[Resent with email-friendly short links -- DL]
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
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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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