From bb2b9269f2da9e26840440218587992e86bc6e53 Mon Sep 17 00:00:00 2001
From: Hiroshi Shirosaki <h.shirosaki@gmail.com>
Date: Wed, 11 Nov 2015 11:54:51 +0900
Subject: [PATCH] Add waiting for autoload in rb_const_defined_0

* variable.c (rb_const_defined_0): add waiting for autoload.
  defined? works properly when other thread is autoloading.
* test/ruby/test_autoload.rb (test_defined_with_autoload):
  add a test for the above.
---
 test/ruby/test_autoload.rb | 22 ++++++++++++++++++++++
 variable.c                 | 23 ++++++++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/test/ruby/test_autoload.rb b/test/ruby/test_autoload.rb
index a672e0b..c71668e 100644
--- a/test/ruby/test_autoload.rb
+++ b/test/ruby/test_autoload.rb
@@ -234,6 +234,28 @@ p Foo::Bar
     end
   end
 
+  def test_defined_with_autoload
+    ruby_impl_require do |called_with|
+      Tempfile.create(%w(autoload .rb)) do |file|
+        file.puts "class AutoloadTest; module B; end; end"
+        file.flush
+        add_autoload(file.path)
+        begin
+          thrs = []
+          2.times do
+            thrs << Thread.new do
+              Thread.pass; assert_equal("constant", defined? Object::AutoloadTest::B)
+            end
+          end
+          thrs.each(&:join)
+        ensure
+          remove_autoload_constant
+        end
+        assert_equal [file.path], called_with.uniq
+      end
+    end
+  end
+
   def add_autoload(path)
     (@autoload_paths ||= []) << path
     ::Object.class_eval {autoload(:AutoloadTest, path)}
diff --git a/variable.c b/variable.c
index c8264b1..a01fbb6 100644
--- a/variable.c
+++ b/variable.c
@@ -2493,8 +2493,29 @@ rb_const_defined_0(VALUE klass, ID id, int exclude, int recurse, int visibility)
 		return (int)Qfalse;
 	    }
 	    if (ce->value == Qundef && !check_autoload_required(tmp, id, 0) &&
-		    !rb_autoloading_value(tmp, id, 0))
+		    !rb_autoloading_value(tmp, id, 0)) {
+		VALUE load;
+		struct autoload_data_i *ele;
+		struct autoload_state state;
+		if (!(load = autoload_data(tmp, id)) ||
+			!(ele = check_autoload_data(load))) {
+		    return (int)Qfalse;
+		}
+		state.thread = rb_thread_current();
+		if (ele->state && (ele->state->thread != state.thread)) {
+	            list_add_tail(&ele->state->waitq.head, &state.waitq.node);
+		    /*
+		     * autoload_reset in other thread will resume us and remove us
+		     * from the waitq list
+		     */
+		    do {
+			rb_thread_sleep_deadly();
+		    } while (state.thread != Qfalse);
+		    /* retry to look up the autoloaded constant. */
+		    continue;
+		}
 		return (int)Qfalse;
+	    }
 	    return (int)Qtrue;
 	}
 	if (!recurse) break;
-- 
2.5.0