Make setting and accessing class ivars lock-free #13594

casperisfine · 2025-06-12T08:48:33Z

Now that class fields have been deletated to a T_IMEMO/class_fields when we're in multi-ractor mode, we can read and write class instance variable in an atomic way using Read-Copy-Update (RCU).

Note when in multi-ractor mode, we always use RCU. In theory we don't need to, instead if we ensured the field is written before the shape is updated it would be safe.

Benchmark:

Warning[:experimental] = false

class Foo
  @foo = 1
  @bar = 2
  @baz = 3
  @egg = 4
  @spam = 5

  class << self
    attr_reader :foo, :bar, :baz, :egg, :spam
  end
end

ractors = 8.times.map do
  Ractor.new do
    1_000_000.times do
      Foo.bar + Foo.baz * Foo.egg - Foo.spam
    end
  end
end

if Ractor.method_defined?(:value)
  ractors.each(&:value)
else
  ractors.each(&:take)
end

This branch vs Ruby 3.4:

$ hyperfine -w 1 'ruby --disable-all ../test.rb' './miniruby ../test.rb'

Benchmark 1: ruby --disable-all ../test.rb
  Time (mean ± σ):      3.162 s ±  0.071 s    [User: 2.783 s, System: 10.809 s]
  Range (min … max):    3.093 s …  3.337 s    10 runs

Benchmark 2: ./miniruby ../test.rb
  Time (mean ± σ):     208.7 ms ±   4.6 ms    [User: 889.7 ms, System: 6.9 ms]
  Range (min … max):   202.8 ms … 222.0 ms    14 runs

Summary
  ./miniruby ../test.rb ran
   15.15 ± 0.47 times faster than ruby --disable-all ../test.rb

@foo

Now that class fields have been deletated to a T_IMEMO/class_fields when we're in multi-ractor mode, we can read and write class instance variable in an atomic way using Read-Copy-Update (RCU). Note when in multi-ractor mode, we always use RCU. In theory we don't need to, instead if we ensured the field is written before the shape is updated it would be safe. Benchmark: ```ruby Warning[:experimental] = false class Foo @foo = 1 @bar = 2 @baz = 3 @Egg = 4 @spam = 5 class << self attr_reader :foo, :bar, :baz, :egg, :spam end end ractors = 8.times.map do Ractor.new do 1_000_000.times do Foo.bar + Foo.baz * Foo.egg - Foo.spam end end end if Ractor.method_defined?(:value) ractors.each(&:value) else ractors.each(&:take) end ``` This branch vs Ruby 3.4: ```bash $ hyperfine -w 1 'ruby --disable-all ../test.rb' './miniruby ../test.rb' Benchmark 1: ruby --disable-all ../test.rb Time (mean ± σ): 3.162 s ± 0.071 s [User: 2.783 s, System: 10.809 s] Range (min … max): 3.093 s … 3.337 s 10 runs Benchmark 2: ./miniruby ../test.rb Time (mean ± σ): 208.7 ms ± 4.6 ms [User: 889.7 ms, System: 6.9 ms] Range (min … max): 202.8 ms … 222.0 ms 14 runs Summary ./miniruby ../test.rb ran 15.15 ± 0.47 times faster than ruby --disable-all ../test.rb ```

launchable-app · 2025-06-12T12:05:15Z

❌ Tests Failed

✖️no tests failed ✔️61995 tests passed(2 flakes)

casperisfine force-pushed the lockfree-class-ivar branch from 4b06936 to d2b1261 Compare June 12, 2025 10:13

byroot enabled auto-merge (rebase) June 12, 2025 10:13

auto-merge was automatically disabled June 12, 2025 11:14
Head branch was pushed to by a user without write access

casperisfine force-pushed the lockfree-class-ivar branch from d2b1261 to 32b8aeb Compare June 12, 2025 11:14

casperisfine force-pushed the lockfree-class-ivar branch from 32b8aeb to 631f026 Compare June 12, 2025 11:51

byroot enabled auto-merge (rebase) June 12, 2025 12:16

byroot merged commit a74c385 into ruby:master Jun 12, 2025
93 of 6500 97 checks passed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Make setting and accessing class ivars lock-free #13594

Make setting and accessing class ivars lock-free #13594

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Make setting and accessing class ivars lock-free #13594

Make setting and accessing class ivars lock-free #13594

Conversation

Uh oh!

Uh oh!

❌ Tests Failed

Uh oh!

Uh oh!

Uh oh!