[ruby-core:55079] [ruby-trunk - Feature #8426] Implement class hierarchy method caching

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


Good day, Koichi

"sparse array" - is a lightweight hash structure which maps 32bit integers to st_data_t values.
It is more compact and faster replacement for st_table for integers (aka st_init_numtable).
It is CPU cache friendly on read, and it's hash function is tuned against ID pattern
(tuned is a great word, I were just lucky. At least, every other "better" hash function,
 like MurmurHash3 finalization, produce worse overall performance, and I could not explain why).

I've made it as a replacement for all usages of st_table as symbol table in my patch: methods,
constants, ivars, - and it shows noticeable performance gain (~5-8%). When James Golick makes
its method caching patch, I recommend him to use "sparse array", and he reports it efficiency.

It will be even better to embed sa_table into rb_classext_struct and do not allocate it separately.
If patch will be accepted, I could made such change.

Considering uint64_t - it should be 64bit value, so that there is no need to check for overflow
(even if one increments it 4_000_000_000 per second, it will take 70 years to overflow).
So that, it should be

   #if HAVE_UINT64_T
     typedef uint64_t version_t;
   #else
     typedef long long version_t ;
   #endif



----------------------------------------
Feature #8426: Implement class hierarchy method caching
https://bugs.ruby-lang.org/issues/8426#change-39450

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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