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://xrl.us/oqi2f
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://xrl.us/oqi2h
"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://xrl.us/oqi2j
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://xrl.us/oqi2m
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://xrl.us/oqi2o
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://xrl.us/oqi2q
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://xrl.us/oqi2s
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://xrl.us/oqi2u
So Jerry fixed it.
http://xrl.us/oqi2w
"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://xrl.us/oqi2y
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://xrl.us/oqi24
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://xrl.us/oqi26
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://xrl.us/oqi28
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://xrl.us/oqi3a
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://xrl.us/oqi3c
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://xrl.us/oqi3e
"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://xrl.us/oqi3g
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://xrl.us/oqi3i
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://xrl.us/oqi3k
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://xrl.us/oqi3n
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://xrl.us/oqi3p
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://xrl.us/oqi3r
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://xrl.us/oqi3t
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://xrl.us/oqi3v
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://xrl.us/oqi3x
"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://xrl.us/oqi3z
"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://xrl.us/oqi33
"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://xrl.us/oqi35
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://xrl.us/oqi37
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://xrl.us/oqi39
Perl5 Bug Summary
Someone was very busy this summer.
261 new + 1028 open = 1289
http://xrl.us/oqi4b
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://xrl.us/oqi4d
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://xrl.us/oqi4f
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://xrl.us/oqi4h
http://xrl.us/oqi4j
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://xrl.us/oqi22
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
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 or attending a YAPC to help support the development of
Perl.
--
stubborn tiny lights vs. clustering darkness forever ok?
