This Week on perl5-porters - 16-22 January 2006
"Class::Autouse" test fails on "blead"
"Class::Autouse" allows you to defer the loading of a class until you
actually get around to calling a method belonging to it, and the test
suite checks what happens when the class to be "use"d cannot be
compiled. The test that used to work, worked no longer, and Adam
Kennedy, the author, was wondering what changes had occurred in
"bleadperl" that could explain the problem.
Nicholas tracked it down to change #25599, a fix by Rafael
Garcia-Suarez for the bug that caused "CORE::require" to ignore the
"CORE::". (That is, if "require" was overridden, there was no way to
specify the underlying "require"). Rafael fixed the fix in fix #26881.
Class::Autouse
http://search.cpan.org/dist/Class-Autouse/
Squash a bug, get a new one free
http://xrl.us/jqvn
Cached %ENV on cygwin
Tim Bunce dropped in with a bug that cropped up on the "dbi-dev"
mailing list, someone having trouble getting "DBD::Oracle" and Cygwin
playing nicely together, and offered his theory about what was going
wrong. Andy Hassall correlated that with a message on a Cygwin
development list and confirmed Tim's theory.
Yitzchak Scott-Thoennes didn't have time to look at the code, but
offered some tips on how to restructure the test suite to work around
the limitation (which is, to quote Tim, that manipulating %ENV doesn't
alter the process's own environment variables until a subprocess is
spawned).
Too clever by half
http://xrl.us/jqvo
Dead part of constant expression is nonconstant
Gisle Aas reported that the Sun C compiler spits out endless "dead
part of constant expression is nonconstant" warnings when the macro
"Newx" is encountered in the source, and wondered what to do about it.
It is in fact a compiler bug. Alan Burlison had filed a bug report
with the Sun group and had updated perlsolaris.pod with the workaround
(adding a switch to ignore the warning in question, pending resolution
of the bug in the compiler).
Gisle evidently thought that this was a suboptimal hack, and rewrote
part of the macros guts in a new way, replacing a ternary by a series
of logical ands, thus making the warning disappear altogether. Alan
was impressed.
Gisle in action
http://xrl.us/jqvp
"until ()" is not like "while ()"
John Nurick wondered in bug #38254 why "while ()" behaves like "while
(1)", but "until ()" won't compile. He pointed out that making "until
()" equivalent to "until (1)" would be quite useless (as useless as
"while (0)"), but a good case could be made for making it equivalent
to "until (0)".
Yizchak showed that "until ( () )" worked as expected (if slightly
non-obvious), but otherwise no lexer wizards chose to come up with a
two-line patch to make Perl DWIM.
A call to orthogonality
http://xrl.us/jqvq
Another "defined %foo::" bugfix
Rafael found another problem pertaining to "defined %foo::" by smoking
Inline. The following no longer worked:
package test;
sub import { print defined %some::random::stash:: ? "not ok" :
"ok", "\n" }
1;
And fixed it up with a short, sharp patch (#26867).
Always test scary modules before a release
http://xrl.us/jqvr
Documentation discrepancy over "-DPERL_EMERGENCY_SBRK"
Stas Bekman noted that it is possible to set aside an emergency pool
of memory so that perl could do something useful after "die"ing, and
perlvar.pod explains how to set it up. On the other hand, the INSTALL
file fails to make any mention of it and wondered what was the best
thing to do about it. Rafael committed change #26878 to clarify the
issue.
Save some for later
http://xrl.us/jqvs
Impossible seeming bug
Hal Morris tripped if the "if(0)/elsif(0==undef)" bug (the reported
line number being that of the "if", not the "elsif". The is because of
the way the internal representation of the program discards the
information concerning the line number of the "elsif". When a problem
occurs, the line number of the "if" is all that remains, so that is
what is used in the warning message.
Paul Johnson wished it was fixed, because it would make
"Devel::Cover"'s branch and condition coverage easier to understand.
David Landgren pointed to the previous thread on the matter.
This can't be right
http://xrl.us/jqvt
Nor was it back then
http://xrl.us/jqvu
"Pod::Simple::Search" and non-case-preserving filesystems
Allison Randal cast her attention to a late-December post from Craig
Berry, who was having trouble with "Pod::Simple::Search" on VMS and
had supplied a patch to resolve the problems he had encountered
(relating to the fact that FOO and foo can refer to the same file).
Allison gave details of three minor problems she had encountered with
the patch, proposed fixes and asked if Craig could verify the
correctness on VMS, which would allow her to release 3.04.
Craig took Allison's amendments for a spin, ironed out a few kinks and
gave it the thumbs up.
Shiny cross-platform goodness
http://xrl.us/jqvv
Avoiding realloc
Nicholas Clark had a look at way perl allocates memory for scalars. Up
until now the exact size has always been requested, and the allocated
size is recorded. This helps avoid unnecessary trips to the heap when
a string shrinks and then grows yet stays within the size of the
original allocation.
On the assumption that "malloc" implementations silently round up
anyway, because it simplifies the internal bookkeeping, it makes sense
to round up the requested size silently on perl's side anyway, because
then scalars that creep a little bit past the initial requested size
might still remain within the initial requested size, thereby avoiding
a costly "realloc".
Nicholas then set about trying to determine the exact number of bytes
that are in fact allocated for all small allocation values (where
small means between 1 and 256). It turns out that a brute force "round
up to nearest multiple of 4 on a 32-bit CPU" rule wasn't particularly
effective. "malloc" sometimes allocates much more, especially on
FreeBSD. Nicholas wanted to know whether it would be worth the effort
to probe for these sizes at "Configure" time, build a lookup table,
and tweak the already monstrous "PERL_STRLEN_ROUNDUP" macro to use it
for short allocation sizes.
Nicholas simply wanted to minimise the number of calls made to
"sv_grow", without requiring any extra code or tests elsewhere in the
interpreter. Gisle was unconvinced, reasoning that it takes memory
away from "malloc" that "malloc" may be able to deploy more
effectively elsewhere at some further point in time.
Use a lookup table to save memory
http://xrl.us/jqvw
*au revoir*, and LVALUE matches
Dave Mitchell wrote to say that he was going off-line for a month
(visiting India), without a computer, and thus the longest time with
out access to one since 1979. Let's hope he reads the summaries when
he gets back to catch up. Nicholas noted that he had to revert one of
Dave's recent changes (#26410, which fixes infinite loops in the
regexp engine on a tainted scalar) as it caused an unexpected failure
to occur elsewhere. Dave still found time to analyse the problem
carefully, and judged the behaviour to be ideally a new feature for
5.10.
Abigail didn't like the consequences that an unnecessary "/g" on a
match could now be sufficient grounds for a program to die. All this
reminded Rafael about two changes he applied a couple of years ago,
noting the similarities between the problems raised then and now. Rick
Delaney proposed a patch that fixed the test, but admitted to not
understanding all the ramifications, having merely lifted code from
elsewhere in the interpreter that deals with the same sort of issues.
Dave Mitchell, no doubt in a Wifi bubble at the local airport, said
that his patch was indeed wrong, and should be backed out from "blead"
as well. And pointed to very old, deep magic as probably being the
source of the problem, such as the hack that enabled "local $a[0] =
$a[0]". The tests have now been marked TODO, so that someone can think
about them again in time for 5.9.4.
No fix is better than a bad fix
http://xrl.us/jqvx
"bleadperl" regression testing
Steve Peters has been a busy man, testing many, many modules against
"blead" and gave a clean bill of health to nearly 4 dozen modules. 8
passed with warnings and several big and/or scary ones failed ("TT2",
"Kwiki", "DBI", "Devel::Hints" and "HTML::Mason". And if that wasn't
enough, he also cooked up some patches and sent them off to the
respective module authors.
Gisle noted a problem with "Perl_newSVrv" as a result, which Rafael
fixed up with change #26885.
Test... everything
http://xrl.us/jqvy
Asserting that non-"NULL" parameters are passed to "av_*"
A while ago, in change #26513, Gisle added assertions to ensure that
the "av_*()" functions are indeed given "av"s as arguments. Nicholas
noted that "Template::Toolkit" fails the assertion, managing to pass a
"NULL" to "av_fetch" at one point.
Gisle wanted to know whether Nicholas wanted "NULL"s to be allowed
again, pointing out that in an ideal world, "TT" should not have
called "av_fetch" the way it did.
Nicholas's point of view was that the assertion changes the API
behaviour in a non-trivial (albeit better) way, and thus not really
allowable for the maintenance branch, and said that it was Rafael's
call as to whether he wanted it in "blead". Rafael decided to keep it.
Theory meets reality
http://xrl.us/jqvz
Compiling "blead" on VMS
John E. Malmberg wrote in with a status report for "blead" on VMS,
saying that 6 tests were failing, and gave a rundown on what was
happening, or what he was going to do. Steve Peters and Craig Berry
either pointed to or wrote a couple of changes that should have
resolved the issues John was encountering.
Marcus Holland-Moritz tried to reproduce the failures on a testdrive
machine without luck, but did manage to isolate the changes that
triggered the errors, and warned Nicholas that if he had integrated
those changes into "maint" then the errors would pop up there as well.
6 test failures
http://xrl.us/jqv2
After checking out a copy of "[EMAIL PROTECTED]" (meaning the source tree
for perl as of change #26913), John found that only one test,
lib/ExtUtils/t/Manifest, was failing. Craig Berry was at a loss as to
how to deal with the failure. VMS has a much richer set of privileges
than Unix. If the test is run from a process with high privileges, it
succeeds. If run with lower privileges, it fails, as a result of what
is, deep down, a rather sensible security decision in the design of
VMS (that permissions do not necessarily follow a copied file). Craig
pondered how to fix it. chromatic pragmatically suggested that a skip
was in order. Craig amended the skip to nail down the semantics of the
test more precisely.
5 down, 1 to go
http://xrl.us/jqv3
Devel-PPPort-3.07
Steve Hay noted that the current version of "Devel::PPPort" is missing
both "SvPV_nolen_const" and "SvPV_nomg_const" and wondered what the
reason was. Marcus Holland-Moritz pleaded not guilty, having missed
the information in the 1500 messages remaining to be read in his "p5p"
folder.
Marcus also provided the magic POD recipe required for documentation,
which would have allowed the information to be extracted
automatically, in which case he would have noticed them and included
them in the release.
Reflecting on what Marcus said, Jim Cromie noticed some discrepancies
between embed.fnc and pad.c and wondered what the reason was. Marcus
pointed out that that is what happens when people document macros or
functions that are not strictly part of the public API. So more of a
feature than a bug.
Working according to spec
http://xrl.us/jqv4
Reducing calls to "getprotoby{name,number}" by "IO::Socket::INET"
Gisle found that the seemingly innocuous program
use IO::Socket::INET;
my $a = IO::Socket::INET->new("www.perl.org:80");
my $b = IO::Socket::INET->new("www.perl.com:80");
... opened /etc/protocols on his linux system 4 times, which he
thought was rather wasteful, and proposed a patch to cache the results
and also work correctly on systems with borked /etc/protocols (which
in itself is cause for a number of bug reports filed against LWP).
Graham Barr (author and maintainer of IO::Socket::INET) liked the
idea, and folded the change into his own repository for an upcoming
release.
IO, IO, it's off to less work we go
http://xrl.us/jqv5
Roland Illig asked why "perlcc" cannot compile a program he wrote in
bug report #38279. Given Dave Mitchell's reply to a similar bug last
week, it's safe to assume that "perlcc" is *never* going to compile
that program.
It doesn't work any more
http://xrl.us/jqv6
And it probably won't ever, either
http://xrl.us/jqv7
"flock" does not work properly on (old) Solaris systems
"Sign Writing" (what were his/her parents thinking?) filed bug #38282
wherein we learnt that old Solaris versions have trouble "flock"ing.
Abe Timmerman provided a snippet to help Sign research the issue.
After investigating a bit more, Sign found that a similar program
written in Python worked correctly.
With a bit more help from Abe, Sign was able to solve the problem, who
discovered "that perl drops the lock when duping the filehandle, but
it appears to be related to duping it to something like STDOUT or
STDERR. Perl tries to preserve these if the operation fails, but if
it's explicitly closed before the dup, it works."
flocking hell
http://xrl.us/jqv8
Enabling cumulative profiling with "-Dusesitecustomize"
Nicholas Clark was annoyed the way that "gcc"'s profiling mechanism
consists of overwriting the contents of "$0.gmon" with the information
gathered during the profiling run. This is exceptionally annoying when
you are trying to generate cumulative data from multiple runs.
After his first work-around attempt with a shell wrapper was foiled by
too-clever code that acquired the necessary information directly from
$^X, he devised a crafty solution involving "-Dusesitecustomize".
After getting this to work, he benchmarked SpamAssassin's test suite
and found that the most expensive routine was (*surprise!*)
<S_regmatch>.
Gisle Aas astutely observed that it would be more useful to benchmark
SA doing real work, rather than the test suite, since, in theory, the
suite is mainly testing fiddly edge cases.
Now all we need is for someone to analys the results
http://xrl.us/jqv9
Cross-compiling Perl
John Clark wrote to relate his difficulties in cross-compiling perl.
Specifically, going from "i686"/"gnu libc" to "i586"/"uClibc". Nothing
too radical, like going from an IBM rs6000 to a PDP-11, but
nevertheless John was surprising by the number of little niggly
problems he encountered.e
This prompted Philippe Ney to recall that he succeeded in
cross-compiling for "i386-uClibc", but only with static linking, and
was hoping that someone had managed to succeed in making dynamic
linking work.
No-one, apparently, had.
Cross-eyed and painless
http://xrl.us/jqwa
5.8.8 RC1
The Release Candidate 1 for Perl 5.8.8 has been published by Nicholas.
But then, you already knew that.
H.Merijn Brand published his DOR (defined or) patch that syncs with
the codebase as it currently stands.
Reports of compile and test successes started to roll in.
Take it for a spin
http://xrl.us/jqwb
Allowing "chr(65535)" in regexps
Marc Lehmann filed bug #38293, saying that using "chr(65535)" in a
regular expression results in the warning:
Malformed UTF-8 character (character 0xffff) in regexp compilation
... and yet "chr(65534)" works just fine. Both characters are
guaranteed to be illegal characters that can be used for internal
processing (sort of like an ultra-hyper-uber "\0" for end-of-string
markers I suppose). Gisle made a good argument for why it would be
handy for this to work in Perl.
Sadahiro Tomoyuki pointed out that all you have to do is "no warnings
'utf8';" to suppress the message. Tels traced down the error to a
section of code in "Perl_uvuni_to_utf8_flags" that was doing a rather
long-winded test, making Tels wonder whether the test was botching its
conclusion.
Marc, Tomoyuki and Yitzchak then started discussing Unicode arcana
which started to make my eyes glaze over, and as this is the last item
of the summary, you'll just have to click on the link to find out out
more.
The $65535 question
http://xrl.us/jqwc
New Core Modules
Podlators 2.0.1
Russ Allbery reported that the problem concerning parser objects
that cannot be reused has been resolved, along with a few other
minor issues.
http://xrl.us/jqwd
http://search.cpan.org/dist/podlators/
Archive-Tar-1.28
Jos I. Boumans uploaded "Archive-Tar-1.28". Paul Marquess pointed
out that the latest version of "Compress::Zlib" has some nice
features that will make "Archive::Tar"'s life easier in the
future.
http://xrl.us/jqwe
http://search.cpan.org/dist/Archive-Tar/
Perl5 Bug Summary
1526 open tickets.
http://xrl.us/jqwf
http://rt.perl.org/rt3/NoAuth/perl5/Overview.html
In Brief
Konrad Eisele noted that while it is not possible to tie a subroutine
reference, he nevertheless proposed a patch for "Perl_mod()", which
would at least make it produce a sensible error message.
http://xrl.us/jqwg
Seung-Ho Han asked where to find information on functions like
"svref_2object" and "rv2sv", and was directed to look at perlguts and
the "perldoc B" command.
http://xrl.us/jqwh
Steve Hay discovered that "maint"'s perlapi refers to 5.9.3, instead
of 5.8.8 in relation to documentation on "Newx"/"Newxc"/"Newxz".
http://xrl.us/jqwi
Steve also noted that "New()" and its ilk have been replaced by the
"Newx()" family, due to a redesign in how memory leaks are trapped,
and wondered whether "NEWSV()" should be replaced by "newSV()"
throughout the core (whilst retaining the "NEWSV()" definition for XS
compatibility). Gisle agreed, and thus is was done, as change #26901.
http://xrl.us/jqwj
Dave Mitchell noticed that Copying contains version 1 of the GPL (the
GNU General Public Licence that governs the use of Perl) but that
pod/perlgpl.pod contains version 2. He thought that the same version
should be used in both places, but didn't know whether version 1 or 2
should be used. And that version 3 was just around the corner...
http://xrl.us/jqwk
Vadim Konovalov thought that the fact that statically linking of Perl
extensions on Win32 was made functional was worthy of being mentioned
in the release notes for the upcoming "maint" and "blead" releases.
http://xrl.us/jqwm
Nicholas Clark found that "SOFT_CAST" in perl.h appeared to date back
from around 5.003 and wondered if these days it was just excess
baggage. Andy Dougherty concurred, and so "SOFT_CAST" was cast off.
http://xrl.us/jqwn
About this summary
This summary was written by David Landgren. As they say, better late
than never.
Information concerning bugs referenced in this summary (as #nnnnn) may
be viewed at http://rt.perl.org/rt3/Ticket/Display.html?id=nnnnn
Information concerning patches to maint or blead referenced in this
summary (as #nnnnn) may be viewed at
http://public.activestate.com/cgi-bin/perlbrowse?patch=nnnnn
If you want a bookmarklet approach to viewing bugs and change reports,
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