[ruby-core:115251] [Ruby master Bug#19989] Fix refinement refine performance

5 Nov 2023

      Issue #19989 has been reported by bkuhlmann (Brooke Kuhlmann).

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Bug #19989: Fix refinement refine performance
https://bugs.ruby-lang.org/issues/19989

* Author: bkuhlmann (Brooke Kuhlmann)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) +YJIT [arm64-darwin22.4.0]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
## Why

Hello. 👋 Would it be possible to improve the performance of refining an object as I'm seeing a significant performance cost? I know some of this is already known but, when searching through existing issues, I couldn't find any issue that specifically mentioned or called attention to `refine` performance.

My C skills are not that great but it seems that `rb_mod_refine` ([source](https://github.com/ruby/ruby/blob/master/eval.c#L1412-L1459)) might be the primary source of complexity and performance degradation?

By fixing this, we could improve refinement performance and encourage more adoption since refinements are a powerful way to make small adjustments to the language without resorting to more complicated solutions -- or worse -- using monkey patches.

## How

Here's the benchmark I'm using:

``` 
#! /usr/bin/env ruby
# frozen_string_literal: true

require "bundler/inline"

gemfile true do
  source "https://rubygems.org"

  gem "benchmark-ips"
end

Benchmark.ips do |benchmark|
  benchmark.config time: 5, warmup: 2

  benchmark.report "With" do
    Module.new do
      refine String do
        def dud = true
      end
    end
  end

  benchmark.report "Without" do
    Module.new do
      def dud = true
    end
  end

  benchmark.compare!
end
```

When running the above, I'm getting the following results (this is a random sample):

**Ruby 2.6.6** (ruby 2.6.6p146 (2020-03-31 revision 67876) [-darwin22])

*ℹ️ Temporarily refactored the benchmark to not use endless methods for this version.*

``` 
Warming up --------------------------------------
                With   745.000  i/100ms
             Without    67.593k i/100ms
Calculating -------------------------------------
                With     10.849k (±168.6%) i/s -     18.625k in   5.359230s
             Without    680.199k (± 5.8%) i/s -      3.447M in   5.085558s

Comparison:
             Without:   680198.8 i/s
                With:    10849.1 i/s - 62.70x  slower
```

**Ruby 3.2.2** (ruby 3.2.2 (2023-03-30 revision e51014f9c0) +YJIT [arm64-darwin22.4.0])

``` 
Warming up --------------------------------------
                With   959.000  i/100ms
             Without   297.091k i/100ms
Calculating -------------------------------------
                With     21.856k (±198.5%) i/s -     30.688k in   5.509103s
             Without      3.281M (± 5.8%) i/s -     16.637M in   5.082246s

Comparison:
             Without:  3281310.6 i/s
                With:    21856.1 i/s - 150.13x  slower
```

**Ruby 3.3.3 Preview 2** (ruby 3.3.0preview2 (2023-09-14 master e50fcca9a7) +YJIT [arm64-darwin22.6.0])

``` 
Warming up --------------------------------------
                With     1.044k i/100ms
             Without   288.264k i/100ms
Calculating -------------------------------------
                With     24.044k (±192.0%) i/s -     29.232k in   5.305651s
             Without      3.096M (± 8.0%) i/s -     15.566M in   5.059470s

Comparison:
             Without:  3095640.6 i/s
                With:    24043.8 i/s - 128.75x  slower
```

## Notes

Here's the environment I'm using:

- **macOS**: 13.6.1, Apple M1

-- 
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