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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00417.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00360.html

"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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00379.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00392.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00415.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00449.html

  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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00451.html

  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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00483.html

  So Jerry fixed it.

    http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00455.html

"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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00460.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00487.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00491.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00385.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00367.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00386.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00436.html

"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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00456.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00408.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00489.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00391.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00481.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00454.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00442.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00361.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00362.html

"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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00470.html

"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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00471.html

"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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00472.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00492.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00494.html

Perl5 Bug Summary

  Someone was very busy this summer.

    261 new + 1028 open = 1289
    http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00396.html
    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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00378.html

  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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00479.html

  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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00448.html
    http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00458.html

  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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-08/msg00473.html

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
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