Re: [Parseperl-discuss] Performance hacks

[Chris D. <ch...@ch...>]

On Jul 20, 2006, at 2:42 AM, Adam Kennedy wrote:

>>> my $doc = PPI::Document->new( $something,
>>>     readonly => 1,
>>>     );
>> I was thinking something quite similar earlier today, but I  
>> couldn't think of a good way to implement it without either 1)  
>> sprinkling "if ($self->top->readonly)" everywhere, or 2) multiple  
>> inheritance or mixin of a ::Mutable class for the non-readonly case.
>
> Agreed, actually checking it in every ->prune call would be onerous  
> and slow things down, and doing some form of mutation or mixin for  
> non-read-only seems infeasible without having entire seperate  
> trees, tripling the number of classes. :/

Like you suggested, I'll play with PPI-XS before actually trying to  
optimize PPI, but this is an interesting topic.

How about using caches with epoch number?  It might still be too much  
overhead (especially in $self->top), but here's some noodling:

package PPI::Node;

   sub remove {
      ...
      $self->top->inc_epoch;
      ...
   }

   sub inc_epoch {
      $self->{epoch}++;
      # maybe delete some caches pre-emptively?
   }

   sub epoch {
      $self->{epoch} || 0;
   }

   sub content {
      my ($self) = @_;
      my $epoch = $self->top->epoch;
      $self->{cache} = {epoch => $epoch} if (!$self->{cache} || $self- 
 >{cache}->{epoch} != $epoch);
      return $self->{cache}->{content} ||= join q{}, map { $_- 
 >content } @{$self->{children}};
   }

If the lexer can be exempt from caching and the ratio of reads to  
writes is large (like Perl::Critic), this could be a win, but I'm not  
sure.


Chris

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