 | |
459 | =head2 LVALUE functions for lists |
460 | |
461 | The old perltodo notes that lvalue functions don't work for list or hash |
462 | slices. This would be good to fix. |
463 | |
464 | =head2 LVALUE functions in the debugger |
465 | |
466 | The old perltodo notes that lvalue functions don't work in the debugger. This |
467 | would be good to fix. |
468 | |
469 | =head2 _ prototype character |
470 | |
471 | Study the possibility of adding a new prototype character, C<_>, meaning |
472 | "this argument defaults to $_". |
473 | |
474 | =head2 @INC source filter to Filter::Simple |
475 | |
476 | The second return value from a sub in @INC can be a source filter. This isn't |
477 | documented. It should be changed to use Filter::Simple, tested and documented. |
478 | |
479 | =head2 regexp optimiser optional |
480 | |
481 | The regexp optimiser is not optional. It should configurable to be, to allow |
482 | its performance to be measured, and its bugs to be easily demonstrated. |
483 | |
484 | =head2 UNITCHECK |
485 | |
486 | Introduce a new special block, UNITCHECK, which is run at the end of a |
487 | compilation unit (module, file, eval(STRING) block). This will correspond to |
488 | the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the |
489 | O.pm/B.pm backend framework depends on it. |
490 | |
491 | =head2 optional optimizer |
492 | |
493 | Make the peephole optimizer optional. Currently it performs two tasks as |
494 | it walks the optree - genuine peephole optimisations, and necessary fixups of |
495 | ops. It would be good to find an efficient way to switch out the |
496 | optimisations whilst keeping the fixups. |
497 | |
498 | =head2 You WANT *how* many |
499 | |
500 | Currently contexts are void, scalar and list. split has a special mechanism in |
501 | place to pass in the number of return values wanted. It would be useful to |
502 | have a general mechanism for this, backwards compatible and little speed hit. |
503 | This would allow proposals such as short circuiting sort to be implemented |
504 | as a module on CPAN. |
505 | |
506 | =head2 lexical aliases |
507 | |
508 | Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>. |
509 | |
510 | =head2 entersub XS vs Perl |
511 | |
512 | At the moment pp_entersub is huge, and has code to deal with entering both |
513 | perl and XS subroutines. Subroutine implementations rarely change between |
514 | perl and XS at run time, so investigate using 2 ops to enter subs (one for |
515 | XS, one for perl) and swap between if a sub is redefined. |
2810d901 |
516 | |
517 | =head2 Self ties |
518 | |
519 | self ties are currently illegal because they caused too many segfaults. Maybe |
520 | the causes of these could be tracked down and self-ties on all types re- |
521 | instated. |
0bdfc961 |
522 | |
523 | =head2 Optimize away @_ |
524 | |
525 | The old perltodo notes "Look at the "reification" code in C<av.c>". |
526 | |
527 | =head2 switch ops |
528 | |
529 | The old perltodo notes "Although we have C<Switch.pm> in core, Larry points to |
530 | the dormant C<nswitch> and C<cswitch> ops in F<pp.c>; using these opcodes would |
531 | be much faster." |
532 | |
533 | =head2 What hooks would assertions need? |
534 | |
535 | Assertions are in the core, and work. However, assertions needed to be added |
536 | as a core patch, rather than an XS module in ext, or a CPAN module, because |
537 | the core has no hooks in the necessary places. It would be useful to |
538 | investigate what hooks would need to be added to make it possible to provide |
539 | the full assertion support from a CPAN module, so that we aren't constraining |
540 | the imagination of future CPAN authors. |
541 | |
542 | |
543 | |
544 | |
545 | |
546 | |
547 | |
548 | =head1 Big projects |
549 | |
550 | Tasks that will get your name mentioned in the description of the "Highlights |
551 | of 5.10" |
552 | |
553 | =head2 make ithreads more robust |
554 | |
555 | Generally make ithreads more robust. See also L<iCOW> |
556 | |
557 | This task is incremental - even a little bit of work on it will help, and |
558 | will be greatly appreciated. |
559 | |
560 | =head2 iCOW |
561 | |
562 | Sarathy and Arthur have a proposal for an improved Copy On Write which |
563 | specifically will be able to COW new ithreads. If this can be implemented |
564 | it would be a good thing. |
565 | |
566 | =head2 (?{...}) closures in regexps |
567 | |
568 | Fix (or rewrite) the implementation of the C</(?{...})/> closures. |
569 | |
570 | =head2 A re-entrant regexp engine |
571 | |
572 | This will allow the use of a regex from inside (?{ }), (??{ }) and |
573 | (?(?{ })|) constructs. |