in reply to Re^3: Error handling in chained method calls
in thread Error handling in chained method calls

> Hm. I'm pretty sure that Perl already does method caching, so adding your own would be redundant.

I wonder how. Perl would either need to be informed in advance that the methods are immutable or monitor the complete inheritance chain for new methods.¹

But I haven't done any benchmarks yet ... IMHO there should be a notable performance gain.

> But mostly, why?

Well ask Gabor... I can only speculate that he wants to gather more detailed debug informations.

ATM I can say more about the how than the why.

Cheers Rolf

1) of course I would appreciate to learn more about a nifty mechanism to improve performance...

  • Comment on Re^4: Error handling in chained method calls

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Re^5: Error handling in chained method calls
by Corion (Patriarch) on Oct 24, 2010 at 19:00 UTC

    Perl caches methods. It recalculates them on every modification of (any) @ISA. At least I think that what happens for example in RT 62341 against parent.pm for example.

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Re^5: Error handling in chained method calls
by BrowserUk (Patriarch) on Oct 24, 2010 at 18:58 UTC
    I wonder how.

    From: perlapi:

    gv_fetchmeth

    Returns the glob with the given name and a defined subroutine or NULL . The glob lives in the given stash , or in the stashes accessible via @ISA and UNIVERSAL::.

    The argument level should be either 0 or -1. If level==0 , as a side-effect creates a glob with the given name in the given stash which in the case of success contains an alias for the subroutine, and sets up caching info for this glob.

    This function grants "SUPER" token as a postfix of the stash name. The GV returned from gv_fetchmeth may be a method cache entry, which is not visible to Perl code. So when calling call_sv , you should not use the GV directly; instead, you should use the method's CV, which can be obtained from the GV with the GvCV macro.

    See also mro::invalidate_all_method_caches()

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
      Wow, I'm impressed.

      An idealized benchmark shows only a 25% gain by memoizing, so I agree, it doesn't worth it.

                  Rate  classic memoized
classic  75415/s       --     -19%
memoized 93110/s      23%       --

      [download]
      Read more... (1494 Bytes)

      Cheers Rolf

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        An idealized benchmark

        Hm. I'm not sure that "idealized" really described your benchmark. And neither does "memoized"--more like "hard-coded".

        Are you really suggesting that every user of every class should build a lexical cache of every method for each class they use, in each package they use it, and then hard-code all their method calls in terms of that lexical cache?

        I've removed your hard-coded version as unrealistic, and replaced with paranoid() reflecting the OPs suggested methodology. I've also added a realistically memoised version of that suggestion to show that it doesn't help: 

        use strict;

my $obj = Class->new;

sub classic {
  $obj->meth0->meth1->meth2->meth3->meth4->meth5->meth6->meth7->meth8-
+>meth9;
}

sub paranoid {
    $obj and ref $obj and my $ref0 = $obj->can('meth0');
    $obj and ref $obj and my $ref1 = $obj->can('meth1');
    $obj and ref $obj and my $ref2 = $obj->can('meth2');
    $obj and ref $obj and my $ref3 = $obj->can('meth3');
    $obj and ref $obj and my $ref4 = $obj->can('meth4');
    $obj and ref $obj and my $ref5 = $obj->can('meth5');
    $obj and ref $obj and my $ref6 = $obj->can('meth6');
    $obj and ref $obj and my $ref7 = $obj->can('meth7');
    $obj and ref $obj and my $ref8 = $obj->can('meth8');
    $obj and ref $obj and my $ref9 = $obj->can('meth9');
    $obj->$ref0->$ref1->$ref2->$ref3->$ref4->$ref5->$ref6->$ref7->$ref
+8->$ref9;
}

my %memo;
sub memoized {
    $obj and ref $obj and my $ref0 = $memo{ meth0 } || $obj->can('meth
+0');
    $obj and ref $obj and my $ref1 = $memo{ meth1 } || $obj->can('meth
+1');
    $obj and ref $obj and my $ref2 = $memo{ meth2 } || $obj->can('meth
+2');
    $obj and ref $obj and my $ref3 = $memo{ meth3 } || $obj->can('meth
+3');
    $obj and ref $obj and my $ref4 = $memo{ meth4 } || $obj->can('meth
+4');
    $obj and ref $obj and my $ref5 = $memo{ meth5 } || $obj->can('meth
+5');
    $obj and ref $obj and my $ref6 = $memo{ meth6 } || $obj->can('meth
+6');
    $obj and ref $obj and my $ref7 = $memo{ meth7 } || $obj->can('meth
+7');
    $obj and ref $obj and my $ref8 = $memo{ meth8 } || $obj->can('meth
+8');
    $obj and ref $obj and my $ref9 = $memo{ meth9 } || $obj->can('meth
+9');
    $obj->$ref0->$ref1->$ref2->$ref3->$ref4->$ref5->$ref6->$ref7->$ref
+8->$ref9;
}

use Benchmark qw/cmpthese/;

cmpthese(1E6,
     {
      classic  => \&classic,
      paranoid => \&paranoid,
      memoized => \&memoized,
     });


package Class;

sub new { bless {}, $_[0] }

sub meth0 { $_[0] }
sub meth1 { $_[0] }
sub meth2 { $_[0] }
sub meth3 { $_[0] }
sub meth4 { $_[0] }
sub meth5 { $_[0] }
sub meth6 { $_[0] }
sub meth7 { $_[0] }
sub meth8 { $_[0] }
sub meth9 { $_[0] }

__END__
C:\test>junk
             Rate memoized paranoid  classic
memoized 101102/s       --      -9%     -65%
paranoid 111099/s      10%       --     -61%
classic  286123/s     183%     158%       --

        [download]

        I was tempted to add a Moose example, but that would be just like bear-baiting.

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
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