[ruby/matrix] Make frozen matrices Ractor shareable

Merged: https://github.com/ruby/ruby/pull/3869

lib/matrix.rb

@@ -532,7 +532,8 @@ class Matrix
   alias map! collect!
 
   def freeze
-    @rows.freeze
+    @rows.each(&:freeze).freeze
+
     super
   end
 
@@ -2141,6 +2142,9 @@ class Vector
     all?(&:zero?)
   end
 
+  #
+  # Makes the matrix frozen and Ractor-shareable
+  #
   def freeze
     @elements.freeze
     super

test/matrix/test_matrix.rb

@@ -818,4 +818,13 @@ class TestMatrix < Test::Unit::TestCase
     assert_equal(Matrix[[(1-2i), 1], [(0-1i), 2], [0, 3]], @c1.adjoint)
     assert_equal(Matrix.empty(0,2), @e1.adjoint)
   end
+
+  def test_ractor
+    obj1 = @m1.freeze
+
+    obj2 = Ractor.new obj1 do |obj|
+      obj
+    end.take
+    assert_same obj1, obj2
+  end if defined?(Ractor)
 end