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This Week on perl5-porters - 16-22 March 2008

posted by grinder on 2008.03.29 18:02   Printer-friendly

This Week on perl5-porters - 16-22 March 2008

"I suspect that by now the Parrot code base has moved on sufficiently that it's faster and cleaner to start from scratch than to try to merge over that code. I might be wrong, but I'd suggest keeping "redo from start" as an option." -- Nicholas Clark, not wishing to flog a dead horse.

Topics of Interest

Lexical and

We now return you to last week's discussion about Fatal (issuing a warning become a fatal error that halts execution) and how Paul Fenwick has begun work to make the effect lexical (that is, scoped to the current code block).

First off, it appears that use lethal has lost out to use autodie, which doesn't seem like an improvement, but it has the pumpking's favour.

As the code was more or less ready to be pulled into the code base, the question was what to do about dual-lifing the module, since lexical pragmas aren't available in 5.8 and below. Nonetheless, it would be nice to get rid of the AUTOLOAD craziness on 5.8 and 5.6. Further backwards compatibility would not be required as it is doubtful that anyone stuck on such ancient versions would be using Fatal in the first place.

Aristotle Pagaltzis thought it would be useful to have shorthand import lists to make warnings from all core functions dealing with, for instance, I/O, to invoke the Fatal machinery. He was also a little doubtful about wedging the pragma into the Fatal namespace. It would be better to have Fatal and the autodie pragma be APIs into the same underlying code.

There was a certain amount of discussion about what happens when Fatal is used at the package level, and then a no autodie pragma is invoked in a scope. Paul hinted that he'd be happy to implement whatever the concensus turned out to be, but while there wasn't exactly disagreement over anything, some of the corner cases had some pretty horrible choices.

The messages that Fatal produces when it does its stuff also came under fire. Paul said he'd look cleaning that up. Aristotle even volunteered to chip in with the task if needed.

  one thread 
  and another 

Wanted: interesting self contained task

Nicholas Clark was a bit sad that the idea of learning about how to hack on perl's internals attracted so little interest. He concluded that it would not be worth the effort to write up a conference talk on the matter if it was likely that no new people became interested in hacking on perl.

Rick Delaney disagreed and said he that thought the self-contained task idea was worth pursuing. All that is needed is to find another task, and set up a mentor.

  rewrite the peep-hole optimiser 

Perl @ 33536

Nicholas Clark released another snapshot that is asymptotically approaching 5.8.9. At this point the ExtUtils::Install issues haven't quite settled down on Windows (but subsequent patches to the list indicate that this is close to being fixed).

Improvements in this snapshot include the quashing of intermittent threads failures and that it builds out of the box on Stratus VOS.

Steve Hay mentioned that there a couple of his patches that ought to go in as they quieten a number of compiler warnings on Windows. 

Devel::Size and bleadperl

Tels noticed (in bug #33530) that Devel::Size was no longer buildable under bleadperl, mainly due to the promotion of regexps to first-class REGEXP datatypes. Reini Urban fixed it up as best he could and added an error message that pleased Paul Johnson's sense of whimsy. 

perl and CPAN distributors

It all started out with the simple wish of Gabor Szabo to hoist the information about Perl ports from out onto the Perl5 wiki in order to allow many hands keep it up to date.

The thread then developed into a long discussion about how distributors of operating systems (such as Debian) go about including Perl in their distribution. There was much talk about the relative merits of strategies for dealing with architecture-dependant (read: XS) components, dual-life modules, and fitting in the distribution packaging schemes.

Rafael Garcia-Suarez hinted that he wanted to take a fresh approach to these issues in 5.12.

One of the main problems, articulated by Michael G. Schwern, is the persistent (literally) difficulty in modifying @INC locally, without resorting to sub-optimal hacks like

In the final analysis, we need to allow Perl to allow itself to be driven by the host packaging system whilst retaining the ability for a local site to include a fresh new Perl module of which the packaging system has not yet caught up with. 

Is posix_fallocate() a possible candidate for

Joshau Hoblitt wondered if there was any interest in exposing the posix_fallocate function to Perl, which allows one to ask the host for enough contiguous space in which to write out really huge files, the idea being to minimise fragmentation as far as possible.

Craig A. Berry replied that any serious patch would be seriously considered. 

Eliminate cut-n-paste code in dump.c

Jim Cromie spotted a quick way to chop around 150 lines from dump.c. Reini Urban noted that part of the code in question was duplicated in various B and Op modules, so it would be nice to expose the underlying code via an API, which would simplify the task of keeping these ancillary modules in sync. 

Faster safe signals?

Nicholas Clark wondered if we could have faster safe signals by pushing the safe signal check down out of the core runloop into a small number of suitably hot opcodes.

Tim Bunce wondered if adding branch prediction hints in suitable places might not produce an even greater performance boost.

All of the experiments tended to produce results whose differences were lost in the noise. 

perl 5.10.1 plan

Dave Mitchell asked what was needed in order to release 5.10.1, such as outright breakages from 5.8.x and fixes for new things in 5.10.0, such as some of the quirky edges in given/when, where it is important to nail them down quickly before too many people get used to them the way they are now.

Michael G. Schwern mentioned the @_ slowdown (which is no more), problems with ExtUtils::Install, making sure things build out of the box on Vista and a list of issues that have arisen with smart matching. 

local $@ has an unwanted side effect

Yuval Kogman described a scenario in which local $@ doesn't do the right thing. It boils down to the latter day DESTROY method interfering with the orderly behaviour of unwinding exceptions and transferring information via $@.

After a long discussion as to whether it would be possible to fix the current behaviour, short of introducing a putative @@ variable, David Nicol suggested a documentation improvement to describe exactly how things are now, and that's what made it in. 

Bug tracking system

RT sucks. Bugzilla rulez.


TODO of the week

(based on a suggestion by Nicholas Clark in private correspondence).

Here's your chance to get your name in lights, or at least in the following section of "This Week on perl5-porters". Take a TODO item, and... do it! Each week, a random TODO will be featured. To start the ball rolling, we have:

Merge common code in installperl and installman

There are some common subroutines and a common BEGIN block in installperl and installman. These should probably be merged. It would also be good to check for duplication in all the utility scripts supplied in the source tarball. It might be good to move them all to a subdirectory, but this would require careful checking to find all places that call them, and change those correctly.

Patches of Interest

ExtUtils::Install under Cygwin

Steve Hay thought he had the patch to end all patches to get POSIX::access working sensibly on Cygwin using all the compilers he could get his hands on. No-one commented on it, apart from Yves Orton via IRC, so Nicholas Clark committed it. 

New and old bugs from RT

PERL_NO_SHORT_NAMES incompatible with perl.h (#51762)

Michael Fowler (of the Debian Project) identified a problem with PERL_NO_SHORT_NAMES which results in undefined symbols occurring at link time. No answers as yet. 

open(OUT, ">-") is not open(OUT, ">", "-") (#51842)

Himanshu G. tripped over the 3-arg open and >- (STDOUT). Ronald J. Kimball asked how the documentation could be improved to clarify the situation. 

Deparse interpolation in regex literal (#51848)

Zsban Ambrus uncovered a deparsing problem in 5.10 (but not 5.8) whereby qr/${x}y/ produces /$xy/, which is definitely wrong. 

UTF-8 non-characters (#51918)

Chris Hall opened a ticket to say that the Encode distribution's decode and encode routines only recognise U+FFFF as a non-character, but 65 others, such as U+FFFE and U+10FFFF and waved through as being valid characters. 

Inconsistent handling of characters with value > 0x7FFF_FFFF and other issues (#51936)

Even more scary stuff about Unicode non-characters and 13-byte extended sequences that fairly had my head spinning. 

Typo on regular expression at perlopentut manual page. (#51964)

Pancho found a very silly typo in a code fragment in the documentation, so Rafael fixed it.

  a patch to remove one character 

Document $var, $arg, $type and $ntype XS variables (#51992)

Michael G. Schwern was annoyed at the way perlxs waffles on about these variables without ever really getting around to explaining what they are. Michael promised that is someone could explain them to him then he would make improvements to the documentation. 

Warn/abort on attempted perl exit (#52000)

John Gardiner Myers offered a patch (but no tests) to convert an attempt to call exit into a warning. This is a highly desirable feature to have in a multi-threaded environment where a single exit can really ruin your day (especially when the exit comes hidden in something downloaded from CPAN)...

The patch makes a Perl stack trace available to a __WARN__ handler so that the offending code can be tracked down. 

Perl5 Bug Summary

  1795 (+9 -6) 

In Brief

Sérgio Durigan Júnior had a few questions about compiling a 64-bit Perl in a 32-bit system following on from his problems with failed tests on PPC64. H.Merijn Brand set him straight.

  64 bits for all 

Sérgio also asked about make distclean and config.arch but received no answers. 

But feedback from H.Merijn on how to solve his problem in a better way led to the resurrection of the rarely used config.over technique for overwriting Configure behaviour. 

As well as some problems when setting the libraries' installation path. 

Having pulled the rug up over things long since swept away and forgotten about, Sérgio added some smarts to make distclean remove config.arch. H.Merijn applied the concept, if not the patch itself, to Makefile.SH. 

Paul Green reported that a smoke of perl@33536 on Stratus VOS issued a number of errors that were all due to Stratus VOS's own take on reality, and not (or nearly never) Perl's fault. He thus lifted Stratus's option to stall the release of 5.8.9.

  98.68% ok 

Jim Cromie wrote a patch to improve IS_NUM_COMPARE by coalescing all the opcode numbers involved to be contiguous. He was a bit peeved that it didn't reduce the resulting assembly code, but figured that at least it renders the code less sensitive to the ability of the C compiler to perform sophisticated optimisations. 

Thanks in large part to Eric Wilhelm's tireless efforts, Perl is again a participant in Google's Summer of Code (at least as far as the northern hemisphere is concerned).

  it's official 

And regarding the GSoC, there is a list of Things To Do. 

Reini Urban uploaded his Mperl compiler and optree debugger. No-one commented. 

Robin Barker added some optional verbosity to and friends. Unapplied. 

Gerard Goossen stripped out some unnecessarily complex code when dealing with MAD. Unapplied. 

As tweaked the keys for sub and var attributes to avoid clashes with arrow operators. 

Michael G. Schwern reported that the patent for "Software Package Verification" was nothing to worry about. There had been some concern in the past that Perl's test infrastructure could have been covered by its scope. 

H.Merijn Brand reported that perl's Configure script had been ported to meta-3.5-20 . 

Vincent Pit went looking for double warnings for single errors, and found two. perl -we '\&$x' used to spit out the same error twice (along with four others). 

and perl -we 'my $a; substr $a, 0, 10, "foo"' did much the same, so he arranged things to have $a silently upgraded to an empty string beforehand. Both patches applied. 

Last week's summary

  This Week on perl5-porters - 9-15 March 2008 

About this summary

This summary was written by David Landgren. It is hopelessly late; I crave the indulgence of my readers. It was my birthday this week, or at least the attendant celebrations, and on top of that, a supermarket chain obsessed more with profit motives than the well-being of its clients sold my family beef well past its due date, and, well, I'll spare you the details...

Weekly summaries are published on and posted on a mailing list, (subscription: ). The archive is at . Corrections and comments are welcome.

If you found this summary useful, please consider contributing to the Perl Foundation to help support the development of Perl.

The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.

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