This Week on perl5-porters - (12-18 June 2006)

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This Week on perl5-porters - 12-18 June 2006

   "I'm still a big fan of partial solutions. But to get a good partial
   solution, you can't just rush into it without thinking about what the
   tradeoffs really are." -- Mark-Jason Dominus, on reversible debugging

Topics of Interest

Regular expressions: bugs, tests and benchmarks

   As the changes Yves Orton made to the regular expression engine get
   worked over by the smoke testers and other more adventurous souls, a
   couple of problems have come to light.

   Nicholas Clark found that the following snippet caused a segfault
   during global destruction.

     $a = qr/(xx|yy)/;
     sub a {'xx' =~ $a and print 'ok'};
     threads->new(\&a)->join();

   Yves fixed that up with a one-line change (a reference counting
   adjustment).

     Ha ha ha plonk
     http://xrl.us/nnup

   Dave Mitchell caught another one, simply by running a build and
   watching "ext/re/t/regop.pl" lose it, which Rafael Garcia-Suarez
   corrected with a guard to "re_debug_flags", but wondered why it was
   being set to "NULL" in the first place. Answer: it happens during
   global destruction.

     Changing of the guards
     http://xrl.us/nnuq

   Jarkko Hietaniemi found some other problems with the trie code on
   Tru64 in conjunction with "-DDEBUGGING". After a quick examination,
   Yves couldn't find a good explanation why, but suggested a couple of
   nice places for setting breakpoints.

   After running down a few dead ends, Jarkko finally narrowed the
   problem down to taking the address of something on the stack. Hoisting
   the declaration outwards fixed the problem.

     A class of his own
     http://xrl.us/nnur

   Yves made an appeal for more tests that exercise Unicode pattern
   matching. Not the funky, contrived examples that the porters come up
   with to exercise obscure parts of the code base, but real
   honest-to-goodness matches that happen in Real Life.

     If you test it, they will come
     http://xrl.us/nnus

   Tels came back with some late comments on the trie enhancements. Yves
   had an answer to all of the questions, going so far as to suggest that
   a nice optimisation would be to convert patterns consisting of a
   single "EXACT" node to an "index()" call, thereby avoiding
   "regmatch()" altogether.

     Avanti!
     http://xrl.us/nnut

   Yves caught a bug before anyone could step on it.

     The unguarded moment
     http://xrl.us/nnuu

   Dave Mitchell also did some more follow-up work on his efforts to
   remove recursion from the regular expression engine.

     Switched on state
     http://xrl.us/nnuv

Could Perl get Reversible Debugging?

   Adam Kennedy had recently encountered two discussions of reversible
   debugging, and wondered how plausible this could be for Perl.
   (Reversible debugging is the idea of being able to undo the previous
   "r"un or "n"ext statement, and recover the previous state. (History
   trivia: Roedy Green wrote a language called Abundance in the 70s that
   provided support for this mechanism. He called it jaunting)).

   Randy W. Sims thought that a system that merely recorded the current
   system state by snapshot would be good enough. You could not go back
   in time and change things, but you could at least look at them again.
   Useful if you missed something.

   Some things cannot be reversed anyway: system calls, network writes,
   different paths might cause cleanup handlers to never be called.

   Jesse pointed to Leon Brocard's "Devel::ebug", which offers an "undo"
   mechanism. Mark-Jason Dominus mapped out the different points on the
   continuum, showing what was easy, simple and fairly useless all the
   way to difficult, hard and very useful, but we should be able to get
   something good at a reasonable cost. His suggestion was to teach the
   debugger to record all the commands during a session, and then allow
   one to restart the session, replaying all the commands up to some
   point in the stream.

   Richard Foley explained that this latter trick was already available
   in the current debugger. It's called "rerun".

   David Nicol suggested forking a new copy of the program at each perl
   statement, and communicate between the prior state processes to
   determine the difference in state. This would of course entail immense
   resource costs. Alternately, a fork and dump on each statement would
   merely chew disk space, instead of RAM. But at the end of the thread,
   Adam came back and explained that he didn't really care to go back and
   re-execute the program from a given point. He just wanted to be able
   to go back and look at what had happened as a disinterested observer
   (a bit like TV).

     We need a "come from" instruction
     http://xrl.us/nnuw

New, improved "perlbrowse"

   Dave Mitchell announced a new release of the "perlbrowse" tool, that
   allows the porters to look at the source code from the point of view
   of the repository, and view the changes made to the code base over
   time.

     Whiter than #ffffff
     http://xrl.us/nnux

Big Perl 5 advocacy thread

   One of the biggest threads to hit p5p in months, which goes to show
   that there's still interest in the beast.

   Yves Orton kicked off the thread, writing about the problem of Perl 5
   and Perl 6 and it sounded like a replay of the Osborne Effect (Adam
   Osborne built a phenomenally successful portable computer in the
   1980s, and preannounced the arrival of a new faster model. People
   stopped buying the current model, waiting for the new one to be
   released. The competition ate the company).

   Some of the main points:

   *   We need to get 5.10 out the door.

   *   A Seal of Approval for qualifying CPAN modules.

   *   Send Andy Lester some papers that he can publish on
       "perlfoundation.org".

   *   Perl is a write-only language. Parentheses, no parenthesis, "or"
       *versus* "||". (This subthread pushed Tom Christiansen into
       penning a couple of missives).

   *   At least two technical book publishers consider that the Perl
       market is done.

   *   Perl sucks as a desktop applications language (think: "Tk",
       "perlWx"). "Tk" looks ancient, "perlWx" documentation sucks.

   *   "gettext" doesn't work very well if the initial language is not
       English and you want to add a English translation.

   *   Installing Perl on Windows should be as easy as installing Firefox
       plug-ins.

   *   Prerequisites specifications for CPAN modules sucks.

   *   Perl releases are slowing down, as are new language enhancements.

   *   Core support for Win32 sucks.

     Yeah, but we knew all that
     http://xrl.us/nnuy

Patches of Interest

"Hash::Util::FieldHash"

   Lots of internals talk here, and not enough time to summarise the
   ramifications.

     It's that U magic
     http://xrl.us/nnuz

Proper use of "enum"s

   Thanks to Intel's optinagging compiler, Andy Lester straightened out
   the mess of "enum"s being mixed with non-"enum"s, especially in
   relation to "svtype"s.

     http://xrl.us/nnu3

Static cleanup in pp_sort.c

   Andy then tidied up "S_qsortsvu()" and made "embed.fnc" refer to it
   (for error checking) and used the macro'ed version where applicable.

     http://xrl.us/nnu4

universal.c "does" it

   Rafael added the "DOES" method to "UNIVERSAL" following on from
   chromatic's desire several weeks ago to try and make "UNIVERSAL" more
   useful, or rather, less abused. He then hinted that chromatic was
   probably in the best place to write the appropriate documentation.

     http://xrl.us/nnu5

   Andy slotted it into the right place in embed.fnc.

     http://xrl.us/nnu6

   And chromatic delivered the documentation goods.

     http://xrl.us/nnu7

Watching the smoke signals

Smoke [5.9.4] 28397 FAIL(F) hp-ux 11.23/64 (ia64/2 cpu)

   Dave Mitchell observed that this failure "was caused by the
   interesting fact that a detached thread still counts towards the "A
   thread exited while %d threads were running" warning, in violation of
   the docs". And so he fixed it.

     http://xrl.us/nnu8

New and old bugs from RT

Wishlist about "Sys::Syslog" (#35406)

   Keisuke Hirata filed a bug report about "Sys::Syslog" and bundled the
   patch used to fix the problem. Sbastien Aperghis-Tramoni announced
   that it had been included in version 0.16, now available from your
   neighbourhood CPAN mirror.

     A dream comes true
     http://xrl.us/nnu9

Cygperl allows reading of write-only file descriptors (#39325)

   Both David Landgren and Dr. Ruud tried to make sense of this bug.
   Sébastien A-T thought that it may be a manifestation of another
   Cygwin-ism that had caused him grief in the past.

     Too Unix to be Windows, too Windows to be Unix?
     http://xrl.us/nnva

"Data::Dumper" fails to escape bless class name (#39420)

   Any users out there still using ' (apostrophe) in their class names?
   Well don't, because "Data::Dumper" has forgotten about it.

     http://xrl.us/nnvb

"Carp" can't find "Carp::Heavy" (#39440)

   Funny how things come in waves. This was another manifestation of last
   week's bug about what happens to Carp when perl runs out of file
   handles.

     FITNR
     http://xrl.us/nnvc

file level my variables are invisible inside anonymous subs (#39489)

   By another strange coincidence, this bug has also been fixed in the
   next release.

     Waiting for 5.10
     http://xrl.us/nnvd

Core dump on process exit with "tie %SIG" (#39504)

   John Gardiner Myers discovered a way to make perl dump core, and
   suspected that the act of "tie"ing %SIG may have something to do with
   it.

     Where porters fear to tread
     http://xrl.us/nnve

   And another data point:

     Curiouser and curiouser
     http://xrl.us/nnvf

Perl5 Bug Summary

     3 closed and 6 open: 1491 total
     http://xrl.us/nnvg

     They're all here
     http://rt.perl.org/rt3/NoAuth/perl5/Overview.html

New Core Modules

   *   "Test-Harness" version 2.62 uploaded by Andy Lester.

         http://xrl.us/nnvh

   *   "Sys-Syslog" version 0.15 uploaded by Sébastien Aperghis-Tramoni.

         http://xrl.us/nnvi

In Brief

   A new website, "win32.perl.org" opened its doors this week.

     Contribute! Contribute!
     http://xrl.us/nnvj

   Ravi Sastry Kadali, from the IBM zOS USS Development team reported
   having ported 5.8.7 onto IBM z/OS. The team had to make some changes
   to the source, and wanted to contribute them back to the porters.

   Rafael explained that ideally, they should try and port "blead", and
   send the required changes back for integration. These changes can then
   be ported over to the maintenance branch if not compatibility problems
   are encountered.

     http://xrl.us/nnvk

   Steve Stiert then sent in the patch anyway. Jarkko Hietaniemi had a
   look at it.

     http://xrl.us/nnvm

   Daniel Frederick Crisman had yet another shot at reworking quote-like
   operators in "perlop".

     When in doubt, use brute force
     http://xrl.us/nnvn

   Yves sent in a patch to fix some segmentation faults during global
   destruction (in relation to his regexp work) and also tweaked
   "Benchmark" to stop it from hitting infinite loops.

     Two for the price of one
     http://xrl.us/nnvo

   Tom Schindl was bitten by the "map" in void context memory wastage
   problem, that neither "foreach", nor more recent versions of Perl, for
   that matter.

     http://xrl.us/nnvp

   Jarkko reworked the gcc warnings selection mechanism, to allow the
   porters, and more specifically Andy Lester, to enable all sorts of
   wacky compiler switches to see what happens.

     --warn-if-non-halting
     http://xrl.us/nnvq

   Philip M. Gollucci attempted to perform a speed comparison from 5.6.2
   to "blead", but the results were flawed because he used perl binaries
   compiled with debugging. He promised to redo them again, without
   debugging.

     http://xrl.us/nnvr

   Shlomi Fish wrote in to say that he had found a bug with "perl -d" not
   printing the current code line.

     So perlbug it
     http://xrl.us/nnvs

   John E. Malberg found a show stopper in blead concerning Unicode.
   Sadahiro Tomoyuki proposed a fix, and Craig A. Berry committed the
   change.

     http://xrl.us/nnvt

   Yitzchak Scott-Thoennes recalled that in the core there are actual
   arrays of arrays (and not arrays of references to arrays), but could
   not recall where.

     http://xrl.us/nnvu

   Salvador Fandiño took another stab at adding macros to Perl5.

     http://xrl.us/nnvv

   Andreas J. Koenig discovered that the APC archive is missing files
   28373-28377.

     We have backups, right?
     http://xrl.us/nnvw

About this summary

   This summary was written by David Landgren. Last week's summary...

     http://xrl.us/nnvx

   ... attracted a reply from Yves, who followed up on the issue of
   pluggable regexp engines for "maint". The problem is one of a bad
   design call, made in the distant past, for which Nicholas Clark is
   pondering a "deeply evil" workaround.

   Tels also replied, with a plug for his "Math::String" module, that
   lets one perform automagical increments (and decrements) on just about
   anything that looks incrementable. And if it doesn't work with
   Unicode, file a bug report so that Tels can fix it.

   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
   mailing list, (subscription: [email protected]). 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 to help support the development of Perl.
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