With the merging of the FX User Thread and the native event thread, we have lost the serialization between the rendering done by the Prism Render Thread and the events processed by the FX App thread.

Eventually we want to allow the rendering of frame N on the Prism Render Thread to run in parallel with the event code, animation code, and other user runnables running on the JavaFX App Thread preparing frame N+1 by modifying the scene graph.

Until the rest of the system is ready to support this, however, we need to ensure that the FX App Thread is not running at the same time the Prism Render Thread is doing any rendering.