Fix deadlock that can occur when child live thread tries to load a constant after writing to the stream.

actionpack/lib/action_controller/metal/live.rb

@@ -205,7 +205,12 @@ module ActionController
       private
 
         def each_chunk(&block)
-          while str = @buf.pop
+          loop do
+            str = nil
+            ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+              str = @buf.pop
+            end
+            break unless str
             yield str
           end
         end

actionpack/test/controller/live_stream_test.rb

@@ -150,6 +150,20 @@ module ActionController
         response.stream.close
       end
 
+      def write_sleep_autoload
+        path = File.join(File.dirname(__FILE__), "../fixtures")
+        ActiveSupport::Dependencies.autoload_paths << path
+
+        response.headers["Content-Type"] = "text/event-stream"
+        response.stream.write "before load"
+        sleep 0.01
+        ::LoadMe
+        response.stream.close
+        latch.count_down
+
+        ActiveSupport::Dependencies.autoload_paths.reject! {|p| p == path}
+      end
+
       def thread_locals
         tc.assert_equal "aaron", Thread.current[:setting]
 
@@ -281,6 +295,14 @@ module ActionController
       assert_equal "text/event-stream", @response.headers["Content-Type"]
     end
 
+    def test_delayed_autoload_after_write_within_interlock_hook
+      # Simulate InterlockHook
+      ActiveSupport::Dependencies.interlock.start_running
+      res = get :write_sleep_autoload
+      res.each {}
+      ActiveSupport::Dependencies.interlock.done_running
+    end
+
     def test_async_stream
       rubinius_skip "https://github.com/rubinius/rubinius/issues/2934"
 

actionpack/test/fixtures/load_me.rb

@@ -0,0 +1,2 @@
+class LoadMe
+end