Disallow sending CUDA tensors over RPC for current RPC agents. (#33604)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33604
For our current RPC agents, this PR disallows sending CUDA tensors
over RPC and asks users to copy them explicitly to CPU. Currently, this seems
to be the easiest contract to guarantee for our current RPC agents, otherwise
if we do support this transparently it gets a little tricky in terms of whether
a CUDA tensor on the client should be sent to CPU/GPU of the remote end and
also which GPU device on the remote end.
In the future, the TensorPipe RPC agent can have its own specific handling of
CUDA tensors.
Closes https://github.com/pytorch/pytorch/issues/28881
ghstack-source-id: 100166120
Test Plan: waitforbuildbot
Differential Revision: D20020183
fbshipit-source-id: ca4d43d2a24e8fcd3a60b21e654aa0e953e756cb
