This Week on perl5-porters - 27 January-2 February 2008
"It's a very naive implementation [...]. Given the scary comments
Nicholas added in that code, I'd be grateful to see whether one can
come up with a case where that breaks" -- Rafael Garcia-Suarez,
warning about warning about undef.
Topics of Interest
Integrating blead changes back to maint
Some of the changes regarding Safe for 5.10 crept into the 5.8
maintenance track during change #33111, and Jerry D. Hedden wondered
if this was a bug or a feature. Nicholas Clark cursed Perforce but
felt that it could all go into 5.8 in the long run.
entering a zone of turbulence
http://xrl.us/bfs2g
Sure enough, black smoke emerged from the chimney of Steve Hay's lab.
Smoke [5.8.8] 33111 FAIL(F) MSWin32 WinXP/.Net SP2 (x86/2 cpu)
http://xrl.us/bfs2i
Similarly, the integration of consting goodness in change #33119 also
caused grief on Cygwin. Jerry wondered if the blead changes in #32681
needed to be integrated as well.
http://xrl.us/bfs2k
5.8.x "usemymalloc" failures
In a discussion in a bug report (see #50352 below), it will be
revealed that Perl's own "malloc" is usually faster than the "malloc"
delivered with the C library. Jerry D. Hedden removed the
"-Uusemymalloc" from his Cygwin build, thereby switching from the
system "malloc" to Perl's, thereby gaining a boost in speed for free.
He reported success for 5.10 and blead, but a few tests failed in 5.8.
In fact, the error appears to be there as far as he was able to go
back in history.
there was a reason for this
http://xrl.us/bfs2n
MM_Win32.t failures (caused by "PathTools" upgrade)
Steve Hay noticed that the major rewrite to Win32's "catdir",
"catfile" and "canonpath" caused major failures in
"ExtUtils::MakeMaker" handling on Windows. The more Steve looked, the
more he found the new behaviour confusing.
Michael G. Schwern believed that part of the problem was the use of
"catdir", when in fact "catpath" was what was called for (regarding
the handling of "C:" as a volume specification).
Ken Williams chalked it up as another case of ""File::Spec" is just
hard to use correctly".
but Path::Class makes it fun!
http://xrl.us/bfs2p
http://xrl.us/bfs2r
"next" resetting match variables - bug or feature?
Nicholas Clark was puzzled by ext/B/t/deparse.t issuing a warning on
5.10 but not on 5.11, and narrowed it down to what remained in a match
variable at the beginning of a loop. There was a difference, depending
on whether the loop had reached the end of its scope, or had been
short-circuited via a "next".
coming up next
http://xrl.us/bfs2t
Make Perl Y2038 safe
After the initial silence following Michael G. Schwern's plea to make
Perl survive 2038, the thread kicked off in earnest this past week.
Some people believed that it was just a question of having a 64-bit
machine and 64-bit "time_t" datatype. To a certain extent, this is
already the case for many platforms other than Unix, be they IBM
mainframes, VMS minis or even Windows micros. In this case, 32-bit
"time_t" quantities are shims over datatypes of greater precision,
provided only for compatibility with Unix.
The real problem is that of programs that store 4-byte "time_t"
quantities in binary files. The other problem is with "localtime"
which is currently specified for 32 bit quantities, which means that
if the system can handle the year 2050 as an epoch, it might be unable
to format it a readable manner. And one nice thing that "localtime"
does, more or less for free, is to figure out which time zone you're
in.
Craig Berry suggested that the first step would be to plan some tests
to check the results of date arithmetic that push past 2038, mark them
as TODO, and then go about fixing them. It would seem evident that
some %Config variables would be useful to help people determine what
is implemented natively and what needs to be worked around.
Mark Mielke pointed out that the "DateTime" modules are perfectly
2038-safe, but you still run into problems if you try to map a
DateTime value outside the 1970-2038 range onto an 32-bit epoch value.
Unfortunately, for some people, it's just too slow.
Aaron Crane gave a fascinating historical overview of time handling in
Unix.
TAI64 for attosecond precision, anyone?
http://xrl.us/bfs2v
op/sprintf.t and op/write.t failures with mingw-runtime-3.14
Rob "Sisyphus" observed incorrect "sprintf" behaviour with the latest
MinGW runtime and wondered if anyone else had encountered the problem.
He was hesitant to label it a MinGW bug, since simple C programs using
"sprintf" worked as expected.
Yitzchak Scott-Thoennes said that he'd heard that the MinGW developers
had tweaked the behaviour of "vnsprintf", and that put Rob on the
right track.
bug, many eyes, shallow
http://xrl.us/bfs2x
Patches of Interest
Fix "uc"/"lc" warnings in CGI.pm
Now that "lc(undef)" issues a warning as it return an empty string,
one of the first (no doubt of many) consequences was that "CGI"'s test
suite issued a couple of warnings. Lincoln Stein folded the fix into
his copy of "CGI".
old horse, new tricks
http://xrl.us/bfs2z
At that point, Nicholas Clark noticed that there were some gratuitous
differences between the core version and that on CPAN, and hoped that
the porters and Lincoln could reconcile the differences. No word back
from Lincoln as we went to press.
get back together again
http://xrl.us/bfs23
Unwanted warnings from "PerlIO::scalar"
Ben Morrow produced a cut-down code sample that showed a spurious
warning when opening a scalar as an output stream. He proposed a
patch, but Hugo van der Sanden thought it would cause an overdose of
magic.
http://xrl.us/bfs25
Fix regression in File/DosGlob.pm
Alex Davies encountered a globbing problem in "File::DosGlob" and was
amazed to discover that things had been like that since the year 2000.
Steve Hay accepted the patch.
http://xrl.us/bfs27
Don't forbid brace groups with g++ 4.2.2
Robin Barker noticed that the restriction against using brace groups,
that appeared in 2006 for versions of g++ available at the time, no
longer seemed to be required for the current g++ 4.2. This in turn
allowed other warnings that g++ issued over the *REFCNT_inc macros to
go away. Rafael accepted the patch.
http://xrl.us/bfs29
New and old bugs from RT
IRIX hints (#33849)
Andy Dougherty came back with a new attempt to teach "Configure" how
to the the right thing on the IRIX platform.
over to you, Mr. Cantrell
http://xrl.us/bfs3b
Safe and "use encoding 'utf8'" (#48419)
Back in December, Ville Luolajan-Mikkola reported that trying to use
"Safe" and "encoding :utf8" results in a fight, and the program loses.
Rafael Garcia-Suarez suggested importing the needed methods into the
Safe compartment might be a suitable work-around, but he was doubtful
that Safe could be fixed safely.
putting the accent on safety
http://xrl.us/bfs3d
Newbie redirect error (#50266)
James Nemanich stumbled across the RT queue and filed a bug about
perl, not realising that in fact the bug was in his own code. People
pointed him to Perlmonks, "Perl::Critic", pragmas "strict" and
"warnings", the Learn Perl mailing list (empty message to
"[EMAIL PROTECTED]" if you want to help) and Alexandr Ciornii
went as far as rewriting the original code in modern day, idiomatic
Perl.
all part of the service
http://xrl.us/bfs3f
"CGITempFile" causes "Insecure dependency in sprintf" in perl 5.10.0
(#50322)
Steve Hay used "CGI" and uncovered a bug due to the fact that in 5.10,
"printf" format strings are now considered tainted. In the case of
"CGI", the routine in question reads the contents of an environment
variable when composing the canonical name of the temporary file.
Steffen Müller suggested a couple of fixes to resolve the issue, the
first one being the least intrusive, the second one being more to his
likely.
Tim Jenness wondered why "CGI" didn't use "File::Spec->tmpdir"
instead, since this particular wheel has already been invented over
there.
taint fun
http://xrl.us/bfs3h
Lincoln Stein stopped by to say that he was going to use Steffen's fix
in an upcoming 3.33 release.
still accepting patches
http://xrl.us/bfs3j
Perl 5.10 "Storable" extremely slow for large trees of data (#50352)
Clinton Pierce had a data structure that when dumped with
"Data::Dumper", produced about 8Mb of output. The same structure takes
less than a second to be dumped with "Storable", as long as perl 5.6
is used. If perl 5.10 is employed instead, the time taken balloons out
to 5 to 8 seconds.
Naturally he wanted to know whether this was a bug. Nicholas Clark
suggested he take the 2.18 version available on CPAN (which is bundled
with 5.10) to see if there was any difference on 5.6 (thereby
isolating the problem to the module or the core. Unfortunately Clinton
was on a Windows box without a compiler. Fortunately, Steve Hay was
around and he was able to compile 2.18 on 5.6, and confirmed the
slowdown on both 5.8 and 5.10 (while 5.6 remained fast).
After some more research, Steve reported that the choice of "malloc"
(Perl's or the C library) made a very significant difference to the
time taken. In both cases, Perl's own "malloc" was a couple of orders
of magnitude faster. He noted that Activestate built their Perl
distribution on Windows with the system "malloc" since it was a
necessary precondition for their "fork" emulation.
Curiously enough, Clinton's 5.6 installation was already using the
system "malloc". No-one was able to pin down the precise reason for
the slowdown, although it was likely that 5.8 and 5.10's full UTF-8
implementation may be a culprit.
fancy a strawberry?
http://xrl.us/bfs3m
perlop.pod - misnomer in % operator documentation (#50364)
Martin Becker suggested a more mathematically precise definition of
the modulus operator, and provided a patch to prove it.
unapplied
http://xrl.us/bfs3o
unexpected "exit" in "open3()" on win32 (#50374)
Alex Davies reported a curious set of circumstances that would cause
"IPC::Open3" exit when you least expected it.
this is a feature?
http://xrl.us/bfs3q
"GIMME_V" broken with 5.10.0/GCC and XS (#50386)
Robert May reported some strife with "GIMME_V" always returning
"G_VOID" regardless of context with an Activestate perl and XS
compiled with gcc. On the other hand, the same code compiled with VC++
6 behaved as expected.
Jan Dubois explained that this was due to a difference in how gcc and
VC++ laid out their bitfields. It turns out that VC++ is rather
profligate in its use of memory to store a number of bitfields, and
Jan promised to deliver a patch that would allow VC to be more
parsimonious in its memory consumption.
Armed with this information, Robert was able to twiddle a switch on
gcc to order it to lay out bitfields in an identical manner to VC++,
which solved his immediate problem.
Unfortunately, a blanket compiler switch override would then cause a
gcc for a Strawberry Perl to compile his XS module incorrectly, and
thus Rob needed to know how one could figure out what compiler was
used to build the perl within a Makefile.PL. Jan suggested probing for
values in the "Config" hash, as well as all you ever wanted to know
but were too afraid to ask about distinguishing an Activestate build
of perl from a perl built directly from source.
http://xrl.us/bfs3s
Jan followed up with a patch to lock down the underlying sizes used in
constructing bitfields.
http://xrl.us/bfs3u
"Filter::Util::Call" problem with $_ (#50430)
Ambrus Zsban reported an oddity with an identity source filter (that
is, one that doesn't transform anything). If he removed an innocuous
assignment to $_, everything stopped working.
deep filter voodoo
http://xrl.us/bfs3w
Perl5 Bug Summary
321 new + 1491 open = 1812 (15 created, 1 closed)
http://xrl.us/bfs3y
http://rt.perl.org/rt3/NoAuth/perl5/Overview.html
New Core Modules
B-Generate 1.12_03
Jim Cromie uploaded a development version of "B::Generate" that
behaves correctly with 5.10 and 5.11 (although it segfaults on
5.8). He was hoping to be made co-maintainer of the module, and
had a couple of questions for the porters, although no-one
ventured their opinion.
http://xrl.us/bfs32
He also had some special "B" portability macros fall out as a
consequence of the above.
http://xrl.us/bfs34
This is the BBC
Devel-Cover-0.63
"OP_SETSTATE" is no longer. Paul Johnson said he'd get around to
fixing it.
http://xrl.us/bfs36
Devel-StackTrace-1.15
Non-existent documentation leaves the implementation open to
interpretation. Nicholas locked the implementation down and
Devel::StackTrace had bet the wrong way. Dave Rolsky released 1.16
to CPAN.
http://xrl.us/bfs38
Net-DNS-0.62
The test file t/04-packet-unique-push.t failed in a build, but ran
successfully within the debugger.
the worst sort of failure
http://xrl.us/bfs4a
In Brief
John E. Malmberg commented that showing the pid when running under
"-Dv" would be more useful if it were rendered as hex under VMS, since
all the other VMS utilities do so. Craig A. Berry wondered if that
just didn't make things more confusing compared to how Perl works on
all the other platforms
http://xrl.us/bfs4c
Robin Barker's patch to silence compiler warnings about clobbering
volatile C stack variables was deemed suitable by Rafael
Garcia-Suarez.
http://xrl.us/bfs4e
Steven Schubiger's consting of util.c made it in.
http://xrl.us/bfs4g
He also added some consting tweaks to toke.c and universal.c, which
Rafael applied.
Andy would approve
http://xrl.us/bfs4i
He also managed to pull off a remarkable "const char *const str" in
taint.c.
http://xrl.us/bfs4k
Moritz Lenz reported an issue that cropped up on Perlmonks, where a
simple regexp ran 1.5 orders of magnitude more slowly on 5.10. Andreas
König identified the problem as being change #27903, in which Dave
Mitchell removed some recursion trickery. Neither Dave nor Yves Orton
were around to comment on the issue.
http://xrl.us/bfs4n
Yitzchak found a code example in "POSIX" that had drifted out of focus
and suggested how to make it work again. Applied.
$b be banished
http://xrl.us/bfs4p
Steve Hay tidied up some compiler warnings on Win32, but Nicholas
Clark came up with a better technique.
Moritz may also have uncovered a problem building blead with a
parallel make, although the jury is still out.
http://xrl.us/bfs4r
http://xrl.us/bfs4t
change #33109 trumps change #33106
http://xrl.us/bfs4v
Scott T. Hildreth reported a segfault with "Term::ReadLine::Gnu".
Rafael was inclined to think the problem was a signal handler issue
and wondered if "libreadline" was to blame.
http://xrl.us/bfs4x
brian d foy was trying to clarify smart match behaviour in "when",
when the "when" contained a "&&". He was troubled by differences in
what the documentation said and what the implementation did.
learning perl, TNG
http://xrl.us/bfs4z
Jerry D. Hedden todoified yet another "threads::shared" bug concerning
a shared object that is attached to a shared scalar.
http://xrl.us/bfs43
The bug in "ExtUtils::CBuilder" not honouring "extra_compiler_flags",
that leads to the "GIMME_V" problem was filed by Robert May as a
ticket on the "ExtUtils::CBuilder" queue.
http://xrl.us/bfs45
http://rt.cpan.org//Ticket/Display.html?id=32806
Daniel Frederick Crisman spotted a typo in a test name from last
week's additions from Abigail regarding the test of "for reverse ...".
http://xrl.us/bfs47
Daniel also identified a possible POD markup error in the Japanese POD
question last week.
ceci n'est pas une pipe
http://xrl.us/bfs63
Robert May thought that the POD in encoding.pm talked about side
effects far too much, so he dragged out the chain-saw and removed two
duplicate sections.
may cause drowsiness
http://xrl.us/bfs49
Reini Urban made some progress with his perl compiler project this
week.
just in time
http://xrl.us/bfs5b
Robin Barker noticed some sub-optimal POD formatting in "File::Find"
with C<{ bydepth =E<gt> 1 }> and proposed an alternative.
try writing that in POD
http://xrl.us/bfs5d
Nicholas Clark took a lateral thinking approach to solving the
parallel make bug for "SDBM_File" by provoking the same error but in
the "POSIX" module.
but not all the time
http://xrl.us/bfs5f
Philippe Bruhat ran into a spot of bother trying to build 5.8.8 with a
particularly recent version of the gcc compiler. Andy Dougherty and
Andreas König gave him a couple of work-arounds, and Nicholas promised
to make sure 5.8.9 (coming Real Soon Now) should have the fix.
going by the book
http://xrl.us/bfs5h
Watching the smoke signals, failure reports came in from Steve Hay for
Win32, as far as change #33169. No reports from other platforms.
About this summary
last week's
http://xrl.us/bfs5j
Yitzchak Scott-Thoennes clarified the panic on copying a freed scalar:
I thought the magic of @ARGV was part of the problem, Yitzchak said
that any array at all will suffer the same erroneous behaviour.
http://xrl.us/bfs5m
This summary was written by David Landgren.
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