how to under ensure ensure_shared_grads?

[luochao1024]

I am kind of confused of the ensure_shared_grads here https://github.com/ikostrikov/pytorch-a3c/blob/master/train.py#L13. Here, the grad is synced only when it is None. I think we need to set shared_param._grad = param.grad all the time because I don't see we sync the grad anywhere except here. Would anyone give me some hints about it?

[TolgaOk]

When you shared the model parameters grad attribute is not shared, so each process needs to have their own grad attribute and that's why we only need to assign it once for every process.