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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00344.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00406.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00557.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00607.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00609.html

Yves caught a bug before anyone could step on it.

  The unguarded moment
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00375.html

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

  Switched on state
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00534.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00431.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00464.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00477.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00332.html

Proper use of enums

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

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00338.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00356.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00367.html

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

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00468.html

And chromatic delivered the documentation goods.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00592.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00564.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00363.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00384.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00359.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00386.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00472.html

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 tieing %SIG may have something to do with it.

  Where porters fear to tread
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00523.html

And another data point:

  Curiouser and curiouser
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00539.html

Perl5 Bug Summary

  3 closed and 6 open: 1491 total
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00352.html

  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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00358.html
  • Sys-Syslog version 0.15 uploaded by Sébastien Aperghis-Tramoni.
      http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00353.html

In Brief

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

  Contribute! Contribute!
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00335.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00382.html

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

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00593.html

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

  When in doubt, use brute force
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00404.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00424.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00433.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00448.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00469.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00575.html

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

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00383.html

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://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00506.html

Salvador Fandiño took another stab at adding macros to Perl5.

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00482.html

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

  We have backups, right?
  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00543.html

About this summary

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

  http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2006-06/msg00461.html

... 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: perl5-summary-subscribe@perl.org). The archive is at http://dev.perl.org/perl5/list-summaries/. Corrections and comments are welcome.

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