[Feature #21028] ObjectSpace#find_path_to_unshareable_object

osyoyu · mame · osyoyu · commit 01f73389b58b · 2025-07-22T00:11:19.000+09:00
Co-authored-by: Yusuke Endoh &lt;mame@ruby-lang.org&gt;
diff --git a/ext/objspace/lib/objspace.rb b/ext/objspace/lib/objspace.rb
@@ -132,4 +132,28 @@ def dump_shapes(output: :file, since: 0)
     return nil if output == :stdout
     ret
   end
+
+  # call-seq:
+  #    ObjectSpace.find_path_to_unshareable_object(obj) -> array | nil
+  #
+  # Find a path from obj to an unshareable object that prevents obj from being shareable.
+  #
+  # Returns an array showing the path from obj to the unshareable object, or nil if
+  # obj is already shareable.
+  def find_path_to_unshareable_object(obj, path = [], visited = {})
+    path += [obj]
+    return if visited[obj]
+    visited[obj] = true
+
+    return if Ractor.shareable?(obj)
+
+    objs = ObjectSpace.reachable_objects_from(obj)
+    return path if objs.all? { Ractor.shareable?(it) }
+
+    objs.each do |obj2|
+      res = find_path_to_unshareable_object(obj2, path, visited)
+      return res if res
+    end
+    return nil
+  end
 end
diff --git a/test/objspace/test_ractor.rb b/test/objspace/test_ractor.rb
@@ -1,4 +1,5 @@
 require "test/unit"
+require "objspace"
 
 class TestObjSpaceRactor < Test::Unit::TestCase
   def test_tracing_does_not_crash
@@ -52,4 +53,50 @@ def fin
       ractors.each(&:join)
     RUBY
   end
+
+  def test_find_path_to_unshareable_object
+    # Direct shareable object
+    assert_nil(ObjectSpace.find_path_to_unshareable_object(1))
+    assert_nil(ObjectSpace.find_path_to_unshareable_object(true))
+    assert_nil(ObjectSpace.find_path_to_unshareable_object(:symbol))
+    assert_nil(ObjectSpace.find_path_to_unshareable_object("frozen".freeze))
+
+    # Direct unshareable object
+    obj = "unfrozen"
+    path = ObjectSpace.find_path_to_unshareable_object(obj)
+    assert_equal([obj], path)
+
+    # Hash containing unshareable object
+    obj = { a: 1, b: "frozen".freeze, c: "unfrozen" }
+    path = ObjectSpace.find_path_to_unshareable_object(obj)
+    assert_equal([
+      { a: 1, b: "frozen".freeze, c: "unfrozen" },
+      "unfrozen"
+    ], path)
+    assert_equal(true, path.include?(obj[:c]))
+
+    # Array containing unshareable object
+    obj = [1, 2, "unfrozen", "frozen".freeze]
+    path = ObjectSpace.find_path_to_unshareable_object(obj)
+    assert_not_nil(path)
+    assert_equal(obj, path[0])
+    assert_equal(true, path.include?(obj[2]))
+
+    # Custom class
+    klass = Class.new do
+      attr_accessor :value
+    end
+    obj = klass.new
+    obj.value = "unfrozen"
+    path = ObjectSpace.find_path_to_unshareable_object(obj)
+    assert_equal(obj, path[0])
+    assert_equal(true, path.include?(obj.value))
+
+    # Circular reference
+    obj1 = { name: "obj1" }
+    obj2 = { name: "obj2", ref: obj1 }
+    obj1[:ref] = obj2
+    path = ObjectSpace.find_path_to_unshareable_object(obj1)
+    assert(path.any? { |o| o.is_a?(String) && !o.frozen? })
+  end
 end
