nick at ccl4
May 21, 2008, 3:49 AM
Post #7 of 9
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Re: [perl #54186] IO::Seekable + POSIX -> constant subroutines redefined
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On Sat, May 17, 2008 at 12:10:28AM +0100, Nicholas Clark wrote:
> On Sat, May 17, 2008 at 01:01:23AM +0200, Sbastien Aperghis-Tramoni wrote:
> > Nicholas Clark wrote:
> >
> > >POSIX.xs had this code in AUTOLOAD, to call into POSIX::int_macro_int
> > >
> > > if ($NON_CONSTS{$constname}) {
> > > my ($val, $error) = &int_macro_int($constname, $_[0]);
> > > croak $error if $error;
> > > *$AUTOLOAD = sub { &int_macro_int($constname, $_[0]) };
> > > } else {
> >
> > Isn't this the standard way constant are handled by ExtUtils::Constant?
>
> No. It's not a constant function. It's 5 macros that process arguments,
> wrapped in a single C function.
I can't count. It's 6, not 5. Anyway, I removed int_macro_int with change
33896, and improved the XS with change 33897
Change 33896 by nicholas[at]mouse-mill on 2008/05/21 09:18:00
Eliminate POSIX::int_macro_int, and all the complex AUTOLOAD fandango
that creates closures round it. Instead, wrap WEXITSTATUS, WIFEXITED,
WIFSIGNALED, WIFSTOPPED, WSTOPSIG and WTERMSIG directly with XS.
The shared library is slightly larger, but dynamic memory usage savings
beat this, even within one thread of one process. Simpler code too.
Change 33897 by nicholas[at]mouse-mill on 2008/05/21 10:31:32
Replaced the WEXITSTATUS, WIFEXITED, WIFSIGNALED, WIFSTOPPED, WSTOPSIG
and WTERMSIG wrappers with one wrapper using the XS "ALIAS" feature.
This gets the shared object size back below the size before the removal
of int_macro_int. It looks like there are other space savings to be
made this way.
I think I spent a bit more time on my code to measure the memory usage of the
old and new (attached)approaches. (attached as posix.pl, along with before and
after output.) By swapping from 6 XS wrappers to 1 using "ALIAS", change 33897
made the shared library shrink from 105944 to 105784 bytes. There are other
similar savings to be made in POSIX.xs, and probably in other core XS code.
This could make an "interesting" "cage-cleaner" type TODO task, if anyone's
game.
Bottom line of the two changes is that comparable memory usage from use POSIX;
drops from 153606 to 152563 bytes, and if one actually uses all 6 functions,
from 153641 to 152563 bytes. There's no AUTOLOAD now, so there's no change in
memory on running them. Oh, and they run fewer ops, so will be faster too.
See the script for the explaination of the games needed to cope with AUTOLOADed
stubs causing Devel::Size to see things in other packages.
Only user visible change is that if you call the 6 with too many arguments you
now actually get an error:
Was:
$ ./perl -Ilib -MPOSIX -we 'WEXITSTATUS(3,2,3)'
$
Now:
$ ./perl -Ilib -MPOSIX -we 'WEXITSTATUS(3,2,3)'
Usage: WEXITSTATUS(status) at -e line 1.
Is this fair game to inflict on buggy users of 5.10.0?
Nicholas Clark
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33825
posix.pl
