This Week on perl5-porters - (22-28 May 2006)

This Week on perl5-porters - 22-28 May 2006

   This isn't supposed to happen, obviously. It's unusual for "Configure"
   to pick up libraries that it can't, in fact, use. -- Andy Dougherty,
   commenting bug #39195

Topics of Interest

"Scalar::Util::weaken", to have or have not

   There was further discussion of the XS version of "Scalar::Util" and
   the fact that it offers a "weaken" function which is vital to avoid
   resource leaks when freeing self-referential structures.
   (Specifically, it offers a method from Perl-space to intervene
   directly on the underlying mechanism used for managing garbage
   collection).

     There were five philosophers at a table
     http://xrl.us/mxwq

   Adam Kennedy proposed "Task::Weaken" as an elegant way (insofar as a
   wart may be considered elegant) of dealing with the problem of trying
   to create a dependency on the particular "Scalar::Util" version that
   happens to contain the "weaken" routine.

     Not the other one
     http://xrl.us/mxwr

Following up on thread safety issues and opcode hints

   Last month, Nicholas Clark discovered some obscure bugs that could
   lead to race problems, with critical memory accesses not protected by
   mutexes, or memory allocations going astray. He managed to sort out a
   number of problems, and reported that there were a number of issues
   that would need to be addressed.

     The fearsome five
     http://xrl.us/mxws

Regular expression engine improvements

   Yves Orton ran a post-mortem on his recent work to convert "/[c]/" to
   "/c/", and realised that a lot of the difficulty can be traced back to
   the memory allocation strategy used. By its very nature, the strategy
   rules out a number of interesting optimisation possibilities, because
   a regexp is built with a two-pass compilation, and during the second
   pass, too much information has already been discarded, so at that
   point it is already too late to be able to consider a certain number
   of transforms.

   Save more information up front, and then you stand a better chance of
   being able to apply some useful optimisations to the resulting
   opcodes. Hugo van der Sanden wondered whether it would be possible to
   produce an opcode stream that would be amenable to processing by the
   existing peephole optimiser.

   Yves wanted to push a lot of the smarts from "study_chunk" and
   "regtail" into the parse phase. And wrapped up with a patch to tidy
   the debug output somewhat, and improve the trie code.

     Gentlemen, study your engine
     http://xrl.us/mxwt

   Andy Lester wanted to add some consting goodness to regcomp.c and
   regexec.c, which would have caused Yves considerable pain, since he
   was in the middle of some deep core hackery, and didn't want to face
   the nightmare of a three-way diff.

     Not now
     http://xrl.us/mxwu

   After that, Yves delivered a verily impressive patch of new, shiny
   goodness to the regexp engine. And if that wasn't enough, he also took
   Andy's own consting work and folded that in as well. After a bit of
   adjustment due to other patches going into "blead" at the same time,
   Rafael managed to get everything in place and running nicely.

     Right now
     http://xrl.us/mxwv

A tutorial on Unicode

   Juerd Waalboer wrote a very nice tutorial to help people get started
   with Unicode. A number of people contributed ideas and suggestions.
   Juerd sifted through these and produced a second version. As we went
   to press, inclusion in the core was pending.

     Unicode decoded
     http://xrl.us/mxww

"sprintf" and tainted format strings

   Dave Mitchell revisited the "sprintf('%n')" issue that made the
   headlines back in December, and thought that it might be wise to apply
   taint checks to the format string (the first argument to "sprintf",
   proposed a relaxed or strict interpretation to what tainting would
   imply and asked for opinions on the matter.

   Andy Lester favoured the strict approach (*any* use of a tainted
   format string fails), but recalled that the idea had been dismissed
   rapidly when put forward during the previous discussions. Steve Peters
   thought that it was more a case of being set aside than anything else,
   and expressed surprise at the fact that format strings do not already
   have taint checking.

   Rick Delaney wondered what exactly did Steve and Dave mean, and put
   forward a couple of snippets to see if he understood the issues.

     Just when you thought it was safe
     http://xrl.us/mxwx

Shooting yourself in the foot with overloading

   Jarkko Hietaniemi was led astray by a somewhat unhelpful "Use of
   uninitialized value in hash element" warning caused by overloading,
   and wondered if a better message could be generated if overloading was
   involved.

   While not directly answering Jarkko's question, Joshua ben Jore
   mentioned that even more overloading fun can be had when using
   "Devel::Cover", since applying "defined" to an object will trigger
   stringification there, but not during normal execution. Paul Johnson
   was most surprised to hear this, and asked for a test case. David
   Landgren provided a small example that exposes the problem.

   Yves Orton confirmed that he had run into this problem when developing
   "Data::Dump::Streamer", and had had to jump through considerable hoops
   to work around it.

     Gun, meet foot
     http://xrl.us/mxwy

Patches of Interest

Test infrastructure improvements

   Yves Orton noticed a problem due a recent tweak to "Test::Harness",
   and fixed it so as to stop harness from printing the summary table
   header for each row. Which does, it should be agreed, get tedious
   after a while.

     No more excessive scrolling
     http://xrl.us/mxwz

   At about the same, Andy Lester changed "t/TEST" to queue up the names
   of the tests that fail, to dump them at the end of the run. This means
   one gets all the failing tests in one convenient chunk.

     No more scrolling back
     http://xrl.us/mxw2

More goodness from Andy

   In his ongoing quest to const, Andy Lester sent in some refactoring
   for av.c, which crushed some incorrect uses of "SvREFCNT_inc", removed
   unnecessary temporary variables and brought the usual suspects into
   line.

     http://xrl.us/mxw3

   And a parameter to "Perl_magic_existspack" in mg.c that could be made
   "const".

     http://xrl.us/mxw4

   And a similar treatment for "Perl_gv_check" in gv.c.

     http://xrl.us/mxw5

"Pod::Html" should not convert "foo" to ``foo''

   Gisle Aas hated this mis-feature, since most modern fonts produce a
   spectacularly ugly result. After a bit of a detour into the realm of
   "troff", it was decided to just use plain double-quotes instead.

     http://xrl.us/mxw6

Relaxing the tests in Dynaloader.t

   Jarkko found that Sébastien Aperghis-Tramoni's tests in Dynaloader.t
   were too platform-specific to be useful. After a bit of discussion it
   was decided to loosen up the test which attempted to trap the message
   generated when the loading of a non-existent shared library is
   attempted.

     Eggs, bacon, sausage and spam
     http://xrl.us/mxw7

New and old bugs from RT

Memory leak from "eval "sub { \$foo = 22 "" (#37231)

   This used to leak memory (that is, trying to "eval" a broken
   subroutine definition). Dave Mitchell made it leak less. And then
   after sitting back and looking at his handiwork, Dave made completely
   water-proof. Nicholas Clark still managed to poke a hole in it.
   Unruffled, Dave countered with a King's Gambit that appeared to keep
   any remaining errant allocations in cast-iron casing.

     http://xrl.us/mxw8

"IPC::Open2::open2" failures (#39127)

   Dave Mitchell had a look at the source code, and noted that there was
   a race condition depending on whether the child dies before or after
   the parent tries to write to it. Furthermore, there is no easy way to
   fix the problem as is, which is why "IPC::Run" may be a better
   alternative all round. Dave suggested a documentation patch to clarify
   the situation.

     http://xrl.us/mi7r

"IO::Socket::connect" returns wrong "errno" on timeout (#39178)

   "mlelstv" showed some discrepancies in error messages depending on
   whether it was the first or subsequent time that a socket connection
   failed, and traced it down to a $! not being cleared before a system
   call.

     http://xrl.us/mxw9

Optimizer bug in "qr//" flags (#39185)

   "johnpc" reported a bug in patterns using "qr//" flags. Dave Mitchell
   reported that this had been fixed in "blead", but not yet backported
   to the maintenance branch.

     http://xrl.us/mxxa

CPAN configuration stuck at "Select your continent" (#39186)

   Mark-Jason Dominus was in the middle of configuring his "CPAN" client
   when things started to go horribly wrong. Andreas Koenig wanted to
   have a look at Mark's MIRRORED.BY file. Mark took one look at the file
   and saw that it was corrupt (well, empty), and therefore knew what to
   do.

     Delete and start over
     http://xrl.us/mxxb

"perlfunc" on "reverse" in scalar context (#39187)

   Ted Pride had never noticed that "reverse" also works on scalars:

     my $rev = reverse('forward'); # $rev contains drawrof

   mainly because the documentation is slightly too clever for its own
   good.

     http://xrl.us/mxxc

Error Report (#39195)

   Sriram Madduri had configured a perl build, but at link-time the build
   failed with some unknown libraries that "Configure" had specified.
   Andy Dougherty spotted what he thought was the cause of the problem,
   but we didn't hear back from Sriram, so we don't know if it's fixed.

     http://xrl.us/mxxd

"File::BOM" hangs during test (#39211)

   Redirected to the module author. "File::BOM" isn't core.

     y otras chicas del montón
     http://xrl.us/mxxe

Null pattern causing expected behaviour (#39212)

   If it's causing the expected behaviour...

     it's not a bug
     http://xrl.us/mxxf

Optimiser doesn't constant fold $] or $^V (#39214)

   Benjamin Smith wished that $] or $^V were constant-folded. This could
   be useful, because then one could include sections of code for
   specific versions of Perl that would be optimised away at compile time
   if not applicable. Unfortunately, since these variables are, well,
   variable, and not constant (in other words, you may assign to them),
   this isn't going to work.

     http://xrl.us/mxxg

"Pod::HTML" should use &entities; for quotes (#39215)

   Johan Vromans thought that this would be a nice idea. Gisle Aas
   explained why it might be a bad idea, and that in any event,
   "Pod::HTML" had been tweaked to no longer emit the pugly `` and ''
   blots.

     http://xrl.us/mxxh

Compiling With "nmake" (#39226)

   William C. Smith wanted to compile Perl with "nmake". Yves showed him
   how to do just that.

     http://xrl.us/mxxi

Perl5 Bug Summary

   The previous week's bug summary, omitted from the previous summary
   (oops):

     7 created + 12 closed = 1507
     http://xrl.us/mxxj

   And this week:

     8 created and 22 (!) closed = 1493
     http://xrl.us/mxxk

   Hey! we broke through the 1500 barrier!

     Now, with added shinyness
     http://rt.perl.org/rt3/NoAuth/perl5/Overview.html

New Core Modules

   *   Version 0.60 of "version" had a bit of trouble settling down in
       "blead", but after smoothing a few rough edges it all came
       together.

         http://xrl.us/mxxm

   *   "Test-Harness" 2.60 was released by Andy Lester.

         http://xrl.us/mxxn

   *   "Sys-Syslog" 0.14 was released by Sébastien Aperghis-Tramoni,
       featuring a number of bug fixes, and enhancements to the both the
       code and test suite.

         http://xrl.us/mxxp

In Brief

   Marcus Holland-Moritz documented and completed a few holes in the
   orthogonality of literal string macros, mainly as a service to XS
   developers. Applied.

     http://xrl.us/mxxq

   Anno Siegel had some difficulties adding a core module because it was
   building man pages when it was not supposed to. Rafael provided the
   necessary "MakeMaker" magic to make it do the right thing at the right
   time.

     http://xrl.us/mxxs

   Andy Lester's second refactoring of pp_sys.c from last week went in as
   change #28279.

     http://xrl.us/mrb3

   Alberto Simões thought that the problem of regexp slowness with $' and
   $` could be solved elegantly by making them lexical. Dave Mitchell
   demonstrated why this was not possible (existing code would break).

     http://xrl.us/mxxt

   Torsten Foertsch wanted to know how to trap a warning generated at
   global destruction time. The test infrastructure doesn't appear up to
   the task, because at global destruct time, all the tests have long
   since finished. chromatic recommended running the test in a child, and
   examining its output.

     http://xrl.us/mxxu

   perlhack.pod was confused about "POPSTACK", so Dave Mitchell and Jan
   Dubois tightened the documentation. Deep core hackers rejoiced.

     http://xrl.us/mxxv

   Dave also improved the "-Dpv" parser debugging output.

     http://xrl.us/mxxw

   Philip M. Gollucci was having trouble with "Perl_croak" and "nullch"
   at patch level 27529.

     http://xrl.us/mxxx

   Jarkko noticed that there are no execute bits on semaphores on Mac
   OS/X, and tweaked the documentation to clarify the situation.

     http://xrl.us/mxxy

   Alex Davies cooked up a patch to "shrink the object size for
   pp_sys.c", but as the savings came at the cost of code legibility,
   with no apparent run-time benefit, Rafael chose to decline it.

     http://xrl.us/mxxz

About this summary

   This summary was written by David Landgren. Yes, late enough to be
   next week's summary. Sorry, this week I have been dealing with
   assorted crises.

   Last week's summary attracted a response from Dave Nicol, who
   explained his linked list master plan in more detail.

     Action stations
     http://xrl.us/mxx2

   If you want a bookmarklet approach to viewing bugs and change reports,
   there are a couple of bookmarklets that you might find useful on my
   page of Perl stuff:

     http://www.landgren.net/perl/

   Weekly summaries are published on http://use.perl.org/ and posted on a
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   archive is at http://dev.perl.org/perl5/list-summaries/. Corrections
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-- 
"It's overkill of course, but you can never have too much overkill."