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Add LICENSE, finish 2012-09-10 summary

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@@ -4,7 +4,11 @@ Perl 5 Porters Weekly: September 10-September 16, 2012
Welcome to Perl 5 Porters Weekly, a summary of the email traffic on
the perl5-porters email list. Once again subroutine signatures dominated
the list. I'll put all of the discussion about them at the end of this
-summary.
+summary. I've added an "official" license to these summaries. It's
+[Creative Commons BY-NC 3.0][License]. You can find the summary of rights
+granted by that license by following that link. The full license text is
+available in the [github repo][github]. Obviously, the content of emails
+quoted here are owned by their respective authors.
This week's dusty thread is [CALL FOR DOCS: how to dual life?][1] from the
week of August 6, 2012. Rik was looking for a volunteer to document the
@@ -118,10 +122,174 @@ objects into the core (someday.)
**Named prototypes (again)**
-I O U a summary to be named later
+Recall that [last week][], there was a big technical discussion about what the
+default behavior for a subroutine signature (aka named prototype) ought to
+be. Some argued for a read-only alias to @\_, and some argued for a
+read-write copy following the principle of least surprise, and still others
+argued for read-write aliases which would eliminate the overhead of @\_ setup.
+Nicholas Clark answered:
+
+ Perl 6 specifies that the default is an alias (to avoid a copy, for
+ speed) and read-only (for the least surprise):
+
+ http://perlcabal.org/syn/S06.html#Parameters_and_arguments
+
+ In an ideal world these seem sane defaults, because they are made for
+ sane reasons. We're not *confident* that we are able to implement
+ read-only aliases (of read-write values). But
+
+ a) Chip had proposed a working patch
+ b) And asked for help measuring its impact
+ c) No-one helped.
+
+ So a good start here would be for SOMEONE TO VOLUNTEER to help get that
+ restarted. To at least get an answer to "is this approach going to
+ work?" (and possibly "does it look likely that no approach would work?")
+
+But, Ricardo Signes wrote just a bit later that:
+
+ The reasonable default is copy, because decades of Perl programming have
+ told us that our arguments are copies. That is, as was said elsewhere
+ in this thread, we'd codifying existing patterns here.
+
+Which seems to be the dispostive word on the matter. Chip Salzenberg added:
+
+ I agree here for four reasons:
+
+ 1. Rik is right
+ 2. Copies happen a lot; we'd be better off making copies faster (and
+ use less memory) than making them rarer or (as I once thought was a
+ good idea) introducing readonly aliases
+ 3. I already have a patch half-done, the "minimal copy" patch, to make
+ copies smaller; I haven't gotten round tuition for them but I have
+ high expectation of having them ready for 5.18
+ 4. It's possible to keep small strings in bodiless SVs, or making COW
+ good (if it isn't), which also makes copying cheaper
+
+Later, Jesse Luehrs applied the patch in question (which creates read-only
+aliases to $_[0], etc) to measure its impact as Nicholas asked above and
+reported that:
+
+ [P]reliminary benchmarks don't look promising:
+
+ Current:
+ ./perl -Ilib lib/unicore/mktables -C lib/unicore -P pod -maketest
+ -makelist - 14.40s user 0.10s system 99% cpu 14.565 total
+ With SVt_BIND patch:
+ ./perl -Ilib lib/unicore/mktables -C lib/unicore -P pod -maketest
+ -makelist - 16.23s user 0.09s system 99% cpu 16.372 total
+
+ Copies might actually turn out to be faster than read-only aliases,
+ given the way the perl 5 interpreter is implemented.
+
+There was also a serious digression that took on a life of its own, mostly
+revolving around how P5P interacts with feature suggestions, commentary on
+the same, and how the Perl community ought to spend more effort on
+performance enhancements than new shinies.
+
+David Golden wrote:
+
+ [M]any people on p5p express dissatisfaction with the status quo
+ [ed. about performance], yet are unable or unwilling to:
+
+ (a) climb up the learning curve to contribute effectively
+
+ (b) take on less demanding tasks, freeing up the time of experts
+
+ Until more people do (a) or (b), the "hard" problems will continue to
+ suffer a lack of tuits.
+
+Nicholas Clark added:
+
+ There are SIX HUNDRED subscribers to the list. About SIXTY are active in
+ e-mail discussions. Of the order of SIX people actually commit stuff.
+
+ And yet somehow the sixty (plus) seem to assume that if an idea is worth
+ talking about *to death* then somehow that is enough to steer the six
+ (busy) people into acting upon it.
+
+ If one looks at the archives from (say) 2003 compared with 2012
+ one notices two things
+
+ 1: 2003 has many more medium sized threads
+ 2012 has either massive threads, or messages with ZERO or one reply
+
+ 2: 2003 has far more discussion of code
+
+ People cared just as much about perl then. But more people helped do
+ things.
+
+ I'd like us to get back to that. I don't know how.
+
+Peter Rabbitson argued that p5p ought to more carefully weigh the impact of
+adding features to core since the Perl core has been famously reluctant to
+remove bits of the language.
+
+ [T]he level of scrutiny before inclusion does not seem to match the fact
+ that perl5 does not have a backtrack mechanism. I do not know what
+ would constitute "enough" scrutiny. I just know (based on past
+ achievements) that we do not scrutinize new syntax enough.
+
+To support the claim that Perl's performance has deteriorated over time,
+[Steffen Schwigon][perf] posted some summaries of his work comparing Perl
+version X vs. Perl version Y doing fibonacci sequence generation. He
+writes:
+
+ fib (plain subs) in Perl is ~2500x slower than symmetric
+ implementation with C
+
+ - C comparison not part of Perl::Formance, done separately
+
+ * fibOO (selfmade/Moose/Mouse) is ~1.5x slower than plain subs
+
+ * fibMXDeclare is about ~500x times slower than plain subs.
+
+ - yes, that's 120000 times slower than C, sorry.
+
+ - but probably due to some follow-up effects like huge mem triggering
+ swapping or similar
+
+ - anyway, the number itself is not an artifact or mistake, it's
+ stable over different Perl versions, it's a complete mess,
+ therefore I don't run it often
+
+ Trends, still fibonacci:
+
+ * Perl 5.10 to 5.14 improved a runtime of 90s down to 76s.
+
+ * Perl 5.16 deteriorated back to ~90s runtime.
+
+ * The overhead of "threaded" over "non-threaded"
+
+ ... was in 5.10 ~5% more time
+ ... got worse in 5.12 to ~15% more time
+ ... improved in 5.14 to nearly zero
+ ... and is now back worse in 5.16 with ~20% more time
+
+ * I don't have conclusive 5.17.x numbers due to current issues, but
+ first experiments seem to indicate a trend towards more slowness.
+
+Dave Mitchell wrote (not specifically in reply to the above):
+
+ The idea that p5p doesn't care about, nor does anything related to
+ performance, is a bit of a myth. There have been lots of optimisations
+ added over the years. These tend to be low-key affairs: no major new
+ language syntax, nor porting to shiny new VMs etc (that's what the perl6
+ effort is for); but in many small, but accumulative ways we've been
+ fixing things. E.g. regex Tries; reorganising SV structures so they're
+ smaller and quicker.
+
+ I think the net affect of these efforts is that we've managed to
+ generally avoid perl5 slowing down any further over years as new
+ features and bug fixes have been added (which would normally have the
+ accumulative effect of gradually slowing things down).
+
+[Read the thread][10]
[avoid csh]: http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/
+[License]: http://creativecommons.org/licenses/by-nc/3.0/
+[github]: https://github.com/mrallen1/P5P-Weekly
[1]: http://byte-me.org/perl-5-porters-weekly-august-6-august-12-2012/#5
[2]: mailto:rjbs@cpan.org
[3]: http://www.nntp.perl.org/group/perl.perl5.porters/2012/09/msg191905.html
@@ -131,5 +299,6 @@ I O U a summary to be named later
[7]: http://www.nntp.perl.org/group/perl.perl5.porters/2012/09/msg192287.html
[8]: http://www.nntp.perl.org/group/perl.perl5.porters/2012/09/msg192299.html
[9]: http://www.nntp.perl.org/group/perl.perl5.porters/2012/09/msg192365.html
-
-
+[10]: http://www.nntp.perl.org/group/perl.perl5.porters/2012/09/msg191477.html
+[last week]: http://byte-me.org/perl-5-porters-weekly-september-3-september-9-2012/
+[perf]: http://www.nntp.perl.org/group/perl.perl5.porters/2012/09/msg192181.html
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