How to run threading while using Keras and tensorflow

Hi, I would like to test some hyperparameters, with using threading, that will be much faster. But when I run threading on DQN and DDQN algorithm, the error says:
<Tensor Tensor("dense_1/kernel:0", shape=(2, 32), dtype=float32_ref) is not an element of this graph>
Seems Keras can't support threading, but your A3C works, it's strange for me. 