This Week on perl5-porters - 25-31 August 2008

This Week on perl5-porters - 25-31 August 2008

   "I must admit that I find Perl's Unicode support completely baffling.
   I've read the documentation multiple times, and while I can now
   predict when it won't work, I still have no idea how to get it to do
   what I want. It's kind of frustrating; I don't know if I'm just dim,
   or if I'm missing some magic bit of documentation, or if the support
   is just really confusing." -- Russ Allbery, shooting fish in a barrel.

Topics of Interest

Profiling parallel tests

   On the 17th of August, Nicholas Clark kicked off a thread about
   applying Test::Harness's version 3 goodness to the task of running the
   core test suite, which offers a satisfying halving of the time taken.

   One thing that surprised him was how much CPU the harness itself used:
   if that could be reduced, things would go even faster. Andy Armstrong
   thought that O(N²) algorithms might be extracting their dues from
   large numbers of test files.

   Over the following couple of days, Aristotle Pagaltzis pondered
   various strategies for rewriting the hot spots. Steve Hay was dismayed
   to discover that no parallelism was available on the Windows platform,
   since the technique requires being able perform a "select" system call
   on a file handle, and Windows doesn't like doing things that way.

     blogged
     http://use.perl.org/~nicholas/journal/37137

     http://xrl.us/oqi2f

Wrong RE match in 5.10.0

   Gisle Aas mentioned that a slightly impaired regular expression used
   to dump core on 5.8.8. These days, with an iterative engine under the
   hood of 5.10, it no longer dumps core... unfortunately, it returns the
   wrong result. Bram was able to simplify the test case to highlight
   what was happening.

   Abigail showed that the problem was in fact that * (0 or many times)
   is implemented as "no more than 32766 times". This is horribly
   reminiscent of CP/M, and Dave Mitchell thought that it would be really
   nice if this limit could die a quick death. Nicholas Clark was unsure
   as to how that could be brought about.

   In the meantime, it would be better if hitting this limit caused the
   engine to die, rather than merely warn (which you don't even hear
   about if warnings are switched off).

     shades of Advice from Klortho, #11912
     http://xrl.us/oqi2h

"dprofpp" enhanced

   With all the cool kids playing around with "Devel::NYTProf", it was
   good to see someone lavish some tender loving care on "Devel::DProf".
   Which is what Daniel Pfeiffer did by adding some new functionality to
   "dprofpp". No-one picked the patch up.

     http://xrl.us/oqi2j

Regaining 'O's

   H.Merijn Brand was saddened by smoke tests failing, simply because a
   UTF-8 locale was in use and "Pod::Man" was getting needlessly confused
   and thus marring an otherwise perfect run.

   After a moment of confusion, Russ Allbery realised that the problem
   probably lay with "Pod::Simple", and all that was needed was to add an
   "=encoding" directive to the POD test file. After some Unicode
   guidance from Juerd Waalboer, Russ saw the light and prepared a patch
   that solved the problems and looked sane at the same time.

   Russ was a little scared by what the Correct Use of Unicode entailed
   in a program and thought it was incredibly complex. Juerd explained
   that there were three main techniques for dealing with Unicode, and
   showed where PHP, Perl 5 and Perl 6 fitted in the grand scheme.

     http://xrl.us/oqi2m

Proposed pragma/module "ensure"

   Chris Hall has written a pragmatic module currently named "ensure"
   that attempts to check for undefined subroutine. The denizens of
   "comp.lang.perl.modules" advised him to get in touch with the porters
   (on this list) for guidance and feedback on the idea. Unfortunately he
   received none.

     http://xrl.us/oqi2o

Moving lib/ modules to ext/?

   Nicholas Clark explained that he had not got very far in the process
   of moving core modules from /lib to /ext, and noted that it would
   probably take off once the move to git was complete.

     http://xrl.us/oqi2q

   When Jerry D. Hedden pointed out that non-XS modules get built
   incorrectly, Nicholas wondered if it were as simple as looking for XS
   files in the build directory and in the process discovered a
   sub-optimal "File::Find" construct that had been in the "installperl"
   Makefile target all the way back to change #18.

     http://xrl.us/oqi2s

   Nicholas went ahead and committed the fix that Jerry wrote to deal
   with the above problem, and in doing so, he came to the conclusion
   that it would probably fix a bug that no-one had reported yet.

     http://xrl.us/oqi2u

   So Jerry fixed it.

     http://xrl.us/oqi2w

"unless(...)" terser than "if(!...)"

   Nicholas noticed that an "unless($x)" uses one less op than "if(!$x)",
   and so he asked whether it was possible to optimise the latter into
   the former (or, more precisely, where one would go about doing it).

   Vincent Pit returned a day later with a proof of concept patch which
   did just that. As usual with Vincent's patches, after explaining the
   difficulty in addressing all that needs to be taken care of, one is
   surprised by how little C code is needed to solve the problem.

   Graham Barr warned that overloading can cause "unless" to behave in a
   most curious manner, but Yitzchak Scott-Thoennes thought that it
   wouldn't be an issue in practice.

     http://xrl.us/oqi2y

Blead changes to "ExtUtils::CBuilder"

   Ken Williams wondered about the reasoning for a line that played
   around with name of the linker and compiler executables used to
   compile external C code. Reini Urban explained that Cygwin's
   implementation of "EU::CB" is derived from
   "ExtUtils::CBuilder::Platform::Unix", and the patch is to undo the
   brain damage in the parent.

   Ken was not in favour of adding a hack to undo a mistake, and wanted
   to fix the problem upstream. Nicholas Clark summarised the problem
   nicely, explaining that traditionally on Unix, the same front-end
   program can be used for the tasks of compiling and linking. Other
   platforms require one to use the linker program directly, and the perl
   configuration doesn't really capture this distinction nicely.

   So Nicholas wrote a TODO item for it, which you may read about below.

     http://xrl.us/oqi24

Probably unwanted behaviour of lexical filehandles

   Dr. Ruud ran into two types of behaviour when opening a input pipe,
   depending on whether a package variable or a lexical variable was
   used. Dave Mitchell explained that the results are due to the fact
   that package variables aren't cleaned up during global destruction
   (unless you ask for it nicely), whereas lexical variables are always
   destructed.

     http://xrl.us/oqi26

TODO of the week

Split "linker" from "compiler"

   Right now, Configure probes for two commands, and sets two variables:

   *   "cc" (in cc.U)

       This variable holds the name of a command to execute a C compiler
       which can resolve multiple global references that happen to have
       the same name. Usual values are cc and gcc. Fervent ANSI compilers
       may be called c89. AIX has xlc.

   *   "ld" (in dlsrc.U)

       This variable indicates the program to be used to link libraries
       for dynamic loading. On some systems, it is ld. On ELF systems, it
       should be $cc. Mostly, we'll try to respect the hint file setting.

   There is an implicit historical assumption from around Perl5.000alpha
   something, that $cc is also the correct command for linking object
   files together to make an executable. This may be true on Unix, but
   it's not true on other platforms, and there are a maze of work arounds
   in other places (such as Makefile.SH) to cope with this.

   Ideally, we should create a new variable to hold the name of the
   executable linker program, probe for it in Configure, and centralise
   all the special case logic there or in hints files.

   A small bikeshed issue remains - what to call it, given that $ld is
   already taken (arguably for the wrong thing now, but on SunOS 4.1 it
   is the command for creating dynamically-loadable modules) and $link
   could be confused with the Unix command line executable of the same
   name, which does something completely different. Andy Dougherty makes
   the counter argument "In parrot, I tried to call the command used to
   link object files and libraries into an executable link, since that's
   what my vaguely-remembered DOS and VMS experience suggested. I don't
   think any real confusion has ensued, so it's probably a reasonable
   name for perl5 to use."

   "Alas, I've always worried that introducing it would make things
   worse, since now the module building utilities would have to look for
   $Config{link} and institute a fall-back plan if it weren't found."
   Although I can see that as confusing, given that $Config{d_link} is
   true when (hard) links are available.

Patches of Interest

Safer environment iteration

   Milosz Tanski wrote a patch to avoid race conditions when iterating
   %ENV in embedded interpreters in multi-threaded applications. Rafaël
   Garcia-Suarez applied the patch.

     http://xrl.us/oqi28

Stop lib/ExtUtils/t/Embed.t from generating libperl.a

   Jerry D. Hedden observed that a test file produced a bogus libperl.a
   file on Cygwin that would up being installed by accident. So he
   patched things to ensure that the test cleans up properly after
   itself. Reini Urban wondered how he had not managed to notice this in
   the past, and promised to take the code for a spin.

     http://xrl.us/oqi3a

Add open "|-" and open "-|" to "perlopentut"

   Shlomi Fish added some documentation for the magic files "-|" and "|-"
   that are used to open input and output pipes. Tom Christiansen wrote a
   eloquent response to the question that someone raised regarding
   singly- and doubly-quoted strings, arguing convincingly that one
   should always use double quoted strings, unless there was a very good
   reason not to.

   One of the most important reasons is merely the visual cue: it's
   easier to see a double quote ("), rather than a single quote ('),
   where certain fonts may make it very difficult to discriminate between
   it and a back-tick.

   Much discussion followed. No-one commented that at around 1000 lines
   long, "perlopentut" is no longer a tutorial, but more of a Compleat
   Reference, and thus probably needs less, rather than more, prose.

     http://xrl.us/oqi3c

Clarify documentation on "exists" regarding autovivification

   Moritz Lenz made a laudable effort at making the documentation clearer
   by removing a sentence, rather than adding one. And this was applied.

     seeking clarity, one paragraph at a time
     http://xrl.us/oqi3e

"autodie" 1.991 patch

   Paul Fenwick announced the latest version of his "autodie" work.
   Nicholas Clark admitted that he was unlikely to review anything major
   until 5.8.9 goes out the door.

     http://xrl.us/oqi3g

Watching the smoke signals

Smoke [5.11.0] 34226 FAIL(F) MSWin32 WinXP/.Net SP3 (x86/2 cpu)

   Steve Hay's Windows smokes started going bad with a failure in
   op/local.t. This highlighted a problem with shell quote characters and
   test.pl's "runperl" function. Nicholas Clark was uncertain as to what
   it was that caused the failure to arise, but change #34228 got things
   back into line again.

     http://xrl.us/oqi3i

New and old bugs from RT

"Class::Struct" accessor overrides not called from constructor (#29230)

   Renée Bäcker wrote a patch to address the problem which appears to
   have fallen through the cracks.

     getting it out
     http://xrl.us/oqi3k

Repeated spaces on shebang line stops option parsing (#30660)

   Renée also noticed that a shebang line containing extra spaces (such
   as "-s -w") will fail to notice the subsequent switches (-w in this
   case). After a couple of tweaks from H.Merijn Brand and Nicholas
   Clark, the code was adjusted to deal with this problem.

     lost in space
     http://xrl.us/oqi3n

Loss of stack elements with a do block inside a return (#38809)

   Vincent Pit returned to the issue of

     sub foo { do { return do { 1; 2 } }; 3 }

   returning "undef". He had proposed a patch some time ago, but after
   studying the emitted opcodes, came up with an improved patch to
   address the problem. And then came back the next day with an improved,
   improved patch, and some improved tests to go along with it.

     http://xrl.us/oqi3p

Removing deprecated features for 5.10? (#41480)

   Renée noted that Nicholas had noted that using arrays and hashes as
   references had been deprecated as far back as 5.8. It so happens that
   the warning for undesirable syntax is present in blead (which will one
   day become 5.12). The unanswered question is whether or not removing
   the code required that deals with it would simplify matters or not.

     http://xrl.us/oqi3r

Subclassing "CGI::Pretty" dies in "new" (#41572)

   Renée also had a patch for this. Nicholas forwarded it to Lincoln
   Stein, and would fold it back into the core once he got word back from
   Lincoln.

     http://xrl.us/oqi3t

Backwards logic in "perluniintro" (5.10.0) (#58218)

   Brad Baxter noted that the documentation that shows how to deal with
   the detection of invalid data for a given encoding had its logic
   backwards. Dr. Ruud suggested a couple of code variants that were an
   improvement on the existing logic, one of which Rafaël Garcia-Suarez
   applied to the documentation.

     http://xrl.us/oqi3v

Speed lost on "/^(foo|bar|baz)$/" match (#58280)

   Michael G. Schwern, following up on scurrilous Internet rumours,
   discovered that captured alternations are in fact slower in 5.10 than
   they were in 5.8. Steve Peters and Tels confirmed the finding. No word
   as to why this is the case.

     http://xrl.us/oqi3x

"Unicode::UCD::charinfo()" does not work on 21 Han codepoints (#58428)

   Karl Williamson discovered Unicode problems that he traced to magic
   numbers causing upper bounds to hide more recent Unicode additions.
   Renée created a patch to fix the problem. Karl also came back with a
   solution that worked with all Unicode database versions from 4.1 and
   beyond, and imagined that it would work for older versions as well.

     http://xrl.us/oqi3z

"Unicode::UCD::casefold()" does not work as documented, nor probably as 
intended (#58430)

   Similarly, Karl found a number of problems relating to the
   implementation for Unicode case folding, and saw that it was such a
   mess that it couldn't work at all. No-one stepped up to try and
   improve matters.

     http://xrl.us/oqi33

"perl -d:DProf" handles shift of @_ with & function wrong (#58446)

   A person, whom some people call Tim, reported that "Devel::DProf"
   failed to deal correctly with @_ being aliased via magic &sub passing.

     http://xrl.us/oqi35

Crash on exit with fork done in do FILE on Win32 (#58468)

   Alex Davies encountered a problem with a "do 'file'" after a program
   has forked on the Windows platform. No-one reported that they had
   confirmed the problem, much less propose a correction, even though
   Alex had gone to the trouble of figuring out why perl was crashing on
   a null pointer.

     http://xrl.us/oqi37

Assigning "*a = \&a" drops a reference (#58480)

   Nicholas Clark noted that recent changes that had shifted code around
   now caused the assignment of something to one's own typeglob to leak a
   reference. He thought he knew how to fix the matter, and called for
   some TODO tests, if anyone was in the mood for volunteering.

   Zefram thought that the code Nicholas had used to demonstrate the
   problem was incorrect.

     http://xrl.us/oqi39

Perl5 Bug Summary

   Someone was very busy this summer.

     261 new + 1028 open = 1289
     http://xrl.us/oqi4b
     http://rt.perl.org/rt3/NoAuth/perl5/Overview.html

In Brief

   Nicholas had been observing an occasional assertion failure in
   "S_sv_del_backref". After struggling for a while to reproduce it at
   all, Dave Mitchell nailed it with a tweak to a macro in sv.c.

     safer global destruction
     http://xrl.us/oqi4d

   Rick McGee reported running into grief attempting to marry 5.10 and
   FreeBSD 7.0. Alas, neither Nicholas Clark, nor Scott T. Hildreth nor
   Reini Urban were able to reproduce the problem, although Nicholas
   suspected it was probably a compiler issue.

     http://xrl.us/oqi4f

   Jerry D. Hedden announced that the TODO related to "threads::shared"
   is done, and so the item could be removed (if in fact the work he did
   on "threads::shared" was indeed what "perltodo" was referring to).

     http://xrl.us/oqi4h
     http://xrl.us/oqi4j

   Vincent Pit ran into a precedence nit in "Test::Builder" (or more
   specifically "!$x and $y, 'foo'") which meant that a test that should
   have failed didn't.

     back to the drawing board
     http://xrl.us/oqi22

Last week's summary

   There wasn't one. I enjoyed a lazy summer doing home renovations,
   camping, hiking, swimming, drinking, eating and using computers as
   little as possible.

About this summary

   This summary was written by David Landgren.

   Weekly summaries are published on http://use.perl.org/ and posted on a
   mailing list, (subscription: perl5-summary-subscribe@perl.org). The
   archive is at http://dev.perl.org/perl5/list-summaries/. Corrections
   and comments are welcome.

   If you found this summary useful, please consider contributing to the
   Perl Foundation or attending a YAPC to help support the development of
   Perl.

-- 
stubborn tiny lights vs. clustering darkness forever ok?

• This Week on perl5-porters - 25-31 August 2008 by David Landgren