[ruby/psych] Make Ractor-ready.

Config is Ractor-local.

Benchmarking reveals that using `Ractor.local_storage` for storing cache
is similar to accessing a constant (~15% slower).

1 files changed, 17 insertions, 3 deletions

diff --git a/ext/psych/lib/psych/visitors/visitor.rb b/ext/psych/lib/psych/visitors/visitor.rb
index 3f4ba64e57..35f8f81f18 100644
--- a/ext/psych/lib/psych/visitors/visitor.rb
+++ b/ext/psych/lib/psych/visitors/visitor.rb
@@ -8,12 +8,26 @@ module Psych
 
       private
 
-      DISPATCH = Hash.new do |hash, klass|
-        hash[klass] = "visit_#{klass.name.gsub('::', '_')}"
+      # @api private
+      def self.dispatch_cache
+        Hash.new do |hash, klass|
+          hash[klass] = :"visit_#{klass.name.gsub('::', '_')}"
+        end
+      end
+
+      if defined?(Ractor)
+        def dispatch
+          Ractor.current[:Psych_Visitors_Visitor] ||= Visitor.dispatch_cache
+        end
+      else
+        DISPATCH = dispatch_cache
+        def dispatch
+          DISPATCH
+        end
       end
 
       def visit target
-        send DISPATCH[target.class], target
+        send dispatch[target.class], target
       end
     end
   end