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1=head1 NAME
2
3perltodo - Perl TO-DO List
4
5=head1 DESCRIPTION
e50bb9a1 6
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7This is a list of wishes for Perl. The tasks we think are smaller or easier
8are listed first. Anyone is welcome to work on any of these, but it's a good
9idea to first contact I<perl5-porters@perl.org> to avoid duplication of
10effort. By all means contact a pumpking privately first if you prefer.
e50bb9a1 11
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12Whilst patches to make the list shorter are most welcome, ideas to add to
13the list are also encouraged. Check the perl5-porters archives for past
14ideas, and any discussion about them. One set of archives may be found at:
e50bb9a1 15
0bdfc961 16 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
938c8732 17
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18What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
19not, but if your patch is incorporated, then we'll add your name to the
20F<AUTHORS> file, which ships in the official distribution. How many other
21programming languages offer you 1 line of immortality?
938c8732 22
4e577f8b 23=head1 The roadmap to 5.10
938c8732 24
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25The roadmap to 5.10 envisages feature based releases, as various items in this
26TODO are completed.
27
02f21748 28=head2 Needed for a 5.9.5 release
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29
30=over
31
32=item *
c1f116f6 33
02f21748 34Implement L</_ prototype character>
4e577f8b 35
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36=item *
37
02f21748 38Review smart match semantics in light of Perl 6 developments.
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39
40=item *
c1f116f6 41
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42Review assertions. Review syntax to combine assertions. Assertions could take
43advantage of the lexical pragmas work. L</What hooks would assertions need?>
4e577f8b 44
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45=item *
46
02f21748 47C<encoding> should be turned into a lexical pragma (probably).
c1f116f6 48
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49=back
50
51=head2 Needed for a 5.9.6 release
52
53Stabilisation. If all goes well, this will be the equivalent of a 5.10-beta.
e50bb9a1 54
0bdfc961 55=head1 Tasks that only need Perl knowledge
e50bb9a1 56
0bdfc961 57=head2 common test code for timed bail out
e50bb9a1 58
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59Write portable self destruct code for tests to stop them burning CPU in
60infinite loops. This needs to avoid using alarm, as some of the tests are
61testing alarm/sleep or timers.
e50bb9a1 62
0bdfc961 63=head2 POD -> HTML conversion in the core still sucks
e50bb9a1 64
938c8732 65Which is crazy given just how simple POD purports to be, and how simple HTML
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66can be. It's not actually I<as> simple as it sounds, particularly with the
67flexibility POD allows for C<=item>, but it would be good to improve the
68visual appeal of the HTML generated, and to avoid it having any validation
69errors. See also L</make HTML install work>, as the layout of installation tree
70is needed to improve the cross-linking.
938c8732 71
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72The addition of C<Pod::Simple> and its related modules may make this task
73easier to complete.
74
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75=head2 Parallel testing
76
b2e2905c 77(This probably impacts much more than the core: also the Test::Harness
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78and TAP::* modules on CPAN.)
79
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80The core regression test suite is getting ever more comprehensive, which has
81the side effect that it takes longer to run. This isn't so good. Investigate
82whether it would be feasible to give the harness script the B<option> of
83running sets of tests in parallel. This would be useful for tests in
84F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
85
86Questions to answer
87
88=over 4
89
90=item 1
91
92How does screen layout work when you're running more than one test?
93
94=item 2
95
96How does the caller of test specify how many tests to run in parallel?
97
98=item 3
99
100How do setup/teardown tests identify themselves?
101
102=back
103
104Pugs already does parallel testing - can their approach be re-used?
105
0bdfc961 106=head2 Make Schwern poorer
e50bb9a1 107
613bd4f7 108We should have tests for everything. When all the core's modules are tested,
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109Schwern has promised to donate to $500 to TPF. We may need volunteers to
110hold him upside down and shake vigorously in order to actually extract the
111cash.
3958b146 112
0bdfc961 113=head2 Improve the coverage of the core tests
e50bb9a1 114
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115Use Devel::Cover to ascertain the core modules's test coverage, then add
116tests that are currently missing.
30222c0f 117
0bdfc961 118=head2 test B
e50bb9a1 119
0bdfc961 120A full test suite for the B module would be nice.
e50bb9a1 121
0bdfc961 122=head2 A decent benchmark
e50bb9a1 123
617eabfa 124C<perlbench> seems impervious to any recent changes made to the perl core. It
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125would be useful to have a reasonable general benchmarking suite that roughly
126represented what current perl programs do, and measurably reported whether
127tweaks to the core improve, degrade or don't really affect performance, to
128guide people attempting to optimise the guts of perl. Gisle would welcome
129new tests for perlbench.
6168cf99 130
0bdfc961 131=head2 fix tainting bugs
6168cf99 132
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133Fix the bugs revealed by running the test suite with the C<-t> switch (via
134C<make test.taintwarn>).
e50bb9a1 135
0bdfc961 136=head2 Dual life everything
e50bb9a1 137
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138As part of the "dists" plan, anything that doesn't belong in the smallest perl
139distribution needs to be dual lifed. Anything else can be too. Figure out what
140changes would be needed to package that module and its tests up for CPAN, and
141do so. Test it with older perl releases, and fix the problems you find.
e50bb9a1 142
0bdfc961 143=head2 Improving C<threads::shared>
722d2a37 144
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145Investigate whether C<threads::shared> could share aggregates properly with
146only Perl level changes to shared.pm
722d2a37 147
0bdfc961 148=head2 POSIX memory footprint
e50bb9a1 149
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150Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
151various times worked to cut it down. There is probably still fat to cut out -
152for example POSIX passes Exporter some very memory hungry data structures.
e50bb9a1 153
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154=head2 embed.pl/makedef.pl
155
156There is a script F<embed.pl> that generates several header files to prefix
157all of Perl's symbols in a consistent way, to provide some semblance of
158namespace support in C<C>. Functions are declared in F<embed.fnc>, variables
159in F<interpvar.h> and F<thrdvar.h>. Quite a few of the functions and variables
160are conditionally declared there, using C<#ifdef>. However, F<embed.pl>
161doesn't understand the C macros, so the rules about which symbols are present
162when is duplicated in F<makedef.pl>. Writing things twice is bad, m'kay.
163It would be good to teach C<embed.pl> to understand the conditional
164compilation, and hence remove the duplication, and the mistakes it has caused.
e50bb9a1 165
0bdfc961 166=head1 Tasks that need a little sysadmin-type knowledge
e50bb9a1 167
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168Or if you prefer, tasks that you would learn from, and broaden your skills
169base...
e50bb9a1 170
cd793d32 171=head2 make HTML install work
e50bb9a1 172
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173There is an C<installhtml> target in the Makefile. It's marked as
174"experimental". It would be good to get this tested, make it work reliably, and
175remove the "experimental" tag. This would include
176
177=over 4
178
179=item 1
180
181Checking that cross linking between various parts of the documentation works.
182In particular that links work between the modules (files with POD in F<lib/>)
183and the core documentation (files in F<pod/>)
184
185=item 2
186
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187Work out how to split C<perlfunc> into chunks, preferably one per function
188group, preferably with general case code that could be used elsewhere.
189Challenges here are correctly identifying the groups of functions that go
190together, and making the right named external cross-links point to the right
191page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
192C<endservent>, two or more C<=items> giving the different parameter lists, such
193as
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194
195 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
adebf063 196 =item substr EXPR,OFFSET,LENGTH
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197 =item substr EXPR,OFFSET
198
199and different parameter lists having different meanings. (eg C<select>)
200
201=back
3a89a73c 202
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203=head2 compressed man pages
204
205Be able to install them. This would probably need a configure test to see how
206the system does compressed man pages (same directory/different directory?
207same filename/different filename), as well as tweaking the F<installman> script
208to compress as necessary.
209
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210=head2 Add a code coverage target to the Makefile
211
212Make it easy for anyone to run Devel::Cover on the core's tests. The steps
213to do this manually are roughly
214
215=over 4
216
217=item *
218
219do a normal C<Configure>, but include Devel::Cover as a module to install
220(see F<INSTALL> for how to do this)
221
222=item *
223
224 make perl
225
226=item *
227
228 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
229
230=item *
231
232Process the resulting Devel::Cover database
233
234=back
235
236This just give you the coverage of the F<.pm>s. To also get the C level
237coverage you need to
238
239=over 4
240
241=item *
242
243Additionally tell C<Configure> to use the appropriate C compiler flags for
244C<gcov>
245
246=item *
247
248 make perl.gcov
249
250(instead of C<make perl>)
251
252=item *
253
254After running the tests run C<gcov> to generate all the F<.gcov> files.
255(Including down in the subdirectories of F<ext/>
256
257=item *
258
259(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
260to get their stats into the cover_db directory.
261
262=item *
263
264Then process the Devel::Cover database
265
266=back
267
268It would be good to add a single switch to C<Configure> to specify that you
269wanted to perform perl level coverage, and another to specify C level
270coverage, and have C<Configure> and the F<Makefile> do all the right things
271automatically.
272
02f21748 273=head2 Make Config.pm cope with differences between built and installed perl
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274
275Quite often vendors ship a perl binary compiled with their (pay-for)
276compilers. People install a free compiler, such as gcc. To work out how to
277build extensions, Perl interrogates C<%Config>, so in this situation
278C<%Config> describes compilers that aren't there, and extension building
279fails. This forces people into choosing between re-compiling perl themselves
280using the compiler they have, or only using modules that the vendor ships.
281
282It would be good to find a way teach C<Config.pm> about the installation setup,
283possibly involving probing at install time or later, so that the C<%Config> in
284a binary distribution better describes the installed machine, when the
285installed machine differs from the build machine in some significant way.
286
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287=head2 linker specification files
288
289Some platforms mandate that you provide a list of a shared library's external
290symbols to the linker, so the core already has the infrastructure in place to
291do this for generating shared perl libraries. My understanding is that the
292GNU toolchain can accept an optional linker specification file, and restrict
293visibility just to symbols declared in that file. It would be good to extend
294F<makedef.pl> to support this format, and to provide a means within
295C<Configure> to enable it. This would allow Unix users to test that the
296export list is correct, and to build a perl that does not pollute the global
297namespace with private symbols.
298
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299=head2 Cross-compile support
300
301Currently C<Configure> understands C<-Dusecrosscompile> option. This option
302arranges for building C<miniperl> for TARGET machine, so this C<miniperl> is
303assumed then to be copied to TARGET machine and used as a replacement of full
304C<perl> executable.
305
d1307786 306This could be done little differently. Namely C<miniperl> should be built for
a229ae3b 307HOST and then full C<perl> with extensions should be compiled for TARGET.
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308This, however, might require extra trickery for %Config: we have one config
309first for HOST and then another for TARGET.
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310
311=head1 Tasks that need a little C knowledge
312
313These tasks would need a little C knowledge, but don't need any specific
314background or experience with XS, or how the Perl interpreter works
315
316=head2 Make it clear from -v if this is the exact official release
89007cb3 317
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318Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
319usually defines one local patch, of the form "MAINT12345" or "RC1". The output
320of perl -v doesn't report that a perl isn't an official release, and this
89007cb3 321information can get lost in bugs reports. Because of this, the minor version
fa11829f 322isn't bumped up until RC time, to minimise the possibility of versions of perl
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323escaping that believe themselves to be newer than they actually are.
324
325It would be useful to find an elegant way to have the "this is an interim
326maintenance release" or "this is a release candidate" in the terse -v output,
327and have it so that it's easy for the pumpking to remove this just as the
328release tarball is rolled up. This way the version pulled out of rsync would
329always say "I'm a development release" and it would be safe to bump the
330reported minor version as soon as a release ships, which would aid perl
331developers.
332
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333This task is really about thinking of an elegant way to arrange the C source
334such that it's trivial for the Pumpking to flag "this is an official release"
335when making a tarball, yet leave the default source saying "I'm not the
336official release".
337
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338=head2 Ordering of "global" variables.
339
340F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
341per-thread under ithreads, where the variables are actually elements in a
342structure. As C dictates, the variables must be laid out in order of
343declaration. There is a comment
344C</* Important ones in the first cache line (if alignment is done right) */>
345which implies that at some point in the past the ordering was carefully chosen
346(at least in part). However, it's clear that the ordering is less than perfect,
347as currently there are things such as 7 C<bool>s in a row, then something
348typically requiring 4 byte alignment, and then an odd C<bool> later on.
349(C<bool>s are typically defined as C<char>s). So it would be good for someone
350to review the ordering of the variables, to see how much alignment padding can
351be removed.
352
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353It's also worth checking that all variables are actually used. Perl 5.8.0
354shipped with C<PL_nrs> still defined in F<thrdvar.h>, despite it being unused
355since a change over a year earlier. Had this been spotted before release, it
356could have been removed, but now it has to remain in the 5.8.x releases to
357keep the structure the same size, to retain binary compatibility.
358
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359It's probably worth checking if all need to be the types they are. For example
360
361 PERLVAR(Ierror_count, I32) /* how many errors so far, max 10 */
362
363might work as well if stored in a signed (or unsigned) 8 bit value, if the
364comment is accurate. C<PL_multi_open> and C<PL_multi_close> can probably
365become C<char>s. Finding variables to downsize coupled with rearrangement
366could shrink the interpreter structure; a size saving which is multiplied by
367the number of threads running.
368
fee0a0f7 369=head2 Profile Perl - am I hot or not?
62403a3c 370
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371The Perl source code is stable enough that it makes sense to profile it,
372identify and optimise the hotspots. It would be good to measure the
373performance of the Perl interpreter using free tools such as cachegrind,
374gprof, and dtrace, and work to reduce the bottlenecks they reveal.
375
376As part of this, the idea of F<pp_hot.c> is that it contains the I<hot> ops,
377the ops that are most commonly used. The idea is that by grouping them, their
378object code will be adjacent in the executable, so they have a greater chance
379of already being in the CPU cache (or swapped in) due to being near another op
380already in use.
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381
382Except that it's not clear if these really are the most commonly used ops. So
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383as part of exercising your skills with coverage and profiling tools you might
384want to determine what ops I<really> are the most commonly used. And in turn
385suggest evictions and promotions to achieve a better F<pp_hot.c>.
62403a3c 386
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387=head2 Shrink struct context
388
389In F<cop.h>, we have
390
391 struct context {
392 U32 cx_type; /* what kind of context this is */
393 union {
394 struct block cx_blk;
395 struct subst cx_subst;
396 } cx_u;
397 };
398
399There are less than 256 values for C<cx_type>, and the constituent parts
400C<struct block> and C<struct subst> both contain some C<U8> and C<U16> fields,
401so it should be possible to move them to the first word, and share space with
402a C<U8> C<cx_type>, saving 1 word.
403
404=head2 Allocate OPs from arenas
405
406Currently all new OP structures are individually malloc()ed and free()d.
407All C<malloc> implementations have space overheads, and are now as fast as
408custom allocates so it would both use less memory and less CPU to allocate
409the various OP structures from arenas. The SV arena code can probably be
410re-used for this.
411
a229ae3b 412=head2 Improve win32/wince.c
0bdfc961 413
a229ae3b 414Currently, numerous functions look virtually, if not completely,
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415identical in both C<win32/wince.c> and C<win32/win32.c> files, which can't
416be good.
0bdfc961 417
0bdfc961 418=head1 Tasks that need a knowledge of XS
e50bb9a1 419
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420These tasks would need C knowledge, and roughly the level of knowledge of
421the perl API that comes from writing modules that use XS to interface to
422C.
423
f23930d5 424=head2 shrink C<PVBM>s
4a750395 425
35b64ab6 426By removing unused elements and careful re-ordering, the structures for C<AV>s,
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427C<HV>s, C<CV>s and C<GV>s have recently been shrunk considerably. C<PVIO>s
428probably aren't worth it, as typical programs don't use more than 8, and
429(at least) C<Filter::Util::Call> uses C<SvPVX>/C<SvCUR>/C<SvLEN> on a C<PVIO>,
430so it would mean code changes to modules on CPAN. C<PVBM>s might have some
431savings to win.
4a750395 432
cd793d32 433=head2 autovivification
e50bb9a1 434
cd793d32 435Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
e50bb9a1 436
0bdfc961 437This task is incremental - even a little bit of work on it will help.
e50bb9a1 438
0bdfc961 439=head2 Unicode in Filenames
e50bb9a1 440
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441chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
442opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
443system, truncate, unlink, utime, -X. All these could potentially accept
444Unicode filenames either as input or output (and in the case of system
445and qx Unicode in general, as input or output to/from the shell).
446Whether a filesystem - an operating system pair understands Unicode in
447filenames varies.
e50bb9a1 448
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449Known combinations that have some level of understanding include
450Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
451OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
452create Unicode filenames, what forms of Unicode are accepted and used
453(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
454and so on, varies. Finding the right level of interfacing to Perl
455requires some thought. Remember that an OS does not implicate a
456filesystem.
e50bb9a1 457
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458(The Windows -C command flag "wide API support" has been at least
459temporarily retired in 5.8.1, and the -C has been repurposed, see
460L<perlrun>.)
969e704b 461
0bdfc961 462=head2 Unicode in %ENV
969e704b 463
0bdfc961 464Currently the %ENV entries are always byte strings.
e50bb9a1 465
0bdfc961 466=head2 use less 'memory'
e50bb9a1 467
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468Investigate trade offs to switch out perl's choices on memory usage.
469Particularly perl should be able to give memory back.
e50bb9a1 470
0bdfc961 471This task is incremental - even a little bit of work on it will help.
0abe3f7c 472
0bdfc961 473=head2 Re-implement C<:unique> in a way that is actually thread-safe
0abe3f7c 474
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475The old implementation made bad assumptions on several levels. A good 90%
476solution might be just to make C<:unique> work to share the string buffer
477of SvPVs. That way large constant strings can be shared between ithreads,
478such as the configuration information in F<Config>.
0abe3f7c 479
0bdfc961 480=head2 Make tainting consistent
0abe3f7c 481
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482Tainting would be easier to use if it didn't take documented shortcuts and
483allow taint to "leak" everywhere within an expression.
0abe3f7c 484
0bdfc961 485=head2 readpipe(LIST)
0abe3f7c 486
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487system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
488running a shell. readpipe() (the function behind qx//) could be similarly
489extended.
0abe3f7c 490
d1307786 491=head2 strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
e50bb9a1 492
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493Maybe create a utility that checks after each libperl.a creation that
494none of the above (nor sprintf(), vsprintf(), or *SHUDDER* gets())
495ever creep back to libperl.a.
e50bb9a1 496
d1307786 497 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'
e50bb9a1 498
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499Note, of course, that this will only tell whether B<your> platform
500is using those naughty interfaces.
f86a8bc5 501
0bdfc961 502=head1 Tasks that need a knowledge of the interpreter
3298bd4d 503
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504These tasks would need C knowledge, and knowledge of how the interpreter works,
505or a willingness to learn.
3298bd4d 506
d10fc472 507=head2 Attach/detach debugger from running program
1626a787 508
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509The old perltodo notes "With C<gdb>, you can attach the debugger to a running
510program if you pass the process ID. It would be good to do this with the Perl
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511debugger on a running Perl program, although I'm not sure how it would be
512done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
1626a787 513
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514=head2 LVALUE functions for lists
515
516The old perltodo notes that lvalue functions don't work for list or hash
517slices. This would be good to fix.
518
519=head2 LVALUE functions in the debugger
520
521The old perltodo notes that lvalue functions don't work in the debugger. This
522would be good to fix.
523
524=head2 _ prototype character
525
526Study the possibility of adding a new prototype character, C<_>, meaning
527"this argument defaults to $_".
528
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529=head2 regexp optimiser optional
530
531The regexp optimiser is not optional. It should configurable to be, to allow
532its performance to be measured, and its bugs to be easily demonstrated.
533
534=head2 UNITCHECK
535
536Introduce a new special block, UNITCHECK, which is run at the end of a
537compilation unit (module, file, eval(STRING) block). This will correspond to
538the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
539O.pm/B.pm backend framework depends on it.
540
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541=head2 delete &function
542
543Allow to delete functions. One can already undef them, but they're still
544in the stash.
545
546=head2 Make readpipe overridable
547
548so we can override qx// as well.
549
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550=head2 optional optimizer
551
552Make the peephole optimizer optional. Currently it performs two tasks as
553it walks the optree - genuine peephole optimisations, and necessary fixups of
554ops. It would be good to find an efficient way to switch out the
555optimisations whilst keeping the fixups.
556
557=head2 You WANT *how* many
558
559Currently contexts are void, scalar and list. split has a special mechanism in
560place to pass in the number of return values wanted. It would be useful to
561have a general mechanism for this, backwards compatible and little speed hit.
562This would allow proposals such as short circuiting sort to be implemented
563as a module on CPAN.
564
565=head2 lexical aliases
566
567Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
568
569=head2 entersub XS vs Perl
570
571At the moment pp_entersub is huge, and has code to deal with entering both
572perl and XS subroutines. Subroutine implementations rarely change between
573perl and XS at run time, so investigate using 2 ops to enter subs (one for
574XS, one for perl) and swap between if a sub is redefined.
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575
576=head2 Self ties
577
578self ties are currently illegal because they caused too many segfaults. Maybe
579the causes of these could be tracked down and self-ties on all types re-
580instated.
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581
582=head2 Optimize away @_
583
584The old perltodo notes "Look at the "reification" code in C<av.c>".
585
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586=head2 What hooks would assertions need?
587
588Assertions are in the core, and work. However, assertions needed to be added
589as a core patch, rather than an XS module in ext, or a CPAN module, because
590the core has no hooks in the necessary places. It would be useful to
591investigate what hooks would need to be added to make it possible to provide
592the full assertion support from a CPAN module, so that we aren't constraining
593the imagination of future CPAN authors.
594
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595=head2 Properly Unicode safe tokeniser and pads.
596
597The tokeniser isn't actually very UTF-8 clean. C<use utf8;> is a hack -
598variable names are stored in stashes as raw bytes, without the utf-8 flag
599set. The pad API only takes a C<char *> pointer, so that's all bytes too. The
600tokeniser ignores the UTF-8-ness of C<PL_rsfp>, or any SVs returned from
601source filters. All this could be fixed.
602
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603=head1 Big projects
604
605Tasks that will get your name mentioned in the description of the "Highlights
606of 5.10"
607
608=head2 make ithreads more robust
609
4e577f8b 610Generally make ithreads more robust. See also L</iCOW>
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611
612This task is incremental - even a little bit of work on it will help, and
613will be greatly appreciated.
614
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615One bit would be to write the missing code in sv.c:Perl_dirp_dup.
616
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617=head2 iCOW
618
619Sarathy and Arthur have a proposal for an improved Copy On Write which
620specifically will be able to COW new ithreads. If this can be implemented
621it would be a good thing.
622
623=head2 (?{...}) closures in regexps
624
625Fix (or rewrite) the implementation of the C</(?{...})/> closures.
626
627=head2 A re-entrant regexp engine
628
629This will allow the use of a regex from inside (?{ }), (??{ }) and
630(?(?{ })|) constructs.