This Week on perl5-porters (17-23 May 2004)
Rafael Garcia-Suarez
This week, your P5P summary is featuring phases of the moon, and other
funny things that always make the day of the average perl hacker.
Shell.pm
Bug #29585 describes how the Shell module fails to handle filenames
with spaces in them. Tassilo provided a patch, but Slaven Rezic pointed
out that one could argue that rm("my file") should remove two files,
my and file: rm("*") does globbing, after all. Moreover, Shell
escapes some characters and not some others.
Therefore Tassilo concluded that "there are many possible ways of fixing
Shell.pm, but each of them leaves quite a lot to be desired", and Rafael
commented that Shell was mostly a toy module.
http://groups.google.com/groups?selm=rt-3.0.9-29585-87427.8.22064370668613%40perl.org
Scoping bug
Jason Rhinelander found a semantic oddity related to scoping of the
$<digit> variables (#29701): in the condition of an if() block, the $1
which is set by a regexp match is still seen after the following block;
the $1 which is set by a match in the condition of a while() block isn't
seen after the said block.
Rafael comments that this may not be a bug, but doesn't remember why
exactly. (Thinking about it, probably because if(), unlike while(), can
be followed by two blocks).
http://groups.google.com/groups?selm=rt-3.0.9-29701-87741.16.8398876872253%40perl.org
File::Find and parameters
Roger Yager proposed a patch to File::Find to allow to pass arguments to
the callback subroutine. Gisle Aas mentioned the classical alternative
solution, to use a closure as a callback; but, as Mark-Jason Dominus
pointed out, this solution isn't always convenient. Thus, a
documentation patch to File::Find seems to be appropriate.
http://groups.google.com/groups?selm=auto-000000152005%40eyestreet.com
Thread creation time and phases of the moon
Jamie Lokier remarked submitted a detailed bug report (#29637) about the
factors that might influence the creation time of a new thread. It
appears that it's "highly sensitive to conditions that shouldn't affect
the time": for example, changing the name of a subroutine, or even a
space in a comment. This seems to be related to the number of
mprotect(2) system calls issued during memory allocation. Those calls
come from the malloc() implementation used on the system. Jamie provided
enough clues to make Dave Mitchell find a solution: the bug was in the
function used to clone pointer tables. Thread cloning time is now
apparently faster by a 10% factor.
http://groups.google.com/groups?selm=rt-3.0.9-29637-87553.11.6565004757339%40perl.org
Tainting and UTF-8
Stas Bekman and Rob Mueller found a situation where turning taintedness
on a scalar removes its UTF-8 flag. Sadahiro Tomoyuki proposed a patch,
that makes the internal routine sv_utf8_upgrade_flags() understand a
sufficient amount of magic to handle taintedness. As a side-effect, his
patch makes utf8::upgrade() less tolerant to read-only arguments.
http://groups.google.com/groups?selm=40AC475F.4010208%40stason.org
Autovivification of new lexicals
Shinya Hayakawa proposed a patch to allow lexicals just declared via
"my" to be autovivified, as in :
(my $x)->{foo} # creates a hash
Rafael doesn't have a strong opinion about this language feature. Hugo
isn't opposed to, but remarks that the patch lacks regression tests.
http://groups.google.com/groups?selm=200405211244.31291.tetryl%40tokyoprogrammer.com
In brief
Steve Hay found a way to make perl crash with two files, using the
autouse module. Nobody commented. (Bug #29708.)
http://groups.google.com/groups?selm=rt-3.0.9-29708-87779.17.2965328304932%40perl.org
Chip Salzenberg found a bug in the "@a = sort(@a)" in-place
optimization, which was promptly fixed by Dave Mitchell.
http://groups.google.com/groups?selm=rt-3.0.9-29790-87979.16.2445637115601%40perl.org
Rafiq Ismael found a regular expression and a string against which it
should match, that makes a threaded perl segfault, but not a
non-threaded perl. (Bug #29650.)
http://groups.google.com/groups?selm=rt-3.0.9-29650-87589.10.6574674663369%40perl.org
Dave Mitchell fixed a parsing error in the Switch module (bug #28966)
by adding "case" as a keyword in Text::Balanced.
About this summary
This summary was written by Rafael Garcia-Suarez. Weekly summaries are
published on http://use.perl.org/ and posted on a mailing list, which
subscription address is perl5-summa...@perl.org. Comments and
corrections welcome.
Dave Mitchell
> Thread creation time and phases of the moon
> Jamie Lokier remarked submitted a detailed bug report (#29637) about the
> factors that might influence the creation time of a new thread. It
> appears that it's "highly sensitive to conditions that shouldn't affect
> the time": for example, changing the name of a subroutine, or even a
> space in a comment. This seems to be related to the number of
> mprotect(2) system calls issued during memory allocation. Those calls
> come from the malloc() implementation used on the system. Jamie provided
> enough clues to make Dave Mitchell find a solution: the bug was in the
> function used to clone pointer tables. Thread cloning time is now
> apparently faster by a 10% factor.
Just to clarify - I fixed a bug that would occasionally make thread
creation 1000% slower than normal, and also did a slight enhancement that
made all cloning ~10% faster. Two mostly unrelated fixes. The malloc() /
mprotect() stuff turned out to be a red herring.
--
A walk of a thousand miles begins with a single step...
then continues for another 1,999,999 or so.