This Week on perl5-porters - 11-20 November 2005
The crackdown. A number of bugs were fixed this week, possibly
obsolete code was scrutinised, Hugo patched the regexp engine and Perl
on Windows was improved.
"h2ph" finds "gcc"'s include directory
Brendan O'Dea posted a patch to use the "gcc" command line switch
"--print-libgcc-file-name" to locate the "gcc" include directory. The
previous technique of parsing "gcc -v" no longer works on version 4.
H.Merijn Brand wanted to know when "--print-libgcc-file-name" was
introduced (otherwise things would start failing for older gcc
compilers). Brendan said that he had reached as far back as 2.95, and
the switch was supported. Abe Timmerman chipped in with a justifiably
ancient 2.7.2.2 gcc compiler that also supported the switch.
Jason Vas Dias pointed to bug #37582 that he had filed on the issue,
and that the patch had been applied by Steve Peters as change #26074.
Brendan's patch
http://xrl.us/iiau
Jason's patch
https://rt.perl.org/rt3/Ticket/Display.html?id=37582
Eliminating discrete arenaroots
Jim Cromie issued a reworked, tested on threaded and unthreaded, patch
to remove the fifteen different type-specific arenaroots, and asked
people to have a smoke. Nicholas Clark went over the patch very
carefully and made a number of suggestions, and Jim proposed a
revision of the patch, which Nicholas applied as #26139.
After looking at Nicholas's reworking of the patch, Jim added a number
of corrections to the comments in the code, and then posted a series
of benchmark results showing that the patch should have made things go
faster (with the usual proviso about statistics).
Later in the week, Jim came back with another patch that gathered the
arenas into a linked list. This has some upsides and some downsides,
but notably, it allows the possibility of exposing the arena to allow
performance tuning.
The elimination
http://xrl.us/iiav
Benchmark results
http://xrl.us/iiaw
RFC - linked list of arenas
http://xrl.us/iiax
A better warning in maint
Yitzchak Scott-Thoennes asked whether change #22807, which makes "$^O
!~ /xxx/" emit the warning "Useless use of negative pattern binding
(!~ in void context)" instead of "Useless use of not in void context"
should be applied to maint. Nicholas yelped in pain and whispered
something about perl 5.10. Yitzchak sympathised, and went through his
own blead patches, evaluating which ones were worthy (safe enough) to
be applied to maint.
The question
http://xrl.us/iiay
Yitzchak's list
http://xrl.us/iiaz
"h2xs" and backwards compatibility
Steven Schubiger voiced his disquiet over the way h2xs ties the Perl
version of the module to the module of perl installed on the author's
machine (even when it might run perfectly well on any number of prior
versions).
Rafael Garcia-Suarez agreed that the orginal design decisions was
probably incorrect and Nicholas remembered a previous thread on the
matter, which Steven tracked down. Sébastien Aperghis-Tramoni was
annoyed by modules that failed to install on 5.8.5 because they
required 5.8.7, and wondered if it wouldn't be better to focus on the
branch version (that is, 5.8), rather than relying on the subversion
(the x in 5.8.x), and offered a patch. And also pointed out that
"XSLoader" is backwards-compatible as far back as "5.005_04".
Rafael declined to pick up the patch, pointing out that there is no
way of ensuring that code that runs on 5.8.x will run on 5.8.x-1 and
lower.
This latter point prompted David Nicol to ask whether any
documentation existed relating feature to version, and when the
feature moved from absent, to experimental, to robust.
Doubts over h2xs
http://xrl.us/iia2
2001, a Perl odyssey
http://xrl.us/iia3
Abigail and the regexp engine
Abigail posted some code where it was expected that "'A B' =~
/^(.)\s+.$(?(1))/" should match. In 5.005 it used to work, but from
5.6.0 and beyond it fails.
Andreas König tried to track down the patch that caused the change in
behaviour, but "gcc" got in the way. In fact, depending on whether he
used version 3.2.3 or 4.0.3 the pattern matched, or didn't,
respectively.
Hugo van der Sanden burnt a precious tuit or two and rummaged around
in the regexp engine internals and made a one-line change that fixed
the problem, but said that he didn't have time to study the
ramifications implied by the patch and noted that ""intuit_start" is
probably the least maintainable piece of code in perl".
Now why would you want to do a thing like that?
http://xrl.us/iia4
Tracking down a Win32 smoke failure
One of Steve Hay's boxes phoned home with a smoke failure. After first
ignoring it and hoping it would just go away of its own accord, Steve
had a closer look and noticed that it was a real bug, and only
occurred when "PERL_IMPLICIT_SYS" was defined. Unfortunately, this
particular "#define" is needed by ActivePerl, and Steve tracked the
change in behaviour down to patch #26108. A three line change to tweak
stacks in "BEGIN" blocks.
Nicholas shrunk the problem down to a neat
#!./perl -w
BEGIN {
$SIG{INT} = sub {exit(0)};
kill 'INT', $$;
}
which causes a little known routine named "S_unwind_handler_stack" to
blow up. After a certain amount of detective work, he was able to show
quite clearly *why* the code was failing, but was at a loss as to
*how* to fix it.
Steve Hay pointed to a thread from last year where Jan Dubois posted a
patch that seemed promising at the time, but for whatever reason was
never polished and applied to blead.
Jan spoke up and offered a bit more detail about how the patch worked,
and what it needed in order to be complete. The next day he came back
with a much better version. Stever Peters applied it and all the tests
passed. Yay Jan!
Smoke issues forth
http://xrl.us/iia5
The offending patch
http://public.activestate.com/cgi-bin/perlbrowse?patch=26108
"free to wrong pool", circa January 2004
http://xrl.us/iia6
Is "STRANGE_MALLOC" still useful?
Nicholas wondered about the different code paths taken depending on
whether "STRANGE_MALLOC" is defined. He wondered whether it would be
safe to assume that "malloc"/"realloc"/"free" work correctly these
days, and that by chainsawing it out we would escape some
no-longer-needed complexity?
Andy Dougherty supplied a valuable history lesson, explaining why
things came to be the way they are. And concurring that at this point
in time, it could possibly get the axe, but it would be important to
try out a couple of big applications to see how they fare.
Compare the simple code path to the complex code path
http://xrl.us/iia7
Sarathy's 1995 summary of the problem
http://xrl.us/iia8
When errors are reported on the wrong line
David Hillman crafted a detailed bug report concerning errors being
reported on the wrong line (which of course tends to drive people
insane when they try debugging it).
Dave Mitchell, noting the relative frequency with which these sorts of
bug reports tend to appear, wondering what the cost benefit ratio
would be of using up more memory per op in order to keep accurate
track of the current line.
Jim Cromie came up with what he termed a rather ugly solution to the
matter. Then again, beauty is in the eye of the beholder. Dave
Mitchell followed up with some preliminary numbers on the memory cost.
The concensus is that a certain amount of memory could be traded for
the peace of mind it would bring.
The bug report
http://xrl.us/iia9
An ugly fix
http://xrl.us/iiba
Sun Studio compiler for Linux
Steve Peters tweaked hints/linux.sh to get the Sun Studio compilers
for Linux up and running. The results are promising, although the
patch, in Steve's own opinion, needs work.
He also used it to take a look at Jarkko Hietaniemi's "valgrind"
finding from last month.
The tweak
http://xrl.us/iibb
Problems with sprintf()
http://xrl.us/iibc
Jarkko's valgrind discovery last month
http://xrl.us/iibd
Perl 5 Bug Summary
The current number of open issues stands at 1508.
The bugs at the beginning of the week
http://xrl.us/iibe
The Bug Summary
http://rt.perl.org/rt3/NoAuth/perl5/Overview.html
In brief
"abs2rel("/foo/bar", "/foo/bar")" should return '.' or something else
sensible, according to Ken Williams (and not an empty string). After
asking around if anything other than "File::Spec" relied on the
behaviour, Ken went ahead and fixed the problem in "Path::Class".
http://xrl.us/iibf
"local" and "thread::shared" don't mix. "dean" filed bug #37671
showing how localising variables bound to shared variables can cause
the shared variable to become undefined. At least in version 5.8.4.
http://xrl.us/iibg
"Compress::Zlib" should now build nicely on Win32 environments, now
that Paul Marquess has fixed a lurking "binmode" bug.
http://xrl.us/iibh
Recent "const"ing changes to the codebase had broken "perlbug"'s
ability to grok patchlevel.h. Yitzchak filed a patch to make it work
again and threw some compatibility future-proofing into the bargain.
http://xrl.us/iibi
Dynamically appending code to an existing file. Jos I. Boumans wants
to do this from time to time, and showed several techniques for
implementing it, however, only two methods work. Looking at
"pp_require" in pp_ctl.c, it looks as if the code is going straight to
the file, rather than going through a higher layer. Jos asked if this
could or should be fixed, or nailed down in the documentation. No
takers.
http://xrl.us/iibj
Another source of segmentation faults killed. Peter Dintelmann
followed on from last week and continued to nail segfaults. He noted
that executing the code snippet "PerlIO::get_layers undef" would end
in grief and patched universal.c to make it work correctly (or rather,
not crash). Applied by Steve Peters as #26144.
http://xrl.us/iibk
Vadim Konovalov supplied a patch make WinCE compile blead and wondered
whether ./wince shouldn't be made a subdirectory of the ./win32
directory in the source tree. H.Merijn made a few remarks about the
patch, basically prodding Vadim to give himself and Rainer a bit more
credit in the README.
http://xrl.us/iibm
When in doubt, use brute force. "fbriere" noted a cute bug: if you
require a module that dies when it is loaded, it fails the first time.
But the second time, it succeeds!
http://xrl.us/iibn
Andy Lester took a preliminary run through the codebase and axed the
ancient RCS commit comments in the source. (These days the codebase is
managed in a Perforce repository).
http://xrl.us/iibo
About this summary
This summary was written by David Landgren.
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
Weekly summaries are published on http://use.perl.org/ and posted on a
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