[ruby/psych] Optimize cache with `compare_by_identity`

Using `compare_by_identity` gives a 4x performance boost on cache hits.
Benchmark in https://github.com/JuanitoFatas/fast-ruby/issues/189

3 files changed, 5 insertions, 2 deletions

diff --git a/ext/psych/lib/psych/visitors/visitor.rb b/ext/psych/lib/psych/visitors/visitor.rb
index 35f8f81f18..e2585c0c77 100644
--- a/ext/psych/lib/psych/visitors/visitor.rb
+++ b/ext/psych/lib/psych/visitors/visitor.rb
@@ -12,7 +12,7 @@ module Psych
       def self.dispatch_cache
         Hash.new do |hash, klass|
           hash[klass] = :"visit_#{klass.name.gsub('::', '_')}"
-        end
+        end.compare_by_identity
       end
 
       if defined?(Ractor)
diff --git a/ext/psych/lib/psych/visitors/yaml_tree.rb b/ext/psych/lib/psych/visitors/yaml_tree.rb
index 986c57be70..ac6777aeb5 100644
--- a/ext/psych/lib/psych/visitors/yaml_tree.rb
+++ b/ext/psych/lib/psych/visitors/yaml_tree.rb
@@ -80,7 +80,7 @@ module Psych
           raise(TypeError, "Can't dump #{target.class}") unless method
 
           h[klass] = method
-        end
+        end.compare_by_identity
       end
 
       def start encoding = Nodes::Stream::UTF8
diff --git a/test/psych/test_ractor.rb b/test/psych/test_ractor.rb
index 90e40360c0..2f8d5ca18d 100644
--- a/test/psych/test_ractor.rb
+++ b/test/psych/test_ractor.rb
@@ -24,6 +24,9 @@ class TestPsychRactor < Test::Unit::TestCase
   end
 
   def test_ractor_config
+    # Config is ractor-local
+    # Test is to make sure it works, even though usage is probably very low.
+    # The methods are not documented and might be deprecated one day
     assert_ractor(<<~RUBY, require_relative: 'helper')
       r = Ractor.new do
         Psych.add_builtin_type 'omap' do |type, val|