From: "funny_falcon (Yura Sokolov)" <funny.falcon@...>
Date: 2013-05-20T19:10:22+09:00
Subject: [ruby-core:55088] [ruby-trunk - Feature #8426] Implement class hierarchy method caching


Issue #8426 has been updated by funny_falcon (Yura Sokolov).


ko1 (Koichi Sasada) wrote:
> (2013/05/20 18:21), Charlie Somerville wrote:
>  > funny_falcon explained this well. It's significantly faster in this case
>  > when compared to st_table.
>  
>  Thanks guys, I understand. Maybe it is used to implement weak reference
>  from super class to sub classes, right?

"sparse array" uses 32bit keys for being as small and CPU cache friendly as possible.
So that, it could not store 64bit pointers :-(

I have an idea of other light hash structure (inspired by khash), but I do not bench it yet.

Any way, I think James's linked list for subclasses is most suitable for this task.
Why change it to hash?
----------------------------------------
Feature #8426: Implement class hierarchy method caching
https://bugs.ruby-lang.org/issues/8426#change-39457

Author: charliesome (Charlie Somerville)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


=begin
This patch adds class hierarchy method caching to CRuby. This is the algorithm used by JRuby and Rubinius.

Currently, Ruby's method caches can only be expired globally. This means libraries that dynamically define methods or extend objects at runtime (eg. OpenStruct) can cause quite a significant performance hit.

With this patch, each class carries a monotonically increasing sequence number. Whenever an operation which would ordinarily cause a global method cache invalidation is performed, the sequence number on the affected class and all subclasses (classes hold weak references to their subclasses) is incremented, invalidating only method caches for those classes.

In this patch I've also split the (({getconstant})) VM instruction into two separate instructions - (({getclassconstant})) and (({getcrefconstant})). It's hoped that (({getclassconstant})) can start using class hierarchy caching with not much more effort. This change does affect compatibility in a minor way. Without this patch, (({nil::SomeConstant})) will look up (({SomeConstant})) in the current scope in CRuby (but not JRuby or Rubinius). With this patch, (({nil::SomeConstant})) will raise an exception.

The patch and all its commits can be viewed here: https://github.com/charliesome/ruby/compare/trunk...klasscache-trunk

Big thanks to James Golick, who originally wrote this patch for Ruby 1.9.3.
=end


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