* Re-apply r33078, thread-safe autoload which is reverted at r33093.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@33146 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_autoload.rb

@@ -1,4 +1,6 @@
 require 'test/unit'
+require 'tempfile'
+require 'thread'
 require_relative 'envutil'
 
 class TestAutoload < Test::Unit::TestCase
@@ -53,4 +55,112 @@ p Foo::Bar
       assert_equal(tmpfile, b.autoload?(:X), bug4565)
     }
   end
+
+  def test_require_explicit
+    file = Tempfile.open(['autoload', '.rb'])
+    file.puts 'class Object; AutoloadTest = 1; end'
+    file.close
+    add_autoload(file.path)
+    begin
+      assert_nothing_raised do
+        assert(require file.path)
+        assert_equal(1, ::AutoloadTest)
+      end
+    ensure
+      remove_autoload_constant
+    end
+  end
+
+  def test_threaded_accessing_constant
+    file = Tempfile.open(['autoload', '.rb'])
+    file.puts 'sleep 0.5; class AutoloadTest; X = 1; end'
+    file.close
+    add_autoload(file.path)
+    begin
+      assert_nothing_raised do
+        t1 = Thread.new { ::AutoloadTest::X }
+        t2 = Thread.new { ::AutoloadTest::X }
+        [t1, t2].each(&:join)
+      end
+    ensure
+      remove_autoload_constant
+    end
+  end
+
+  def test_threaded_accessing_inner_constant
+    file = Tempfile.open(['autoload', '.rb'])
+    file.puts 'class AutoloadTest; sleep 0.5; X = 1; end'
+    file.close
+    add_autoload(file.path)
+    begin
+      assert_nothing_raised do
+        t1 = Thread.new { ::AutoloadTest::X }
+        t2 = Thread.new { ::AutoloadTest::X }
+        [t1, t2].each(&:join)
+      end
+    ensure
+      remove_autoload_constant
+    end
+  end
+
+  def test_nameerror_when_autoload_did_not_define_the_constant
+    file = Tempfile.open(['autoload', '.rb'])
+    file.puts ''
+    file.close
+    add_autoload(file.path)
+    begin
+      assert_raise(NameError) do
+        AutoloadTest
+      end
+    ensure
+      remove_autoload_constant
+    end
+  end
+
+  def test_override_autoload
+    file = Tempfile.open(['autoload', '.rb'])
+    file.puts ''
+    file.close
+    add_autoload(file.path)
+    begin
+      eval %q(class AutoloadTest; end)
+      assert_equal(Class, AutoloadTest.class)
+    ensure
+      remove_autoload_constant
+    end
+  end
+
+  def test_override_while_autoloading
+    file = Tempfile.open(['autoload', '.rb'])
+    file.puts 'class AutoloadTest; sleep 0.5; end'
+    file.close
+    add_autoload(file.path)
+    begin
+      # while autoloading...
+      t = Thread.new { AutoloadTest }
+      sleep 0.1
+      # override it
+      eval %q(AutoloadTest = 1)
+      t.join
+      assert_equal(1, AutoloadTest)
+    ensure
+      remove_autoload_constant
+    end
+  end
+
+  def add_autoload(path)
+    eval <<-END
+      class ::Object
+        autoload :AutoloadTest, #{path.dump}
+      end
+    END
+  end
+
+  def remove_autoload_constant
+    eval <<-END
+      class ::Object
+        remove_const(:AutoloadTest)
+      end
+    END
+  end
 end